x264源代码简单分析：编码器主干部分-2
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H.264源代码分析文章列表：
【编码 - x264】
x264源代码简单分析：概述
x264源代码简单分析：x264命令行工具（x264.exe）
x264源代码简单分析：编码器主干部分-1
x264源代码简单分析：编码器主干部分-2
x264源代码简单分析：x264_slice_write()
x264源代码简单分析：滤波（Filter）部分
x264源代码简单分析：宏块分析（Analysis）部分-帧内宏块（Intra）
x264源代码简单分析：宏块分析（Analysis）部分-帧间宏块（Inter）
x264源代码简单分析：宏块编码（Encode）部分
x264源代码简单分析：熵编码（Entropy Encoding）部分
FFmpeg与libx264接口源代码简单分析
【解码 - libavcodec H.264 解码器】
FFmpeg的H.264解码器源代码简单分析：概述
FFmpeg的H.264解码器源代码简单分析：解析器（Parser）部分
FFmpeg的H.264解码器源代码简单分析：解码器主干部分
FFmpeg的H.264解码器源代码简单分析：熵解码（EntropyDecoding）部分
FFmpeg的H.264解码器源代码简单分析：宏块解码（Decode）部分-帧内宏块（Intra）
FFmpeg的H.264解码器源代码简单分析：宏块解码（Decode）部分-帧间宏块（Inter）
FFmpeg的H.264解码器源代码简单分析：环路滤波（Loop Filter）部分
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本文继续记录x264编码器主干部分的源代码。上一篇文章记录x264_encoder_open()，x264_encoder_headers()，和x264_encoder_close()这三个函数，本文记录x264_encoder_encode()函数。
函数调用关系图
X264编码器主干部分的源代码在整个x264中的位置如下图所示。
单击查看更清晰的图片
X264编码器主干部分的函数调用关系如下图所示。
单击查看更清晰的图片
从图中可以看出，x264主干部分最复杂的函数就是x264_encoder_encode()，该函数完成了编码一帧YUV为H.264码流的工作。与之配合的还有打开编码器的函数x264_encoder_open()，关闭编码器的函数x264_encoder_close()，以及输出SPS/PPS/SEI这样的头信息的x264_encoder_headers()。
x264_validate_parameters()：检查输入参数（例如输入图像的宽高是否为正数）。
x264_predict_16x16_init()：初始化Intra16x16帧内预测汇编函数。
x264_predict_4x4_init()：初始化Intra4x4帧内预测汇编函数。
x264_pixel_init()：初始化像素值计算相关的汇编函数（包括SAD、SATD、SSD等）。
x264_dct_init()：初始化DCT变换和DCT反变换相关的汇编函数。
x264_mc_init()：初始化运动补偿相关的汇编函数。
x264_quant_init()：初始化量化和反量化相关的汇编函数。
x264_deblock_init()：初始化去块效应滤波器相关的汇编函数。
x264_lookahead_init()：初始化Lookahead相关的变量。x264_ratecontrol_new()：初始化码率控制相关的变量。
x264_sps_write()：输出SPS
x264_pps_write()：输出PPS
x264_sei_version_write()：输出SEI
x264_encoder_encode()编码一帧YUV为H.264码流。它调用了下面的函数：
x264_frame_pop_unused()：获取1个x264_frame_t类型结构体fenc。如果frames.unused[]队列不为空，就调用x264_frame_pop()从unused[]队列取1个现成的；否则就调用x264_frame_new()创建一个新的。
x264_frame_copy_picture()：将输入的图像数据拷贝至fenc。
x264_lookahead_put_frame()：将fenc放入lookahead.next.list[]队列，等待确定帧类型。
x264_lookahead_get_frames()：通过lookahead分析帧类型。该函数调用了x264_slicetype_decide()，x264_slicetype_analyse()和x264_slicetype_frame_cost()等函数。经过一些列分析之后，最终确定了帧类型信息，并且将帧放入frames.current[]队列。
x264_frame_shift()：从frames.current[]队列取出1帧用于编码。
x264_reference_update()：更新参考帧队列。
x264_reference_reset()：如果为IDR帧，调用该函数清空参考帧列表。
x264_reference_hierarchy_reset()：如果是非IDR的I帧、P帧、B帧（可做为参考帧），调用该函数。
x264_reference_build_list()：创建参考帧列表list0和list1。
x264_ratecontrol_start()：开启码率控制。
x264_slice_init()：创建 Slice Header。
x264_slices_write()：编码数据（最关键的步骤）。其中调用了x264_slice_write()完成了编码的工作（注意“x264_slices_write()”和“x264_slice_write()”名字差了一个“s”）。
x264_encoder_frame_end()：编码结束后做一些后续处理，例如记录一些统计信息。其中调用了x264_encoder_encapsulate_nals()封装NALU（添加起始码），调用x264_frame_push_unused()将fenc重新放回frames.unused[]队列，并且调用x264_ratecontrol_end()结束码率控制。
x264_encoder_close()用于关闭解码器，其中释放了libx264初始化的时候使用的各种变量。它调用了下面的函数：
x264_lookahead_delete()：释放Lookahead相关的变量。
x264_ratecontrol_summary()：汇总码率控制信息。
x264_ratecontrol_delete()：关闭码率控制。
上一篇文章已经记录了x264_encoder_open()，x264_encoder_headers()，和x264_encoder_close()这三个函数的源代码。本文继续上一篇文章的内容，记录x264_encoder_encode()函数的源代码。
x264_encoder_encode()
x264_encoder_encode()是libx264的API函数，用于编码一帧YUV为H.264码流。该函数的声明如下所示。/* x264_encoder_encode: * encode one picture. * *pi_nal is the number of NAL units outputted in pp_nal. * returns the number of bytes in the returned NALs. * returns negative on error and zero if no NAL units returned. * the payloads of all output NALs are guaranteed to be sequential in memory. */int x264_encoder_encode( x264_t *, x264_nal_t **pp_nal, int *pi_nal, x264_picture_t *pic_in, x264_picture_t *pic_out );x264_encoder_encode()的定义如下所示。
/**************************************************************************** * x264_encoder_encode: * XXX: i_poc : is the poc of the current given picture * i_frame : is the number of the frame being coded * ex: type frame poc * I 0 2*0 * P 1 2*3 * B 2 2*1 * B 3 2*2 * P 4 2*6 * B 5 2*4 * B 6 2*5 * * 注释和处理：雷霄骅 * http://blog.csdn.net/leixiaohua1020 * leixiaohua1020@126.com ****************************************************************************///编码一帧数据int x264_encoder_encode( x264_t *h, x264_nal_t **pp_nal, int *pi_nal, x264_picture_t *pic_in, x264_picture_t *pic_out ){ x264_t *thread_current, *thread_prev, *thread_oldest; int i_nal_type, i_nal_ref_idc, i_global_qp; int overhead = NALU_OVERHEAD;#if HAVE_OPENCL if( h->opencl.b_fatal_error ) return -1;#endif if( h->i_thread_frames > 1 ) { thread_prev = h->thread[ h->i_thread_phase ]; h->i_thread_phase = (h->i_thread_phase + 1) % h->i_thread_frames; thread_current = h->thread[ h->i_thread_phase ]; thread_oldest = h->thread[ (h->i_thread_phase + 1) % h->i_thread_frames ]; x264_thread_sync_context( thread_current, thread_prev ); x264_thread_sync_ratecontrol( thread_current, thread_prev, thread_oldest ); h = thread_current; } else { thread_current = thread_oldest = h; } h->i_cpb_delay_pir_offset = h->i_cpb_delay_pir_offset_next; /* no data out */ *pi_nal = 0; *pp_nal = NULL; /* ------------------- Setup new frame from picture -------------------- */ if( pic_in != NULL ) { /* 1: Copy the picture to a frame and move it to a buffer */ //步骤1 //fenc存储了编码帧 //获取一帧的空间fenc，用来存放待编码的帧 x264_frame_t *fenc = x264_frame_pop_unused( h, 0 ); if( !fenc ) return -1; //外部像素数据传递到内部系统 //pic_in（外部结构体x264_picture_t）到fenc（内部结构体x264_frame_t） if( x264_frame_copy_picture( h, fenc, pic_in ) < 0 ) return -1; //宽和高都确保是16的整数倍（宏块宽度的整数倍） if( h->param.i_width != 16 * h->mb.i_mb_width || h->param.i_height != 16 * h->mb.i_mb_height ) x264_frame_expand_border_mod16( h, fenc );//扩展至16整数倍 fenc->i_frame = h->frames.i_input++; if( fenc->i_frame == 0 ) h->frames.i_first_pts = fenc->i_pts; if( h->frames.i_bframe_delay && fenc->i_frame == h->frames.i_bframe_delay ) h->frames.i_bframe_delay_time = fenc->i_pts - h->frames.i_first_pts; if( h->param.b_vfr_input && fenc->i_pts <= h->frames.i_largest_pts ) x264_log( h, X264_LOG_WARNING, "non-strictly-monotonic PTS\n" ); h->frames.i_second_largest_pts = h->frames.i_largest_pts; h->frames.i_largest_pts = fenc->i_pts; if( (fenc->i_pic_struct < PIC_STRUCT_AUTO) || (fenc->i_pic_struct > PIC_STRUCT_TRIPLE) ) fenc->i_pic_struct = PIC_STRUCT_AUTO; if( fenc->i_pic_struct == PIC_STRUCT_AUTO ) {#if HAVE_INTERLACED int b_interlaced = fenc->param ? fenc->param->b_interlaced : h->param.b_interlaced;#else int b_interlaced = 0;#endif if( b_interlaced ) { int b_tff = fenc->param ? fenc->param->b_tff : h->param.b_tff; fenc->i_pic_struct = b_tff ? PIC_STRUCT_TOP_BOTTOM : PIC_STRUCT_BOTTOM_TOP; } else fenc->i_pic_struct = PIC_STRUCT_PROGRESSIVE; } if( h->param.rc.b_mb_tree && h->param.rc.b_stat_read ) { if( x264_macroblock_tree_read( h, fenc, pic_in->prop.quant_offsets ) ) return -1; } else x264_stack_align( x264_adaptive_quant_frame, h, fenc, pic_in->prop.quant_offsets ); if( pic_in->prop.quant_offsets_free ) pic_in->prop.quant_offsets_free( pic_in->prop.quant_offsets ); //降低分辨率处理（原来的一半），线性内插 //注意这里并不是6抽头滤波器的半像素内插 if( h->frames.b_have_lowres ) x264_frame_init_lowres( h, fenc ); /* 2: Place the frame into the queue for its slice type decision */ //步骤2 //fenc放入lookahead.next.list[]队列，等待确定帧类型 x264_lookahead_put_frame( h, fenc ); if( h->frames.i_input <= h->frames.i_delay + 1 - h->i_thread_frames ) { /* Nothing yet to encode, waiting for filling of buffers */ pic_out->i_type = X264_TYPE_AUTO; return 0; } } else { //输入数据为空的时候（Flush Encoder？），不需要lookahead /* signal kills for lookahead thread */ x264_pthread_mutex_lock( &h->lookahead->ifbuf.mutex ); h->lookahead->b_exit_thread = 1; x264_pthread_cond_broadcast( &h->lookahead->ifbuf.cv_fill ); x264_pthread_mutex_unlock( &h->lookahead->ifbuf.mutex ); } h->i_frame++; /* 3: The picture is analyzed in the lookahead */ // 步骤3 //通过lookahead分析帧类型 if( !h->frames.current[0] ) x264_lookahead_get_frames( h ); if( !h->frames.current[0] && x264_lookahead_is_empty( h ) ) return x264_encoder_frame_end( thread_oldest, thread_current, pp_nal, pi_nal, pic_out ); /* ------------------- Get frame to be encoded ------------------------- */ /* 4: get picture to encode */ //从frames.current[]队列取出1帧[0]用于编码 h->fenc = x264_frame_shift( h->frames.current ); /* If applicable, wait for previous frame reconstruction to finish */ if( h->param.b_sliced_threads ) if( x264_threadpool_wait_all( h ) < 0 ) return -1; if( h->i_frame == h->i_thread_frames - 1 ) h->i_reordered_pts_delay = h->fenc->i_reordered_pts; if( h->reconfig ) { x264_encoder_reconfig_apply( h, &h->reconfig_h->param ); h->reconfig = 0; } if( h->fenc->param ) { x264_encoder_reconfig_apply( h, h->fenc->param ); if( h->fenc->param->param_free ) { h->fenc->param->param_free( h->fenc->param ); h->fenc->param = NULL; } } // ok to call this before encoding any frames, since the initial values of fdec have b_kept_as_ref=0 //更新参考帧队列frames.reference[].若为B帧则不更新 //重建帧fdec移植参考帧列表，新建一个fdec if( x264_reference_update( h ) ) return -1; h->fdec->i_lines_completed = -1; if( !IS_X264_TYPE_I( h->fenc->i_type ) ) { int valid_refs_left = 0; for( int i = 0; h->frames.reference[i]; i++ ) if( !h->frames.reference[i]->b_corrupt ) valid_refs_left++; /* No valid reference frames left: force an IDR. */ if( !valid_refs_left ) { h->fenc->b_keyframe = 1; h->fenc->i_type = X264_TYPE_IDR; } } if( h->fenc->b_keyframe ) { h->frames.i_last_keyframe = h->fenc->i_frame; if( h->fenc->i_type == X264_TYPE_IDR ) { h->i_frame_num = 0; h->frames.i_last_idr = h->fenc->i_frame; } } h->sh.i_mmco_command_count = h->sh.i_mmco_remove_from_end = 0; h->b_ref_reorder[0] = h->b_ref_reorder[1] = 0; h->fdec->i_poc = h->fenc->i_poc = 2 * ( h->fenc->i_frame - X264_MAX( h->frames.i_last_idr, 0 ) ); /* ------------------- Setup frame context ----------------------------- */ /* 5: Init data dependent of frame type */ if( h->fenc->i_type == X264_TYPE_IDR ) { //I与IDR区别 //注意IDR会导致参考帧列清空，而I不会 //I图像之后的图像可以引用I图像之间的图像做运动参考 /* reset ref pictures */ i_nal_type = NAL_SLICE_IDR; i_nal_ref_idc = NAL_PRIORITY_HIGHEST; h->sh.i_type = SLICE_TYPE_I; //若是IDR帧，则清空所有参考帧 x264_reference_reset( h ); h->frames.i_poc_last_open_gop = -1; } else if( h->fenc->i_type == X264_TYPE_I ) { //I与IDR区别 //注意IDR会导致参考帧列清空，而I不会 //I图像之后的图像可以引用I图像之间的图像做运动参考 i_nal_type = NAL_SLICE; i_nal_ref_idc = NAL_PRIORITY_HIGH; /* Not completely true but for now it is (as all I/P are kept as ref)*/ h->sh.i_type = SLICE_TYPE_I; x264_reference_hierarchy_reset( h ); if( h->param.b_open_gop ) h->frames.i_poc_last_open_gop = h->fenc->b_keyframe ? h->fenc->i_poc : -1; } else if( h->fenc->i_type == X264_TYPE_P ) { i_nal_type = NAL_SLICE; i_nal_ref_idc = NAL_PRIORITY_HIGH; /* Not completely true but for now it is (as all I/P are kept as ref)*/ h->sh.i_type = SLICE_TYPE_P; x264_reference_hierarchy_reset( h ); h->frames.i_poc_last_open_gop = -1; } else if( h->fenc->i_type == X264_TYPE_BREF ) { //可以作为参考帧的B帧，这是个特色 i_nal_type = NAL_SLICE; i_nal_ref_idc = h->param.i_bframe_pyramid == X264_B_PYRAMID_STRICT ? NAL_PRIORITY_LOW : NAL_PRIORITY_HIGH; h->sh.i_type = SLICE_TYPE_B; x264_reference_hierarchy_reset( h ); } else /* B frame */ { //最普通 i_nal_type = NAL_SLICE; i_nal_ref_idc = NAL_PRIORITY_DISPOSABLE; h->sh.i_type = SLICE_TYPE_B; } //重建帧与编码帧的赋值... h->fdec->i_type = h->fenc->i_type; h->fdec->i_frame = h->fenc->i_frame; h->fenc->b_kept_as_ref = h->fdec->b_kept_as_ref = i_nal_ref_idc != NAL_PRIORITY_DISPOSABLE && h->param.i_keyint_max > 1; h->fdec->mb_info = h->fenc->mb_info; h->fdec->mb_info_free = h->fenc->mb_info_free; h->fenc->mb_info = NULL; h->fenc->mb_info_free = NULL; h->fdec->i_pts = h->fenc->i_pts; if( h->frames.i_bframe_delay ) { int64_t *prev_reordered_pts = thread_current->frames.i_prev_reordered_pts; h->fdec->i_dts = h->i_frame > h->frames.i_bframe_delay ? prev_reordered_pts[ (h->i_frame - h->frames.i_bframe_delay) % h->frames.i_bframe_delay ] : h->fenc->i_reordered_pts - h->frames.i_bframe_delay_time; prev_reordered_pts[ h->i_frame % h->frames.i_bframe_delay ] = h->fenc->i_reordered_pts; } else h->fdec->i_dts = h->fenc->i_reordered_pts; if( h->fenc->i_type == X264_TYPE_IDR ) h->i_last_idr_pts = h->fdec->i_pts; /* ------------------- Init ----------------------------- */ /* build ref list 0/1 */ //创建参考帧列表list0和list1 x264_reference_build_list( h, h->fdec->i_poc ); /* ---------------------- Write the bitstream -------------------------- */ /* Init bitstream context */ //用于输出 if( h->param.b_sliced_threads ) { for( int i = 0; i < h->param.i_threads; i++ ) { bs_init( &h->thread[i]->out.bs, h->thread[i]->out.p_bitstream, h->thread[i]->out.i_bitstream ); h->thread[i]->out.i_nal = 0; } } else { bs_init( &h->out.bs, h->out.p_bitstream, h->out.i_bitstream ); h->out.i_nal = 0; } if( h->param.b_aud ) { int pic_type; if( h->sh.i_type == SLICE_TYPE_I ) pic_type = 0; else if( h->sh.i_type == SLICE_TYPE_P ) pic_type = 1; else if( h->sh.i_type == SLICE_TYPE_B ) pic_type = 2; else pic_type = 7; x264_nal_start( h, NAL_AUD, NAL_PRIORITY_DISPOSABLE ); bs_write( &h->out.bs, 3, pic_type ); bs_rbsp_trailing( &h->out.bs ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + NALU_OVERHEAD; } h->i_nal_type = i_nal_type; h->i_nal_ref_idc = i_nal_ref_idc; if( h->param.b_intra_refresh ) { if( IS_X264_TYPE_I( h->fenc->i_type ) ) { h->fdec->i_frames_since_pir = 0; h->b_queued_intra_refresh = 0; /* PIR is currently only supported with ref == 1, so any intra frame effectively refreshes * the whole frame and counts as an intra refresh. */ h->fdec->f_pir_position = h->mb.i_mb_width; } else if( h->fenc->i_type == X264_TYPE_P ) { int pocdiff = (h->fdec->i_poc - h->fref[0][0]->i_poc)/2; float increment = X264_MAX( ((float)h->mb.i_mb_width-1) / h->param.i_keyint_max, 1 ); h->fdec->f_pir_position = h->fref[0][0]->f_pir_position; h->fdec->i_frames_since_pir = h->fref[0][0]->i_frames_since_pir + pocdiff; if( h->fdec->i_frames_since_pir >= h->param.i_keyint_max || (h->b_queued_intra_refresh && h->fdec->f_pir_position + 0.5 >= h->mb.i_mb_width) ) { h->fdec->f_pir_position = 0; h->fdec->i_frames_since_pir = 0; h->b_queued_intra_refresh = 0; h->fenc->b_keyframe = 1; } h->fdec->i_pir_start_col = h->fdec->f_pir_position+0.5; h->fdec->f_pir_position += increment * pocdiff; h->fdec->i_pir_end_col = h->fdec->f_pir_position+0.5; /* If our intra refresh has reached the right side of the frame, we're done. */ if( h->fdec->i_pir_end_col >= h->mb.i_mb_width - 1 ) { h->fdec->f_pir_position = h->mb.i_mb_width; h->fdec->i_pir_end_col = h->mb.i_mb_width - 1; } } } if( h->fenc->b_keyframe ) { //每个关键帧前面重复加上SPS和PPS /* Write SPS and PPS */ if( h->param.b_repeat_headers ) { /* generate sequence parameters */ x264_nal_start( h, NAL_SPS, NAL_PRIORITY_HIGHEST ); x264_sps_write( &h->out.bs, h->sps ); if( x264_nal_end( h ) ) return -1; /* Pad AUD/SPS to 256 bytes like Panasonic */ if( h->param.i_avcintra_class ) h->out.nal[h->out.i_nal-1].i_padding = 256 - bs_pos( &h->out.bs ) / 8 - 2*NALU_OVERHEAD; overhead += h->out.nal[h->out.i_nal-1].i_payload + h->out.nal[h->out.i_nal-1].i_padding + NALU_OVERHEAD; /* generate picture parameters */ x264_nal_start( h, NAL_PPS, NAL_PRIORITY_HIGHEST ); x264_pps_write( &h->out.bs, h->sps, h->pps ); if( x264_nal_end( h ) ) return -1; if( h->param.i_avcintra_class ) h->out.nal[h->out.i_nal-1].i_padding = 256 - h->out.nal[h->out.i_nal-1].i_payload - NALU_OVERHEAD; overhead += h->out.nal[h->out.i_nal-1].i_payload + h->out.nal[h->out.i_nal-1].i_padding + NALU_OVERHEAD; } /* when frame threading is used, buffering period sei is written in x264_encoder_frame_end */ if( h->i_thread_frames == 1 && h->sps->vui.b_nal_hrd_parameters_present ) { x264_hrd_fullness( h ); x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_buffering_period_write( h, &h->out.bs ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; } } /* write extra sei */ //下面很大一段代码用于写入SEI（一部分是为了适配其他的解码器）========================================== for( int i = 0; i < h->fenc->extra_sei.num_payloads; i++ ) { x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_write( &h->out.bs, h->fenc->extra_sei.payloads[i].payload, h->fenc->extra_sei.payloads[i].payload_size, h->fenc->extra_sei.payloads[i].payload_type ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; if( h->fenc->extra_sei.sei_free ) { h->fenc->extra_sei.sei_free( h->fenc->extra_sei.payloads[i].payload ); h->fenc->extra_sei.payloads[i].payload = NULL; } } if( h->fenc->extra_sei.sei_free ) { h->fenc->extra_sei.sei_free( h->fenc->extra_sei.payloads ); h->fenc->extra_sei.payloads = NULL; h->fenc->extra_sei.sei_free = NULL; } //特殊的SEI信息（Avid等解码器需要） if( h->fenc->b_keyframe ) { /* Avid's decoder strictly wants two SEIs for AVC-Intra so we can't insert the x264 SEI */ if( h->param.b_repeat_headers && h->fenc->i_frame == 0 && !h->param.i_avcintra_class ) { /* identify ourself */ x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); if( x264_sei_version_write( h, &h->out.bs ) ) return -1; if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; } if( h->fenc->i_type != X264_TYPE_IDR ) { int time_to_recovery = h->param.b_open_gop ? 0 : X264_MIN( h->mb.i_mb_width - 1, h->param.i_keyint_max ) + h->param.i_bframe - 1; x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_recovery_point_write( h, &h->out.bs, time_to_recovery ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; } } if( h->param.i_frame_packing >= 0 && (h->fenc->b_keyframe || h->param.i_frame_packing == 5) ) { x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_frame_packing_write( h, &h->out.bs ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; } /* generate sei pic timing */ if( h->sps->vui.b_pic_struct_present || h->sps->vui.b_nal_hrd_parameters_present ) { x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_pic_timing_write( h, &h->out.bs ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; } /* As required by Blu-ray. */ if( !IS_X264_TYPE_B( h->fenc->i_type ) && h->b_sh_backup ) { h->b_sh_backup = 0; x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_dec_ref_pic_marking_write( h, &h->out.bs ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; } if( h->fenc->b_keyframe && h->param.b_intra_refresh ) h->i_cpb_delay_pir_offset_next = h->fenc->i_cpb_delay; /* Filler space: 10 or 18 SEIs' worth of space, depending on resolution */ if( h->param.i_avcintra_class ) { /* Write an empty filler NAL to mimic the AUD in the P2 format*/ x264_nal_start( h, NAL_FILLER, NAL_PRIORITY_DISPOSABLE ); x264_filler_write( h, &h->out.bs, 0 ); if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + NALU_OVERHEAD; /* All lengths are magic lengths that decoders expect to see */ /* "UMID" SEI */ x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); if( x264_sei_avcintra_umid_write( h, &h->out.bs ) < 0 ) return -1; if( x264_nal_end( h ) ) return -1; overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD; int unpadded_len; int total_len; if( h->param.i_height == 1080 ) { unpadded_len = 5780; total_len = 17*512; } else { unpadded_len = 2900; total_len = 9*512; } /* "VANC" SEI */ x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); if( x264_sei_avcintra_vanc_write( h, &h->out.bs, unpadded_len ) < 0 ) return -1; if( x264_nal_end( h ) ) return -1; h->out.nal[h->out.i_nal-1].i_padding = total_len - h->out.nal[h->out.i_nal-1].i_payload - SEI_OVERHEAD; overhead += h->out.nal[h->out.i_nal-1].i_payload + h->out.nal[h->out.i_nal-1].i_padding + SEI_OVERHEAD; } //写入SEI代码结束======================================================== /* Init the rate control */ /* FIXME: Include slice header bit cost. */ //码率控制单元初始化 x264_ratecontrol_start( h, h->fenc->i_qpplus1, overhead*8 ); i_global_qp = x264_ratecontrol_qp( h ); pic_out->i_qpplus1 = h->fdec->i_qpplus1 = i_global_qp + 1; if( h->param.rc.b_stat_read && h->sh.i_type != SLICE_TYPE_I ) { x264_reference_build_list_optimal( h ); x264_reference_check_reorder( h ); } if( h->i_ref[0] ) h->fdec->i_poc_l0ref0 = h->fref[0][0]->i_poc; /* ------------------------ Create slice header ----------------------- */ //创建Slice Header x264_slice_init( h, i_nal_type, i_global_qp ); /*------------------------- Weights -------------------------------------*/ //加权预测 if( h->sh.i_type == SLICE_TYPE_B ) x264_macroblock_bipred_init( h ); x264_weighted_pred_init( h ); if( i_nal_ref_idc != NAL_PRIORITY_DISPOSABLE ) h->i_frame_num++; /* Write frame */ h->i_threadslice_start = 0; h->i_threadslice_end = h->mb.i_mb_height; if( h->i_thread_frames > 1 ) { x264_threadpool_run( h->threadpool, (void*)x264_slices_write, h ); h->b_thread_active = 1; } else if( h->param.b_sliced_threads ) { if( x264_threaded_slices_write( h ) ) return -1; } else{ //真正的编码——编码1个图像帧（注意这里“slices”后面有“s”） if( (intptr_t)x264_slices_write( h ) ) return -1; } //结束的时候做一些处理，记录一些统计信息 //输出NALU //输出重建帧 return x264_encoder_frame_end( thread_oldest, thread_current, pp_nal, pi_nal, pic_out );}从源代码可以看出，x264_encoder_encode()的流程大致如下：
（1）调用x264_frame_pop_unused获取一个空的fenc（x264_frame_t类型）用于存储一帧编码像素数据。下文将会按照步骤对上述函数进行简单的分析。
（2）调用x264_frame_copy_picture()将外部结构体的pic_in（x264_picture_t类型）的数据拷贝给内部结构体的fenc（x264_frame_t类型）。
（3）调用x264_lookahead_put_frame()将fenc放入Lookahead模块的队列中，等待确定帧类型。
（4）调用x264_lookahead_get_frames()分析Lookahead模块中一个帧的帧类型。分析后的帧保存在frames.current[]中。
（5）调用x264_frame_shift()从frames.current[]中取出分析帧类型之后的fenc。
（6）调用x264_reference_update()更新参考帧队列frames.reference[]。
（7）如果编码帧fenc是IDR帧，调用x264_reference_reset()清空参考帧队列frames.reference[]。
（8）调用x264_reference_build_list()创建参考帧列表List0和List1。
（9）根据选项做一些配置：a)如果b_aud不为0，输出AUD类型NALUb)在当前帧是关键帧的情况下，如果b_repeat_headers不为0，调用x264_sps_write()和x264_pps_write()输出SPS和PPS。c)输出一些特殊的SEI信息，用于适配各种解码器。（10）调用x264_slice_init()初始化Slice Header信息。
（11）调用x264_slices_write()进行编码。该部分是libx264的核心，在后续文章中会详细分析。（12）调用x264_encoder_frame_end()做一些编码后的后续处理。
x264_frame_pop_unused()
x264_frame_pop_unused()用于获取1个x264_frame_t类型结构体fenc。该函数的定义位于common\frame.c，如下所示。//获取一帧的编码帧fenc或者重建帧fdecx264_frame_t *x264_frame_pop_unused( x264_t *h, int b_fdec ){ x264_frame_t *frame; if( h->frames.unused[b_fdec][0] )//unused队列不为空 frame = x264_frame_pop( h->frames.unused[b_fdec] );//从unused队列取 else frame = x264_frame_new( h, b_fdec );//分配一帧空间 if( !frame ) return NULL; frame->b_last_minigop_bframe = 0; frame->i_reference_count = 1; frame->b_intra_calculated = 0; frame->b_scenecut = 1; frame->b_keyframe = 0; frame->b_corrupt = 0; frame->i_slice_count = h->param.b_sliced_threads ? h->param.i_threads : 1; memset( frame->weight, 0, sizeof(frame->weight) ); memset( frame->f_weighted_cost_delta, 0, sizeof(frame->f_weighted_cost_delta) ); return frame;}从源代码可以看出，如果frames.unused[]队列不为空，x264_frame_pop_unused()就调用x264_frame_pop()从unused[]队列取1个现成的；否则就调用x264_frame_new()创建一个新的。下面看一下这两个函数。
x264_frame_pop()
x264_frame_pop()用于从一个队列的尾部取出一个帧。该函数的定义位于common\frame.c，如下所示。//从队列的尾部取出一帧x264_frame_t *x264_frame_pop( x264_frame_t **list ){ x264_frame_t *frame; int i = 0; assert( list[0] ); while( list[i+1] ) i++; frame = list[i]; list[i] = NULL; return frame;}从源代码中可以看出，x264_frame_pop()首先通过一个while()循环找到队列尾部的元素，然后将该元素作为返回值返回。
x264_frame_new()
