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FFmpeg的库函数源代码分析文章列表：
【架构图】
【通用】
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：内存的分配和释放（av_malloc()、av_free()等）
FFmpeg 源代码简单分析：常见结构体的初始化和销毁（AVFormatContext，AVFrame等）
FFmpeg 源代码简单分析：av_find_decoder()和av_find_encoder()
FFmpeg 源代码简单分析：avcodec_open2()
FFmpeg 源代码简单分析：avcodec_close()
【解码】
图解FFMPEG打开媒体的函数avformat_open_input
FFmpeg 源代码简单分析：avformat_open_input()
FFmpeg 源代码简单分析：avformat_find_stream_info()
FFmpeg 源代码简单分析：av_read_frame()
FFmpeg 源代码简单分析：avcodec_decode_video2()
FFmpeg 源代码简单分析：avformat_close_input()
【编码】
FFmpeg 源代码简单分析：avformat_alloc_output_context2()
FFmpeg 源代码简单分析：avformat_write_header()
FFmpeg 源代码简单分析：avcodec_encode_video()
FFmpeg 源代码简单分析：av_write_frame()
FFmpeg 源代码简单分析：av_write_trailer()
【其它】
FFmpeg源代码简单分析：日志输出系统（av_log()等）
FFmpeg源代码简单分析：结构体成员管理系统-AVClass
FFmpeg源代码简单分析：结构体成员管理系统-AVOption
FFmpeg源代码简单分析：libswscale的sws_getContext()
FFmpeg源代码简单分析：libswscale的sws_scale()
FFmpeg源代码简单分析：libavdevice的avdevice_register_all()
FFmpeg源代码简单分析：libavdevice的gdigrab
【脚本】
【H.264】
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ffmpeg中的av_read_frame()的作用是读取码流中的音频若干帧或者视频一帧。例如，解码视频的时候，每解码一个视频帧，需要先调用 av_read_frame()获得一帧视频的压缩数据，然后才能对该数据进行解码（例如H.264中一帧压缩数据通常对应一个NAL）。
对该函数源代码的分析是很久之前做的了，现在翻出来，用博客记录一下。
上代码之前，先参考了其他人对av_read_frame()的解释，在此做一个参考：
通过av_read_packet(***)，读取一个包，需要说明的是此函数必须是包含整数帧的，不存在半帧的情况，以ts流为例，是读取一个完整的PES包（一个完整pes包包含若干视频或音频es包），读取完毕后，通过av_parser_parse2(***)分析出视频一帧（或音频若干帧），返回，下次进入循环的时候，如果上次的数据没有完全取完，则st = s->cur_st;不会是NULL，即再此进入av_parser_parse2(***)流程，而不是下面的av_read_packet（**）流程，这样就保证了，如果读取一次包含了N帧视频数据（以视频为例），则调用av_read_frame（***）N次都不会去读数据，而是返回第一次读取的数据，直到全部解析完毕。
av_read_frame()的声明位于libavformat\avformat.h，如下所示。
/** * Return the next frame of a stream. * This function returns what is stored in the file, and does not validate * that what is there are valid frames for the decoder. It will split what is * stored in the file into frames and return one for each call. It will not * omit invalid data between valid frames so as to give the decoder the maximum * information possible for decoding. * * If pkt->buf is NULL, then the packet is valid until the next * av_read_frame() or until avformat_close_input(). Otherwise the packet * is valid indefinitely. In both cases the packet must be freed with * av_free_packet when it is no longer needed. For video, the packet contains * exactly one frame. For audio, it contains an integer number of frames if each * frame has a known fixed size (e.g. PCM or ADPCM data). If the audio frames * have a variable size (e.g. MPEG audio), then it contains one frame. * * pkt->pts, pkt->dts and pkt->duration are always set to correct * values in AVStream.time_base units (and guessed if the format cannot * provide them). pkt->pts can be AV_NOPTS_VALUE if the video format * has B-frames, so it is better to rely on pkt->dts if you do not * decompress the payload. * * @return 0 if OK, < 0 on error or end of file */int av_read_frame(AVFormatContext *s, AVPacket *pkt);av_read_frame()使用方法在注释中写得很详细，用中文简单描述一下它的两个参数：
s：输入的AVFormatContext
pkt：输出的AVPacket
如果返回0则说明读取正常。
函数调用结构图
函数调用结构图如下所示。
av_read_frame()
av_read_frame()的定义位于libavformat\utils.c，如下所示：
