ffmpeg源码分析之av_register_all()
1.muxer/demuxer和ecoder/decoder在代码实现上有很多相同的地方，但是最大的差别是：
muxer/demuxer使用的结构是AVInputFormat/AVOutputFormat
encoder/decoder用的是AVCodec结构
muxer/demuxer和ecoder/decoder相同的地方有：
1>都是在av_register_all()中初始化的。
2>都是以链表的形式保存在全局变量中
muxer/demuxer分别保存在全局变量AVOutputForamt *first_oformat和
AVInputFormat *first_iforst中
encoder/decoder都是保存在全局变量AVCodec *first_avcodec中。
以flv格式为例：
av_regeister_all()进行如下的操纵：将支持flv格式的flv_muxer和flv_demuxer变量分别注册到全局变量first_oformat和first_iformat链表的最后位置。
下面是具体的代码：
REGISTER_MUXDEMUX(FLV, flv);//
#define REGISTER_MUXDEMUX(FLV, flv) REGISTER_MUXER(FLV, flv); REGISTER_DEMUXER(FLB, x)
#define REGISTER_MUXER(X, x)//REGISTER_MUXER(FLV, flv) \
{ \
extern AVOutputFormat ff_flv_muxer; //建立一个对象，将该对象保存到链表的尾部 \
if (CONFIG_FLV_MUXER) \
av_register_output_format(&ff_flv_muxer); \
}
libavformat文件中的Format.c中有两个全局变量： /** head of registered input format linked list */ static AVInputFormat *first_iformat = NULL;//链表的头 /** head of registered output format linked list */ static AVOutputFormat *first_oformat = NULL;//head static AVInputFormat **last_iformat = &first_iformat;//链表的尾 static AVOutputFormat **last_oformat = &first_oformat;//链表的尾
void av_register_output_format(AVOutputFormat *format)
{
AVOutputFormat **p = last_oformat;
format->next = NULL;
/*遍历链表，初次调用的时候会令first_oformat指向format*/
while(*p || avpriv_atomic_ptr_cas((void * volatile *)p, NULL, format))
p = &(*p)->next;
last_oformat = &format->next; //(->为1级优先级，&为2级)
}
void *avpriv_atomic_ptr_cas(void * volatile *ptr, void *oldval, void *newval)
{
if (*ptr == oldval) {
*ptr = newval;
return oldval;
}
return *ptr;
}
同理：解复用也是一样的道理！
2.
av_register_all()中的avcodec_register_all()的分析：
通过该函数初始化encoder/decoder。
并不是每种编码方式都支持encode和decode，所以有以下三种注册方式：
#define REGISTER_ENCODER(FLV, flv) \
{ \
extern AVCodec ff_flv_encoder; \
if (CONFIG_FLV_ENCODER) \
avcodec_register(&ff_##x##_encoder); \
}
#define REGISTER_DECODER(FLV, flv) \
{ \
extern AVCodec ff_flv_decoder; \
if (CONFIG_FLV_DECODER) \
avcodec_register(&ff_flv_decoder); \
}
#define REGISTER_ENCDEC(FLV, flv) REGISTER_ENCODER(FLV, flv); REGISTER_DECODER(FLV, flv)
以编码为例：
同样的在libavcodec中的Utils.c中有两个全局变量：
static AVCodec *first_avcodec = NULL;//链表头 static AVCodec **last_avcodec = &first_avcodec; //链表尾