x264_frame_new()用于新建一个x264_frame_t。该函数的定义位于common\frame.c，如下所示。//新建一个帧//b_fdec：取1的时候为重建帧fdec，取0的时候为编码帧fencstatic x264_frame_t *x264_frame_new( x264_t *h, int b_fdec ){ x264_frame_t *frame; //注意转换后只有3种colorspace：X264_CSP_NV12(对应YUV420),X264_CSP_NV16(对应YUV422),X264_CSP_I444(对应YUV444) int i_csp = x264_frame_internal_csp( h->param.i_csp ); int i_mb_count = h->mb.i_mb_count; int i_stride, i_width, i_lines, luma_plane_count; int i_padv = PADV << PARAM_INTERLACED; int align = 16;#if ARCH_X86 || ARCH_X86_64 if( h->param.cpu&X264_CPU_CACHELINE_64 ) align = 64; else if( h->param.cpu&X264_CPU_CACHELINE_32 || h->param.cpu&X264_CPU_AVX2 ) align = 32;#endif#if ARCH_PPC int disalign = 1<<9;#else int disalign = 1<<10;#endif //给frame分配内存，并置零 CHECKED_MALLOCZERO( frame, sizeof(x264_frame_t) ); PREALLOC_INIT /* allocate frame data (+64 for extra data for me) */ //以像素为单位的宽高 i_width = h->mb.i_mb_width*16; i_lines = h->mb.i_mb_height*16; i_stride = align_stride( i_width + 2*PADH, align, disalign ); if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 ) { //YUV422,YUV420情况 luma_plane_count = 1; frame->i_plane = 2; for( int i = 0; i < 2; i++ ) { frame->i_width[i] = i_width >> i; frame->i_lines[i] = i_lines >> (i && i_csp == X264_CSP_NV12); frame->i_stride[i] = i_stride; } } else if( i_csp == X264_CSP_I444 ) { //YUV444情况 luma_plane_count = 3; frame->i_plane = 3; for( int i = 0; i < 3; i++ ) { frame->i_width[i] = i_width; frame->i_lines[i] = i_lines; frame->i_stride[i] = i_stride; } } else goto fail; //赋值赋值赋值... frame->i_csp = i_csp; frame->i_width_lowres = frame->i_width[0]/2; frame->i_lines_lowres = frame->i_lines[0]/2; frame->i_stride_lowres = align_stride( frame->i_width_lowres + 2*PADH, align, disalign<<1 ); for( int i = 0; i < h->param.i_bframe + 2; i++ ) for( int j = 0; j < h->param.i_bframe + 2; j++ ) PREALLOC( frame->i_row_satds[i][j], i_lines/16 * sizeof(int) ); frame->i_poc = -1; frame->i_type = X264_TYPE_AUTO; frame->i_qpplus1 = X264_QP_AUTO; frame->i_pts = -1; frame->i_frame = -1; frame->i_frame_num = -1; frame->i_lines_completed = -1; frame->b_fdec = b_fdec; frame->i_pic_struct = PIC_STRUCT_AUTO; frame->i_field_cnt = -1; frame->i_duration = frame->i_cpb_duration = frame->i_dpb_output_delay = frame->i_cpb_delay = 0; frame->i_coded_fields_lookahead = frame->i_cpb_delay_lookahead = -1; frame->orig = frame; if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 ) { int chroma_padv = i_padv >> (i_csp == X264_CSP_NV12); int chroma_plane_size = (frame->i_stride[1] * (frame->i_lines[1] + 2*chroma_padv)); PREALLOC( frame->buffer[1], chroma_plane_size * sizeof(pixel) ); if( PARAM_INTERLACED ) PREALLOC( frame->buffer_fld[1], chroma_plane_size * sizeof(pixel) ); } /* all 4 luma planes allocated together, since the cacheline split code * requires them to be in-phase wrt cacheline alignment. */ for( int p = 0; p < luma_plane_count; p++ ) { int luma_plane_size = align_plane_size( frame->i_stride[p] * (frame->i_lines[p] + 2*i_padv), disalign ); if( h->param.analyse.i_subpel_refine && b_fdec ) { /* FIXME: Don't allocate both buffers in non-adaptive MBAFF. */ PREALLOC( frame->buffer[p], 4*luma_plane_size * sizeof(pixel) ); if( PARAM_INTERLACED ) PREALLOC( frame->buffer_fld[p], 4*luma_plane_size * sizeof(pixel) ); } else { PREALLOC( frame->buffer[p], luma_plane_size * sizeof(pixel) ); if( PARAM_INTERLACED ) PREALLOC( frame->buffer_fld[p], luma_plane_size * sizeof(pixel) ); } } frame->b_duplicate = 0; if( b_fdec ) /* fdec frame */ { //重建帧fdec PREALLOC( frame->mb_type, i_mb_count * sizeof(int8_t) ); PREALLOC( frame->mb_partition, i_mb_count * sizeof(uint8_t) ); PREALLOC( frame->mv[0], 2*16 * i_mb_count * sizeof(int16_t) ); PREALLOC( frame->mv16x16, 2*(i_mb_count+1) * sizeof(int16_t) ); PREALLOC( frame->ref[0], 4 * i_mb_count * sizeof(int8_t) ); if( h->param.i_bframe ) { PREALLOC( frame->mv[1], 2*16 * i_mb_count * sizeof(int16_t) ); PREALLOC( frame->ref[1], 4 * i_mb_count * sizeof(int8_t) ); } else { frame->mv[1] = NULL; frame->ref[1] = NULL; } PREALLOC( frame->i_row_bits, i_lines/16 * sizeof(int) ); PREALLOC( frame->f_row_qp, i_lines/16 * sizeof(float) ); PREALLOC( frame->f_row_qscale, i_lines/16 * sizeof(float) ); if( h->param.analyse.i_me_method >= X264_ME_ESA ) PREALLOC( frame->buffer[3], frame->i_stride[0] * (frame->i_lines[0] + 2*i_padv) * sizeof(uint16_t) << h->frames.b_have_sub8x8_esa ); if( PARAM_INTERLACED ) PREALLOC( frame->field, i_mb_count * sizeof(uint8_t) ); if( h->param.analyse.b_mb_info ) PREALLOC( frame->effective_qp, i_mb_count * sizeof(uint8_t) ); } else /* fenc frame */ { //编码帧fenc if( h->frames.b_have_lowres ) { int luma_plane_size = align_plane_size( frame->i_stride_lowres * (frame->i_lines[0]/2 + 2*PADV), disalign ); PREALLOC( frame->buffer_lowres[0], 4 * luma_plane_size * sizeof(pixel) ); for( int j = 0; j <= !!h->param.i_bframe; j++ ) for( int i = 0; i <= h->param.i_bframe; i++ ) { PREALLOC( frame->lowres_mvs[j][i], 2*h->mb.i_mb_count*sizeof(int16_t) ); PREALLOC( frame->lowres_mv_costs[j][i], h->mb.i_mb_count*sizeof(int) ); } PREALLOC( frame->i_propagate_cost, (i_mb_count+7) * sizeof(uint16_t) ); for( int j = 0; j <= h->param.i_bframe+1; j++ ) for( int i = 0; i <= h->param.i_bframe+1; i++ ) PREALLOC( frame->lowres_costs[j][i], (i_mb_count+3) * sizeof(uint16_t) ); } if( h->param.rc.i_aq_mode ) { PREALLOC( frame->f_qp_offset, h->mb.i_mb_count * sizeof(float) ); PREALLOC( frame->f_qp_offset_aq, h->mb.i_mb_count * sizeof(float) ); if( h->frames.b_have_lowres ) PREALLOC( frame->i_inv_qscale_factor, (h->mb.i_mb_count+3) * sizeof(uint16_t) ); } } PREALLOC_END( frame->base ); if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 ) { int chroma_padv = i_padv >> (i_csp == X264_CSP_NV12); frame->plane[1] = frame->buffer[1] + frame->i_stride[1] * chroma_padv + PADH; if( PARAM_INTERLACED ) frame->plane_fld[1] = frame->buffer_fld[1] + frame->i_stride[1] * chroma_padv + PADH; } for( int p = 0; p < luma_plane_count; p++ ) { int luma_plane_size = align_plane_size( frame->i_stride[p] * (frame->i_lines[p] + 2*i_padv), disalign ); if( h->param.analyse.i_subpel_refine && b_fdec ) { for( int i = 0; i < 4; i++ ) { frame->filtered[p][i] = frame->buffer[p] + i*luma_plane_size + frame->i_stride[p] * i_padv + PADH; frame->filtered_fld[p][i] = frame->buffer_fld[p] + i*luma_plane_size + frame->i_stride[p] * i_padv + PADH; } frame->plane[p] = frame->filtered[p][0]; frame->plane_fld[p] = frame->filtered_fld[p][0]; } else { frame->filtered[p][0] = frame->plane[p] = frame->buffer[p] + frame->i_stride[p] * i_padv + PADH; frame->filtered_fld[p][0] = frame->plane_fld[p] = frame->buffer_fld[p] + frame->i_stride[p] * i_padv + PADH; } } if( b_fdec ) { M32( frame->mv16x16[0] ) = 0; frame->mv16x16++; if( h->param.analyse.i_me_method >= X264_ME_ESA ) frame->integral = (uint16_t*)frame->buffer[3] + frame->i_stride[0] * i_padv + PADH; } else { if( h->frames.b_have_lowres ) { int luma_plane_size = align_plane_size( frame->i_stride_lowres * (frame->i_lines[0]/2 + 2*PADV), disalign ); for( int i = 0; i < 4; i++ ) frame->lowres[i] = frame->buffer_lowres[0] + (frame->i_stride_lowres * PADV + PADH) + i * luma_plane_size; for( int j = 0; j <= !!h->param.i_bframe; j++ ) for( int i = 0; i <= h->param.i_bframe; i++ ) memset( frame->lowres_mvs[j][i], 0, 2*h->mb.i_mb_count*sizeof(int16_t) ); frame->i_intra_cost = frame->lowres_costs[0][0]; memset( frame->i_intra_cost, -1, (i_mb_count+3) * sizeof(uint16_t) ); if( h->param.rc.i_aq_mode ) /* shouldn't really be initialized, just silences a valgrind false-positive in x264_mbtree_propagate_cost_sse2 */ memset( frame->i_inv_qscale_factor, 0, (h->mb.i_mb_count+3) * sizeof(uint16_t) ); } } if( x264_pthread_mutex_init( &frame->mutex, NULL ) ) goto fail; if( x264_pthread_cond_init( &frame->cv, NULL ) ) goto fail;#if HAVE_OPENCL frame->opencl.ocl = h->opencl.ocl;#endif return frame;fail: x264_free( frame ); return NULL;}从源代码中可以看出，x264_frame_new()声明了一个frame指针，并在后续过程中对该frame的成员变量进行内存分配和注释。需要注意的是编码帧fenc和重建帧fdec初始化的变量是不一样的——函数的输入参数b_fdec不为0的时候初始化重建帧，否则初始化编码帧。在这个函数中涉及到一个简单的函数x264_frame_internal_csp()，用于把种类繁多的外部Colorspace转换为简单的内部Colorspace。
x264_frame_internal_csp()
x264_frame_internal_csp()用于把外部Colorspace转换为内部Colorspace。该函数的定义如下所示。
//注意转换后只有3种内部colorspace：X264_CSP_NV12(对应YUV420),X264_CSP_NV16(对应YUV422),X264_CSP_I444(对应YUV444)static int x264_frame_internal_csp( int external_csp ){ switch( external_csp & X264_CSP_MASK ) { case X264_CSP_NV12: case X264_CSP_I420: case X264_CSP_YV12: return X264_CSP_NV12; case X264_CSP_NV16: case X264_CSP_I422: case X264_CSP_YV16: case X264_CSP_V210: return X264_CSP_NV16; case X264_CSP_I444: case X264_CSP_YV24: case X264_CSP_BGR: case X264_CSP_BGRA: case X264_CSP_RGB: return X264_CSP_I444; default: return X264_CSP_NONE; }}x264_frame_copy_picture()
x264_frame_copy_picture()用于将外部结构体x264_picture_t的数据拷贝给内部结构体x264_frame_t。该函数的定义位于common\frame.c，如下所示。//拷贝帧数据//src（外部结构体x264_picture_t）到dst（内部结构体x264_frame_t）int x264_frame_copy_picture( x264_t *h, x264_frame_t *dst, x264_picture_t *src ){ int i_csp = src->img.i_csp & X264_CSP_MASK; //注意转换后只有3种内部colorspace：X264_CSP_NV12(对应YUV420),X264_CSP_NV16(对应YUV422),X264_CSP_I444(对应YUV444) if( dst->i_csp != x264_frame_internal_csp( i_csp ) ) { x264_log( h, X264_LOG_ERROR, "Invalid input colorspace\n" ); return -1; }#if HIGH_BIT_DEPTH if( !(src->img.i_csp & X264_CSP_HIGH_DEPTH) ) { x264_log( h, X264_LOG_ERROR, "This build of x264 requires high depth input. Rebuild to support 8-bit input.\n" ); return -1; }#else if( src->img.i_csp & X264_CSP_HIGH_DEPTH ) { x264_log( h, X264_LOG_ERROR, "This build of x264 requires 8-bit input. Rebuild to support high depth input.\n" ); return -1; }#endif if( BIT_DEPTH != 10 && i_csp == X264_CSP_V210 ) { x264_log( h, X264_LOG_ERROR, "v210 input is only compatible with bit-depth of 10 bits\n" ); return -1; } //赋值赋值赋值 dst->i_type = src->i_type; dst->i_qpplus1 = src->i_qpplus1; dst->i_pts = dst->i_reordered_pts = src->i_pts; dst->param = src->param; dst->i_pic_struct = src->i_pic_struct; dst->extra_sei = src->extra_sei; dst->opaque = src->opaque; dst->mb_info = h->param.analyse.b_mb_info ? src->prop.mb_info : NULL; dst->mb_info_free = h->param.analyse.b_mb_info ? src->prop.mb_info_free : NULL; uint8_t *pix[3]; int stride[3]; if( i_csp == X264_CSP_V210 ) { stride[0] = src->img.i_stride[0]; pix[0] = src->img.plane[0]; h->mc.plane_copy_deinterleave_v210( dst->plane[0], dst->i_stride[0], dst->plane[1], dst->i_stride[1], (uint32_t *)pix[0], stride[0]/sizeof(uint32_t), h->param.i_width, h->param.i_height ); } else if( i_csp >= X264_CSP_BGR ) { stride[0] = src->img.i_stride[0]; pix[0] = src->img.plane[0]; if( src->img.i_csp & X264_CSP_VFLIP ) { pix[0] += (h->param.i_height-1) * stride[0]; stride[0] = -stride[0]; } int b = i_csp==X264_CSP_RGB; h->mc.plane_copy_deinterleave_rgb( dst->plane[1+b], dst->i_stride[1+b], dst->plane[0], dst->i_stride[0], dst->plane[2-b], dst->i_stride[2-b], (pixel*)pix[0], stride[0]/sizeof(pixel), i_csp==X264_CSP_BGRA ? 4 : 3, h->param.i_width, h->param.i_height ); } else { int v_shift = CHROMA_V_SHIFT; get_plane_ptr( h, src, &pix[0], &stride[0], 0, 0, 0 ); //拷贝像素 h->mc.plane_copy( dst->plane[0], dst->i_stride[0], (pixel*)pix[0], stride[0]/sizeof(pixel), h->param.i_width, h->param.i_height ); if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 ) { get_plane_ptr( h, src, &pix[1], &stride[1], 1, 0, v_shift ); h->mc.plane_copy( dst->plane[1], dst->i_stride[1], (pixel*)pix[1], stride[1]/sizeof(pixel), h->param.i_width, h->param.i_height>>v_shift ); } else if( i_csp == X264_CSP_I420 || i_csp == X264_CSP_I422 || i_csp == X264_CSP_YV12 || i_csp == X264_CSP_YV16 ) { int uv_swap = i_csp == X264_CSP_YV12 || i_csp == X264_CSP_YV16; get_plane_ptr( h, src, &pix[1], &stride[1], uv_swap ? 2 : 1, 1, v_shift ); get_plane_ptr( h, src, &pix[2], &stride[2], uv_swap ? 1 : 2, 1, v_shift ); h->mc.plane_copy_interleave( dst->plane[1], dst->i_stride[1], (pixel*)pix[1], stride[1]/sizeof(pixel), (pixel*)pix[2], stride[2]/sizeof(pixel), h->param.i_width>>1, h->param.i_height>>v_shift ); } else //if( i_csp == X264_CSP_I444 || i_csp == X264_CSP_YV24 ) { get_plane_ptr( h, src, &pix[1], &stride[1], i_csp==X264_CSP_I444 ? 1 : 2, 0, 0 ); get_plane_ptr( h, src, &pix[2], &stride[2], i_csp==X264_CSP_I444 ? 2 : 1, 0, 0 ); h->mc.plane_copy( dst->plane[1], dst->i_stride[1], (pixel*)pix[1], stride[1]/sizeof(pixel), h->param.i_width, h->param.i_height ); h->mc.plane_copy( dst->plane[2], dst->i_stride[2], (pixel*)pix[2], stride[2]/sizeof(pixel), h->param.i_width, h->param.i_height ); } } return 0;}从源代码可以看出，x264_frame_t和x264_picture_t结构体中很多字段是一模一样的，x264_frame_copy_picture()只是简单地将x264_picture_t中字段的值赋值给了x264_frame_t。
