此前写了好几篇ffmpeg源代码分析文章,列表如下:
图解FFMPEG打开媒体的函数avformat_open_input
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 : av_read_frame()
ffmpeg 源代码简单分析 : avcodec_decode_video2()
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前一阵子看了一下ffmpeg的源代码,并且做了一些注释,在此贴出来以作备忘。
本文分析一下ffmpeg注册复用器,编码器等的函数av_register_all()。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,才能使用复用器,编码器等。
可见解复用器注册都是用
REGISTER_DEMUXER (X,x)
例如:
REGISTER_DEMUXER (AAC, aac)
可见复用器注册都是用
REGISTER_MUXER (X,x))
例如:
REGISTER_MUXER (ADTS, adts)
既有解复用器又有复用器的话,可以用
REGISTER_MUXDEMUX (X,x));
例如:
REGISTER_MUXDEMUX (AC3, ac3);
我们来看一下宏的定义,这里以解复用器为例:
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#define REGISTER_DEMUXER(X,x) { \
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extern AVInputFormat ff_##x##_demuxer; \
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if(CONFIG_##X##_DEMUXER) av_register_input_format(&ff_##x##_demuxer); }
注意:define里面的##可能不太常见,它的含义就是拼接两个字符串,比如
#define Conn(x,y) x##y
那么
int n = Conn(123,456); 结果就是n=123456;
我们以REGISTER_DEMUXER (AAC, aac)为例,则它等效于
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extern AVInputFormat ff_aac_demuxer;
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if(CONFIG_AAC_DEMUXER) av_register_input_format(&ff_aac_demuxer);
从上面这段代码我们可以看出,真正注册的函数是av_register_input_format(&ff_aac_demuxer),那我就看看这个和函数的作用,查看一下av_register_input_format()的代码:
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void av_register_input_format(AVInputFormat *format)
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{
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AVInputFormat **p;
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p = &first_iformat;
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while (*p != NULL) p = &(*p)->next;
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*p = format;
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format->next = NULL;
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}
这段代码是比较容易理解的,首先先提一点,first_iformat是个什么东东呢?其实它是Input Format链表的头部地址,是一个全局静态变量,定义如下:
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static AVInputFormat *first_iformat = NULL;
由此我们可以分析出av_register_input_format()的含义,一句话概括就是:遍历链表并把当前的Input Format加到链表的尾部。
至此REGISTER_DEMUXER (X, x)分析完毕。
同理,复用器道理是一样的,只是注册函数改为av_register_output_format();
既有解复用器又有复用器的话,有一个宏定义:
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#define REGISTER_MUXDEMUX(X,x) REGISTER_MUXER(X,x); REGISTER_DEMUXER(X,x)
可见是分别注册了复用器和解复用器。
此外还有网络协议的注册,注册函数为ffurl_register_protocol(),在此不再详述。
下面贴出它的源代码(allformats.c)
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#include "avformat.h"
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#include "rtp.h"
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#include "rdt.h"
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#include "url.h"
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#define REGISTER_MUXER(X,x) { \
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extern AVOutputFormat ff_##x##_muxer; \
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if(CONFIG_##X##_MUXER) av_register_output_format(&ff_##x##_muxer); }
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#define REGISTER_DEMUXER(X,x) { \
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extern AVInputFormat ff_##x##_demuxer; \
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if(CONFIG_##X##_DEMUXER) av_register_input_format(&ff_##x##_demuxer); }
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#define REGISTER_MUXDEMUX(X,x) REGISTER_MUXER(X,x); REGISTER_DEMUXER(X,x)
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#define REGISTER_PROTOCOL(X,x) { \
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extern URLProtocol ff_##x##_protocol; \
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if(CONFIG_##X##_PROTOCOL) ffurl_register_protocol(&ff_##x##_protocol, sizeof(ff_##x##_protocol)); }
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void av_register_all(void)
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{
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static int initialized;
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if (initialized)
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return;
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initialized = 1;
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avcodec_register_all();
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REGISTER_MUXER (A64, a64);
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REGISTER_DEMUXER (AAC, aac);
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REGISTER_MUXDEMUX (AC3, ac3);
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REGISTER_DEMUXER (ACT, act);
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REGISTER_DEMUXER (ADF, adf);
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REGISTER_MUXER (ADTS, adts);
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REGISTER_MUXDEMUX (ADX, adx);
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REGISTER_DEMUXER (AEA, aea);
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REGISTER_MUXDEMUX (AIFF, aiff);
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REGISTER_MUXDEMUX (AMR, amr);
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REGISTER_DEMUXER (ANM, anm);
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REGISTER_DEMUXER (APC, apc);
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REGISTER_DEMUXER (APE, ape);
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REGISTER_DEMUXER (APPLEHTTP, applehttp);
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REGISTER_MUXDEMUX (ASF, asf);
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REGISTER_MUXDEMUX (ASS, ass);
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REGISTER_MUXER (ASF_STREAM, asf_stream);
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REGISTER_MUXDEMUX (AU, au);
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REGISTER_MUXDEMUX (AVI, avi);
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REGISTER_DEMUXER (AVISYNTH, avisynth);
