ffmpeg 源代码简单分析 ： avcodec_register_all()

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FFmpeg的库函数源代码分析文章列表：

【架构图】

FFmpeg源代码结构图 - 解码

FFmpeg源代码结构图 - 编码

【通用】

FFmpeg 源代码简单分析：av_register_all()

FFmpeg 源代码简单分析：avcodec_register_all()

FFmpeg 源代码简单分析：内存的分配和释放（av_malloc()、av_free()等）

FFmpeg 源代码简单分析：常见结构体的初始化和销毁（AVFormatContext，AVFrame等）

FFmpeg 源代码简单分析：avio_open2()

FFmpeg 源代码简单分析：av_find_decoder()和av_find_encoder()

FFmpeg 源代码简单分析：avcodec_open2()

FFmpeg 源代码简单分析：avcodec_close()

【解码】

图解FFMPEG打开媒体的函数avformat_open_input

FFmpeg 源代码简单分析：avformat_open_input()

FFmpeg 源代码简单分析：avformat_find_stream_info()

FFmpeg 源代码简单分析：av_read_frame()

FFmpeg 源代码简单分析：avcodec_decode_video2()

FFmpeg 源代码简单分析：avformat_close_input()

【编码】

FFmpeg 源代码简单分析：avformat_alloc_output_context2()

FFmpeg 源代码简单分析：avformat_write_header()

FFmpeg 源代码简单分析：avcodec_encode_video()

FFmpeg 源代码简单分析：av_write_frame()

FFmpeg 源代码简单分析：av_write_trailer()

【其它】

FFmpeg源代码简单分析：日志输出系统（av_log()等）

FFmpeg源代码简单分析：结构体成员管理系统-AVClass

FFmpeg源代码简单分析：结构体成员管理系统-AVOption

FFmpeg源代码简单分析：libswscale的sws_getContext()

FFmpeg源代码简单分析：libswscale的sws_scale()

FFmpeg源代码简单分析：libavdevice的avdevice_register_all()

FFmpeg源代码简单分析：libavdevice的gdigrab

【脚本】

FFmpeg源代码简单分析：makefile

FFmpeg源代码简单分析：configure

【H.264】

FFmpeg的H.264解码器源代码简单分析：概述

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本文分析一下ffmpeg注册编解码器等的函数avcodec_register_all()（注意不是av_register_all()，那是注册所有东西的）。该函数在所有基于ffmpeg的应用程序中几乎都是第一个被调用的。只有调用了该函数，才能使用编解码器等。

之前已经写过一篇文章了：

ffmpeg 源代码简单分析 ： av_register_all()

其实注册编解码器和注册复用器解复用器道理是差不多的，重复的内容不再多说。

编码器的注册是：

REGISTER_ENCODER (X,x);

例如：

REGISTER_ENCODER (LJPEG, ljpeg);

解码器的注册是：

REGISTER_DECODER (X,x);

例如：

REGISTER_DECODER (H264, h264);

既包含编码器有包含解码器的注册是：

REGISTER_ENCDEC  (X,x);

例如：

REGISTER_ENCDEC  (BMP, bmp);

此外还有几种注册：

Parser：

REGISTER_PARSER  (X,x);

例如：

REGISTER_PARSER  (H264, h264);

BSF（bitstream filters，比特流滤镜，有一个常用：h264_mp4toannexb）：

REGISTER_BSF     (X,x);

例如：

REGISTER_BSF     (H264_MP4TOANNEXB, h264_mp4toannexb);

HWACCEL（hardware accelerators，硬件加速器）：

REGISTER_HWACCEL (X,x);

例如：

REGISTER_HWACCEL (H264_DXVA2, h264_dxva2);

我们来看一下宏的定义，这里以编解码器为例：

#define REGISTER_ENCODER(X,x) { \          extern AVCodec ff_##x##_encoder; \          if(CONFIG_##X##_ENCODER)  avcodec_register(&ff_##x##_encoder); }#define REGISTER_DECODER(X,x) { \          extern AVCodec ff_##x##_decoder; \          if(CONFIG_##X##_DECODER)  avcodec_register(&ff_##x##_decoder); }#define REGISTER_ENCDEC(X,x)  REGISTER_ENCODER(X,x); REGISTER_DECODER(X,x)

在这里，我发现其实编码器和解码器用的注册函数都是一样的：avcodec_register()

以REGISTER_DECODER (H264, h264)为例，就是等效于

extern AVCodec ff_h264_decoder; if(CONFIG_H264_DECODER)  avcodec_register(&ff_h264_decoder);