x264_lookahead_put_frame()
x264_lookahead_put_frame()将编码帧放入Lookahead模块的队列中，等待确定帧类型。该函数的定义位于encoder\lookahead.c，如下所示。//x264_frame_t放入x264_sync_frame_list_t队列void x264_lookahead_put_frame( x264_t *h, x264_frame_t *frame ){ if( h->param.i_sync_lookahead ) x264_sync_frame_list_push( &h->lookahead->ifbuf, frame ); else x264_sync_frame_list_push( &h->lookahead->next, frame );//放入next队列}从源代码可以看出，i_sync_lookahead不为0的时候，会将编码帧放入lookahead.ifbuf[]中，否则会将编码帧放入lookahead.next[]中。放入帧的时候会调用x264_sync_frame_list_push()。
x264_sync_frame_list_push()
x264_sync_frame_list_push()用于向x264_sync_frame_list_t类型的队列中放入一个帧。该函数的定义位于common\frame.c，如下所示。void x264_sync_frame_list_push( x264_sync_frame_list_t *slist, x264_frame_t *frame ){ x264_pthread_mutex_lock( &slist->mutex ); while( slist->i_size == slist->i_max_size ) x264_pthread_cond_wait( &slist->cv_empty, &slist->mutex ); //放入 slist->list[ slist->i_size++ ] = frame; x264_pthread_mutex_unlock( &slist->mutex ); x264_pthread_cond_broadcast( &slist->cv_fill );}从源代码中可以看出，x264_sync_frame_list_push()将frame放在了x264_sync_frame_list_t.list的尾部。
x264_lookahead_get_frames()
x264_lookahead_get_frames()通过lookahead模块分析帧类型。该函数的定义位于encoder\lookahead.c，如下所示。//通过lookahead分析帧类型void x264_lookahead_get_frames( x264_t *h ){ if( h->param.i_sync_lookahead ) { /* We have a lookahead thread, so get frames from there */ x264_pthread_mutex_lock( &h->lookahead->ofbuf.mutex ); while( !h->lookahead->ofbuf.i_size && h->lookahead->b_thread_active ) x264_pthread_cond_wait( &h->lookahead->ofbuf.cv_fill, &h->lookahead->ofbuf.mutex ); x264_lookahead_encoder_shift( h ); x264_pthread_mutex_unlock( &h->lookahead->ofbuf.mutex ); } else { /* We are not running a lookahead thread, so perform all the slicetype decide on the fly */ //currect[]必须为空，next不能为空？ if( h->frames.current[0] || !h->lookahead->next.i_size ) return; //分析lookahead->next->list帧的类型 x264_stack_align( x264_slicetype_decide, h ); //更新lookahead->last_nonb x264_lookahead_update_last_nonb( h, h->lookahead->next.list[0] ); int shift_frames = h->lookahead->next.list[0]->i_bframes + 1; //lookahead->next.list移动到lookahead->ofbuf.list x264_lookahead_shift( &h->lookahead->ofbuf, &h->lookahead->next, shift_frames ); /* For MB-tree and VBV lookahead, we have to perform propagation analysis on I-frames too. */ if( h->lookahead->b_analyse_keyframe && IS_X264_TYPE_I( h->lookahead->last_nonb->i_type ) ) x264_stack_align( x264_slicetype_analyse, h, shift_frames ); //lookahead->ofbuf.list帧移动到frames->current x264_lookahead_encoder_shift( h ); }}从源代码中可以看出，x264_lookahead_get_frames()调用了x264_slicetype_decide()用于确定帧类型。在这里需要注意，Lookahead模块的代码量比较大，暂时不做详细的分析，仅简单理一下脉络。
x264_slicetype_decide()
x264_slicetype_decide()用于确定帧类型，该函数的定义位于encoder\slicetype.c，如下所示。//确定帧的类型（I、B、P）void x264_slicetype_decide( x264_t *h ){ x264_frame_t *frames[X264_BFRAME_MAX+2]; x264_frame_t *frm; int bframes; int brefs; if( !h->lookahead->next.i_size ) return; int lookahead_size = h->lookahead->next.i_size; //遍历next队列 for( int i = 0; i < h->lookahead->next.i_size; i++ ) { if( h->param.b_vfr_input ) { if( lookahead_size-- > 1 ) h->lookahead->next.list[i]->i_duration = 2 * (h->lookahead->next.list[i+1]->i_pts - h->lookahead->next.list[i]->i_pts); else h->lookahead->next.list[i]->i_duration = h->i_prev_duration; } else h->lookahead->next.list[i]->i_duration = delta_tfi_divisor[h->lookahead->next.list[i]->i_pic_struct]; h->i_prev_duration = h->lookahead->next.list[i]->i_duration; h->lookahead->next.list[i]->f_duration = (double)h->lookahead->next.list[i]->i_duration * h->sps->vui.i_num_units_in_tick / h->sps->vui.i_time_scale; if( h->lookahead->next.list[i]->i_frame > h->i_disp_fields_last_frame && lookahead_size > 0 ) { h->lookahead->next.list[i]->i_field_cnt = h->i_disp_fields; h->i_disp_fields += h->lookahead->next.list[i]->i_duration; h->i_disp_fields_last_frame = h->lookahead->next.list[i]->i_frame; } else if( lookahead_size == 0 ) { h->lookahead->next.list[i]->i_field_cnt = h->i_disp_fields; h->lookahead->next.list[i]->i_duration = h->i_prev_duration; } } if( h->param.rc.b_stat_read ) { //b_stat_read在2pass模式的第2遍才不为0 /* Use the frame types from the first pass */ for( int i = 0; i < h->lookahead->next.i_size; i++ ) h->lookahead->next.list[i]->i_type = x264_ratecontrol_slice_type( h, h->lookahead->next.list[i]->i_frame ); } else if( (h->param.i_bframe && h->param.i_bframe_adaptive) || h->param.i_scenecut_threshold || h->param.rc.b_mb_tree || (h->param.rc.i_vbv_buffer_size && h->param.rc.i_lookahead) ) x264_slicetype_analyse( h, 0 );//分析帧的类型（I、B、P） //=========================================================================== for( bframes = 0, brefs = 0;; bframes++ ) { //从next队列取出1个 frm = h->lookahead->next.list[bframes]; //BREF的处理 if( frm->i_type == X264_TYPE_BREF && h->param.i_bframe_pyramid < X264_B_PYRAMID_NORMAL && brefs == h->param.i_bframe_pyramid ) { //BREF改成B frm->i_type = X264_TYPE_B; x264_log( h, X264_LOG_WARNING, "B-ref at frame %d incompatible with B-pyramid %s \n", frm->i_frame, x264_b_pyramid_names[h->param.i_bframe_pyramid] ); } /* pyramid with multiple B-refs needs a big enough dpb that the preceding P-frame stays available. smaller dpb could be supported by smart enough use of mmco, but it's easier just to forbid it. */ else if( frm->i_type == X264_TYPE_BREF && h->param.i_bframe_pyramid == X264_B_PYRAMID_NORMAL && brefs && h->param.i_frame_reference <= (brefs+3) ) { frm->i_type = X264_TYPE_B; x264_log( h, X264_LOG_WARNING, "B-ref at frame %d incompatible with B-pyramid %s and %d reference frames\n", frm->i_frame, x264_b_pyramid_names[h->param.i_bframe_pyramid], h->param.i_frame_reference ); } //Keyframe处理 if( frm->i_type == X264_TYPE_KEYFRAME ) frm->i_type = h->param.b_open_gop ? X264_TYPE_I : X264_TYPE_IDR; /* Limit GOP size */ if( (!h->param.b_intra_refresh || frm->i_frame == 0) && frm->i_frame - h->lookahead->i_last_keyframe >= h->param.i_keyint_max ) { if( frm->i_type == X264_TYPE_AUTO || frm->i_type == X264_TYPE_I ) frm->i_type = h->param.b_open_gop && h->lookahead->i_last_keyframe >= 0 ? X264_TYPE_I : X264_TYPE_IDR; int warn = frm->i_type != X264_TYPE_IDR; if( warn && h->param.b_open_gop ) warn &= frm->i_type != X264_TYPE_I; if( warn ) { x264_log( h, X264_LOG_WARNING, "specified frame type (%d) at %d is not compatible with keyframe interval\n", frm->i_type, frm->i_frame ); frm->i_type = h->param.b_open_gop && h->lookahead->i_last_keyframe >= 0 ? X264_TYPE_I : X264_TYPE_IDR; } } if( frm->i_type == X264_TYPE_I && frm->i_frame - h->lookahead->i_last_keyframe >= h->param.i_keyint_min ) { if( h->param.b_open_gop ) { h->lookahead->i_last_keyframe = frm->i_frame; // Use display order if( h->param.b_bluray_compat ) h->lookahead->i_last_keyframe -= bframes; // Use bluray order frm->b_keyframe = 1; } else frm->i_type = X264_TYPE_IDR; } if( frm->i_type == X264_TYPE_IDR ) { /* Close GOP */ //设置当前帧为“上一个关键帧” h->lookahead->i_last_keyframe = frm->i_frame; frm->b_keyframe = 1; if( bframes > 0 ) { bframes--; h->lookahead->next.list[bframes]->i_type = X264_TYPE_P; } } if( bframes == h->param.i_bframe || !h->lookahead->next.list[bframes+1] ) { if( IS_X264_TYPE_B( frm->i_type ) ) x264_log( h, X264_LOG_WARNING, "specified frame type is not compatible with max B-frames\n" ); if( frm->i_type == X264_TYPE_AUTO || IS_X264_TYPE_B( frm->i_type ) ) frm->i_type = X264_TYPE_P; } if( frm->i_type == X264_TYPE_BREF ) brefs++; if( frm->i_type == X264_TYPE_AUTO ) frm->i_type = X264_TYPE_B; else if( !IS_X264_TYPE_B( frm->i_type ) ) break; } if( bframes ) h->lookahead->next.list[bframes-1]->b_last_minigop_bframe = 1; h->lookahead->next.list[bframes]->i_bframes = bframes; /* insert a bref into the sequence */ if( h->param.i_bframe_pyramid && bframes > 1 && !brefs ) { h->lookahead->next.list[bframes/2]->i_type = X264_TYPE_BREF; brefs++; } /* calculate the frame costs ahead of time for x264_rc_analyse_slice while we still have lowres */ if( h->param.rc.i_rc_method != X264_RC_CQP ) { x264_mb_analysis_t a; int p0, p1, b; p1 = b = bframes + 1; x264_lowres_context_init( h, &a ); frames[0] = h->lookahead->last_nonb; memcpy( &frames[1], h->lookahead->next.list, (bframes+1) * sizeof(x264_frame_t*) ); if( IS_X264_TYPE_I( h->lookahead->next.list[bframes]->i_type ) ) p0 = bframes + 1; else // P p0 = 0; x264_slicetype_frame_cost( h, &a, frames, p0, p1, b, 0 ); if( (p0 != p1 || bframes) && h->param.rc.i_vbv_buffer_size ) { /* We need the intra costs for row SATDs. */ x264_slicetype_frame_cost( h, &a, frames, b, b, b, 0 ); /* We need B-frame costs for row SATDs. */ p0 = 0; for( b = 1; b <= bframes; b++ ) { if( frames[b]->i_type == X264_TYPE_B ) for( p1 = b; frames[p1]->i_type == X264_TYPE_B; ) p1++; else p1 = bframes + 1; x264_slicetype_frame_cost( h, &a, frames, p0, p1, b, 0 ); if( frames[b]->i_type == X264_TYPE_BREF ) p0 = b; } } } /* Analyse for weighted P frames */ if( !h->param.rc.b_stat_read && h->lookahead->next.list[bframes]->i_type == X264_TYPE_P && h->param.analyse.i_weighted_pred >= X264_WEIGHTP_SIMPLE ) { x264_emms(); x264_weights_analyse( h, h->lookahead->next.list[bframes], h->lookahead->last_nonb, 0 ); } /* shift sequence to coded order. use a small temporary list to avoid shifting the entire next buffer around */ int i_coded = h->lookahead->next.list[0]->i_frame; if( bframes ) { int idx_list[] = { brefs+1, 1 }; for( int i = 0; i < bframes; i++ ) { int idx = idx_list[h->lookahead->next.list[i]->i_type == X264_TYPE_BREF]++; frames[idx] = h->lookahead->next.list[i]; frames[idx]->i_reordered_pts = h->lookahead->next.list[idx]->i_pts; } frames[0] = h->lookahead->next.list[bframes]; frames[0]->i_reordered_pts = h->lookahead->next.list[0]->i_pts; memcpy( h->lookahead->next.list, frames, (bframes+1) * sizeof(x264_frame_t*) ); } for( int i = 0; i <= bframes; i++ ) { h->lookahead->next.list[i]->i_coded = i_coded++; if( i ) { x264_calculate_durations( h, h->lookahead->next.list[i], h->lookahead->next.list[i-1], &h->i_cpb_delay, &h->i_coded_fields ); h->lookahead->next.list[0]->f_planned_cpb_duration[i-1] = (double)h->lookahead->next.list[i]->i_cpb_duration * h->sps->vui.i_num_units_in_tick / h->sps->vui.i_time_scale; } else x264_calculate_durations( h, h->lookahead->next.list[i], NULL, &h->i_cpb_delay, &h->i_coded_fields ); }}x264_slicetype_decide()源代码比较长，还没有细看。该函数中调用了一个比较重要的函数x264_slicetype_analyse()。