//获取一个AVPacket/* * av_read_frame - 新版本的ffmpeg用的是av_read_frame，而老版本的是av_read_packet * 。区别是av_read_packet读出的是包，它可能是半帧或多帧，不保证帧的完整性。av_read_frame对 * av_read_packet进行了封装，使读出的数据总是完整的帧 */int av_read_frame(AVFormatContext *s, AVPacket *pkt){ const int genpts = s->flags & AVFMT_FLAG_GENPTS; int eof = 0; if (!genpts) /** * This buffer is only needed when packets were already buffered but * not decoded, for example to get the codec parameters in MPEG * streams. * 一般情况下会调用read_frame_internal(s, pkt) * 直接返回 */ return s->packet_buffer ? read_from_packet_buffer(s, pkt) : read_frame_internal(s, pkt); for (;;) { int ret; AVPacketList *pktl = s->packet_buffer; if (pktl) { AVPacket *next_pkt = &pktl->pkt; if (next_pkt->dts != AV_NOPTS_VALUE) { int wrap_bits = s->streams[next_pkt->stream_index]->pts_wrap_bits; while (pktl && next_pkt->pts == AV_NOPTS_VALUE) { if (pktl->pkt.stream_index == next_pkt->stream_index && (av_compare_mod(next_pkt->dts, pktl->pkt.dts, 2LL << (wrap_bits - 1)) < 0) && av_compare_mod(pktl->pkt.pts, pktl->pkt.dts, 2LL << (wrap_bits - 1))) { //not b frame next_pkt->pts = pktl->pkt.dts; } pktl = pktl->next; } pktl = s->packet_buffer; } /* read packet from packet buffer, if there is data */ if (!(next_pkt->pts == AV_NOPTS_VALUE && next_pkt->dts != AV_NOPTS_VALUE && !eof)) return read_from_packet_buffer(s, pkt); } ret = read_frame_internal(s, pkt); if (ret < 0) { if (pktl && ret != AVERROR(EAGAIN)) { eof = 1; continue; } else return ret; } if (av_dup_packet(add_to_pktbuf(&s->packet_buffer, pkt, &s->packet_buffer_end)) < 0) return AVERROR(ENOMEM); }}read_frame_internal()
read_frame_internal()代码如下所示：
//av_read_frame对他进行了封装static int read_frame_internal(AVFormatContext *s, AVPacket *pkt){ int ret = 0, i, got_packet = 0; AVDictionary *metadata = NULL; //初始化 av_init_packet(pkt); while (!got_packet && !s->parse_queue) { AVStream *st; AVPacket cur_pkt; /* read next packet */ ret = ff_read_packet(s, &cur_pkt); if (ret < 0) { if (ret == AVERROR(EAGAIN)) return ret; /* flush the parsers */ for (i = 0; i < s->nb_streams; i++) { st = s->streams[i]; //需要解析 if (st->parser && st->need_parsing) parse_packet(s, NULL, st->index); } /* all remaining packets are now in parse_queue => * really terminate parsing */ break; } ret = 0; st = s->streams[cur_pkt.stream_index]; if (cur_pkt.pts != AV_NOPTS_VALUE && cur_pkt.dts != AV_NOPTS_VALUE && cur_pkt.pts < cur_pkt.dts) { av_log(s, AV_LOG_WARNING, "Invalid timestamps stream=%d, pts=%s, dts=%s, size=%d\n", cur_pkt.stream_index, av_ts2str(cur_pkt.pts), av_ts2str(cur_pkt.dts), cur_pkt.size); } if (s->debug & FF_FDEBUG_TS) av_log(s, AV_LOG_DEBUG, "ff_read_packet stream=%d, pts=%s, dts=%s, size=%d, duration=%d, flags=%d\n", cur_pkt.stream_index, av_ts2str(cur_pkt.pts), av_ts2str(cur_pkt.dts), cur_pkt.size, cur_pkt.duration, cur_pkt.flags); if (st->need_parsing && !st->parser && !(s->flags & AVFMT_FLAG_NOPARSE)) { st->parser = av_parser_init(st->codec->codec_id); if (!st->parser) { av_log(s, AV_LOG_VERBOSE, "parser not found for codec " "%s, packets or times may be invalid.