ffmpeg 源代码简单分析 ： av_register_all()

原帖地址：http://blog.csdn.net/leixiaohua1020/article/details/12677129；写得非常好，故转之。

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;  }  

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）

/* * 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_protocolvoid 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。