1. av_register_all()
该函数位于 libavformat/allformats.c 中。
该函数主要是注册所有的编解码器、复用/解复用组件等。
/*
* Initialize liavformat and register all the muxers, demuxers and
* protocols. If you do not call this function, then you can select
* exactly which formats you want to support.
*
* @see av_register_input_format()
* @see av_register_output_format()
*/
void av_register_all(void)
{
static AVOnce control = AV_ONCE_INIT;
ff_thread_once(&control, register_all);
}
这里的 AVOnce 和 AV_ONCE_INIT 以及 ff_thread_once 为：
#define AVOnce pthread_once_t
#define AV_ONCE_INIT PTHREAD_ONCE_INIT
#define ff_thread_once(control, routine) pthread_once(control, routine)
在多线程程序中，不管创建了多少个线程，有些初始化动作只能发生一次。
库函数可以通过调用 pthread_once() 实现一次性初始化。
#include <pthread.h>
int pthread_once(pthread_once_t *once_control, void (*init)(void));
利用参数 once_control 的状态，函数 pthread_once() 可以确保无论有多少线程对 pthread_once() 调用了多少次，也只会执行一次由 init 指向的调用者定义函数。
参数 once_control 必须是一指针，指向初始化为 PTHREAD_ONCE_INIT 的静态变量。
调用函数 pthread_once() 时要指定一个指针，指向类型为 pthread_once_t 的特定变量，对该函数的首次调用将修改 once_control 所指向的内容，以便对其后续调用不会再次执行 init。
2. register_all()
该函数首先调用 avcodec_register_all() 注册所有的编解码器，然后注册所有的复用/解复用组件。
static void register_all(void)
{
avcodec_register_all();
/* (de)muxers */
REGISTER_MUXER (A64, a64);
REGISTER_DEMUXER (AA, aa);
REGISTER_DEMUXER (AAC, aac);
REGISTER_MUXDEMUX(AC3, ac3);
REGISTER_DEMUXER (ACM, acm);
REGISTER_DEMUXER (ACT, act);
REGISTER_DEMUXER (ADF, adf);
REGISTER_DEMUXER (ADP, adp);
REGISTER_DEMUXER (ADS, ads);
REGISTER_MUXER (ADTS, adts);
REGISTER_MUXDEMUX(ADX, adx);
REGISTER_DEMUXER (AEA, aea);
REGISTER_DEMUXER (AFC, afc);
REGISTER_MUXDEMUX(AIFF, aiff);
REGISTER_DEMUXER (AIX, aix);
REGISTER_MUXDEMUX(AMR, amr);
REGISTER_DEMUXER (ANM, anm);
REGISTER_DEMUXER (APC, apc);
REGISTER_DEMUXER (APE, ape);
REGISTER_MUXDEMUX(APNG, apng);
REGISTER_DEMUXER (AQTITLE, aqtitle);
REGISTER_MUXDEMUX(ASF, asf);
REGISTER_DEMUXER (ASF_O, asf_o);
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 (BFSTM, bfstm);
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_MUXER (DASH, dash);
REGISTER_MUXDEMUX(DATA, data);
REGISTER_MUXDEMUX(DAUD, daud);
REGISTER_DEMUXER (DCSTR, dcstr);
REGISTER_DEMUXER (DFA, dfa);
REGISTER_MUXDEMUX(DIRAC, dirac);
REGISTER_MUXDEMUX(DNXHD, dnxhd);
REGISTER_DEMUXER (DSF, dsf);
REGISTER_DEMUXER (DSICIN, dsicin);
REGISTER_DEMUXER (DSS, dss);
REGISTER_MUXDEMUX(DTS, dts);
REGISTER_DEMUXER (DTSHD, dtshd);
REGISTER_MUXDEMUX(DV, dv);
REGISTER_DEMUXER (DVBSUB, dvbsub);
REGISTER_DEMUXER (DVBTXT, dvbtxt);
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_MUXER (FIFO, fifo);
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 (FRAMEHASH, framehash);
REGISTER_MUXER (FRAMEMD5, framemd5);
REGISTER_DEMUXER (FRM, frm);
REGISTER_DEMUXER (FSB, fsb);
REGISTER_MUXDEMUX(G722, g722);
REGISTER_MUXDEMUX(G723_1, g723_1);
REGISTER_DEMUXER (G729, g729);