x264_slicetype_analyse()
x264_slicetype_analyse()用于分析帧类型。该函数的定义位于encoder\slicetype.c，如下所示。//分析帧的类型（I、B、P）void x264_slicetype_analyse( x264_t *h, int intra_minigop ){ x264_mb_analysis_t a; x264_frame_t *frames[X264_LOOKAHEAD_MAX+3] = { NULL, }; int num_frames, orig_num_frames, keyint_limit, framecnt; int i_mb_count = NUM_MBS; int cost1p0, cost2p0, cost1b1, cost2p1; // 确定最大的搜索长度 // 在我的调试当中， h->lookahead->next.i_size = 4 int i_max_search = X264_MIN( h->lookahead->next.i_size, X264_LOOKAHEAD_MAX ); int vbv_lookahead = h->param.rc.i_vbv_buffer_size && h->param.rc.i_lookahead; /* For determinism we should limit the search to the number of frames lookahead has for sure * in h->lookahead->next.list buffer, except at the end of stream. * For normal calls with (intra_minigop == 0) that is h->lookahead->i_slicetype_length + 1 frames. * And for I-frame calls (intra_minigop != 0) we already removed intra_minigop frames from there. */ if( h->param.b_deterministic ) i_max_search = X264_MIN( i_max_search, h->lookahead->i_slicetype_length + 1 - intra_minigop ); int keyframe = !!intra_minigop; assert( h->frames.b_have_lowres ); if( !h->lookahead->last_nonb ) return; //frames[0]指向上一次的非B帧 frames[0] = h->lookahead->last_nonb; //frames[] 依次指向 lookahead->next链表中的帧 for( framecnt = 0; framecnt < i_max_search && h->lookahead->next.list[framecnt]->i_type == X264_TYPE_AUTO; framecnt++ ) frames[framecnt+1] = h->lookahead->next.list[framecnt]; x264_lowres_context_init( h, &a ); if( !framecnt ) { if( h->param.rc.b_mb_tree ) x264_macroblock_tree( h, &a, frames, 0, keyframe ); return; } keyint_limit = h->param.i_keyint_max - frames[0]->i_frame + h->lookahead->i_last_keyframe - 1; orig_num_frames = num_frames = h->param.b_intra_refresh ? framecnt : X264_MIN( framecnt, keyint_limit ); /* This is important psy-wise: if we have a non-scenecut keyframe, * there will be significant visual artifacts if the frames just before * go down in quality due to being referenced less, despite it being * more RD-optimal. */ if( (h->param.analyse.b_psy && h->param.rc.b_mb_tree) || vbv_lookahead ) num_frames = framecnt; else if( h->param.b_open_gop && num_frames < framecnt ) num_frames++; else if( num_frames == 0 ) { frames[1]->i_type = X264_TYPE_I; return; } int num_bframes = 0; int num_analysed_frames = num_frames; int reset_start; //通过scenecut()函数判断是否有场景切换，从而确定I帧 if( h->param.i_scenecut_threshold && scenecut( h, &a, frames, 0, 1, 1, orig_num_frames, i_max_search ) ) { frames[1]->i_type = X264_TYPE_I; return; }#if HAVE_OPENCL x264_opencl_slicetype_prep( h, frames, num_frames, a.i_lambda );#endif //允许有B帧的时候 if( h->param.i_bframe ) { if( h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS ) { if( num_frames > 1 ) { char best_paths[X264_BFRAME_MAX+1][X264_LOOKAHEAD_MAX+1] = {"","P"}; int best_path_index = num_frames % (X264_BFRAME_MAX+1); /* Perform the frametype analysis. */ for( int j = 2; j <= num_frames; j++ ) x264_slicetype_path( h, &a, frames, j, best_paths ); num_bframes = strspn( best_paths[best_path_index], "B" ); /* Load the results of the analysis into the frame types. */ for( int j = 1; j < num_frames; j++ ) frames[j]->i_type = best_paths[best_path_index][j-1] == 'B' ? X264_TYPE_B : X264_TYPE_P; } frames[num_frames]->i_type = X264_TYPE_P; } else if( h->param.i_bframe_adaptive == X264_B_ADAPT_FAST ) { for( int i = 0; i <= num_frames-2; ) { //i+2作为Ｐ帧编码的代价 //注：i+2始终为P帧 cost2p1 = x264_slicetype_frame_cost( h, &a, frames, i+0, i+2, i+2, 1 ); if( frames[i+2]->i_intra_mbs[2] > i_mb_count / 2 ) { frames[i+1]->i_type = X264_TYPE_P; frames[i+2]->i_type = X264_TYPE_P; i += 2; continue; }#if HAVE_OPENCL if( h->param.b_opencl ) { int b_work_done = 0; b_work_done |= x264_opencl_precalculate_frame_cost(h, frames, a.i_lambda, i+0, i+2, i+1 ); b_work_done |= x264_opencl_precalculate_frame_cost(h, frames, a.i_lambda, i+0, i+1, i+1 ); b_work_done |= x264_opencl_precalculate_frame_cost(h, frames, a.i_lambda, i+1, i+2, i+2 ); if( b_work_done ) x264_opencl_flush( h ); }#endif //计算代价 //x264_slicetype_frame_cost(,,,p0,p1,b,) //p0 b p1 //p1!=b为B帧，否则为P帧 // i + 1 作为B帧编码的代价 cost1b1 = x264_slicetype_frame_cost( h, &a, frames, i+0, i+2, i+1, 0 ); // i + 1 作为P帧编码的代价 cost1p0 = x264_slicetype_frame_cost( h, &a, frames, i+0, i+1, i+1, 0 ); // i + 2 作为P帧编码的代价 cost2p0 = x264_slicetype_frame_cost( h, &a, frames, i+1, i+2, i+2, 0 ); //如果i+1作为P帧编码的代价 + i+2作为P帧编码的代价 //小于 i+1作为B帧编码的代价 + i+2作为P帧编码的代价 if( cost1p0 + cost2p0 < cost1b1 + cost2p1 ) { //那么i+1将作为P帧编码 //然后直接continue frames[i+1]->i_type = X264_TYPE_P; i += 1; continue; } // arbitrary and untuned #define INTER_THRESH 300 #define P_SENS_BIAS (50 - h->param.i_bframe_bias) // i+1 将作为B帧编码 frames[i+1]->i_type = X264_TYPE_B; int j; for( j = i+2; j <= X264_MIN( i+h->param.i_bframe, num_frames-1 ); j++ ) { int pthresh = X264_MAX(INTER_THRESH - P_SENS_BIAS * (j-i-1), INTER_THRESH/10); // 预测j+1作为P帧编码代价 int pcost = x264_slicetype_frame_cost( h, &a, frames, i+0, j+1, j+1, 1 ); // 如果pcost 满足下述条件， 则确定了一个P帧，跳出循环 if( pcost > pthresh*i_mb_count || frames[j+1]->i_intra_mbs[j-i+1] > i_mb_count/3 ) break; // 否则就是B帧 frames[j]->i_type = X264_TYPE_B; } // 将j帧确定为P帧 frames[j]->i_type = X264_TYPE_P; i = j; } // 最后一帧确定为P帧 frames[num_frames]->i_type = X264_TYPE_P; num_bframes = 0; // 确定有多少个B帧 while( num_bframes < num_frames && frames[num_bframes+1]->i_type == X264_TYPE_B ) num_bframes++; } else { // 确定多少B帧 num_bframes = X264_MIN(num_frames-1, h->param.i_bframe); // 每num_bframes + 1一个P帧， 其余皆为B帧 for( int j = 1; j < num_frames; j++ ) frames[j]->i_type = (j%(num_bframes+1)) ? X264_TYPE_B : X264_TYPE_P; // 最后一帧为P帧 frames[num_frames]->i_type = X264_TYPE_P; } /* Check scenecut on the first minigop. */ // 如果B帧中， 有帧有场景切换， 则改变其为P帧 for( int j = 1; j < num_bframes+1; j++ ) if( h->param.i_scenecut_threshold && scenecut( h, &a, frames, j, j+1, 0, orig_num_frames, i_max_search ) ) { frames[j]->i_type = X264_TYPE_P; num_analysed_frames = j; break; } reset_start = keyframe ? 1 : X264_MIN( num_bframes+2, num_analysed_frames+1 ); } else { //h->param.i_bframe为 0 //则所有的帧皆为P帧 for( int j = 1; j <= num_frames; j++ ) frames[j]->i_type = X264_TYPE_P; reset_start = !keyframe + 1; num_bframes = 0; } /* Perform the actual macroblock tree analysis. * Don't go farther than the maximum keyframe interval; this helps in short GOPs. */ if( h->param.rc.b_mb_tree ) x264_macroblock_tree( h, &a, frames, X264_MIN(num_frames, h->param.i_keyint_max), keyframe ); /* Enforce keyframe limit. */ if( !h->param.b_intra_refresh ) for( int i = keyint_limit+1; i <= num_frames; i += h->param.i_keyint_max ) { //迫使为I帧 frames[i]->i_type = X264_TYPE_I; reset_start = X264_MIN( reset_start, i+1 ); if( h->param.b_open_gop && h->param.b_bluray_compat ) while( IS_X264_TYPE_B( frames[i-1]->i_type ) ) i--; } if( vbv_lookahead ) x264_vbv_lookahead( h, &a, frames, num_frames, keyframe ); /* Restore frametypes for all frames that haven't actually been decided yet. */ for( int j = reset_start; j <= num_frames; j++ ) frames[j]->i_type = X264_TYPE_AUTO;#if HAVE_OPENCL x264_opencl_slicetype_end( h );#endif}通过源代码可以看出，x264_slicetype_analyse()分析了frames[]队列中的视频帧的帧类型。简单总结一下该函数的流程：
（1）如果frames[1]通过scenecut()判断为场景切换，设置为I帧，并且直接返回。有关帧类型判断在代码中已经做了注释，不再详细记录，下文继续看一下x264_slicetype_frame_cost()函数。
（2）如果i_bframe为0，即不使用B帧，则将所有帧都设置为P帧。
（3）如果i_bframe不为0，即使用B帧，则需要进行比较复杂的帧开销计算。这时候需要调用一帧图像开销的计算函数x264_slicetype_frame_cost()。
x264_slicetype_frame_cost()
x264_slicetype_frame_cost()用于计算一帧图像的开销。该函数的定义位于encoder\slicetype.c，如下所示。//一帧图像的开销//x264_slicetype_frame_cost(,,,p0,p1,b,)// p0 b p1static int x264_slicetype_frame_cost( x264_t *h, x264_mb_analysis_t *a, x264_frame_t **frames, int p0, int p1, int b, int b_intra_penalty ){ int i_score = 0; int do_search[2]; const x264_weight_t *w = x264_weight_none; x264_frame_t *fenc = frames[b]; /* Check whether we already evaluated this frame * If we have tried this frame as P, then we have also tried * the preceding frames as B. (is this still true?) */ /* Also check that we already calculated the row SATDs for the current frame. */ //如果已经计算过就不用算了 if( fenc->i_cost_est[b-p0][p1-b] >= 0 && (!h->param.rc.i_vbv_buffer_size || fenc->i_row_satds[b-p0][p1-b][0] != -1) ) i_score = fenc->i_cost_est[b-p0][p1-b]; else { int dist_scale_factor = 128; /* For each list, check to see whether we have lowres motion-searched this reference frame before. */ do_search[0] = b != p0 && fenc->lowres_mvs[0][b-p0-1][0][0] == 0x7FFF; do_search[1] = b != p1 && fenc->lowres_mvs[1][p1-b-1][0][0] == 0x7FFF; if( do_search[0] ) { if( h->param.analyse.i_weighted_pred && b == p1 ) { x264_emms(); x264_weights_analyse( h, fenc, frames[p0], 1 ); w = fenc->weight[0]; } fenc->lowres_mvs[0][b-p0-1][0][0] = 0; } if( do_search[1] ) fenc->lowres_mvs[1][p1-b-1][0][0] = 0; if( p1 != p0 ) dist_scale_factor = ( ((b-p0) << 8) + ((p1-p0) >> 1) ) / (p1-p0); int output_buf_size = h->mb.i_mb_height + (NUM_INTS + PAD_SIZE) * h->param.i_lookahead_threads; int *output_inter[X264_LOOKAHEAD_THREAD_MAX+1]; int *output_intra[X264_LOOKAHEAD_THREAD_MAX+1]; output_inter[0] = h->scratch_buffer2; output_intra[0] = output_inter[0] + output_buf_size;#if HAVE_OPENCL if( h->param.b_opencl ) { x264_opencl_lowres_init(h, fenc, a->i_lambda ); if( do_search[0] ) { x264_opencl_lowres_init( h, frames[p0], a->i_lambda ); x264_opencl_motionsearch( h, frames, b, p0, 0, a->i_lambda, w ); } if( do_search[1] ) { x264_opencl_lowres_init( h, frames[p1], a->i_lambda ); x264_opencl_motionsearch( h, frames, b, p1, 1, a->i_lambda, NULL ); } if( b != p0 ) x264_opencl_finalize_cost( h, a->i_lambda, frames, p0, p1, b, dist_scale_factor ); x264_opencl_flush( h ); i_score = fenc->i_cost_est[b-p0][p1-b]; } else#endif { if( h->param.i_lookahead_threads > 1 ) { x264_slicetype_slice_t s[X264_LOOKAHEAD_THREAD_MAX]; for( int i = 0; i < h->param.i_lookahead_threads; i++ ) { x264_t *t = h->lookahead_thread[i]; /* FIXME move this somewhere else */ t->mb.i_me_method = h->mb.i_me_method; t->mb.i_subpel_refine = h->mb.i_subpel_refine; t->mb.b_chroma_me = h->mb.b_chroma_me; s[i] = (x264_slicetype_slice_t){ t, a, frames, p0, p1, b, dist_scale_factor, do_search, w, output_inter[i], output_intra[i] }; t->i_threadslice_start = ((h->mb.i_mb_height * i + h->param.i_lookahead_threads/2) / h->param.i_lookahead_threads); t->i_threadslice_end = ((h->mb.i_mb_height * (i+1) + h->param.i_lookahead_threads/2) / h->param.i_lookahead_threads); int thread_height = t->i_threadslice_end - t->i_threadslice_start; int thread_output_size = thread_height + NUM_INTS; memset( output_inter[i], 0, thread_output_size * sizeof(int) ); memset( output_intra[i], 0, thread_output_size * sizeof(int) ); output_inter[i][NUM_ROWS] = output_intra[i][NUM_ROWS] = thread_height; output_inter[i+1] = output_inter[i] + thread_output_size + PAD_SIZE; output_intra[i+1] = output_intra[i] + thread_output_size + PAD_SIZE; x264_threadpool_run( h->lookaheadpool, (void*)x264_slicetype_slice_cost, &s[i] ); } for( int i = 0; i < h->param.i_lookahead_threads; i++ ) x264_threadpool_wait( h->lookaheadpool, &s[i] ); } else { h->i_threadslice_start = 0; h->i_threadslice_end = h->mb.i_mb_height; memset( output_inter[0], 0, (output_buf_size - PAD_SIZE) * sizeof(int) ); memset( output_intra[0], 0, (output_buf_size - PAD_SIZE) * sizeof(int) ); output_inter[0][NUM_ROWS] = output_intra[0][NUM_ROWS] = h->mb.i_mb_height; //作为参数的结构体 x264_slicetype_slice_t s = (x264_slicetype_slice_t){ h, a, frames, p0, p1, b, dist_scale_factor, do_search, w, output_inter[0], output_intra[0] }; //一个slice的开销 //输入输出参数都在s结构体中 x264_slicetype_slice_cost( &s ); } /* Sum up accumulators */ if( b == p1 ) fenc->i_intra_mbs[b-p0] = 0; if( !fenc->b_intra_calculated ) { fenc->i_cost_est[0][0] = 0; fenc->i_cost_est_aq[0][0] = 0; } fenc->i_cost_est[b-p0][p1-b] = 0; fenc->i_cost_est_aq[b-p0][p1-b] = 0; int *row_satd_inter = fenc->i_row_satds[b-p0][p1-b]; int *row_satd_intra = fenc->i_row_satds[0][0]; for( int i = 0; i < h->param.i_lookahead_threads; i++ ) { //累加output_inter[]或output_intra[] //这2个变量中存储了整帧的开销 if( b == p1 ) fenc->i_intra_mbs[b-p0] += output_inter[i][INTRA_MBS]; if( !fenc->b_intra_calculated ) { //帧内编码的代价 fenc->i_cost_est[0][0] += output_intra[i][COST_EST]; fenc->i_cost_est_aq[0][0] += output_intra[i][COST_EST_AQ]; } //帧间编码的代价 fenc->i_cost_est[b-p0][p1-b] += output_inter[i][COST_EST]; fenc->i_cost_est_aq[b-p0][p1-b] += output_inter[i][COST_EST_AQ]; if( h->param.rc.i_vbv_buffer_size ) { int row_count = output_inter[i][NUM_ROWS]; memcpy( row_satd_inter, output_inter[i] + NUM_INTS, row_count * sizeof(int) ); if( !fenc->b_intra_calculated ) memcpy( row_satd_intra, output_intra[i] + NUM_INTS, row_count * sizeof(int) ); row_satd_inter += row_count; row_satd_intra += row_count; } } //一帧的开销 i_score = fenc->i_cost_est[b-p0][p1-b]; if( b != p1 )//B帧 i_score = (uint64_t)i_score * 100 / (120 + h->param.i_bframe_bias); else fenc->b_intra_calculated = 1; fenc->i_cost_est[b-p0][p1-b] = i_score; x264_emms(); } } if( b_intra_penalty ) { // arbitrary penalty for I-blocks after B-frames int nmb = NUM_MBS; i_score += (uint64_t)i_score * fenc->i_intra_mbs[b-p0] / (nmb * 8); } //返回一帧的开销值 return i_score;}从源代码可以看出，x264_slicetype_analyse()调用了x264_slicetype_slice_cost()来计算一个slice的开销。
x264_slicetype_slice_cost()
x264_slicetype_slice_cost()用来计算一个slice的开销。该函数的定义位于encoder\slicetype.c，如下所示。//一个slice的开销static void x264_slicetype_slice_cost( x264_slicetype_slice_t *s ){ x264_t *h = s->h; /* Lowres lookahead goes backwards because the MVs are used as predictors in the main encode. * This considerably improves MV prediction overall. */ /* The edge mbs seem to reduce the predictive quality of the * whole frame's score, but are needed for a spatial distribution. */ int do_edges = h->param.rc.b_mb_tree || h->param.rc.i_vbv_buffer_size || h->mb.i_mb_width <= 2 || h->mb.i_mb_height <= 2; int start_y = X264_MIN( h->i_threadslice_end - 1, h->mb.i_mb_height - 2 + do_edges ); int end_y = X264_MAX( h->i_threadslice_start, 1 - do_edges ); int start_x = h->mb.i_mb_width - 2 + do_edges; int end_x = 1 - do_edges; //逐个计算每个MB的开销 for( h->mb.i_mb_y = start_y; h->mb.i_mb_y >= end_y; h->mb.i_mb_y-- ) for( h->mb.i_mb_x = start_x; h->mb.i_mb_x >= end_x; h->mb.i_mb_x-- ) x264_slicetype_mb_cost( h, s->a, s->frames, s->p0, s->p1, s->b, s->dist_scale_factor, s->do_search, s->w, s->output_inter, s->output_intra );}从源代码可以看出，x264_slicetype_slice_cost()循环遍历了每一个宏块，针对每一个宏块调用了x264_slicetype_mb_cost()。
x264_slicetype_mb_cost()
x264_slicetype_mb_cost()用于计算一个宏块的编码代价。该函数的定义位于encoder\slicetype.c，如下所示。//一个MB的开销static void x264_slicetype_mb_cost( x264_t *h, x264_mb_analysis_t *a, x264_frame_t **frames, int p0, int p1, int b, int dist_scale_factor, int do_search[2], const x264_weight_t *w, int *output_inter, int *output_intra ){ x264_frame_t *fref0 = frames[p0]; x264_frame_t *fref1 = frames[p1]; x264_frame_t *fenc = frames[b]; const int b_bidir = (b < p1); const int i_mb_x = h->mb.i_mb_x; const int i_mb_y = h->mb.i_mb_y; const int i_mb_stride = h->mb.i_mb_width; const int i_mb_xy = i_mb_x + i_mb_y * i_mb_stride; const int i_stride = fenc->i_stride_lowres; const int i_pel_offset = 8 * (i_mb_x + i_mb_y * i_stride); const int i_bipred_weight = h->param.analyse.b_weighted_bipred ? 64 - (dist_scale_factor>>2) : 32; int16_t (*fenc_mvs[2])[2] = { &fenc->lowres_mvs[0][b-p0-1][i_mb_xy], &fenc->lowres_mvs[1][p1-b-1][i_mb_xy] }; int (*fenc_costs[2]) = { &fenc->lowres_mv_costs[0][b-p0-1][i_mb_xy], &fenc->lowres_mv_costs[1][p1-b-1][i_mb_xy] }; int b_frame_score_mb = (i_mb_x > 0 && i_mb_x < h->mb.i_mb_width - 1 && i_mb_y > 0 && i_mb_y < h->mb.i_mb_height - 1) || h->mb.i_mb_width <= 2 || h->mb.i_mb_height <= 2; ALIGNED_ARRAY_16( pixel, pix1,[9*FDEC_STRIDE] ); pixel *pix2 = pix1+8; x264_me_t m[2]; int i_bcost = COST_MAX; int list_used = 0; /* A small, arbitrary bias to avoid VBV problems caused by zero-residual lookahead blocks. */ int lowres_penalty = 4; //计算只涉及一个分量 h->mb.pic.p_fenc[0] = h->mb.pic.fenc_buf; //从低分辨率（1/2线性内插）图像中拷贝数据 h->mc.copy[PIXEL_8x8]( h->mb.pic.p_fenc[0], FENC_STRIDE, &fenc->lowres[0][i_pel_offset], i_stride, 8 ); if( p0 == p1 ) goto lowres_intra_mb; // no need for h->mb.mv_min[] h->mb.mv_limit_fpel[0][0] = -8*h->mb.i_mb_x - 4; h->mb.mv_limit_fpel[1][0] = 8*( h->mb.i_mb_width - h->mb.i_mb_x - 1 ) + 4; h->mb.mv_min_spel[0] = 4*( h->mb.mv_limit_fpel[0][0] - 8 ); h->mb.mv_max_spel[0] = 4*( h->mb.mv_limit_fpel[1][0] + 8 ); if( h->mb.i_mb_x >= h->mb.i_mb_width - 2 ) { h->mb.mv_limit_fpel[0][1] = -8*h->mb.i_mb_y - 4; h->mb.mv_limit_fpel[1][1] = 8*( h->mb.i_mb_height - h->mb.i_mb_y - 1 ) + 4; h->mb.mv_min_spel[1] = 4*( h->mb.mv_limit_fpel[0][1] - 8 ); h->mb.mv_max_spel[1] = 4*( h->mb.mv_limit_fpel[1][1] + 8 ); }#define LOAD_HPELS_LUMA(dst, src) \ { \ (dst)[0] = &(src)[0][i_pel_offset]; \ (dst)[1] = &(src)[1][i_pel_offset]; \ (dst)[2] = &(src)[2][i_pel_offset]; \ (dst)[3] = &(src)[3][i_pel_offset]; \ }#define LOAD_WPELS_LUMA(dst,src) \ (dst) = &(src)[i_pel_offset];#define CLIP_MV( mv ) \ { \ mv[0] = x264_clip3( mv[0], h->mb.mv_min_spel[0], h->mb.mv_max_spel[0] ); \ mv[1] = x264_clip3( mv[1], h->mb.mv_min_spel[1], h->mb.mv_max_spel[1] ); \ }#define TRY_BIDIR( mv0, mv1, penalty ) \ { \ int i_cost; \ if( h->param.analyse.i_subpel_refine <= 1 ) \ { \ int hpel_idx1 = (((mv0)[0]&2)>>1) + ((mv0)[1]&2); \ int hpel_idx2 = (((mv1)[0]&2)>>1) + ((mv1)[1]&2); \ pixel *src1 = m[0].p_fref[hpel_idx1] + ((mv0)[0]>>2) + ((mv0)[1]>>2) * m[0].i_stride[0]; \ pixel *src2 = m[1].p_fref[hpel_idx2] + ((mv1)[0]>>2) + ((mv1)[1]>>2) * m[1].i_stride[0]; \ h->mc.avg[PIXEL_8x8]( pix1, 16, src1, m[0].i_stride[0], src2, m[1].i_stride[0], i_bipred_weight ); \ } \ else \ { \ intptr_t stride1 = 16, stride2 = 16; \ pixel *src1, *src2; \ src1 = h->mc.get_ref( pix1, &stride1, m[0].p_fref, m[0].i_stride[0], \ (mv0)[0], (mv0)[1], 8, 8, w ); \ src2 = h->mc.get_ref( pix2, &stride2, m[1].p_fref, m[1].i_stride[0], \ (mv1)[0], (mv1)[1], 8, 8, w ); \ h->mc.avg[PIXEL_8x8]( pix1, 16, src1, stride1, src2, stride2, i_bipred_weight ); \ } \ i_cost = penalty * a->i_lambda + h->pixf.mbcmp[PIXEL_8x8]( \ m[0].p_fenc[0], FENC_STRIDE, pix1, 16 ); \ COPY2_IF_LT( i_bcost, i_cost, list_used, 3 ); \ } //帧间编码（后面还有帧内编码） //处理m[0] m[0].i_pixel = PIXEL_8x8; m[0].p_cost_mv = a->p_cost_mv; m[0].i_stride[0] = i_stride; m[0].p_fenc[0] = h->mb.pic.p_fenc[0]; m[0].weight = w; m[0].i_ref = 0; //加载1/2插值像素点 LOAD_HPELS_LUMA( m[0].p_fref, fref0->lowres ); m[0].p_fref_w = m[0].p_fref[0]; if( w[0].weightfn ) LOAD_WPELS_LUMA( m[0].p_fref_w, fenc->weighted[0] ); //双线预测，处理m[1] if( b_bidir ) { int16_t *mvr = fref1->lowres_mvs[0][p1-p0-1][i_mb_xy]; ALIGNED_ARRAY_8( int16_t, dmv,[2],[2] ); m[1].i_pixel = PIXEL_8x8; m[1].p_cost_mv = a->p_cost_mv; m[1].i_stride[0] = i_stride; m[1].p_fenc[0] = h->mb.pic.p_fenc[0]; m[1].i_ref = 0; m[1].weight = x264_weight_none; LOAD_HPELS_LUMA( m[1].p_fref, fref1->lowres ); m[1].p_fref_w = m[1].p_fref[0]; dmv[0][0] = ( mvr[0] * dist_scale_factor + 128 ) >> 8; dmv[0][1] = ( mvr[1] * dist_scale_factor + 128 ) >> 8; dmv[1][0] = dmv[0][0] - mvr[0]; dmv[1][1] = dmv[0][1] - mvr[1]; CLIP_MV( dmv[0] ); CLIP_MV( dmv[1] ); if( h->param.analyse.i_subpel_refine <= 1 ) M64( dmv ) &= ~0x0001000100010001ULL; /* mv & ~1 */ //双向预测，其中包含了mc.avg[PIXEL_8x8]() TRY_BIDIR( dmv[0], dmv[1], 0 ); if( M64( dmv ) ) { int i_cost; h->mc.avg[PIXEL_8x8]( pix1, 16, m[0].p_fref[0], m[0].i_stride[0], m[1].p_fref[0], m[1].i_stride[0], i_bipred_weight ); i_cost = h->pixf.mbcmp[PIXEL_8x8]( m[0].p_fenc[0], FENC_STRIDE, pix1, 16 ); COPY2_IF_LT( i_bcost, i_cost, list_used, 3 ); } } for( int l = 0; l < 1 + b_bidir; l++ ) { if( do_search[l] ) { int i_mvc = 0; int16_t (*fenc_mv)[2] = fenc_mvs[l]; ALIGNED_4( int16_t mvc[4][2] ); /* Reverse-order MV prediction. */ M32( mvc[0] ) = 0; M32( mvc[2] ) = 0;#define MVC(mv) { CP32( mvc[i_mvc], mv ); i_mvc++; } if( i_mb_x < h->mb.i_mb_width - 1 ) MVC( fenc_mv[1] ); if( i_mb_y < h->i_threadslice_end - 1 ) { MVC( fenc_mv[i_mb_stride] ); if( i_mb_x > 0 ) MVC( fenc_mv[i_mb_stride-1] ); if( i_mb_x < h->mb.i_mb_width - 1 ) MVC( fenc_mv[i_mb_stride+1] ); }#undef MVC if( i_mvc <= 1 ) CP32( m[l].mvp, mvc[0] ); else x264_median_mv( m[l].mvp, mvc[0], mvc[1], mvc[2] ); /* Fast skip for cases of near-zero residual. Shortcut: don't bother except in the mv0 case, * since anything else is likely to have enough residual to not trigger the skip. */ if( !M32( m[l].mvp ) ) { m[l].cost = h->pixf.mbcmp[PIXEL_8x8]( m[l].p_fenc[0], FENC_STRIDE, m[l].p_fref[0], m[l].i_stride[0] ); if( m[l].cost < 64 ) { M32( m[l].mv ) = 0; goto skip_motionest; } } //运动搜索，开销存在m[l].cost中 x264_me_search( h, &m[l], mvc, i_mvc ); m[l].cost -= a->p_cost_mv[0]; // remove mvcost from skip mbs if( M32( m[l].mv ) ) m[l].cost += 5 * a->i_lambda;skip_motionest: CP32( fenc_mvs[l], m[l].mv ); *fenc_costs[l] = m[l].cost; } else { CP32( m[l].mv, fenc_mvs[l] ); m[l].cost = *fenc_costs[l]; } //如果更小就拷贝 //帧间编码开销，存储于i_bcost COPY2_IF_LT( i_bcost, m[l].cost, list_used, l+1 ); } if( b_bidir && ( M32( m[0].mv ) || M32( m[1].mv ) ) ) TRY_BIDIR( m[0].mv, m[1].mv, 5 );lowres_intra_mb://帧内编码 if( !fenc->b_intra_calculated ) { ALIGNED_ARRAY_16( pixel, edge,[36] ); pixel *pix = &pix1[8+FDEC_STRIDE]; pixel *src = &fenc->lowres[0][i_pel_offset]; const int intra_penalty = 5 * a->i_lambda; int satds[3]; int pixoff = 4 / sizeof(pixel); /* Avoid store forwarding stalls by writing larger chunks */ memcpy( pix-FDEC_STRIDE, src-i_stride, 16 * sizeof(pixel) ); for( int i = -1; i < 8; i++ ) M32( &pix[i*FDEC_STRIDE-pixoff] ) = M32( &src[i*i_stride-pixoff] ); //8x8块的SAD/SATD计算 //x3打表计算了V，H，DC三种模式，开销存储在satds[3]数组的3个元素中 h->pixf.intra_mbcmp_x3_8x8c( h->mb.pic.p_fenc[0], pix, satds ); //帧内编码开销，存储于i_icost int i_icost = X264_MIN3( satds[0], satds[1], satds[2] ); if( h->param.analyse.i_subpel_refine > 1 ) { h->predict_8x8c[I_PRED_CHROMA_P]( pix ); int satd = h->pixf.mbcmp[PIXEL_8x8]( pix, FDEC_STRIDE, h->mb.pic.p_fenc[0], FENC_STRIDE ); i_icost = X264_MIN( i_icost, satd ); h->predict_8x8_filter( pix, edge, ALL_NEIGHBORS, ALL_NEIGHBORS ); for( int i = 3; i < 9; i++ ) { h->predict_8x8[i]( pix, edge ); satd = h->pixf.mbcmp[PIXEL_8x8]( pix, FDEC_STRIDE, h->mb.pic.p_fenc[0], FENC_STRIDE ); i_icost = X264_MIN( i_icost, satd ); } } i_icost += intra_penalty + lowres_penalty; //存一下 fenc->i_intra_cost[i_mb_xy] = i_icost; int i_icost_aq = i_icost; if( h->param.rc.i_aq_mode ) i_icost_aq = (i_icost_aq * fenc->i_inv_qscale_factor[i_mb_xy] + 128) >> 8; output_intra[ROW_SATD] += i_icost_aq; if( b_frame_score_mb ) { //累加。[COST_EST]用于整帧的开销计算 output_intra[COST_EST] += i_icost; output_intra[COST_EST_AQ] += i_icost_aq; } } i_bcost += lowres_penalty; /* forbid intra-mbs in B-frames, because it's rare and not worth checking */ /* FIXME: Should we still forbid them now that we cache intra scores? */ if( !b_bidir ) { int i_icost = fenc->i_intra_cost[i_mb_xy]; //帧内开销比帧间更小，b_intra就会取1 int b_intra = i_icost < i_bcost; if( b_intra ) { //赋值给i_bcost i_bcost = i_icost; list_used = 0; } if( b_frame_score_mb ) output_inter[INTRA_MBS] += b_intra;//[INTRA_MBS]统计有多少个帧内模式的宏块 } /* In an I-frame, we've already added the results above in the intra section. */ if( p0 != p1 ) { int i_bcost_aq = i_bcost; if( h->param.rc.i_aq_mode ) i_bcost_aq = (i_bcost_aq * fenc->i_inv_qscale_factor[i_mb_xy] + 128) >> 8; output_inter[ROW_SATD] += i_bcost_aq; if( b_frame_score_mb ) { /* Don't use AQ-weighted costs for slicetype decision, only for ratecontrol. */ //累加。[COST_EST]用于整帧的开销计算 output_inter[COST_EST] += i_bcost; output_inter[COST_EST_AQ] += i_bcost_aq; } } //存储开销i_bcost fenc->lowres_costs[b-p0][p1-b][i_mb_xy] = X264_MIN( i_bcost, LOWRES_COST_MASK ) + (list_used << LOWRES_COST_SHIFT);}#undef TRY_BIDIR宏块开销这里在源代码上写了比较详细的注释，不再详细记录。在这里有一点需要注意：处理的图像是经过1/2线性差值的“低分辨率（lowres）”图片（这样速度更快？），而其中宏块的大小也是以8x8而不是16x16为单位的。
