MPEG-2 文件结构解析

代码实现：mpeg-2文件分析器代码实现

一个完整的MPEG-2文件就是一个PS流文件。

    MPEG-2文件的构造格式如下图：

   

    自己找个mpg文件打开，可以看到文件以0x0000 01B9结束（有些文件不标准没有），即MPEG_Program_end_code，之前有很多个0x0000 00BA字段，即为program pack的开始标志，program pack包的构造如下：

    可以看出program pack由3部分组成：pack_header+system_header+PES_packets,其中system_header当且仅当pack是第一个数据包时才存在。system_header和PES_packets构造如下：

    对照文件内容，各字段顺序、长度如下：

            pack_header： 起始地址：0x0000 0000（这个地址有可能因为文件不一样而不一样）     

               标志：0x00 0x00 0x010xBA（4B）

struct PackHeader{unsigned paddingByte: 2;unsigned program_clock_reference_base: 3;unsigned marker1: 1;unsigned SCR_base1: 15;unsigned marker2: 1;unsigned SCR_base2: 15;unsigned marker3: 1;unsigned SCR_externsion: 9;unsigned marker4: 1;unsigned mutiplex_rate: 22;unsigned marker5: 1;unsigned marker6: 1;unsigned reserved: 5;unsigned stuffing_length: 3;};

           system_header: 起始地址：0x0000 000e

                   标志(4B)：0x00 0x00 0x01 0xBB

                

struct SystemHeader//112bit{unsigned head_length: 16;unsigned marker1: 1;unsigned rate_bound: 22;unsigned marker2: 1;unsigned audio_bound: 6;unsigned fixed_flag: 1;unsigned CSPS_flag: 1;unsigned system_audio_local_flag: 1;unsigned system_video_local_flag: 1;unsigned marker3: 1;unsigned video_bound: 5;unsigned packet_rate_restriction_flag<span style="white-space:pre"></span>: 1;unsigned reserved: 7;unsigned stream_id1: 8;unsigned paddingByte1: 2;unsigned P_STD_buffer_bound_scale1: 1;unsigned P_STD_buffer_size_bound1: 13;unsigned stream_id2: 8;unsigned paddingByte2: 2;unsigned P_STD_buffer_bound_scale2: 1;unsigned P_STD_buffer_size_bound2: 13;};

            PES packet：起始地址：0x0000 0020

                   标志位(3B)：0x 00 00 01

                stream_id(1B)：0xBE(BE为Padding stream)

                PES_packet_length(2B)：0x07 DA，跳过该长度的填充字节，刚好为下一个pack的起始标志：0x000001BA

      从0x0800地址开始为第二个pack包，该包的构造格式为pack_header+PES，分析如下：

            pack_header： 起始地址：0x0000 0800

(此包上面已经讲到，这里不再赘述)

             PES packet：起始地址：0x0000 080e

                   标志位(3B)：0x 00 00 01

                stream_id(1B)：0xE0(视频)

               

struct PESPacket{unsigned PES_packet_length: 16;unsigned paddingByte1: 2;unsigned scrambling_control: 2;unsigned priority: 1;unsigned alignment: 1;unsigned copyright: 1;unsigned original: 1;unsigned PTS_DTS_flag: 2;unsigned ESCR_flag: 1;unsigned ES_rate_flag: 1;unsigned DSM_trick_mode_flag<span style="white-space:pre"></span>: 1;unsigned additional_copy_info_flag<span style="white-space:pre"></span>: 1;unsigned CRC_flag: 1;unsigned extension_flag: 1;unsigned PES_header_data_length<span style="white-space:pre"></span>: 8;unsigned paddingByte2: 4;unsigned PTS_32_30: 3;//pts 的第32-30位unsigned marker1: 1;unsigned PTS_29_15: 15;//pts的第29-15位unsigned marker2: 1;unsigned PTS_14_0: 15;//pts的第14-0位（共33位）unsigned marker3: 1;unsigned paddingByte3: 4;unsigned DTS_32_30: 3;unsigned marker4: 1;unsigned DTS_29_15: 15;unsigned marker5: 1;unsigned DTS_14_0: 15;unsigned marker6: 1;};

    Video Sequence，其结构定义如下：

    图中sequence_header，sequence entension等子内容定义如下：

     

    对各字段顺序、长度分析如下：

             sequence header：起始地址：0x0000 0821

                标志位(4B)：0x00 0x00 0x01 0xB3

                

struct SequenceHeader{unsigned horizontal_size: 12;unsigned vertical_size: 12;unsigned aspect_ratio_info: 4;unsigned frame_rate: 4;unsigned bit_rate: 18;unsigned marker: 1;unsigned VBV_buffer_size: 10;unsigned constrained: 1;unsigned load_intra_Q_matrix<span style="white-space:pre"></span>: 1;unsigned paddingBit: 1;};

             sequence extension：起始地址：0x0000 082d；如果有这一项说明是MPEG-2文件，否则为MPEG-1文件

                标志位(4B)：0x0000 01B5

            

struct SequenceExtension{unsigned start_code_identifer: 4;unsigned profile_level_escape: 1;unsigned profile_level: 7;unsigned progressive: 1;unsigned chroma: 2;unsigned horiz_extension: 2;unsigned vertical_extension: 2;};

    接下来的数据是0x0000 01B8，说明该序列中没有extension&user data[i]（extension data的开始符为0x0000 01B5，user data的开始符为0x0000 01B2），接下来的内容为Group of pictures header。

             Group_of_pictures_header：起始地址：0x0000 0837

                标志位(4B)：0x0000 01B8

                

struct GroupOfPicturesHeader{unsigned time_code: 25;unsigned closed_gop: 1;unsigned broken_link<span style="white-space:pre"></span>: 1;};

             extension & user data[1]：无

             picture header: 起始地址：0x0000 083F

                标志位(4B)：0x0000 0100

struct PictureHeader{unsigned temporal_reference: 10;unsigned picture_coding_type<span style="white-space:pre"></span>: 3;unsigned vbv_delay: 16;unsigned extra_bit_piture: 1;};

             picture coding extension：起始地址：0x0000 0847

                extension_start_code(4B)：0x0000 01B5

               

struct PictureCodingExtension{unsigned extension_start_code_identifier: 4;unsigned f_code_0_0: 4;unsigned f_code_0_1: 4;unsigned f_code_1_0: 4;unsigned f_code_1_1: 4;unsigned intra_dc_presison: 2;unsigned picture_structure: 2;unsigned top_field_first: 1;unsigned frame_pred_frame_dct: 1;unsigned concealment_motion_vectors: 1;unsigned q_scale_type: 1;unsigned intra_vlc_format: 1;unsigned alternate_scan: 1;unsigned repeat_first_field: 1;unsigned chroma_420_type: 1;unsigned progressive_frame: 2;unsigned composite_display_flag: 2;};

             extension & user data[2]：无

             picture data: 起始地址：0x0000 0850（暂时未分析，以后补上）