下面看一下avcodec_register()的源代码：

//注册所有的AVCodecvoid avcodec_register(AVCodec *codec){    AVCodec **p;    //初始化    avcodec_init();    //从第一个开始    p = &first_avcodec;    while (*p != NULL) p = &(*p)->next;    *p = codec;    codec->next = NULL;    if (codec->init_static_data)        codec->init_static_data(codec);}

这段代码是比较容易理解的。首先先提一点，first_avcdec是就是AVCodec链表的头部地址，是一个全局静态变量，定义如下：

/* encoder management */static AVCodec *first_avcodec = NULL;

由此我们可以分析出avcodec_register()的含义，一句话概括就是：遍历链表并把当前的AVCodec加到链表的尾部。

同理，Parser，BSF（bitstream filters，比特流滤镜），HWACCEL（hardware accelerators，硬件加速器）的注册方式都是类似的。不再详述。

下面贴出它的原代码：

/* *雷霄骅 *[e-mail] *中国传媒大学/数字电视技术 *//* * Provide registration of all codecs, parsers and bitstream filters for libavcodec. * Copyright (c) 2002 Fabrice Bellard * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA *//** * @file * Provide registration of all codecs, parsers and bitstream filters for libavcodec. */#include "avcodec.h"//硬件加速#define REGISTER_HWACCEL(X,x) { \          extern AVHWAccel ff_##x##_hwaccel; \          if(CONFIG_##X##_HWACCEL) av_register_hwaccel(&ff_##x##_hwaccel); }#define REGISTER_ENCODER(X,x) { \          extern AVCodec ff_##x##_encoder; \          if(CONFIG_##X##_ENCODER)  avcodec_register(&ff_##x##_encoder); }//定义的宏？宏的速度会快一点？注册AVCodec//extern AVCodec ff_##x##_decoder;//注意：extern表明全局唯一//在h264中，对应的就是ff_h264_decoder//由此可见AVCodecParser的名字是固定的#define REGISTER_DECODER(X,x) { \          extern AVCodec ff_##x##_decoder; \          if(CONFIG_##X##_DECODER)  avcodec_register(&ff_##x##_decoder); }#define REGISTER_ENCDEC(X,x)  REGISTER_ENCODER(X,x); REGISTER_DECODER(X,x)//定义的宏？宏的速度会快一点？注册AVCodecParser//extern AVCodecParser ff_##x##_parser;//在h264中，对应的就是ff_h264_parser//由此可见AVCodecParser的名字是固定的#define REGISTER_PARSER(X,x) { \          extern AVCodecParser ff_##x##_parser; \          if(CONFIG_##X##_PARSER)  av_register_codec_parser(&ff_##x##_parser); }#define REGISTER_BSF(X,x) { \          extern AVBitStreamFilter ff_##x##_bsf; \          if(CONFIG_##X##_BSF)     av_register_bitstream_filter(&ff_##x##_bsf); }void avcodec_register_all(void){    static int initialized;    if (initialized)        return;    initialized = 1;    /* hardware accelerators */    REGISTER_HWACCEL (H263_VAAPI, h263_vaapi);    REGISTER_HWACCEL (H264_DXVA2, h264_dxva2);    REGISTER_HWACCEL (H264_VAAPI, h264_vaapi);    REGISTER_HWACCEL (H264_VDA, h264_vda);    REGISTER_HWACCEL (MPEG1_VDPAU, mpeg1_vdpau);    REGISTER_HWACCEL (MPEG2_DXVA2, mpeg2_dxva2);    REGISTER_HWACCEL (MPEG2_VAAPI, mpeg2_vaapi);    REGISTER_HWACCEL (MPEG2_VDPAU, mpeg2_vdpau);    REGISTER_HWACCEL (MPEG4_VAAPI, mpeg4_vaapi);    REGISTER_HWACCEL (VC1_DXVA2, vc1_dxva2);    REGISTER_HWACCEL (VC1_VAAPI, vc1_vaapi);    REGISTER_HWACCEL (WMV3_DXVA2, wmv3_dxva2);    REGISTER_HWACCEL (WMV3_VAAPI, wmv3_vaapi);    /* video codecs */    REGISTER_ENCODER (A64MULTI, a64multi);    REGISTER_ENCODER (A64MULTI5, a64multi5);    REGISTER_DECODER (AASC, aasc);    REGISTER_ENCDEC  (AMV, amv);    REGISTER_DECODER (ANM, anm);    REGISTER_DECODER (ANSI, ansi);    REGISTER_ENCDEC  (ASV1, asv1);    REGISTER_ENCDEC  (ASV2, asv2);    REGISTER_DECODER (AURA, aura);    REGISTER_DECODER (AURA2, aura2);    REGISTER_ENCDEC  (AVRP, avrp);    REGISTER_DECODER (AVS, avs);    REGISTER_DECODER (BETHSOFTVID, bethsoftvid);    REGISTER_DECODER (BFI, bfi);    REGISTER_DECODER (BINK, bink);    REGISTER_ENCDEC  (BMP, bmp);    REGISTER_DECODER (BMV_VIDEO, bmv_video);    REGISTER_DECODER (C93, c93);    REGISTER_DECODER (CAVS, cavs);    REGISTER_DECODER (CDGRAPHICS, cdgraphics);    REGISTER_DECODER (CINEPAK, cinepak);    REGISTER_ENCDEC  (CLJR, cljr);    REGISTER_DECODER (CSCD, cscd);    REGISTER_DECODER (CYUV, cyuv);    REGISTER_DECODER (DFA, dfa);    REGISTER_DECODER (DIRAC, dirac);    REGISTER_ENCDEC  (DNXHD, dnxhd);    REGISTER_ENCDEC  (DPX, dpx);    REGISTER_DECODER (DSICINVIDEO, dsicinvideo);    REGISTER_ENCDEC  (DVVIDEO, dvvideo);    REGISTER_DECODER (DXA, dxa);    REGISTER_DECODER (DXTORY, dxtory);    REGISTER_DECODER (EACMV, eacmv);    REGISTER_DECODER (EAMAD, eamad);    REGISTER_DECODER (EATGQ, eatgq);    REGISTER_DECODER (EATGV, eatgv);    REGISTER_DECODER (EATQI, eatqi);    REGISTER_DECODER (EIGHTBPS, eightbps);    REGISTER_DECODER (EIGHTSVX_EXP, eightsvx_exp);    REGISTER_DECODER (EIGHTSVX_FIB, eightsvx_fib);    REGISTER_DECODER (ESCAPE124, escape124);    REGISTER_DECODER (ESCAPE130, escape130);    REGISTER_ENCDEC  (FFV1, ffv1);    REGISTER_ENCDEC  (FFVHUFF, ffvhuff);    REGISTER_ENCDEC  (FLASHSV, flashsv);    REGISTER_ENCDEC  (FLASHSV2, flashsv2);    REGISTER_DECODER (FLIC, flic);    REGISTER_ENCDEC  (FLV, flv);    REGISTER_DECODER (FOURXM, fourxm);    REGISTER_DECODER (FRAPS, fraps);    REGISTER_DECODER (FRWU, frwu);    REGISTER_ENCDEC  (GIF, gif);    REGISTER_ENCDEC  (H261, h261);    REGISTER_ENCDEC  (H263, h263);    REGISTER_DECODER (H263I, h263i);    REGISTER_ENCODER (H263P, h263p);    REGISTER_DECODER (H264, h264);    REGISTER_DECODER (H264_CRYSTALHD, h264_crystalhd);    REGISTER_DECODER (H264_VDPAU, h264_vdpau);    REGISTER_ENCDEC  (HUFFYUV, huffyuv);    REGISTER_DECODER (IDCIN, idcin);    REGISTER_DECODER (IFF_BYTERUN1, iff_byterun1);    REGISTER_DECODER (IFF_ILBM, iff_ilbm);    REGISTER_DECODER (INDEO2, indeo2);    REGISTER_DECODER (INDEO3, indeo3);    REGISTER_DECODER (INDEO4, indeo4);    REGISTER_DECODER (INDEO5, indeo5);    REGISTER_DECODER (INTERPLAY_VIDEO, interplay_video);    REGISTER_ENCDEC  (JPEG2000, jpeg2000);    REGISTER_ENCDEC  (JPEGLS, jpegls);    REGISTER_DECODER (JV, jv);    REGISTER_DECODER (KGV1, kgv1);    REGISTER_DECODER (KMVC, kmvc);    REGISTER_DECODER (LAGARITH, lagarith);    REGISTER_ENCODER (LJPEG, ljpeg);    REGISTER_DECODER (LOCO, loco);    REGISTER_DECODER (MDEC, mdec);    REGISTER_DECODER (MIMIC, mimic);    REGISTER_ENCDEC  (MJPEG, mjpeg);    REGISTER_DECODER (MJPEGB, mjpegb);    REGISTER_DECODER (MMVIDEO, mmvideo);    REGISTER_DECODER (MOTIONPIXELS, motionpixels);    REGISTER_DECODER (MPEG_XVMC, mpeg_xvmc);    REGISTER_ENCDEC  (MPEG1VIDEO, mpeg1video);    REGISTER_ENCDEC  (MPEG2VIDEO, mpeg2video);    REGISTER_ENCDEC  (MPEG4, mpeg4);    REGISTER_DECODER (MPEG4_CRYSTALHD, mpeg4_crystalhd);    REGISTER_DECODER (MPEG4_VDPAU, mpeg4_vdpau);    REGISTER_DECODER (MPEGVIDEO, mpegvideo);    REGISTER_DECODER (MPEG_VDPAU, mpeg_vdpau);    REGISTER_DECODER (MPEG1_VDPAU, mpeg1_vdpau);    REGISTER_DECODER (MPEG2_CRYSTALHD, mpeg2_crystalhd);    REGISTER_DECODER (MSMPEG4_CRYSTALHD, msmpeg4_crystalhd);    REGISTER_DECODER (MSMPEG4V1, msmpeg4v1);    REGISTER_ENCDEC  (MSMPEG4V2, msmpeg4v2);    REGISTER_ENCDEC  (MSMPEG4V3, msmpeg4v3);    REGISTER_DECODER (MSRLE, msrle);    REGISTER_ENCDEC  (MSVIDEO1, msvideo1);    REGISTER_DECODER (MSZH, mszh);    REGISTER_DECODER (MXPEG, mxpeg);    REGISTER_DECODER (NUV, nuv);    REGISTER_ENCDEC  (PAM, pam);    REGISTER_ENCDEC  (PBM, pbm);    REGISTER_ENCDEC  (PCX, pcx);    REGISTER_ENCDEC  (PGM, pgm);    REGISTER_ENCDEC  (PGMYUV, pgmyuv);    REGISTER_DECODER (PICTOR, pictor);    REGISTER_ENCDEC  (PNG, png);    REGISTER_ENCDEC  (PPM, ppm);    REGISTER_ENCDEC  (PRORES, prores);    REGISTER_DECODER (PRORES_LGPL, prores_lgpl);    REGISTER_DECODER (PTX, ptx);    REGISTER_DECODER (QDRAW, qdraw);    REGISTER_DECODER (QPEG, qpeg);    REGISTER_ENCDEC  (QTRLE, qtrle);    REGISTER_ENCDEC  (R10K,  r10k);    REGISTER_ENCDEC  (R210,  r210);    REGISTER_ENCDEC  (RAWVIDEO, rawvideo);    REGISTER_DECODER (RL2, rl2);    REGISTER_ENCDEC  (ROQ, roq);    REGISTER_DECODER (RPZA, rpza);    REGISTER_ENCDEC  (RV10, rv10);    REGISTER_ENCDEC  (RV20, rv20);    REGISTER_DECODER (RV30, rv30);    REGISTER_DECODER (RV40, rv40);    REGISTER_DECODER (S302M, s302m);    REGISTER_ENCDEC  (SGI, sgi);    REGISTER_DECODER (SMACKER, smacker);    REGISTER_DECODER (SMC, smc);    REGISTER_ENCDEC  (SNOW, snow);    REGISTER_DECODER (SP5X, sp5x);    REGISTER_DECODER (SUNRAST, sunrast);    REGISTER_ENCDEC  (SVQ1, svq1);    REGISTER_DECODER (SVQ3, svq3);    REGISTER_ENCDEC  (TARGA, targa);    REGISTER_DECODER (THEORA, theora);    REGISTER_DECODER (THP, thp);    REGISTER_DECODER (TIERTEXSEQVIDEO, tiertexseqvideo);    REGISTER_ENCDEC  (TIFF, tiff);    REGISTER_DECODER (TMV, tmv);    REGISTER_DECODER (TRUEMOTION1, truemotion1);    REGISTER_DECODER (TRUEMOTION2, truemotion2);    REGISTER_DECODER (TSCC, tscc);    REGISTER_DECODER (TXD, txd);    REGISTER_DECODER (ULTI, ulti);    REGISTER_DECODER (UTVIDEO, utvideo);    REGISTER_ENCDEC  (V210,  v210);    REGISTER_DECODER (V210X, v210x);    REGISTER_ENCDEC  (V308, v308);    REGISTER_ENCDEC  (V410, v410);    REGISTER_DECODER (VB, vb);    REGISTER_DECODER (VBLE, vble);    REGISTER_DECODER (VC1, vc1);    REGISTER_DECODER (VC1_CRYSTALHD, vc1_crystalhd);    REGISTER_DECODER (VC1_VDPAU, vc1_vdpau);    REGISTER_DECODER (VC1IMAGE, vc1image);    REGISTER_DECODER (VCR1, vcr1);    REGISTER_DECODER (VMDVIDEO, vmdvideo);    REGISTER_DECODER (VMNC, vmnc);    REGISTER_DECODER (VP3, vp3);    REGISTER_DECODER (VP5, vp5);    REGISTER_DECODER (VP6, vp6);    REGISTER_DECODER (VP6A, vp6a);    REGISTER_DECODER (VP6F, vp6f);    REGISTER_DECODER (VP8, vp8);    