REGISTER_DEMUXER (GENH, genh);
REGISTER_MUXDEMUX(GIF, gif);
REGISTER_MUXDEMUX(GSM, gsm);
REGISTER_MUXDEMUX(GXF, gxf);
REGISTER_MUXDEMUX(H261, h261);
REGISTER_MUXDEMUX(H263, h263);
REGISTER_MUXDEMUX(H264, h264);
REGISTER_MUXER (HASH, hash);
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_DEMUXER (IVR, ivr);
REGISTER_MUXDEMUX(JACOSUB, jacosub);
REGISTER_DEMUXER (JV, jv);
REGISTER_MUXER (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_DEMUXER (MJPEG_2000, mjpeg_2000);
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_MUXDEMUX(MPJPEG, mpjpeg);
REGISTER_DEMUXER (MPL2, mpl2);
REGISTER_DEMUXER (MPSUB, mpsub);
REGISTER_DEMUXER (MSF, msf);
REGISTER_DEMUXER (MSNWC_TCP, msnwc_tcp);
REGISTER_DEMUXER (MTAF, mtaf);
REGISTER_DEMUXER (MTV, mtv);
REGISTER_DEMUXER (MUSX, musx);
REGISTER_DEMUXER (MV, mv);
REGISTER_DEMUXER (MVI, mvi);
REGISTER_MUXDEMUX(MXF, mxf);
REGISTER_MUXER (MXF_D10, mxf_d10);
REGISTER_MUXER (MXF_OPATOM, mxf_opatom);
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_MUXER (OGV, ogv);
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_MUXER (RTP_MPEGTS, rtp_mpegts);
REGISTER_MUXDEMUX(RTSP, rtsp);
REGISTER_DEMUXER (SAMI, sami);
REGISTER_MUXDEMUX(SAP, sap);
REGISTER_DEMUXER (SBG, sbg);
REGISTER_MUXDEMUX(SCC, scc);
REGISTER_DEMUXER (SDP, sdp);
REGISTER_DEMUXER (SDR2, sdr2);
REGISTER_DEMUXER (SDS, sds);
REGISTER_DEMUXER (SDX, sdx);
#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_MUXER (SINGLEJPEG, singlejpeg);
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_MUXER (SPX, spx);
REGISTER_MUXDEMUX(SPDIF, spdif);
REGISTER_MUXDEMUX(SRT, srt);
REGISTER_DEMUXER (STR, str);
REGISTER_DEMUXER (STL, stl);
REGISTER_DEMUXER (SUBVIEWER1, subviewer1);
REGISTER_DEMUXER (SUBVIEWER, subviewer);
REGISTER_DEMUXER (SUP, sup);
REGISTER_DEMUXER (SVAG, svag);
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 (THREEDOSTR, threedostr);
REGISTER_DEMUXER (TIERTEXSEQ, tiertexseq);
REGISTER_MUXER (MKVTIMESTAMP_V2, mkvtimestamp_v2);
REGISTER_DEMUXER (TMV, tmv);
REGISTER_MUXDEMUX(TRUEHD, truehd);
REGISTER_MUXDEMUX(TTA, tta);
REGISTER_DEMUXER (TXD, txd);
REGISTER_DEMUXER (TTY, tty);
REGISTER_MUXER (UNCODEDFRAMECRC, uncodedframecrc);
REGISTER_DEMUXER (V210, v210);
REGISTER_DEMUXER (V210X, v210x);
REGISTER_DEMUXER (VAG, vag);
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 (VPK, vpk);
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_MUXER (WEBM_CHUNK, webm_chunk);
REGISTER_MUXER (WEBP, webp);
REGISTER_MUXDEMUX(WEBVTT, webvtt);
REGISTER_DEMUXER (WSAUD, wsaud);
REGISTER_DEMUXER (WSD, wsd);
REGISTER_DEMUXER (WSVQA, wsvqa);
REGISTER_MUXDEMUX(WTV, wtv);
REGISTER_DEMUXER (WVE, wve);
REGISTER_MUXDEMUX(WV, wv);
REGISTER_DEMUXER (XA, xa);
REGISTER_DEMUXER (XBIN, xbin);
REGISTER_DEMUXER (XMV, xmv);
REGISTER_DEMUXER (XVAG, xvag);