av_cold void avcodec_register(AVCodec *codec)
{
AVCodec **p;
avcodec_init();//初始化
p = last_avcodec;
codec->next = NULL;
//遍历链表，和上面的复用的注册时一样的原理
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);
}
static av_cold void avcodec_init(void)
{
static int initialized = 0;
if (initialized != 0)
return;
initialized = 1;
if (CONFIG_DSPUTIL)
ff_dsputil_static_init();
}
到此av_register_all()分析完了：
下面贴出源码：
/*
*@author tongli
*/
void av_register_all(void)
{
static int initialized;
if (initialized)
return;
initialized = 1;
avcodec_register_all();
/* (de)muxers */
REGISTER_MUXER (A64, a64);
REGISTER_DEMUXER (AAC, aac);
REGISTER_MUXDEMUX(AC3, ac3);
REGISTER_DEMUXER (ACT, act);
REGISTER_DEMUXER (ADF, adf);
REGISTER_DEMUXER (ADP, adp);
REGISTER_MUXER (ADTS, adts);
REGISTER_MUXDEMUX(ADX, adx);
REGISTER_DEMUXER (AEA, aea);
REGISTER_DEMUXER (AFC, afc);
REGISTER_MUXDEMUX(AIFF, aiff);
REGISTER_MUXDEMUX(AMR, amr);
REGISTER_DEMUXER (ANM, anm);
REGISTER_DEMUXER (APC, apc);
REGISTER_DEMUXER (APE, ape);
REGISTER_DEMUXER (AQTITLE, aqtitle);
REGISTER_MUXDEMUX(ASF, asf);
REGISTER_MUXDEMUX(ASS, ass);
REGISTER_MUXDEMUX(AST, ast);
REGISTER_MUXER (ASF_STREAM, asf_stream);
REGISTER_MUXDEMUX(AU, au);
REGISTER_MUXDEMUX(AVI, avi);
REGISTER_DEMUXER (AVISYNTH, avisynth);
REGISTER_MUXER (AVM2, avm2);
REGISTER_DEMUXER (AVR, avr);
REGISTER_DEMUXER (AVS, avs);
REGISTER_DEMUXER (BETHSOFTVID, bethsoftvid);
REGISTER_DEMUXER (BFI, bfi);
REGISTER_DEMUXER (BINTEXT, bintext);
REGISTER_DEMUXER (BINK, bink);
REGISTER_MUXDEMUX(BIT, bit);
REGISTER_DEMUXER (BMV, bmv);
REGISTER_DEMUXER (BRSTM, brstm);
REGISTER_DEMUXER (BOA, boa);
REGISTER_DEMUXER (C93, c93);
REGISTER_MUXDEMUX(CAF, caf);
REGISTER_MUXDEMUX(CAVSVIDEO, cavsvideo);
REGISTER_DEMUXER (CDG, cdg);
REGISTER_DEMUXER (CDXL, cdxl);
REGISTER_DEMUXER (CINE, cine);
REGISTER_DEMUXER (CONCAT, concat);
REGISTER_MUXER (CRC, crc);
REGISTER_MUXDEMUX(DATA, data);
REGISTER_MUXDEMUX(DAUD, daud);
REGISTER_DEMUXER (DFA, dfa);
REGISTER_MUXDEMUX(DIRAC, dirac);
REGISTER_MUXDEMUX(DNXHD, dnxhd);
REGISTER_DEMUXER (DSF, dsf);
REGISTER_DEMUXER (DSICIN, dsicin);
REGISTER_MUXDEMUX(DTS, dts);
REGISTER_DEMUXER (DTSHD, dtshd);
REGISTER_MUXDEMUX(DV, dv);
REGISTER_DEMUXER (DXA, dxa);
REGISTER_DEMUXER (EA, ea);