REGISTER_DECODER (VQA, vqa);    REGISTER_ENCDEC  (WMV1, wmv1);    REGISTER_ENCDEC  (WMV2, wmv2);    REGISTER_DECODER (WMV3, wmv3);    REGISTER_DECODER (WMV3_CRYSTALHD, wmv3_crystalhd);    REGISTER_DECODER (WMV3_VDPAU, wmv3_vdpau);    REGISTER_DECODER (WMV3IMAGE, wmv3image);    REGISTER_DECODER (WNV1, wnv1);    REGISTER_DECODER (XAN_WC3, xan_wc3);    REGISTER_DECODER (XAN_WC4, xan_wc4);    REGISTER_DECODER (XL, xl);    REGISTER_ENCDEC  (XWD, xwd);    REGISTER_ENCDEC  (Y41P, y41p);    REGISTER_DECODER (YOP, yop);    REGISTER_ENCDEC  (YUV4, yuv4);    REGISTER_ENCDEC  (ZLIB, zlib);    REGISTER_ENCDEC  (ZMBV, zmbv);    /* audio codecs */    REGISTER_ENCDEC  (AAC, aac);    REGISTER_DECODER (AAC_LATM, aac_latm);    REGISTER_ENCDEC  (AC3, ac3);    REGISTER_ENCODER (AC3_FIXED, ac3_fixed);    REGISTER_ENCDEC  (ALAC, alac);    REGISTER_DECODER (ALS, als);    REGISTER_DECODER (AMRNB, amrnb);    REGISTER_DECODER (AMRWB, amrwb);    REGISTER_DECODER (APE, ape);    REGISTER_DECODER (ATRAC1, atrac1);    REGISTER_DECODER (ATRAC3, atrac3);    REGISTER_DECODER (BINKAUDIO_DCT, binkaudio_dct);    REGISTER_DECODER (BINKAUDIO_RDFT, binkaudio_rdft);    REGISTER_DECODER (BMV_AUDIO, bmv_audio);    REGISTER_DECODER (COOK, cook);    REGISTER_ENCDEC  (DCA, dca);    REGISTER_DECODER (DSICINAUDIO, dsicinaudio);    REGISTER_ENCDEC  (EAC3, eac3);    REGISTER_DECODER (FFWAVESYNTH, ffwavesynth);    REGISTER_ENCDEC  (FLAC, flac);    REGISTER_ENCDEC  (G723_1, g723_1);    REGISTER_DECODER (G729, g729);    REGISTER_DECODER (GSM, gsm);    REGISTER_DECODER (GSM_MS, gsm_ms);    REGISTER_DECODER (IMC, imc);    REGISTER_DECODER (MACE3, mace3);    REGISTER_DECODER (MACE6, mace6);    REGISTER_DECODER (MLP, mlp);    REGISTER_DECODER (MP1, mp1);    REGISTER_DECODER (MP1FLOAT, mp1float);    REGISTER_ENCDEC  (MP2, mp2);    REGISTER_DECODER (MP2FLOAT, mp2float);    REGISTER_DECODER (MP3, mp3);    REGISTER_DECODER (MP3FLOAT, mp3float);    REGISTER_DECODER (MP3ADU, mp3adu);    REGISTER_DECODER (MP3ADUFLOAT, mp3adufloat);    REGISTER_DECODER (MP3ON4, mp3on4);    REGISTER_DECODER (MP3ON4FLOAT, mp3on4float);    REGISTER_DECODER (MPC7, mpc7);    REGISTER_DECODER (MPC8, mpc8);    REGISTER_ENCDEC  (NELLYMOSER, nellymoser);    REGISTER_DECODER (QCELP, qcelp);    REGISTER_DECODER (QDM2, qdm2);    REGISTER_ENCDEC  (RA_144, ra_144);    REGISTER_DECODER (RA_288, ra_288);    REGISTER_DECODER (SHORTEN, shorten);    REGISTER_DECODER (SIPR, sipr);    REGISTER_DECODER (SMACKAUD, smackaud);    REGISTER_ENCDEC  (SONIC, sonic);    REGISTER_ENCODER (SONIC_LS, sonic_ls);    REGISTER_DECODER (TRUEHD, truehd);    REGISTER_DECODER (TRUESPEECH, truespeech);    REGISTER_DECODER (TTA, tta);    REGISTER_DECODER (TWINVQ, twinvq);    REGISTER_DECODER (VMDAUDIO, vmdaudio);    REGISTER_ENCDEC  (VORBIS, vorbis);    REGISTER_DECODER (WAVPACK, wavpack);    REGISTER_DECODER (WMALOSSLESS, wmalossless);    REGISTER_DECODER (WMAPRO, wmapro);    REGISTER_ENCDEC  (WMAV1, wmav1);    REGISTER_ENCDEC  (WMAV2, wmav2);    REGISTER_DECODER (WMAVOICE, wmavoice);    REGISTER_DECODER (WS_SND1, ws_snd1);    /* PCM codecs */    REGISTER_ENCDEC  (PCM_ALAW, pcm_alaw);    REGISTER_DECODER (PCM_BLURAY, pcm_bluray);    REGISTER_DECODER (PCM_DVD, pcm_dvd);    REGISTER_ENCDEC  (PCM_F32BE, pcm_f32be);    REGISTER_ENCDEC  (PCM_F32LE, pcm_f32le);    REGISTER_ENCDEC  (PCM_F64BE, pcm_f64be);    REGISTER_ENCDEC  (PCM_F64LE, pcm_f64le);    REGISTER_DECODER (PCM_LXF, pcm_lxf);    REGISTER_ENCDEC  (PCM_MULAW, pcm_mulaw);    REGISTER_ENCDEC  (PCM_S8, pcm_s8);    REGISTER_DECODER (PCM_S8_PLANAR, pcm_s8_planar);    REGISTER_ENCDEC  (PCM_S16BE, pcm_s16be);    REGISTER_ENCDEC  (PCM_S16LE, pcm_s16le);    REGISTER_DECODER (PCM_S16LE_PLANAR, pcm_s16le_planar);    REGISTER_ENCDEC  (PCM_S24BE, pcm_s24be);    REGISTER_ENCDEC  (PCM_S24DAUD, pcm_s24daud);    REGISTER_ENCDEC  (PCM_S24LE, pcm_s24le);    REGISTER_ENCDEC  (PCM_S32BE, pcm_s32be);    REGISTER_ENCDEC  (PCM_S32LE, pcm_s32le);    REGISTER_ENCDEC  (PCM_U8, pcm_u8);    REGISTER_ENCDEC  (PCM_U16BE, pcm_u16be);    REGISTER_ENCDEC  (PCM_U16LE, pcm_u16le);    REGISTER_ENCDEC  (PCM_U24BE, pcm_u24be);    REGISTER_ENCDEC  (PCM_U24LE, pcm_u24le);    REGISTER_ENCDEC  (PCM_U32BE, pcm_u32be);    REGISTER_ENCDEC  (PCM_U32LE, pcm_u32le);    REGISTER_DECODER (PCM_ZORK , pcm_zork);    /* DPCM codecs */    REGISTER_DECODER (INTERPLAY_DPCM, interplay_dpcm);    REGISTER_ENCDEC  (ROQ_DPCM, roq_dpcm);    REGISTER_DECODER (SOL_DPCM, sol_dpcm);    REGISTER_DECODER (XAN_DPCM, xan_dpcm);    /* ADPCM codecs */    REGISTER_DECODER (ADPCM_4XM, adpcm_4xm);    REGISTER_ENCDEC  (ADPCM_ADX, adpcm_adx);    REGISTER_DECODER (ADPCM_CT, adpcm_ct);    REGISTER_DECODER (ADPCM_EA, adpcm_ea);    REGISTER_DECODER (ADPCM_EA_MAXIS_XA, adpcm_ea_maxis_xa);    REGISTER_DECODER (ADPCM_EA_R1, adpcm_ea_r1);    REGISTER_DECODER (ADPCM_EA_R2, adpcm_ea_r2);    REGISTER_DECODER (ADPCM_EA_R3, adpcm_ea_r3);    REGISTER_DECODER (ADPCM_EA_XAS, adpcm_ea_xas);    REGISTER_ENCDEC  (ADPCM_G722, adpcm_g722);    REGISTER_ENCDEC  (ADPCM_G726, adpcm_g726);    REGISTER_DECODER (ADPCM_IMA_AMV, adpcm_ima_amv);    REGISTER_DECODER (ADPCM_IMA_APC, adpcm_ima_apc);    REGISTER_DECODER (ADPCM_IMA_DK3, adpcm_ima_dk3);    REGISTER_DECODER (ADPCM_IMA_DK4, adpcm_ima_dk4);    REGISTER_DECODER (ADPCM_IMA_EA_EACS, adpcm_ima_ea_eacs);    REGISTER_DECODER (ADPCM_IMA_EA_SEAD, adpcm_ima_ea_sead);    REGISTER_DECODER (ADPCM_IMA_ISS, adpcm_ima_iss);    REGISTER_ENCDEC  (ADPCM_IMA_QT, adpcm_ima_qt);    REGISTER_DECODER (ADPCM_IMA_SMJPEG, adpcm_ima_smjpeg);    REGISTER_ENCDEC  (ADPCM_IMA_WAV, adpcm_ima_wav);    REGISTER_DECODER (ADPCM_IMA_WS, adpcm_ima_ws);    REGISTER_ENCDEC  (ADPCM_MS, adpcm_ms);    REGISTER_DECODER (ADPCM_SBPRO_2, adpcm_sbpro_2);    REGISTER_DECODER (ADPCM_SBPRO_3, adpcm_sbpro_3);    REGISTER_DECODER (ADPCM_SBPRO_4, adpcm_sbpro_4);    REGISTER_ENCDEC  (ADPCM_SWF, adpcm_swf);    REGISTER_DECODER (ADPCM_THP, adpcm_thp);    REGISTER_DECODER (ADPCM_XA, adpcm_xa);    REGISTER_ENCDEC  (ADPCM_YAMAHA, adpcm_yamaha);    /* subtitles */    REGISTER_ENCDEC  (ASS, ass);    REGISTER_ENCDEC  (DVBSUB, dvbsub);    REGISTER_ENCDEC  (DVDSUB, dvdsub);    REGISTER_DECODER (PGSSUB, pgssub);    REGISTER_ENCDEC  (SRT, srt);    REGISTER_ENCDEC  (XSUB, xsub);    /* external libraries */    REGISTER_ENCODER (LIBAACPLUS, libaacplus);    REGISTER_DECODER (LIBCELT, libcelt);    REGISTER_ENCDEC  (LIBDIRAC, libdirac);    REGISTER_ENCODER (LIBFAAC, libfaac);    REGISTER_ENCDEC  (LIBGSM, libgsm);    REGISTER_ENCDEC  (LIBGSM_MS, libgsm_ms);    REGISTER_ENCODER (LIBMP3LAME, libmp3lame);    REGISTER_ENCDEC  (LIBOPENCORE_AMRNB, libopencore_amrnb);    REGISTER_DECODER (LIBOPENCORE_AMRWB, libopencore_amrwb);    REGISTER_ENCDEC (LIBOPENJPEG, libopenjpeg);    REGISTER_ENCDEC  (LIBSCHROEDINGER, libschroedinger);    REGISTER_ENCDEC  (LIBSPEEX, libspeex);    REGISTER_DECODER (LIBSTAGEFRIGHT_H264, libstagefright_h264);    REGISTER_ENCODER (LIBTHEORA, libtheora);    REGISTER_DECODER (LIBUTVIDEO, libutvideo);    REGISTER_ENCODER (LIBVO_AACENC, libvo_aacenc);    REGISTER_ENCODER (LIBVO_AMRWBENC, libvo_amrwbenc);    REGISTER_ENCODER (LIBVORBIS, libvorbis);    REGISTER_ENCDEC  (LIBVPX, libvpx);    REGISTER_ENCODER (LIBX264, libx264);    REGISTER_ENCODER (LIBX264RGB, libx264rgb);    REGISTER_ENCODER (LIBXAVS, libxavs);    REGISTER_ENCODER (LIBXVID, libxvid);    /* text */    REGISTER_DECODER (BINTEXT, bintext);    REGISTER_DECODER  (XBIN, xbin);    REGISTER_DECODER  (IDF, idf);    /* parsers */    REGISTER_PARSER  (AAC, aac);    REGISTER_PARSER  (AAC_LATM, aac_latm);    REGISTER_PARSER  (AC3, ac3);    REGISTER_PARSER  (ADX, adx);    REGISTER_PARSER  (CAVSVIDEO, cavsvideo);    REGISTER_PARSER  (DCA, dca);    REGISTER_PARSER  (DIRAC, dirac);    REGISTER_PARSER  (DNXHD, dnxhd);    REGISTER_PARSER  (DVBSUB, dvbsub);    REGISTER_PARSER  (DVDSUB, dvdsub);    REGISTER_PARSER  (FLAC, flac);    REGISTER_PARSER  (GSM, gsm);    REGISTER_PARSER  (H261, h261);    REGISTER_PARSER  (H263, h263);    REGISTER_PARSER  (H264, h264);    REGISTER_PARSER  (MJPEG, mjpeg);    REGISTER_PARSER  (MLP, mlp);    REGISTER_PARSER  (MPEG4VIDEO, mpeg4video);    REGISTER_PARSER  (MPEGAUDIO, mpegaudio);    REGISTER_PARSER  (MPEGVIDEO, mpegvideo);    REGISTER_PARSER  (PNM, pnm);    REGISTER_PARSER  (RV30, rv30);    REGISTER_PARSER  (RV40, rv40);    REGISTER_PARSER  (VC1, vc1);    REGISTER_PARSER  (VP3, vp3);    REGISTER_PARSER  (VP8, vp8);    /* bitstream filters */    REGISTER_BSF     (AAC_ADTSTOASC, aac_adtstoasc);    REGISTER_BSF     (CHOMP, chomp);    REGISTER_BSF     (DUMP_EXTRADATA, dump_extradata);    REGISTER_BSF     (H264_MP4TOANNEXB, h264_mp4toannexb);    REGISTER_BSF     (IMX_DUMP_HEADER, imx_dump_header);    REGISTER_BSF     (MJPEG2JPEG, mjpeg2jpeg);    REGISTER_BSF     (MJPEGA_DUMP_HEADER, mjpega_dump_header);    REGISTER_BSF     (MP3_HEADER_COMPRESS, mp3_header_compress);    REGISTER_BSF     (MP3_HEADER_DECOMPRESS, mp3_header_decompress);    REGISTER_BSF     (MOV2TEXTSUB, mov2textsub);    REGISTER_BSF     (NOISE, noise);    REGISTER_BSF     (REMOVE_EXTRADATA, remove_extradata);    REGISTER_BSF     (TEXT2MOVSUB, text2movsub);}