x264_frame_shift()
x264_frame_shift()用于从队列头部取出1帧。该函数的定义位于common\frame.c，如下所示。//从队列的头部取出一帧x264_frame_t *x264_frame_shift( x264_frame_t **list ){ x264_frame_t *frame = list[0]; int i; for( i = 0; list[i]; i++ ) list[i] = list[i+1]; assert(frame); return frame;}从源代码可以看出，x264_frame_shift()取出了list[0]并且作为返回值返回。
x264_reference_update()
x264_reference_update()用于更新参考帧队列（将重建帧fdec加入参考帧队列）。该函数的定义位于encoder\encoder.c，如下所示。//更新参考帧队列，若为非参考B帧则不更新//重建帧移植参考帧列表，新建一个重建帧static inline int x264_reference_update( x264_t *h ){//如果不是被参考的帧 if( !h->fdec->b_kept_as_ref ) { if( h->i_thread_frames > 1 ) { x264_frame_push_unused( h, h->fdec ); h->fdec = x264_frame_pop_unused( h, 1 ); if( !h->fdec ) return -1; } return 0; } /* apply mmco from previous frame. */ for( int i = 0; i < h->sh.i_mmco_command_count; i++ ) for( int j = 0; h->frames.reference[j]; j++ ) if( h->frames.reference[j]->i_poc == h->sh.mmco[i].i_poc ) x264_frame_push_unused( h, x264_frame_shift( &h->frames.reference[j] ) ); /* move frame in the buffer */ //重建帧加入参考帧列表 x264_frame_push( h->frames.reference, h->fdec ); //列表满了，则要移除1帧 if( h->frames.reference[h->sps->i_num_ref_frames] ) x264_frame_push_unused( h, x264_frame_shift( h->frames.reference ) ); //重新初始化重建帧fdec h->fdec = x264_frame_pop_unused( h, 1 ); if( !h->fdec ) return -1; return 0;}从源代码可以看出，如果重建帧fdec是不被参考的B帧，则直接返回；如果fdec是被参考的帧，则会调用x264_frame_push()将该帧加入frames.reference[]队列的尾部。如果frames.reference[]已经满了，则会调用x264_frame_shift()和x264_frame_push_unused()将frames.reference[]队列头部的帧移动到frames.unused[]队列。最后函数还会调用x264_frame_pop_unused()获取一个新的重建帧fdec。
x264_reference_reset()
如果编码帧为IDR帧，就会调用x264_reference_reset()函数清空参考帧列表。该函数定义位于encoder\encoder.c，如下所示。//清空所有参考帧static inline void x264_reference_reset( x264_t *h ){//把frames.reference[]中所有帧移动到frames.unused[] while( h->frames.reference[0] ) x264_frame_push_unused( h, x264_frame_pop( h->frames.reference ) ); h->fdec->i_poc = h->fenc->i_poc = 0;}从源代码可以看出，x264_reference_reset()中调用x264_frame_pop()和x264_frame_push_unused()将frames.reference[]队列中的帧移动到frames.unused[]队列中。
x264_slice_init()
x264_slice_init()用于创建Slice Header，初始化其中的信息。该函数的定义位于encoder\encoder.c，如下所示。//创建Slice Headerstatic inline void x264_slice_init( x264_t *h, int i_nal_type, int i_global_qp ){ /* ------------------------ Create slice header ----------------------- */ if( i_nal_type == NAL_SLICE_IDR ) { //I帧 //对x264_slice_header_t进行赋值 x264_slice_header_init( h, &h->sh, h->sps, h->pps, h->i_idr_pic_id, h->i_frame_num, i_global_qp ); /* alternate id */ if( h->param.i_avcintra_class ) { switch( h->i_idr_pic_id ) { case 5: h->i_idr_pic_id = 3; break; case 3: h->i_idr_pic_id = 4; break; case 4: default: h->i_idr_pic_id = 5; break; } } else h->i_idr_pic_id ^= 1; } else { //非IDR帧 x264_slice_header_init( h, &h->sh, h->sps, h->pps, -1, h->i_frame_num, i_global_qp ); //参考帧列表 h->sh.i_num_ref_idx_l0_active = h->i_ref[0] <= 0 ? 1 : h->i_ref[0]; h->sh.i_num_ref_idx_l1_active = h->i_ref[1] <= 0 ? 1 : h->i_ref[1]; if( h->sh.i_num_ref_idx_l0_active != h->pps->i_num_ref_idx_l0_default_active || (h->sh.i_type == SLICE_TYPE_B && h->sh.i_num_ref_idx_l1_active != h->pps->i_num_ref_idx_l1_default_active) ) { h->sh.b_num_ref_idx_override = 1; } } if( h->fenc->i_type == X264_TYPE_BREF && h->param.b_bluray_compat && h->sh.i_mmco_command_count ) { h->b_sh_backup = 1; h->sh_backup = h->sh; } h->fdec->i_frame_num = h->sh.i_frame_num; if( h->sps->i_poc_type == 0 ) { h->sh.i_poc = h->fdec->i_poc; if( PARAM_INTERLACED ) { h->sh.i_delta_poc_bottom = h->param.b_tff ? 1 : -1; h->sh.i_poc += h->sh.i_delta_poc_bottom == -1; } else h->sh.i_delta_poc_bottom = 0; h->fdec->i_delta_poc[0] = h->sh.i_delta_poc_bottom == -1; h->fdec->i_delta_poc[1] = h->sh.i_delta_poc_bottom == 1; } else { /* Nothing to do ? */ } //主要对mb结构体赋初值 x264_macroblock_slice_init( h );}从源代码可以看出，x264_slice_init()调用x264_slice_header_init()完成了Slice Header “通用”的初始化工作，然后根据帧类型的不同，做了一些特殊参数的设置。下面看一下x264_slice_header_init()。
x264_slice_header_init()
x264_slice_header_init()用于对Slice Header进行初始化工作。该函数的定义如下所示。/* Fill "default" values *///对x264_slice_header_t进行赋值static void x264_slice_header_init( x264_t *h, x264_slice_header_t *sh, x264_sps_t *sps, x264_pps_t *pps, int i_idr_pic_id, int i_frame, int i_qp ){ x264_param_t *param = &h->param; /* First we fill all fields */ sh->sps = sps; sh->pps = pps; sh->i_first_mb = 0; sh->i_last_mb = h->mb.i_mb_count - 1; sh->i_pps_id = pps->i_id; sh->i_frame_num = i_frame; sh->b_mbaff = PARAM_INTERLACED; sh->b_field_pic = 0; /* no field support for now */ sh->b_bottom_field = 0; /* not yet used */ sh->i_idr_pic_id = i_idr_pic_id; /* poc stuff, fixed later */ sh->i_poc = 0; sh->i_delta_poc_bottom = 0; sh->i_delta_poc[0] = 0; sh->i_delta_poc[1] = 0; sh->i_redundant_pic_cnt = 0; h->mb.b_direct_auto_write = h->param.analyse.i_direct_mv_pred == X264_DIRECT_PRED_AUTO && h->param.i_bframe && ( h->param.rc.b_stat_write || !h->param.rc.b_stat_read ); if( !h->mb.b_direct_auto_read && sh->i_type == SLICE_TYPE_B ) { if( h->fref[1][0]->i_poc_l0ref0 == h->fref[0][0]->i_poc ) { if( h->mb.b_direct_auto_write ) sh->b_direct_spatial_mv_pred = ( h->stat.i_direct_score[1] > h->stat.i_direct_score[0] ); else sh->b_direct_spatial_mv_pred = ( param->analyse.i_direct_mv_pred == X264_DIRECT_PRED_SPATIAL ); } else { h->mb.b_direct_auto_write = 0; sh->b_direct_spatial_mv_pred = 1; } } /* else b_direct_spatial_mv_pred was read from the 2pass statsfile */ sh->b_num_ref_idx_override = 0; sh->i_num_ref_idx_l0_active = 1; sh->i_num_ref_idx_l1_active = 1; sh->b_ref_pic_list_reordering[0] = h->b_ref_reorder[0]; sh->b_ref_pic_list_reordering[1] = h->b_ref_reorder[1]; /* If the ref list isn't in the default order, construct reordering header */ for( int list = 0; list < 2; list++ ) { if( sh->b_ref_pic_list_reordering[list] ) { int pred_frame_num = i_frame; for( int i = 0; i < h->i_ref[list]; i++ ) { int diff = h->fref[list][i]->i_frame_num - pred_frame_num; sh->ref_pic_list_order[list][i].idc = ( diff > 0 ); sh->ref_pic_list_order[list][i].arg = (abs(diff) - 1) & ((1 << sps->i_log2_max_frame_num) - 1); pred_frame_num = h->fref[list][i]->i_frame_num; } } } sh->i_cabac_init_idc = param->i_cabac_init_idc; sh->i_qp = SPEC_QP(i_qp); sh->i_qp_delta = sh->i_qp - pps->i_pic_init_qp; sh->b_sp_for_swidth = 0; sh->i_qs_delta = 0; int deblock_thresh = i_qp + 2 * X264_MIN(param->i_deblocking_filter_alphac0, param->i_deblocking_filter_beta); /* If effective qp <= 15, deblocking would have no effect anyway */ if( param->b_deblocking_filter && (h->mb.b_variable_qp || 15 < deblock_thresh ) ) sh->i_disable_deblocking_filter_idc = param->b_sliced_threads ? 2 : 0; else sh->i_disable_deblocking_filter_idc = 1; sh->i_alpha_c0_offset = param->i_deblocking_filter_alphac0 << 1; sh->i_beta_offset = param->i_deblocking_filter_beta << 1;}可以看出x264_slice_header_init()对x264_slice_header_t结构体的成员变量进行了赋值。
x264_slices_write()
编码数据（最关键的步骤）。其中调用了x264_slice_write()完成了编码的工作（注意“x264_slices_write()”和“x264_slice_write()”名字差了一个“s”）。//真正的编码——编码1个图像帧//注意“slice”后面有一个“s”//它其中又调用了一个x264_slice_write()//这一点要区分开static void *x264_slices_write( x264_t *h ){ int i_slice_num = 0; int last_thread_mb = h->sh.i_last_mb; /* init stats */ memset( &h->stat.frame, 0, sizeof(h->stat.frame) ); h->mb.b_reencode_mb = 0; //循环每一个slice（一幅图像可以由多个Slice构成） while( h->sh.i_first_mb + SLICE_MBAFF*h->mb.i_mb_stride <= last_thread_mb ) { h->sh.i_last_mb = last_thread_mb; if( !i_slice_num || !x264_frame_new_slice( h, h->fdec ) ) { if( h->param.i_slice_max_mbs ) { if( SLICE_MBAFF ) { // convert first to mbaff form, add slice-max-mbs, then convert back to normal form int last_mbaff = 2*(h->sh.i_first_mb % h->mb.i_mb_width) + h->mb.i_mb_width*(h->sh.i_first_mb / h->mb.i_mb_width) + h->param.i_slice_max_mbs - 1; int last_x = (last_mbaff % (2*h->mb.i_mb_width))/2; int last_y = (last_mbaff / (2*h->mb.i_mb_width))*2 + 1; h->sh.i_last_mb = last_x + h->mb.i_mb_stride*last_y; } else { h->sh.i_last_mb = h->sh.i_first_mb + h->param.i_slice_max_mbs - 1; if( h->sh.i_last_mb < last_thread_mb && last_thread_mb - h->sh.i_last_mb < h->param.i_slice_min_mbs ) h->sh.i_last_mb = last_thread_mb - h->param.i_slice_min_mbs; } i_slice_num++; } else if( h->param.i_slice_count && !h->param.b_sliced_threads ) { int height = h->mb.i_mb_height >> PARAM_INTERLACED; int width = h->mb.i_mb_width << PARAM_INTERLACED; i_slice_num++; h->sh.i_last_mb = (height * i_slice_num + h->param.i_slice_count/2) / h->param.i_slice_count * width - 1; } } h->sh.i_last_mb = X264_MIN( h->sh.i_last_mb, last_thread_mb ); //真正的编码——编码1个Slice //x264_stack_align()应该是平台优化过程中内存对齐的工作 //实际上就是调用x264_slice_write() if( x264_stack_align( x264_slice_write, h ) ) goto fail; //注意这里对i_first_mb进行了赋值 h->sh.i_first_mb = h->sh.i_last_mb + 1; // if i_first_mb is not the last mb in a row then go to the next mb in MBAFF order if( SLICE_MBAFF && h->sh.i_first_mb % h->mb.i_mb_width ) h->sh.i_first_mb -= h->mb.i_mb_stride; } return (void *)0;fail: /* Tell other threads we're done, so they wouldn't wait for it */ if( h->param.b_sliced_threads ) x264_threadslice_cond_broadcast( h, 2 ); return (void *)-1;}在这里需要注意，x264_slices_write()调用了x264_slice_write()。其中x264_slices_write()的单位为帧，而x264_slice_write()的单位为Slice。最常见的情况下一个帧里面只有一个Slice，但是也有可能一个帧里面有多个Slice。
x264_slice_write()
x264_slice_write()是完成编码工作的函数。该函数中包含了去块效应滤波，运动估计，宏块编码，熵编码等模块，它的调用结构大致如下图所示。
x264_encoder_frame_end()