REGISTER_DEMUXER (EA_CDATA, ea_cdata);
REGISTER_MUXDEMUX(EAC3, eac3);
REGISTER_DEMUXER (EPAF, epaf);
REGISTER_MUXER (F4V, f4v);
REGISTER_MUXDEMUX(FFM, ffm);
REGISTER_MUXDEMUX(FFMETADATA, ffmetadata);
REGISTER_MUXDEMUX(FILMSTRIP, filmstrip);
REGISTER_MUXDEMUX(FLAC, flac);
REGISTER_DEMUXER (FLIC, flic);
REGISTER_MUXDEMUX(FLV, flv);
REGISTER_DEMUXER (LIVE_FLV, live_flv);
REGISTER_DEMUXER (FOURXM, fourxm);
REGISTER_MUXER (FRAMECRC, framecrc);
REGISTER_MUXER (FRAMEMD5, framemd5);
REGISTER_DEMUXER (FRM, frm);
REGISTER_MUXDEMUX(G722, g722);
REGISTER_MUXDEMUX(G723_1, g723_1);
REGISTER_DEMUXER (G729, g729);
REGISTER_MUXDEMUX(GIF, gif);
REGISTER_DEMUXER (GSM, gsm);
REGISTER_MUXDEMUX(GXF, gxf);
REGISTER_MUXDEMUX(H261, h261);
REGISTER_MUXDEMUX(H263, h263);
REGISTER_MUXDEMUX(H264, h264);
REGISTER_MUXER (HDS, hds);
REGISTER_MUXDEMUX(HEVC, hevc);
REGISTER_MUXDEMUX(HLS, hls);
REGISTER_DEMUXER (HNM, hnm);
REGISTER_MUXDEMUX(ICO, ico);
REGISTER_DEMUXER (IDCIN, idcin);
REGISTER_DEMUXER (IDF, idf);
REGISTER_DEMUXER (IFF, iff);
REGISTER_MUXDEMUX(ILBC, ilbc);
REGISTER_MUXDEMUX(IMAGE2, image2);
REGISTER_MUXDEMUX(IMAGE2PIPE, image2pipe);
REGISTER_DEMUXER (IMAGE2_ALIAS_PIX, image2_alias_pix);
REGISTER_DEMUXER (IMAGE2_BRENDER_PIX, image2_brender_pix);
REGISTER_DEMUXER (INGENIENT, ingenient);
REGISTER_DEMUXER (IPMOVIE, ipmovie);
REGISTER_MUXER (IPOD, ipod);
REGISTER_MUXDEMUX(IRCAM, ircam);
REGISTER_MUXER (ISMV, ismv);
REGISTER_DEMUXER (ISS, iss);
REGISTER_DEMUXER (IV8, iv8);
REGISTER_MUXDEMUX(IVF, ivf);
REGISTER_MUXDEMUX(JACOSUB, jacosub);
REGISTER_DEMUXER (JV, jv);
REGISTER_MUXDEMUX(LATM, latm);
REGISTER_DEMUXER (LMLM4, lmlm4);
REGISTER_DEMUXER (LOAS, loas);
REGISTER_MUXDEMUX(LRC, lrc);
REGISTER_DEMUXER (LVF, lvf);
REGISTER_DEMUXER (LXF, lxf);
REGISTER_MUXDEMUX(M4V, m4v);
REGISTER_MUXER (MD5, md5);
REGISTER_MUXDEMUX(MATROSKA, matroska);
REGISTER_MUXER (MATROSKA_AUDIO, matroska_audio);
REGISTER_DEMUXER (MGSTS, mgsts);
REGISTER_MUXDEMUX(MICRODVD, microdvd);
REGISTER_MUXDEMUX(MJPEG, mjpeg);
REGISTER_MUXDEMUX(MLP, mlp);
REGISTER_DEMUXER (MLV, mlv);
REGISTER_DEMUXER (MM, mm);
REGISTER_MUXDEMUX(MMF, mmf);
REGISTER_MUXDEMUX(MOV, mov);
REGISTER_MUXER (MP2, mp2);
REGISTER_MUXDEMUX(MP3, mp3);
REGISTER_MUXER (MP4, mp4);