整个代码的过程就是首先确定是不是已经初始化过了（initialized），如果没有，就注册，注册，注册...直到完成所有注册。

函数的调用关系图如下图所示。av_register_all()调用了avcodec_register_all()。因此如果调用过av_register_all()的话就不需要再调用avcodec_register_all()了。

下面附上硬件加速器，编码器/解码器，parser，Bitstream Filter的注册代码。

硬件加速器注册函数是av_register_hwaccel()。

void av_register_hwaccel(AVHWAccel *hwaccel){    AVHWAccel **p = last_hwaccel;    hwaccel->next = NULL;    while(*p || avpriv_atomic_ptr_cas((void * volatile *)p, NULL, hwaccel))        p = &(*p)->next;    last_hwaccel = &hwaccel->next;}

编解码器注册函数是avcodec_register()。

av_cold void avcodec_register(AVCodec *codec){    AVCodec **p;    avcodec_init();    p = last_avcodec;    codec->next = NULL;    while(*p || avpriv_atomic_ptr_cas((void * volatile *)p, NULL, codec))        p = &(*p)->next;    last_avcodec = &codec->next;    if (codec->init_static_data)        codec->init_static_data(codec);}

parser注册函数是av_register_codec_parser()。

void av_register_codec_parser(AVCodecParser *parser){    do {        parser->next = av_first_parser;    } while (parser->next != avpriv_atomic_ptr_cas((void * volatile *)&av_first_parser, parser->next, parser));}

Bitstream Filter注册函数是av_register_bitstream_filter()。

void av_register_bitstream_filter(AVBitStreamFilter *bsf){    do {        bsf->next = first_bitstream_filter;    } while(bsf->next != avpriv_atomic_ptr_cas((void * volatile *)&first_bitstream_filter, bsf->next, bsf));}

后两个函数中的avpriv_atomic_ptr_cas()定义如下。

void *avpriv_atomic_ptr_cas(void * volatile *ptr, void *oldval, void *newval){    if (*ptr == oldval) {        *ptr = newval;        return oldval;    }    return *ptr;}