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_DDS_PIPE, image_dds_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_JPEG_PIPE, image_jpeg_pipe);
REGISTER_DEMUXER (IMAGE_JPEGLS_PIPE, image_jpegls_pipe);
REGISTER_DEMUXER (IMAGE_PAM_PIPE, image_pam_pipe);
REGISTER_DEMUXER (IMAGE_PBM_PIPE, image_pbm_pipe);
REGISTER_DEMUXER (IMAGE_PCX_PIPE, image_pcx_pipe);
REGISTER_DEMUXER (IMAGE_PGMYUV_PIPE, image_pgmyuv_pipe);
REGISTER_DEMUXER (IMAGE_PGM_PIPE, image_pgm_pipe);
REGISTER_DEMUXER (IMAGE_PICTOR_PIPE, image_pictor_pipe);
REGISTER_DEMUXER (IMAGE_PNG_PIPE, image_png_pipe);
REGISTER_DEMUXER (IMAGE_PPM_PIPE, image_ppm_pipe);
REGISTER_DEMUXER (IMAGE_PSD_PIPE, image_psd_pipe);
REGISTER_DEMUXER (IMAGE_QDRAW_PIPE, image_qdraw_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);
REGISTER_DEMUXER (IMAGE_WEBP_PIPE, image_webp_pipe);
REGISTER_DEMUXER (IMAGE_XPM_PIPE, image_xpm_pipe);
/* external libraries */
REGISTER_MUXER (CHROMAPRINT, chromaprint);
REGISTER_DEMUXER (LIBGME, libgme);
REGISTER_DEMUXER (LIBMODPLUG, libmodplug);
REGISTER_MUXDEMUX(LIBNUT, libnut);
REGISTER_DEMUXER (LIBOPENMPT, libopenmpt);
}
2.1 注册解复用器：REGISTER_DEMUXER
#define REGISTER_DEMUXER(X, x)
{
extern AVInputFormat ff_##x##_demuxer;
if (CONFIG_##X##_DEMUXER)
av_register_input_format(&ff_##x##_demuxer);
}
这里的 ## 是拼接两个字符串。
以 REGISTER_DEMUXER (AAC, aac); 则：
#define REGISTER_DEMUXER(AAC, aac)
{
extern AVInputFormat ff_aac_demuxer;
if (CONFIG_AAC_DEMUXER)
av_register_input_format(&ff_aac_demuxer);
}
从这段代码可知，真正注册的函数是 av_register_input_format(&ff_aac_demuxer)。
注：若不想调用 av_register_all 函数注册所有的编解码器还有复用/解复用器，则可以单独调用 av_register_input_format 或 av_register_output_format 函数注册自己想要的解复用/复用器。
2.1.1 av_register_input_format
void av_register_input_format(AVInputFormat *format)
{
AVInputFormat **p = last_iformat;
/* Note, format could be added after the first 2 checks but
* that inplies that *p is no longer NULL */
while (p != &format->next && !format->next &&
avpriv_atomic_ptr_cas((void * volatile *)p, NULL, format))
p = &(*p)->next;
if (!format->next)
last_iformat = &format->next;
}
2.1.2 last_iformat ：(全局变量)
/** head of registed input format linked list */
static AVInputFormat *first_iformat = NULL;
static AVInputFormat **last_iformat = &first_iformat;
last_iformat 和 first_iformat 这两个全局变量共同构成了一个单链表，存放所有注册的解复用器。其中 first_iformat 指向该链表的第一个元素，而 last_iformat 用于指向最后一个元素。
2.1.3 avpriv_atomic_ptr_cas
void *avpriv_atomic_ptr_cas(void *volatile *ptr, void *oldval, void *newval)
{
void *ret;
pthread_mutex_lock(&atomic_lock);
ret = *ptr;
if (ret == oldval)
*ptr = newval;
pthread_mutex_unlock(&atomic_lock);
return ret;
}
从这两点可知，av_register_input_format() 函数的作用是：往 AVInputFormat 单向链表中添加 format。
如下为 AVinputFormat 结构体的具体定义。
2.2 AVInputFormat 结构体
typedef struct AVInputFormat {
/**
* A comma separater list of short names for the format.