REGISTER_DEMUXER (MPC, mpc);
REGISTER_DEMUXER (MPC8, mpc8);
REGISTER_MUXER (MPEG1SYSTEM, mpeg1system);
REGISTER_MUXER (MPEG1VCD, mpeg1vcd);
REGISTER_MUXER (MPEG1VIDEO, mpeg1video);
REGISTER_MUXER (MPEG2DVD, mpeg2dvd);
REGISTER_MUXER (MPEG2SVCD, mpeg2svcd);
REGISTER_MUXER (MPEG2VIDEO, mpeg2video);
REGISTER_MUXER (MPEG2VOB, mpeg2vob);
REGISTER_DEMUXER (MPEGPS, mpegps);
REGISTER_MUXDEMUX(MPEGTS, mpegts);
REGISTER_DEMUXER (MPEGTSRAW, mpegtsraw);
REGISTER_DEMUXER (MPEGVIDEO, mpegvideo);
REGISTER_MUXER (MPJPEG, mpjpeg);
REGISTER_DEMUXER (MPL2, mpl2);
REGISTER_DEMUXER (MPSUB, mpsub);
REGISTER_DEMUXER (MSNWC_TCP, msnwc_tcp);
REGISTER_DEMUXER (MTV, mtv);
REGISTER_DEMUXER (MV, mv);
REGISTER_DEMUXER (MVI, mvi);
REGISTER_MUXDEMUX(MXF, mxf);
REGISTER_MUXER (MXF_D10, mxf_d10);
REGISTER_DEMUXER (MXG, mxg);
REGISTER_DEMUXER (NC, nc);
REGISTER_DEMUXER (NISTSPHERE, nistsphere);
REGISTER_DEMUXER (NSV, nsv);
REGISTER_MUXER (NULL, null);
REGISTER_MUXDEMUX(NUT, nut);
REGISTER_DEMUXER (NUV, nuv);
REGISTER_MUXER (OGA, oga);
REGISTER_MUXDEMUX(OGG, ogg);
REGISTER_MUXDEMUX(OMA, oma);
REGISTER_MUXER (OPUS, opus);
REGISTER_DEMUXER (PAF, paf);
REGISTER_MUXDEMUX(PCM_ALAW, pcm_alaw);
REGISTER_MUXDEMUX(PCM_MULAW, pcm_mulaw);
REGISTER_MUXDEMUX(PCM_F64BE, pcm_f64be);
REGISTER_MUXDEMUX(PCM_F64LE, pcm_f64le);
REGISTER_MUXDEMUX(PCM_F32BE, pcm_f32be);
REGISTER_MUXDEMUX(PCM_F32LE, pcm_f32le);
REGISTER_MUXDEMUX(PCM_S32BE, pcm_s32be);
REGISTER_MUXDEMUX(PCM_S32LE, pcm_s32le);
REGISTER_MUXDEMUX(PCM_S24BE, pcm_s24be);
REGISTER_MUXDEMUX(PCM_S24LE, pcm_s24le);
REGISTER_MUXDEMUX(PCM_S16BE, pcm_s16be);
REGISTER_MUXDEMUX(PCM_S16LE, pcm_s16le);
REGISTER_MUXDEMUX(PCM_S8, pcm_s8);
REGISTER_MUXDEMUX(PCM_U32BE, pcm_u32be);
REGISTER_MUXDEMUX(PCM_U32LE, pcm_u32le);
REGISTER_MUXDEMUX(PCM_U24BE, pcm_u24be);
REGISTER_MUXDEMUX(PCM_U24LE, pcm_u24le);
REGISTER_MUXDEMUX(PCM_U16BE, pcm_u16be);
REGISTER_MUXDEMUX(PCM_U16LE, pcm_u16le);
REGISTER_MUXDEMUX(PCM_U8, pcm_u8);
REGISTER_DEMUXER (PJS, pjs);
REGISTER_DEMUXER (PMP, pmp);
REGISTER_MUXER (PSP, psp);
REGISTER_DEMUXER (PVA, pva);
REGISTER_DEMUXER (PVF, pvf);
REGISTER_DEMUXER (QCP, qcp);
REGISTER_DEMUXER (R3D, r3d);
REGISTER_MUXDEMUX(RAWVIDEO, rawvideo);
REGISTER_DEMUXER (REALTEXT, realtext);