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REGISTER_MUXER (AVM2, avm2);
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REGISTER_DEMUXER (AVS, avs);
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REGISTER_DEMUXER (BETHSOFTVID, bethsoftvid);
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REGISTER_DEMUXER (BFI, bfi);
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REGISTER_DEMUXER (BINTEXT, bintext);
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REGISTER_DEMUXER (BINK, bink);
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REGISTER_MUXDEMUX (BIT, bit);
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REGISTER_DEMUXER (BMV, bmv);
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REGISTER_DEMUXER (C93, c93);
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REGISTER_MUXDEMUX (CAF, caf);
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REGISTER_MUXDEMUX (CAVSVIDEO, cavsvideo);
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REGISTER_DEMUXER (CDG, cdg);
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REGISTER_MUXER (CRC, crc);
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REGISTER_MUXDEMUX (DAUD, daud);
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REGISTER_DEMUXER (DFA, dfa);
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REGISTER_MUXDEMUX (DIRAC, dirac);
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REGISTER_MUXDEMUX (DNXHD, dnxhd);
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REGISTER_DEMUXER (DSICIN, dsicin);
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REGISTER_MUXDEMUX (DTS, dts);
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REGISTER_MUXDEMUX (DV, dv);
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REGISTER_DEMUXER (DXA, dxa);
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REGISTER_DEMUXER (EA, ea);
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REGISTER_DEMUXER (EA_CDATA, ea_cdata);
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REGISTER_MUXDEMUX (EAC3, eac3);
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REGISTER_MUXDEMUX (FFM, ffm);
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REGISTER_MUXDEMUX (FFMETADATA, ffmetadata);
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REGISTER_MUXDEMUX (FILMSTRIP, filmstrip);
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REGISTER_MUXDEMUX (FLAC, flac);
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REGISTER_DEMUXER (FLIC, flic);
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REGISTER_MUXDEMUX (FLV, flv);
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REGISTER_DEMUXER (FOURXM, fourxm);
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REGISTER_MUXER (FRAMECRC, framecrc);
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REGISTER_MUXER (FRAMEMD5, framemd5);
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REGISTER_MUXDEMUX (G722, g722);
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REGISTER_MUXDEMUX (G723_1, g723_1);
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REGISTER_DEMUXER (G729, g729);
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REGISTER_MUXER (GIF, gif);
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REGISTER_DEMUXER (GSM, gsm);
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REGISTER_MUXDEMUX (GXF, gxf);
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REGISTER_MUXDEMUX (H261, h261);
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REGISTER_MUXDEMUX (H263, h263);
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REGISTER_MUXDEMUX (H264, h264);
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REGISTER_DEMUXER (ICO, ico);
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REGISTER_DEMUXER (IDCIN, idcin);
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REGISTER_DEMUXER (IDF, idf);
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REGISTER_DEMUXER (IFF, iff);
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REGISTER_MUXDEMUX (IMAGE2, image2);
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REGISTER_MUXDEMUX (IMAGE2PIPE, image2pipe);
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REGISTER_DEMUXER (INGENIENT, ingenient);
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REGISTER_DEMUXER (IPMOVIE, ipmovie);
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REGISTER_MUXER (IPOD, ipod);
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REGISTER_MUXER (ISMV, ismv);
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REGISTER_DEMUXER (ISS, iss);
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REGISTER_DEMUXER (IV8, iv8);
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REGISTER_MUXDEMUX (IVF, ivf);
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REGISTER_DEMUXER (JV, jv);
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REGISTER_MUXDEMUX (LATM, latm);
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REGISTER_DEMUXER (LMLM4, lmlm4);
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REGISTER_DEMUXER (LOAS, loas);
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REGISTER_DEMUXER (LXF, lxf);
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REGISTER_MUXDEMUX (M4V, m4v);
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REGISTER_MUXER (MD5, md5);
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REGISTER_MUXDEMUX (MATROSKA, matroska);
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REGISTER_MUXER (MATROSKA_AUDIO, matroska_audio);
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REGISTER_MUXDEMUX (MICRODVD, microdvd);
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REGISTER_MUXDEMUX (MJPEG, mjpeg);
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REGISTER_MUXDEMUX (MLP, mlp);
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REGISTER_DEMUXER (MM, mm);
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REGISTER_MUXDEMUX (MMF, mmf);
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REGISTER_MUXDEMUX (MOV, mov);
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REGISTER_MUXER (MP2, mp2);
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REGISTER_MUXDEMUX (MP3, mp3);