* New names may be appended with a minor bump.
*/
const char *name;
/**
* Descriptive name for the format, meant to be more human-readable
* than name. You should use the NULL_IF_CONFIG_SMALL() macro
* to define it.
*/
const char *long_name;
/**
* Can use flags: AVFMT_NOFILE, AVFMT_NEEDNUMBER, AVFMT_SHOW_IDS,
* AVFMT_GENERIC_INDEX, AVFMT_TS_DISCONT, AVFMT_NOBINSEARCH,
* AVFMT_NOGENSEARCH, AVFMT_NO_BYTE_SEEK, AVFMT_SEEK_TO_PTS.
*/
int flags;
/**
* If extensions are defined, then no probe is done. You should
* usually not use extension format guessing because it is not
* reliable enough
*/
const char *extensions;
const struct AVCodecTag * const *codec_tag;
const AVClass *priv_class; ///< AVClass for the private context
/**
* Comma-separated list of mime types.
* It is used check for matching mime types while probing.
* @see av_probe_input_format2
*/
const char *mime_type;
/*****************************************************************
* No fields below this line are part of the public API. They
* may not be used outside of libavformat and can be changed and
* removed at will.
* New public fields should be added right above.
*****************************************************************
*/
struct AVInputFormat *next;
/**
* Raw demuxers store their codec ID here.
*/
int raw_codec_id;
/**
* Size of private data so that it can be allocated in the wrapper.
*/
int priv_data_size;
/**
* Tell if a given file has a chance of being parsed as this format.
* The buffer provided is guaranteed to be AVPROBE_PADDING_SIZE bytes
* big so you do not have to check for that unless you need more.
*/
int (*read_probe)(AVProbeData *);
/**
* Read the format header and initialize the AVFormatContext
* structure. Return 0 if OK. 'avformat_new_stream' should be
* called to create new streams.
*/
int (*read_header)(struct AVFormatContext *);
/**
* Read one packet and put it in 'pkt'. pts and flags are also
* set. 'avformat_new_stream' can be called only if the flag
* AVFMTCTX_NOHEADER is used and only in the calling thread (not in a
* background thread).
* @return 0 on success, < 0 on error.
* When returning an error, pkt must not have been allocated
* or must be freed before returning
*/
int (*read_packet)(struct AVFormatContext *, AVPacket *pkt);
/**
* Close the stream. The AVFormatContext and AVStreams are not
* freed by this function
*/
int (*read_close)(struct AVFormatContext *);
/**
* Seek to a given timestamp relative to the frames in
* stream component stream_index.
* @param stream_index Must not be -1.
* @param flags Selects which direction should be preferred if no exact
* match is available.
* @return >= 0 on success (but not necessarily the new offset)
*/
int (*read_seek)(struct AVFormatContext *,
int stream_index, int64_t timestamp, int flags);
/**
* Get the next timestamp in stream[stream_index].time_base units.
* @return the timestamp or AV_NOPTS_VALUE if an error occurred
*/
int64_t (*read_timestamp)(struct AVFormatContext *s, int stream_index,
int64_t *pos, int64_t pos_limit);
/**
* Start/resume playing - only meaningful if using a network-based format
* (RTSP).
*/
int (*read_play)(struct AVFormatContext *);
/**
* Pause playing - only meaningful if using a network-based format
* (RTSP).
*/
int (*read_pause)(struct AVFormatContext *);
/**
* Seek to timestamp ts.