x264_encoder_frame_end()用于在编码结束后做一些后续处理，例如封装NALU（加上起始码），释放一些中间变量，记录一些统计信息等。该函数的定义位于encoder\encoder.c，如下所示。//结束的时候做一些处理，记录一些统计信息//pp_nal：输出的NALU//pic_out：输出的重建帧static int x264_encoder_frame_end( x264_t *h, x264_t *thread_current, x264_nal_t **pp_nal, int *pi_nal, x264_picture_t *pic_out ){ char psz_message[80]; if( !h->param.b_sliced_threads && h->b_thread_active ) { h->b_thread_active = 0; if( (intptr_t)x264_threadpool_wait( h->threadpool, h ) ) return -1; } if( !h->out.i_nal ) { pic_out->i_type = X264_TYPE_AUTO; return 0; } x264_emms(); /* generate buffering period sei and insert it into place */ if( h->i_thread_frames > 1 && h->fenc->b_keyframe && h->sps->vui.b_nal_hrd_parameters_present ) { x264_hrd_fullness( h ); x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_buffering_period_write( h, &h->out.bs ); if( x264_nal_end( h ) ) return -1; /* buffering period sei must follow AUD, SPS and PPS and precede all other SEIs */ int idx = 0; while( h->out.nal[idx].i_type == NAL_AUD || h->out.nal[idx].i_type == NAL_SPS || h->out.nal[idx].i_type == NAL_PPS ) idx++; x264_nal_t nal_tmp = h->out.nal[h->out.i_nal-1]; memmove( &h->out.nal[idx+1], &h->out.nal[idx], (h->out.i_nal-idx-1)*sizeof(x264_nal_t) ); h->out.nal[idx] = nal_tmp; } //封装一帧数据对应的NALU. //例如给NALU添加起始码0x00000001 int frame_size = x264_encoder_encapsulate_nals( h, 0 ); if( frame_size < 0 ) return -1; /* Set output picture properties */ //pic_out为x264_picture_t类型结构体。是libx264对外的结构体 //fenc,fdec是x264_frame_t类型结构体。是libx264的内部结构体 pic_out->i_type = h->fenc->i_type; pic_out->b_keyframe = h->fenc->b_keyframe; pic_out->i_pic_struct = h->fenc->i_pic_struct; pic_out->i_pts = h->fdec->i_pts; pic_out->i_dts = h->fdec->i_dts; if( pic_out->i_pts < pic_out->i_dts ) x264_log( h, X264_LOG_WARNING, "invalid DTS: PTS is less than DTS\n" ); pic_out->opaque = h->fenc->opaque; pic_out->img.i_csp = h->fdec->i_csp;#if HIGH_BIT_DEPTH pic_out->img.i_csp |= X264_CSP_HIGH_DEPTH;#endif pic_out->img.i_plane = h->fdec->i_plane; //图像数据 for( int i = 0; i < pic_out->img.i_plane; i++ ) { pic_out->img.i_stride[i] = h->fdec->i_stride[i] * sizeof(pixel); pic_out->img.plane[i] = (uint8_t*)h->fdec->plane[i]; } //回收用过的编码帧fenc x264_frame_push_unused( thread_current, h->fenc ); /* ---------------------- Update encoder state ------------------------- */ /* update rc */ int filler = 0; if( x264_ratecontrol_end( h, frame_size * 8, &filler ) < 0 ) return -1; pic_out->hrd_timing = h->fenc->hrd_timing; pic_out->prop.f_crf_avg = h->fdec->f_crf_avg; /* Filler in AVC-Intra mode is written as zero bytes to the last slice * We don't know the size of the last slice until encapsulation so we add filler to the encapsulated NAL */ if( h->param.i_avcintra_class ) { x264_t *h0 = h->thread[0]; int ret = x264_check_encapsulated_buffer( h, h0, h->out.i_nal, frame_size, frame_size + filler ); if( ret < 0 ) return -1; memset( h->out.nal[0].p_payload + frame_size, 0, filler ); h->out.nal[h->out.i_nal-1].i_payload += filler; h->out.nal[h->out.i_nal-1].i_padding = filler; frame_size += filler; } else { while( filler > 0 ) { int f, overhead; overhead = (FILLER_OVERHEAD - h->param.b_annexb); if( h->param.i_slice_max_size && filler > h->param.i_slice_max_size ) { int next_size = filler - h->param.i_slice_max_size; int overflow = X264_MAX( overhead - next_size, 0 ); f = h->param.i_slice_max_size - overhead - overflow; } else f = X264_MAX( 0, filler - overhead ); if( x264_bitstream_check_buffer_filler( h, f ) ) return -1; x264_nal_start( h, NAL_FILLER, NAL_PRIORITY_DISPOSABLE ); x264_filler_write( h, &h->out.bs, f ); if( x264_nal_end( h ) ) return -1; int total_size = x264_encoder_encapsulate_nals( h, h->out.i_nal-1 ); if( total_size < 0 ) return -1; frame_size += total_size; filler -= total_size; } } /* End bitstream, set output */ *pi_nal = h->out.i_nal; *pp_nal = h->out.nal; h->out.i_nal = 0; x264_noise_reduction_update( h ); /* ---------------------- Compute/Print statistics --------------------- */ x264_thread_sync_stat( h, h->thread[0] ); /* Slice stat */ //stat中存储了统计信息 //帧数+1 （根据类型） h->stat.i_frame_count[h->sh.i_type]++; //帧大小 h->stat.i_frame_size[h->sh.i_type] += frame_size; h->stat.f_frame_qp[h->sh.i_type] += h->fdec->f_qp_avg_aq; //统计MB个数，把不同类型的累加起来 for( int i = 0; i < X264_MBTYPE_MAX; i++ ) h->stat.i_mb_count[h->sh.i_type][i] += h->stat.frame.i_mb_count[i]; for( int i = 0; i < X264_PARTTYPE_MAX; i++ ) h->stat.i_mb_partition[h->sh.i_type][i] += h->stat.frame.i_mb_partition[i]; for( int i = 0; i < 2; i++ ) h->stat.i_mb_count_8x8dct[i] += h->stat.frame.i_mb_count_8x8dct[i]; for( int i = 0; i < 6; i++ ) h->stat.i_mb_cbp[i] += h->stat.frame.i_mb_cbp[i]; for( int i = 0; i < 4; i++ ) for( int j = 0; j < 13; j++ ) h->stat.i_mb_pred_mode[i][j] += h->stat.frame.i_mb_pred_mode[i][j]; if( h->sh.i_type != SLICE_TYPE_I ) for( int i_list = 0; i_list < 2; i_list++ ) for( int i = 0; i < X264_REF_MAX*2; i++ ) h->stat.i_mb_count_ref[h->sh.i_type][i_list][i] += h->stat.frame.i_mb_count_ref[i_list][i]; for( int i = 0; i < 3; i++ ) h->stat.i_mb_field[i] += h->stat.frame.i_mb_field[i]; if( h->sh.i_type == SLICE_TYPE_P && h->param.analyse.i_weighted_pred >= X264_WEIGHTP_SIMPLE ) { h->stat.i_wpred[0] += !!h->sh.weight[0][0].weightfn; h->stat.i_wpred[1] += !!h->sh.weight[0][1].weightfn || !!h->sh.weight[0][2].weightfn; } if( h->sh.i_type == SLICE_TYPE_B ) { h->stat.i_direct_frames[ h->sh.b_direct_spatial_mv_pred ] ++; if( h->mb.b_direct_auto_write ) { //FIXME somewhat arbitrary time constants if( h->stat.i_direct_score[0] + h->stat.i_direct_score[1] > h->mb.i_mb_count ) for( int i = 0; i < 2; i++ ) h->stat.i_direct_score[i] = h->stat.i_direct_score[i] * 9/10; for( int i = 0; i < 2; i++ ) h->stat.i_direct_score[i] += h->stat.frame.i_direct_score[i]; } } else h->stat.i_consecutive_bframes[h->fenc->i_bframes]++; psz_message[0] = '\0'; double dur = h->fenc->f_duration; h->stat.f_frame_duration[h->sh.i_type] += dur; //需要计算PSNR if( h->param.analyse.b_psnr ) { //SSD（Sum of Squared Difference）即差值的平方和 int64_t ssd[3] = { h->stat.frame.i_ssd[0], h->stat.frame.i_ssd[1], h->stat.frame.i_ssd[2], }; int luma_size = h->param.i_width * h->param.i_height; int chroma_size = CHROMA_SIZE( luma_size ); //SSD是已经在“滤波”环节计算过的 //SSD简单换算成PSNR，调用x264_psnr() pic_out->prop.f_psnr[0] = x264_psnr( ssd[0], luma_size ); pic_out->prop.f_psnr[1] = x264_psnr( ssd[1], chroma_size ); pic_out->prop.f_psnr[2] = x264_psnr( ssd[2], chroma_size ); //平均值 pic_out->prop.f_psnr_avg = x264_psnr( ssd[0] + ssd[1] + ssd[2], luma_size + chroma_size*2 ); //mean系列的需要累加 h->stat.f_ssd_global[h->sh.i_type] += dur * (ssd[0] + ssd[1] + ssd[2]); h->stat.f_psnr_average[h->sh.i_type] += dur * pic_out->prop.f_psnr_avg; h->stat.f_psnr_mean_y[h->sh.i_type] += dur * pic_out->prop.f_psnr[0]; h->stat.f_psnr_mean_u[h->sh.i_type] += dur * pic_out->prop.f_psnr[1]; h->stat.f_psnr_mean_v[h->sh.i_type] += dur * pic_out->prop.f_psnr[2]; snprintf( psz_message, 80, " PSNR Y:%5.2f U:%5.2f V:%5.2f", pic_out->prop.f_psnr[0], pic_out->prop.f_psnr[1], pic_out->prop.f_psnr[2] ); } //需要计算SSIM if( h->param.analyse.b_ssim ) { //SSIM是已经在“滤波”环节计算过的 pic_out->prop.f_ssim = h->stat.frame.f_ssim / h->stat.frame.i_ssim_cnt; //mean系列的需要累加 h->stat.f_ssim_mean_y[h->sh.i_type] += pic_out->prop.f_ssim * dur; snprintf( psz_message + strlen(psz_message), 80 - strlen(psz_message), " SSIM Y:%.5f", pic_out->prop.f_ssim ); } psz_message[79] = '\0'; //Debug时候输出 x264_log( h, X264_LOG_DEBUG, "frame=%4d QP=%.2f NAL=%d Slice:%c Poc:%-3d I:%-4d P:%-4d SKIP:%-4d size=%d bytes%s\n", h->i_frame, h->fdec->f_qp_avg_aq, h->i_nal_ref_idc, h->sh.i_type == SLICE_TYPE_I ? 'I' : (h->sh.i_type == SLICE_TYPE_P ? 'P' : 'B' ), h->fdec->i_poc, h->stat.frame.i_mb_count_i, h->stat.frame.i_mb_count_p, h->stat.frame.i_mb_count_skip, frame_size, psz_message ); // keep stats all in one place x264_thread_sync_stat( h->thread[0], h ); // for the use of the next frame x264_thread_sync_stat( thread_current, h );#ifdef DEBUG_MB_TYPE{ static const char mb_chars[] = { 'i', 'i', 'I', 'C', 'P', '8', 'S', 'D', '<', 'X', 'B', 'X', '>', 'B', 'B', 'B', 'B', '8', 'S' }; for( int mb_xy = 0; mb_xy < h->mb.i_mb_width * h->mb.i_mb_height; mb_xy++ ) { if( h->mb.type[mb_xy] < X264_MBTYPE_MAX && h->mb.type[mb_xy] >= 0 ) fprintf( stderr, "%c ", mb_chars[ h->mb.type[mb_xy] ] ); else fprintf( stderr, "? " ); if( (mb_xy+1) % h->mb.i_mb_width == 0 ) fprintf( stderr, "\n" ); }}#endif /* Remove duplicates, must be done near the end as breaks h->fref0 array * by freeing some of its pointers. */ for( int i = 0; i < h->i_ref[0]; i++ ) if( h->fref[0][i] && h->fref[0][i]->b_duplicate ) { x264_frame_push_blank_unused( h, h->fref[0][i] ); h->fref[0][i] = 0; } if( h->param.psz_dump_yuv ) x264_frame_dump( h ); x264_emms(); return frame_size;}从源代码可以看出，x264_encoder_frame_end()中大部分代码用于把统计信息记录到x264_t的stat中。此外做了一些后续处理：调用了x264_encoder_encapsulate_nals()封装NALU（添加起始码），调用x264_frame_push_unused()将fenc重新放回frames.unused[]队列，并且调用x264_ratecontrol_end()结束码率控制。
x264_encoder_encapsulate_nals()
x264_encoder_encapsulate_nals()用于封装一帧数据对应的NALU，其代码如下所示。//封装一帧数据对应的NALU.//例如给NALU添加起始码0x00000001static int x264_encoder_encapsulate_nals( x264_t *h, int start ){ x264_t *h0 = h->thread[0]; int nal_size = 0, previous_nal_size = 0; if( h->param.nalu_process ) { for( int i = start; i < h->out.i_nal; i++ ) nal_size += h->out.nal[i].i_payload; return nal_size; } for( int i = 0; i < start; i++ ) previous_nal_size += h->out.nal[i].i_payload; for( int i = start; i < h->out.i_nal; i++ ) nal_size += h->out.nal[i].i_payload; /* Worst-case NAL unit escaping: reallocate the buffer if it's too small. */ int necessary_size = previous_nal_size + nal_size * 3/2 + h->out.i_nal * 4 + 4 + 64; for( int i = start; i < h->out.i_nal; i++ ) necessary_size += h->out.nal[i].i_padding; if( x264_check_encapsulated_buffer( h, h0, start, previous_nal_size, necessary_size ) ) return -1; uint8_t *nal_buffer = h0->nal_buffer + previous_nal_size; //一个一个NALU处理 for( int i = start; i < h->out.i_nal; i++ ) { int old_payload_len = h->out.nal[i].i_payload; h->out.nal[i].b_long_startcode = !i || h->out.nal[i].i_type == NAL_SPS || h->out.nal[i].i_type == NAL_PPS || h->param.i_avcintra_class; //添加起始码 x264_nal_encode( h, nal_buffer, &h->out.nal[i] ); nal_buffer += h->out.nal[i].i_payload; if( h->param.i_avcintra_class ) { h->out.nal[i].i_padding -= h->out.nal[i].i_payload - (old_payload_len + NALU_OVERHEAD); if( h->out.nal[i].i_padding > 0 ) { memset( nal_buffer, 0, h->out.nal[i].i_padding ); nal_buffer += h->out.nal[i].i_padding; h->out.nal[i].i_payload += h->out.nal[i].i_padding; } h->out.nal[i].i_padding = X264_MAX( h->out.nal[i].i_padding, 0 ); } } x264_emms(); return nal_buffer - (h0->nal_buffer + previous_nal_size);}从源代码中可以看出，x264_encoder_encapsulate_nals()调用了另外一个函数x264_nal_encode()逐个给一帧数据中的各个NALU添加起始码以及NALU Header等。
x264_nal_encode()
x264_nal_encode()用于给NALU添加起始码以及NALU Header等。该函数的定义位于common\bitstream.c，如下所示。
/**************************************************************************** * x264_nal_encode: ****************************************************************************///添加起始码void x264_nal_encode( x264_t *h, uint8_t *dst, x264_nal_t *nal ){ uint8_t *src = nal->p_payload; uint8_t *end = nal->p_payload + nal->i_payload; uint8_t *orig_dst = dst; //起始码 ============================================ //annexb格式，起始码为0x00000001 if( h->param.b_annexb ) { if( nal->b_long_startcode ) *dst++ = 0x00; *dst++ = 0x00; *dst++ = 0x00; *dst++ = 0x01; } else /* save room for size later */ dst += 4;//mp4格式 //NALU Header ======================================= /* nal header */ *dst++ = ( 0x00 << 7 ) | ( nal->i_ref_idc << 5 ) | nal->i_type; dst = h->bsf.nal_escape( dst, src, end ); int size = (dst - orig_dst) - 4; /* Write the size header for mp4/etc */ //重新回到起始码的位置，写入mp4格式的起始码（size大小，不含起始码） if( !h->param.b_annexb ) { /* Size doesn't include the size of the header we're writing now. */ orig_dst[0] = size>>24; orig_dst[1] = size>>16; orig_dst[2] = size>> 8; orig_dst[3] = size>> 0; } //NALU负载大小，包含起始码 nal->i_payload = size+4; nal->p_payload = orig_dst; x264_emms();}从源代码可以看出，x264_nal_encode()给NALU数据添加了起始码以及NALU Header。在这里简单总结一下起始码的添加过程。
H.264码流有两种格式：
（1）annexb模式（传统模式）。这种模式下每个NALU包含起始码0x00000001；而且SPS、PPS存储在ES码流中。常见的H.264裸流就是属于这种格式。从源代码中可以看出，x264_nal_encode()根据H.264码流格式的不同分成两种情况给NALU添加起始码：
（2）mp4模式。这种模式下每个NALU不包含起始码，原本存储起始码前4个字节存储的是这个NALU的长度（不包含前4字节）；而且SPS、PPS被单独放在容器的其他位置上。这种H.264一般存储在某些容器中，例如MP4中。
（1）annexb模式下，在每个NALU前面添加0x00000001。
（2）mp4模式下，先计算NALU的长度（不包含前4字节），再将长度信息写入NALU前面的4个字节
至此有关编码器主干部分有关x264_encoder_encode()的源代码就分析完了。从下一篇文章开始将会开始分析编码Slice的函数——x264_slice_write()。
雷霄骅
leixiaohua1020@126.com
http://blog.csdn.net/leixiaohua1020
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