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REGISTER_MUXER (MP4, mp4);
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REGISTER_DEMUXER (MPC, mpc);
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REGISTER_DEMUXER (MPC8, mpc8);
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REGISTER_MUXER (MPEG1SYSTEM, mpeg1system);
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REGISTER_MUXER (MPEG1VCD, mpeg1vcd);
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REGISTER_MUXER (MPEG1VIDEO, mpeg1video);
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REGISTER_MUXER (MPEG2DVD, mpeg2dvd);
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REGISTER_MUXER (MPEG2SVCD, mpeg2svcd);
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REGISTER_MUXER (MPEG2VIDEO, mpeg2video);
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REGISTER_MUXER (MPEG2VOB, mpeg2vob);
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REGISTER_DEMUXER (MPEGPS, mpegps);
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REGISTER_MUXDEMUX (MPEGTS, mpegts);
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REGISTER_DEMUXER (MPEGTSRAW, mpegtsraw);
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REGISTER_DEMUXER (MPEGVIDEO, mpegvideo);
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REGISTER_MUXER (MPJPEG, mpjpeg);
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REGISTER_DEMUXER (MSNWC_TCP, msnwc_tcp);
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REGISTER_DEMUXER (MTV, mtv);
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REGISTER_DEMUXER (MVI, mvi);
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REGISTER_MUXDEMUX (MXF, mxf);
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REGISTER_MUXER (MXF_D10, mxf_d10);
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REGISTER_DEMUXER (MXG, mxg);
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REGISTER_DEMUXER (NC, nc);
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REGISTER_DEMUXER (NSV, nsv);
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REGISTER_MUXER (NULL, null);
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REGISTER_MUXDEMUX (NUT, nut);
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REGISTER_DEMUXER (NUV, nuv);
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REGISTER_MUXDEMUX (OGG, ogg);
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REGISTER_MUXDEMUX (OMA, oma);
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REGISTER_MUXDEMUX (PCM_ALAW, pcm_alaw);
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REGISTER_MUXDEMUX (PCM_MULAW, pcm_mulaw);
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REGISTER_MUXDEMUX (PCM_F64BE, pcm_f64be);
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REGISTER_MUXDEMUX (PCM_F64LE, pcm_f64le);
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REGISTER_MUXDEMUX (PCM_F32BE, pcm_f32be);
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REGISTER_MUXDEMUX (PCM_F32LE, pcm_f32le);
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REGISTER_MUXDEMUX (PCM_S32BE, pcm_s32be);
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REGISTER_MUXDEMUX (PCM_S32LE, pcm_s32le);
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REGISTER_MUXDEMUX (PCM_S24BE, pcm_s24be);
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REGISTER_MUXDEMUX (PCM_S24LE, pcm_s24le);
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REGISTER_MUXDEMUX (PCM_S16BE, pcm_s16be);
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REGISTER_MUXDEMUX (PCM_S16LE, pcm_s16le);
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REGISTER_MUXDEMUX (PCM_S8, pcm_s8);
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REGISTER_MUXDEMUX (PCM_U32BE, pcm_u32be);
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REGISTER_MUXDEMUX (PCM_U32LE, pcm_u32le);
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REGISTER_MUXDEMUX (PCM_U24BE, pcm_u24be);
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REGISTER_MUXDEMUX (PCM_U24LE, pcm_u24le);
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REGISTER_MUXDEMUX (PCM_U16BE, pcm_u16be);
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REGISTER_MUXDEMUX (PCM_U16LE, pcm_u16le);
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REGISTER_MUXDEMUX (PCM_U8, pcm_u8);
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REGISTER_DEMUXER (PMP, pmp);
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REGISTER_MUXER (PSP, psp);
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REGISTER_DEMUXER (PVA, pva);
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REGISTER_DEMUXER (QCP, qcp);
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REGISTER_DEMUXER (R3D, r3d);
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REGISTER_MUXDEMUX (RAWVIDEO, rawvideo);
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REGISTER_DEMUXER (RL2, rl2);
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REGISTER_MUXDEMUX (RM, rm);
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REGISTER_MUXDEMUX (ROQ, roq);
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REGISTER_DEMUXER (RPL, rpl);
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REGISTER_MUXDEMUX (RSO, rso);
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REGISTER_MUXDEMUX (RTP, rtp);
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REGISTER_MUXDEMUX (RTSP, rtsp);
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REGISTER_MUXDEMUX (SAP, sap);
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REGISTER_DEMUXER (SBG, sbg);
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REGISTER_DEMUXER (SDP, sdp);
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#if CONFIG_RTPDEC
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av_register_rtp_dynamic_payload_handlers();
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av_register_rdt_dynamic_payload_handlers();
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#endif
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REGISTER_DEMUXER (SEGAFILM, segafilm);