* Seeking will be done so that the point from which all active streams
* can be presented successfully will be closest to ts and within min/max_ts.
* Active streams are all streams that have AVStream.discard < AVDISCARD_ALL.
*/
int (*read_seek2)(struct AVFormatContext *s, int stream_index,
int64_t min_ts, int64_t ts, int64_t max_ts, int flags);
/**
* Returns device list with it properties.
* @see avdevice_list_devices() for more details.
*/
int (*get_device_list)(struct AVFormatContext *s,
struct AVDeviceInfoList *device_list);
/**
* Initialize device capabilities submodule.
* @see avdevice_capabilities_create() for more details.
*/
int (*create_device_capabilities)(struct AVFormatContext *s,
struct AVDeviceCapabilitiesQuery *caps);
/**
* Free device capabilities submodule.
* @see avdevice_capabilities_free() for more details.
*/
int (*free_device_capabilities)(struct AVFormatContext *s,
struct AVDeviceCapabilitiesQuery *caps);
}AVInputFormat;
AVInputFormat 的一个示例如下：
AVInputFormat ff_flv_demuxer = {
.name = "flv",
.long_name = NULL_IF_CONFIG_SMALL("FLV (Flash Video)"),
.priv_data_size = sizeof(FLVContext),
/* 探测该文件格式是否为 flv */
.read_probe = flv_probe,
/* 读取 flv 的头部 */
.read_header = flv_read_header,
/* 从 flv 文件中读取一个 pkt */
.read_packet = flv_read_packet,
.read_seek = flv_read_seek,
.read_close = flv_read_close,
/* 扩展名 */
.extensions = "flv",
.priv_class = &flv_class,
};
2.3 注册复用器：REGISTER_MUXER
#define REGISTER_MUXER(X, x)
{
extern AVOutputFormat ff_##x##_muxer;
if (CONFIG_##X##_MUXER)
av_register_output_format(&ff_##x##_muxer);
}
2.3.1 av_register_output_format
void av_register_output_format(AVOutputFormat *format)
{
AVOutputFormat **p = last_oformat;
/* Note, format could be added after the first 2 checks but
* that implies that *p is no longer NULL */
while(p != &format->next && !format->next &&
avpriv_atomic_ptr_cas((void * volatile *)p, NULL, format))
p = &(*p)->next;
if (!format->next)
last_oformat = &format->next;
}
同理，该函数是向 AVOutputFormat 单向链表中添加 format。
2.4 AVOutputFormat 结构体
typedef struct AVOutputFormat {
const char *name;
/**
* Descriptive name for the format, meant to be more human-readable
* than name. You should use the NULL_IF_CONFIG_SMALL() macro
* to define it.
*/
const char *long_name;
const char *mime_type;
const char *extensions; /**< comma-separated filename extensions */
/* output support */
enum AVCodecID audio_codec; /**< default audio codec */
enum AVCodecID video_codec; /**< default video codec */
enum AVCodecID subtitle_codec; /**< default subtitle codec */
/**
* can use flags: AVFMT_NOFILE, AVFMT_NEEDNUMBER,
* AVFMT_GLOBALHEADER, AVFMT_NOTIMESTAMPS, AVFMT_VARIABLE_FPS,
* AVFMT_NODIMENSIONS, AVFMT_NOSTREAMS, AVFMT_ALLOW_FLUSH,
* AVFMT_TS_NONSTRICT, AVFMT_TS_NEGATIVE
*/
int flags;
/**
* List of supported codec_id-codec_tag pairs, ordered by "better
* choice first". The arrays are all terminated by AV_CODEC_ID_NONE.
*/
const struct AVCodecTag * const *codec_tag;
const AVClass *priv_class; ///< AVClass for the private context
/*****************************************************************
* No fields below this line are part of the public API. They
* may not be used outside of libavformat and can be changed and
* removed at will.
* New public fields should be added right above.
