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：
#define REGISTER_DEMUXER(X,x) { \
extern AVInputFormat ff_##x##_demuxer; \
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
extern AVInputFormat ff_aac_demuxer; 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：
void av_register_input_format(AVInputFormat *format)
{
AVInputFormat **p;
p = &first_iformat;
while (*p != NULL) p = &(*p)->next;
*p = format;
format->next = NULL;
}
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：
/** head of registered input format linked list */ 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：
#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）
/* *雷霄骅 *[email protected] *中国传媒大学/数字电视技术 */ /* * Register all the formats and protocols * Copyright (c) 2000, 2001, 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 */ #include "avformat.h" #include "rtp.h" #include "rdt.h" #include "url.h" //定义的宏？宏的速度会快一点？注册AVOutputFormat //define中，#用来把参数转换成字符串，##则用来连接前后两个参数，把它们变成一个字符串。 //感觉有点像JAva中的EL，可以随意拼接字符串 #define REGISTER_MUXER(X,x) { \ extern AVOutputFormat ff_##x##_muxer; \ if(CONFIG_##X##_MUXER) av_register_output_format(&ff_##x##_muxer); } //定义的宏？宏的速度会快一点？注册AVInputFormat #define REGISTER_DEMUXER(X,x) { \ extern AVInputFormat ff_##x##_demuxer; \ if(CONFIG_##X##_DEMUXER) av_register_input_format(&ff_##x##_demuxer); } //注册函数av_register_input_format //定义的宏？宏的速度会快一点？两个一起注册！ #define REGISTER_MUXDEMUX(X,x) REGISTER_MUXER(X,x); REGISTER_DEMUXER(X,x) //定义的宏？宏的速度会快一点？注册URLProtocol //extern URLProtocol ff_##x##_protocol; //在librtmp中，对应的就是ff_rtmp_protocol //这样就把librtmp整合起来了 //由此可见URLProtocol的名字是固定的 #define REGISTER_PROTOCOL(X,x) { \ extern URLProtocol ff_##x##_protocol; \ if(CONFIG_##X##_PROTOCOL) ffurl_register_protocol(&ff_##x##_protocol, sizeof(ff_##x##_protocol)); } //注册函数ffurl_register_protocol void av_register_all(void) { static int initialized; if (initialized) return; initialized = 1; //注册所有的codec avcodec_register_all(); //注册所有的MUXER（复用器和解复用器） /* (de)muxers */ REGISTER_MUXER (A64, a64); REGISTER_DEMUXER (AAC, aac); REGISTER_MUXDEMUX (AC3, ac3); REGISTER_DEMUXER (ACT, act); REGISTER_DEMUXER (ADF, adf); REGISTER_MUXER (ADTS, adts); REGISTER_MUXDEMUX (ADX, adx); REGISTER_DEMUXER (AEA, aea); REGISTER_MUXDEMUX (AIFF, aiff); REGISTER_MUXDEMUX (AMR, amr); REGISTER_DEMUXER (ANM, anm); REGISTER_DEMUXER (APC, apc); REGISTER_DEMUXER (APE, ape); REGISTER_DEMUXER (APPLEHTTP, applehttp); REGISTER_MUXDEMUX (ASF, asf); REGISTER_MUXDEMUX (ASS, ass); REGISTER_MUXER (ASF_STREAM, asf_stream); REGISTER_MUXDEMUX (AU, au); REGISTER_MUXDEMUX (AVI, avi); REGISTER_DEMUXER (AVISYNTH, avisynth); REGISTER_MUXER (AVM2, avm2); 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 (C93, c93); REGISTER_MUXDEMUX (CAF, caf); REGISTER_MUXDEMUX (CAVSVIDEO, cavsvideo); REGISTER_DEMUXER (CDG, cdg); REGISTER_MUXER (CRC, crc); REGISTER_MUXDEMUX (DAUD, daud); REGISTER_DEMUXER (DFA, dfa); REGISTER_MUXDEMUX (DIRAC, dirac); REGISTER_MUXDEMUX (DNXHD, dnxhd); REGISTER_DEMUXER (DSICIN, dsicin); REGISTER_MUXDEMUX (DTS, dts); REGISTER_MUXDEMUX (DV, dv); REGISTER_DEMUXER (DXA, dxa); REGISTER_DEMUXER (EA, ea); REGISTER_DEMUXER (EA_CDATA, ea_cdata); REGISTER_MUXDEMUX (EAC3, eac3); 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 (FOURXM, fourxm); REGISTER_MUXER (FRAMECRC, framecrc); REGISTER_MUXER (FRAMEMD5, framemd5); REGISTER_MUXDEMUX (G722, g722); REGISTER_MUXDEMUX (G723_1, g723_1); REGISTER_DEMUXER (G729, g729); REGISTER_MUXER (GIF, gif); REGISTER_DEMUXER (GSM, gsm); REGISTER_MUXDEMUX (GXF, gxf); REGISTER_MUXDEMUX (H261, h261); REGISTER_MUXDEMUX (H263, h263); REGISTER_MUXDEMUX (H264, h264); REGISTER_DEMUXER (ICO, ico); REGISTER_DEMUXER (IDCIN, idcin); REGISTER_DEMUXER (IDF, idf); REGISTER_DEMUXER (IFF, iff); REGISTER_MUXDEMUX (IMAGE2, image2); REGISTER_MUXDEMUX (IMAGE2PIPE, image2pipe); REGISTER_DEMUXER (INGENIENT, ingenient); REGISTER_DEMUXER (IPMOVIE, ipmovie); REGISTER_MUXER (IPOD, ipod); REGISTER_MUXER (ISMV, ismv); REGISTER_DEMUXER (ISS, iss); REGISTER_DEMUXER (IV8, iv8); REGISTER_MUXDEMUX (IVF, ivf); REGISTER_DEMUXER (JV, jv); REGISTER_MUXDEMUX (LATM, latm); REGISTER_DEMUXER (LMLM4, lmlm4); REGISTER_DEMUXER (LOAS, loas); REGISTER_DEMUXER (LXF, lxf); REGISTER_MUXDEMUX (M4V, m4v); REGISTER_MUXER (MD5, md5); REGISTER_MUXDEMUX (MATROSKA, matroska); REGISTER_MUXER (MATROSKA_AUDIO, matroska_audio); REGISTER_MUXDEMUX (MICRODVD, microdvd); REGISTER_MUXDEMUX (MJPEG, mjpeg); REGISTER_MUXDEMUX (MLP, mlp); 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 (MSNWC_TCP, msnwc_tcp); REGISTER_DEMUXER (MTV, mtv); REGISTER_DEMUXER (MVI, mvi); REGISTER_MUXDEMUX (MXF, mxf); REGISTER_MUXER (MXF_D10, mxf_d10); REGISTER_DEMUXER (MXG, mxg); REGISTER_DEMUXER (NC, nc); REGISTER_DEMUXER (NSV, nsv); REGISTER_MUXER (NULL, null); REGISTER_MUXDEMUX (NUT, nut); REGISTER_DEMUXER (NUV, nuv); REGISTER_MUXDEMUX (OGG, ogg); REGISTER_MUXDEMUX (OMA, oma); 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 (PMP, pmp); REGISTER_MUXER (PSP, psp); REGISTER_DEMUXER (PVA, pva); REGISTER_DEMUXER (QCP, qcp); REGISTER_DEMUXER (R3D, r3d); REGISTER_MUXDEMUX (RAWVIDEO, rawvideo); REGISTER_DEMUXER (RL2, rl2); REGISTER_MUXDEMUX (RM, rm); REGISTER_MUXDEMUX (ROQ, roq); REGISTER_DEMUXER (RPL, rpl); REGISTER_MUXDEMUX (RSO, rso); REGISTER_MUXDEMUX (RTP, rtp); REGISTER_MUXDEMUX (RTSP, rtsp); REGISTER_MUXDEMUX (SAP, sap); REGISTER_DEMUXER (SBG, sbg); REGISTER_DEMUXER (SDP, sdp); #if CONFIG_RTPDEC av_register_rtp_dynamic_payload_handlers(); av_register_rdt_dynamic_payload_handlers(); #endif REGISTER_DEMUXER (SEGAFILM, segafilm); REGISTER_MUXER (SEGMENT, segment); REGISTER_DEMUXER (SHORTEN, shorten); REGISTER_DEMUXER (SIFF, siff); REGISTER_DEMUXER (SMACKER, smacker); REGISTER_MUXDEMUX (SMJPEG, smjpeg); REGISTER_DEMUXER (SOL, sol); REGISTER_MUXDEMUX (SOX, sox); REGISTER_MUXDEMUX (SPDIF, spdif); REGISTER_MUXDEMUX (SRT, srt); REGISTER_DEMUXER (STR, str); REGISTER_MUXDEMUX (SWF, swf); 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_DEMUXER (VC1, vc1); REGISTER_MUXDEMUX (VC1T, vc1t); REGISTER_DEMUXER (VMD, vmd); REGISTER_MUXDEMUX (VOC, voc); REGISTER_DEMUXER (VQF, vqf); REGISTER_DEMUXER (W64, w64); REGISTER_MUXDEMUX (WAV, wav); REGISTER_DEMUXER (WC3, wc3); REGISTER_MUXER (WEBM, webm); REGISTER_DEMUXER (WSAUD, wsaud); REGISTER_DEMUXER (WSVQA, wsvqa); REGISTER_MUXDEMUX (WTV, wtv); REGISTER_DEMUXER (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); /* external libraries */ #if CONFIG_LIBMODPLUG REGISTER_DEMUXER (LIBMODPLUG, libmodplug); #endif REGISTER_MUXDEMUX (LIBNUT, libnut); //注册所有的Protocol（位于DEMUXER之前（我的理解~~）） //文件也是一种Protocol /* protocols */ REGISTER_PROTOCOL (APPLEHTTP, applehttp); REGISTER_PROTOCOL (CACHE, cache); REGISTER_PROTOCOL (CONCAT, concat); REGISTER_PROTOCOL (CRYPTO, crypto); REGISTER_PROTOCOL (FILE, file); REGISTER_PROTOCOL (GOPHER, gopher); 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); //如果包含了LibRTMP #if CONFIG_LIBRTMP REGISTER_PROTOCOL (RTMP, rtmpt); REGISTER_PROTOCOL (RTMP, rtmpe); REGISTER_PROTOCOL (RTMP, rtmpte); REGISTER_PROTOCOL (RTMP, rtmps); #endif REGISTER_PROTOCOL (RTP, rtp); REGISTER_PROTOCOL (TCP, tcp); REGISTER_PROTOCOL (TLS, tls); REGISTER_PROTOCOL (UDP, udp); }
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。