REGISTER_DEMUXER (REDSPARK, redspark);
REGISTER_DEMUXER (RL2, rl2);
REGISTER_MUXDEMUX(RM, rm);
REGISTER_MUXDEMUX(ROQ, roq);
REGISTER_DEMUXER (RPL, rpl);
REGISTER_DEMUXER (RSD, rsd);
REGISTER_MUXDEMUX(RSO, rso);
REGISTER_MUXDEMUX(RTP, rtp);
REGISTER_MUXDEMUX(RTSP, rtsp);
REGISTER_DEMUXER (SAMI, sami);
REGISTER_MUXDEMUX(SAP, sap);
REGISTER_DEMUXER (SBG, sbg);
REGISTER_DEMUXER (SDP, sdp);
REGISTER_DEMUXER (SDR2, sdr2);
#if CONFIG_RTPDEC
ff_register_rtp_dynamic_payload_handlers();
ff_register_rdt_dynamic_payload_handlers();
#endif
REGISTER_DEMUXER (SEGAFILM, segafilm);
REGISTER_MUXER (SEGMENT, segment);
REGISTER_MUXER (SEGMENT, stream_segment);
REGISTER_DEMUXER (SHORTEN, shorten);
REGISTER_DEMUXER (SIFF, siff);
REGISTER_DEMUXER (SLN, sln);
REGISTER_DEMUXER (SMACKER, smacker);
REGISTER_MUXDEMUX(SMJPEG, smjpeg);
REGISTER_MUXER (SMOOTHSTREAMING, smoothstreaming);
REGISTER_DEMUXER (SMUSH, smush);
REGISTER_DEMUXER (SOL, sol);
REGISTER_MUXDEMUX(SOX, sox);
REGISTER_MUXDEMUX(SPDIF, spdif);
REGISTER_MUXER (SPEEX, speex);
REGISTER_MUXDEMUX(SRT, srt);
REGISTER_DEMUXER (STR, str);
REGISTER_DEMUXER (SUBVIEWER1, subviewer1);
REGISTER_DEMUXER (SUBVIEWER, subviewer);
REGISTER_MUXDEMUX(SWF, swf);
REGISTER_DEMUXER (TAK, tak);
REGISTER_MUXER (TEE, tee);
REGISTER_DEMUXER (TEDCAPTIONS, tedcaptions);
REGISTER_MUXER (TG2, tg2);
REGISTER_MUXER (TGP, tgp);
REGISTER_DEMUXER (THP, thp);
REGISTER_DEMUXER (TIERTEXSEQ, tiertexseq);
REGISTER_MUXER (MKVTIMESTAMP_V2, mkvtimestamp_v2);
REGISTER_DEMUXER (TMV, tmv);
REGISTER_MUXDEMUX(TRUEHD, truehd);
REGISTER_DEMUXER (TTA, tta);
REGISTER_DEMUXER (TXD, txd);
REGISTER_DEMUXER (TTY, tty);
REGISTER_MUXER (UNCODEDFRAMECRC, uncodedframecrc);
REGISTER_MUXDEMUX(VC1, vc1);
REGISTER_MUXDEMUX(VC1T, vc1t);
REGISTER_DEMUXER (VIVO, vivo);
REGISTER_DEMUXER (VMD, vmd);
REGISTER_DEMUXER (VOBSUB, vobsub);
REGISTER_MUXDEMUX(VOC, voc);
REGISTER_DEMUXER (VPLAYER, vplayer);
REGISTER_DEMUXER (VQF, vqf);
REGISTER_MUXDEMUX(W64, w64);
REGISTER_MUXDEMUX(WAV, wav);
REGISTER_DEMUXER (WC3, wc3);
REGISTER_MUXER (WEBM, webm);
REGISTER_MUXDEMUX(WEBM_DASH_MANIFEST, webm_dash_manifest);
REGISTER_MUXDEMUX(WEBVTT, webvtt);
REGISTER_DEMUXER (WSAUD, wsaud);
REGISTER_DEMUXER (WSVQA, wsvqa);
REGISTER_MUXDEMUX(WTV, wtv);