*****************************************************************
*/
struct AVOutputFormat *next;
/**
* size of private data so that it can be allocated in the wrapper
*/
int priv_data_size;
int (*write_header)(struct AVFormatContext *);
/**
* Write a packet. If AVFMT_ALLOW_FLUSH is set in flags,
* pkt can be NULL in order to flush data buffered in the muxer.
* When flushing, return 0 if there still is more data to flush,
* or 1 if everything was flushed and there is no more buffered
* data.
*/
int (*write_packet)(struct AVFormatContext *, AVPacket *pkt);
int (*write_trailer)(struct AVFormatContext *);
/**
* Currently only used to set pixel format if not YUV420P.
*/
int (*interleave_packet)(struct AVFormatContext *, AVPacket *out,
AVPacket *in, int flush);
/**
* Test if the given codec can be stored in this container.
*
* @return 1 if the codec is supported, 0 if it is not.
* A negative number if unknown.
* MKTAG('A', 'P', 'I', 'C') if the codec is only supported
* as AV_DISPOSITION_ATTACHED_PIC
*/
int (*query_codec)(enum AVCodecID id, int std_compliance);
void (*get_output_timestamp)(struct AVFormatContext *s, int stream,
int64_t *dts, int64_t *wall);
/**
* Allows sending messages from application to device.
*/
int (*control_message)(struct AVFormatContext *s, int type,
void *data, size_t data_size);
/**
* Write an uncoded AVFrame.
*
* See av_write_uncoded_frame() for details.
*
* The library will free *frame afterwards, but the muxer can prevent it
* by setting the pointer to NULL.
*/
int (*write_uncoded_frame)(struct AVFormatContext *, int stream_index,
AVFrame **frame, unsigned flags);
/**
* Returns device list with it properties.
* @see avdevice_list_devices() for more details.
*/
int (*get_device_list)(struct AVFormatContext *s, struct AVDeviceInfoList *device_list);
/**
* Initialize device capabilities submodule.
* @see avdevice_capabilities_create() for more details.
*/
int (*create_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps);
/**
* Free device capabilities submodule.
* @see avdevice_capabilities_free() for more details.
*/
int (*free_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps);
enum AVCodecID data_codec; /**< default data codec */
/**
* Initialize format. May allocate data here, and set any AVFormatContext or
* AVStream parameters that need to be set before packets are sent.
* This method must not write output.
*
* Return 0 if streams were fully configured, 1 if not, negative AVERROR on failure
*
* Any allocations made here must be freed in deinit().
*/
int (*init)(struct AVFormatContext *);
/**
* Deinitialize format. If present, this is called whenever the muxer is being
* destroyed, regardless of whether or not the header has been written.
*
* If a trailer is being written, this is called after write_trailer().
*
* This is called if init() fails as well.
*/
void (*deinit)(struct AVFormatContext *);
/**
* Set up any necessary bitstream filtering and extract any extra data needed
* for the global header.
* Return 0 if more packets from this stream must be checked; 1 if not.
*/
int (*check_bitstream)(struct AVFormatContext *, const AVPacket *pkt);
}AVOutputFormat;
AVOutputFormat 的一个示例如下：
AVOutputFormat ff_flv_muxer = {
.name = "flv",
.long_name = NULL_IF_CONFIG_SMALL("FLV (Flash Video)"),
.mime_type = "video/x-flv",
.extensions = "flv",
.priv_data_size = sizeof(FLVContext),
.audio_codec = CONFIG_LIBMP3LAME ? AV_CODEC_ID_MP3 : AV_CODEC_ID_ADPCM_SWF,
.video_codec = AV_CODEC_ID_FLV1,
.write_header = flv_write_header,
.write_packet = flv_write_packet,
.write_trailer = flv_write_trailer,
.codec_tag = (const AVCodecTag* const []) {
flv_video_codec_ids, flv_audio_codec_ids, 0
},
.flags = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS |
AVFMT_TS_NONSTRICT,
.priv_class = &flv_muxer_class,
};
2.5 注册复用、解复用器：REGISTER_MUXDEMUX
#define REGISTER_MUXDEMUX(X, x) REGISTER_MUXER(X, x); REGISTER_DEMUXER(X, x)