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REGISTER_MUXER (SEGMENT, segment);
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REGISTER_DEMUXER (SHORTEN, shorten);
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REGISTER_DEMUXER (SIFF, siff);
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REGISTER_DEMUXER (SMACKER, smacker);
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REGISTER_MUXDEMUX (SMJPEG, smjpeg);
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REGISTER_DEMUXER (SOL, sol);
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REGISTER_MUXDEMUX (SOX, sox);
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REGISTER_MUXDEMUX (SPDIF, spdif);
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REGISTER_MUXDEMUX (SRT, srt);
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REGISTER_DEMUXER (STR, str);
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REGISTER_MUXDEMUX (SWF, swf);
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REGISTER_MUXER (TG2, tg2);
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REGISTER_MUXER (TGP, tgp);
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REGISTER_DEMUXER (THP, thp);
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REGISTER_DEMUXER (TIERTEXSEQ, tiertexseq);
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REGISTER_MUXER (MKVTIMESTAMP_V2, mkvtimestamp_v2);
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REGISTER_DEMUXER (TMV, tmv);
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REGISTER_MUXDEMUX (TRUEHD, truehd);
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REGISTER_DEMUXER (TTA, tta);
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REGISTER_DEMUXER (TXD, txd);
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REGISTER_DEMUXER (TTY, tty);
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REGISTER_DEMUXER (VC1, vc1);
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REGISTER_MUXDEMUX (VC1T, vc1t);
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REGISTER_DEMUXER (VMD, vmd);
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REGISTER_MUXDEMUX (VOC, voc);
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REGISTER_DEMUXER (VQF, vqf);
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REGISTER_DEMUXER (W64, w64);
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REGISTER_MUXDEMUX (WAV, wav);
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REGISTER_DEMUXER (WC3, wc3);
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REGISTER_MUXER (WEBM, webm);
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REGISTER_DEMUXER (WSAUD, wsaud);
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REGISTER_DEMUXER (WSVQA, wsvqa);
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REGISTER_MUXDEMUX (WTV, wtv);
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REGISTER_DEMUXER (WV, wv);
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REGISTER_DEMUXER (XA, xa);
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REGISTER_DEMUXER (XBIN, xbin);
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REGISTER_DEMUXER (XMV, xmv);
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REGISTER_DEMUXER (XWMA, xwma);
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REGISTER_DEMUXER (YOP, yop);
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REGISTER_MUXDEMUX (YUV4MPEGPIPE, yuv4mpegpipe);
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#if CONFIG_LIBMODPLUG
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REGISTER_DEMUXER (LIBMODPLUG, libmodplug);
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#endif
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REGISTER_MUXDEMUX (LIBNUT, libnut);
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REGISTER_PROTOCOL (APPLEHTTP, applehttp);
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REGISTER_PROTOCOL (CACHE, cache);
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REGISTER_PROTOCOL (CONCAT, concat);
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REGISTER_PROTOCOL (CRYPTO, crypto);
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REGISTER_PROTOCOL (FILE, file);
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REGISTER_PROTOCOL (GOPHER, gopher);
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REGISTER_PROTOCOL (HTTP, http);
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REGISTER_PROTOCOL (HTTPPROXY, httpproxy);
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REGISTER_PROTOCOL (HTTPS, https);
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REGISTER_PROTOCOL (MMSH, mmsh);
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REGISTER_PROTOCOL (MMST, mmst);
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REGISTER_PROTOCOL (MD5, md5);
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REGISTER_PROTOCOL (PIPE, pipe);
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REGISTER_PROTOCOL (RTMP, rtmp);
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#if CONFIG_LIBRTMP
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REGISTER_PROTOCOL (RTMP, rtmpt);
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REGISTER_PROTOCOL (RTMP, rtmpe);
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REGISTER_PROTOCOL (RTMP, rtmpte);
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REGISTER_PROTOCOL (RTMP, rtmps);
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#endif
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REGISTER_PROTOCOL (RTP, rtp);
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REGISTER_PROTOCOL (TCP, tcp);
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REGISTER_PROTOCOL (TLS, tls);
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REGISTER_PROTOCOL (UDP, udp);
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}
整个代码没太多可说的,首先确定是不是已经初始化过了(initialized),如果没有,就调用avcodec_register_all()注册编解码器(这个先不分析),然后就是注册,注册,注册...直到完成所有注册。
PS:曾经研究过一阵子RTMP协议,以及对应的开源工程librtmp。在这里发现有一点值得注意,ffmpeg自带了RTMP协议的支持,只有使用 rtmpt://, rtmpe://, rtmpte://等的时候才会使用librtmp库。
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