REGISTER_MUXDEMUX(WV, wv);
REGISTER_DEMUXER (XA, xa);
REGISTER_DEMUXER (XBIN, xbin);
REGISTER_DEMUXER (XMV, xmv);
REGISTER_DEMUXER (XWMA, xwma);
REGISTER_DEMUXER (YOP, yop);
REGISTER_MUXDEMUX(YUV4MPEGPIPE, yuv4mpegpipe);
/* image demuxers */
REGISTER_DEMUXER (IMAGE_BMP_PIPE, image_bmp_pipe);
REGISTER_DEMUXER (IMAGE_DPX_PIPE, image_dpx_pipe);
REGISTER_DEMUXER (IMAGE_EXR_PIPE, image_exr_pipe);
REGISTER_DEMUXER (IMAGE_J2K_PIPE, image_j2k_pipe);
REGISTER_DEMUXER (IMAGE_PICTOR_PIPE, image_pictor_pipe);
REGISTER_DEMUXER (IMAGE_PNG_PIPE, image_png_pipe);
REGISTER_DEMUXER (IMAGE_SGI_PIPE, image_sgi_pipe);
REGISTER_DEMUXER (IMAGE_SUNRAST_PIPE, image_sunrast_pipe);
REGISTER_DEMUXER (IMAGE_TIFF_PIPE, image_tiff_pipe);
/* protocols */
REGISTER_PROTOCOL(BLURAY, bluray);
REGISTER_PROTOCOL(CACHE, cache);
REGISTER_PROTOCOL(CONCAT, concat);
REGISTER_PROTOCOL(CRYPTO, crypto);
REGISTER_PROTOCOL(DATA, data);
REGISTER_PROTOCOL(FFRTMPCRYPT, ffrtmpcrypt);
REGISTER_PROTOCOL(FFRTMPHTTP, ffrtmphttp);
REGISTER_PROTOCOL(FILE, file);
REGISTER_PROTOCOL(FTP, ftp);
REGISTER_PROTOCOL(GOPHER, gopher);
REGISTER_PROTOCOL(HLS, hls);
REGISTER_PROTOCOL(HTTP, http);
REGISTER_PROTOCOL(HTTPPROXY, httpproxy);
REGISTER_PROTOCOL(HTTPS, https);
REGISTER_PROTOCOL(MMSH, mmsh);
REGISTER_PROTOCOL(MMST, mmst);
REGISTER_PROTOCOL(MD5, md5);
REGISTER_PROTOCOL(PIPE, pipe);
REGISTER_PROTOCOL(RTMP, rtmp);
REGISTER_PROTOCOL(RTMPE, rtmpe);
REGISTER_PROTOCOL(RTMPS, rtmps);
REGISTER_PROTOCOL(RTMPT, rtmpt);
REGISTER_PROTOCOL(RTMPTE, rtmpte);
REGISTER_PROTOCOL(RTMPTS, rtmpts);
REGISTER_PROTOCOL(RTP, rtp);
REGISTER_PROTOCOL(SCTP, sctp);
REGISTER_PROTOCOL(SRTP, srtp);
REGISTER_PROTOCOL(SUBFILE, subfile);
REGISTER_PROTOCOL(TCP, tcp);
REGISTER_PROTOCOL(TLS, tls);
REGISTER_PROTOCOL(UDP, udp);
REGISTER_PROTOCOL(UNIX, unix);
/* external libraries */
REGISTER_DEMUXER (LIBGME, libgme);
REGISTER_DEMUXER (LIBMODPLUG, libmodplug);
REGISTER_MUXDEMUX(LIBNUT, libnut);
REGISTER_DEMUXER (LIBQUVI, libquvi);
REGISTER_PROTOCOL(LIBRTMP, librtmp);
REGISTER_PROTOCOL(LIBRTMPE, librtmpe);
REGISTER_PROTOCOL(LIBRTMPS, librtmps);
REGISTER_PROTOCOL(LIBRTMPT, librtmpt);
REGISTER_PROTOCOL(LIBRTMPTE, librtmpte);
REGISTER_PROTOCOL(LIBSSH, libssh);
REGISTER_PROTOCOL(LIBSMBCLIENT, libsmbclient);
}