\n", avcodec_get_name(st->codec->codec_id)); /* no parser available: just output the raw packets */ st->need_parsing = AVSTREAM_PARSE_NONE; } else if (st->need_parsing == AVSTREAM_PARSE_HEADERS) st->parser->flags |= PARSER_FLAG_COMPLETE_FRAMES; else if (st->need_parsing == AVSTREAM_PARSE_FULL_ONCE) st->parser->flags |= PARSER_FLAG_ONCE; else if (st->need_parsing == AVSTREAM_PARSE_FULL_RAW) st->parser->flags |= PARSER_FLAG_USE_CODEC_TS; } if (!st->need_parsing || !st->parser) { /* no parsing needed: we just output the packet as is */ *pkt = cur_pkt; compute_pkt_fields(s, st, NULL, pkt); if ((s->iformat->flags & AVFMT_GENERIC_INDEX) && (pkt->flags & AV_PKT_FLAG_KEY) && pkt->dts != AV_NOPTS_VALUE) { ff_reduce_index(s, st->index); av_add_index_entry(st, pkt->pos, pkt->dts, 0, 0, AVINDEX_KEYFRAME); } got_packet = 1; } else if (st->discard < AVDISCARD_ALL) { if ((ret = parse_packet(s, &cur_pkt, cur_pkt.stream_index)) < 0) return ret; } else { /* free packet */ av_free_packet(&cur_pkt); } if (pkt->flags & AV_PKT_FLAG_KEY) st->skip_to_keyframe = 0; if (st->skip_to_keyframe) { av_free_packet(&cur_pkt); if (got_packet) { *pkt = cur_pkt; } got_packet = 0; } } if (!got_packet && s->parse_queue) ret = read_from_packet_buffer(&s->parse_queue, &s->parse_queue_end, pkt); if (ret >= 0) { AVStream *st = s->streams[pkt->stream_index]; int discard_padding = 0; if (st->first_discard_sample && pkt->pts != AV_NOPTS_VALUE) { int64_t pts = pkt->pts - (is_relative(pkt->pts) ? RELATIVE_TS_BASE : 0); int64_t sample = ts_to_samples(st, pts); int duration = ts_to_samples(st, pkt->duration); int64_t end_sample = sample + duration; if (duration > 0 && end_sample >= st->first_discard_sample && sample < st->last_discard_sample) discard_padding = FFMIN(end_sample - st->first_discard_sample, duration); } if (st->skip_samples || discard_padding) { uint8_t *p = av_packet_new_side_data(pkt, AV_PKT_DATA_SKIP_SAMPLES, 10); if (p) { AV_WL32(p, st->skip_samples); AV_WL32(p + 4, discard_padding); av_log(s, AV_LOG_DEBUG, "demuxer injecting skip %d\n", st->skip_samples); } st->skip_samples = 0; } if (st->inject_global_side_data) { for (i = 0; i < st->nb_side_data; i++) { AVPacketSideData *src_sd = &st->side_data[i]; uint8_t *dst_data; if (av_packet_get_side_data(pkt, src_sd->type, NULL)) continue; dst_data = av_packet_new_side_data(pkt, src_sd->type, src_sd->size); if (!dst_data) { av_log(s, AV_LOG_WARNING, "Could not inject global side data\n"); continue; } memcpy(dst_data, src_sd->data, src_sd->size); } st->inject_global_side_data = 0; } if (!(s->flags & AVFMT_FLAG_KEEP_SIDE_DATA)) av_packet_merge_side_data(pkt); } av_opt_get_dict_val(s, "metadata", AV_OPT_SEARCH_CHILDREN, &metadata); if (metadata) { s->event_flags |= AVFMT_EVENT_FLAG_METADATA_UPDATED; av_dict_copy(&s->metadata, metadata, 0); av_dict_free(&metadata); av_opt_set_dict_val(s, "metadata", NULL, AV_OPT_SEARCH_CHILDREN); } if (s->debug & FF_FDEBUG_TS) av_log(s, AV_LOG_DEBUG, "read_frame_internal stream=%d, pts=%s, dts=%s, " "size=%d, duration=%d, flags=%d\n", pkt->stream_index, av_ts2str(pkt->pts), av_ts2str(pkt->dts), pkt->size, pkt->duration, pkt->flags); return ret;}read_frame_internal()代码比较长，这里只简单看一下它前面的部分。它前面部分有2步是十分关键的：
（1）调用了ff_read_packet()从相应的AVInputFormat读取数据。
（2）如果媒体频流需要使用AVCodecParser，则调用parse_packet()解析相应的AVPacket。
下面我们分成分别看一下ff_read_packet()和parse_packet()的源代码。
ff_read_packet()
ff_read_packet()的代码比较长，如下所示。
int ff_read_packet(AVFormatContext *s, AVPacket *pkt){ int ret, i, err; AVStream *st; for (;;) { AVPacketList *pktl = s->raw_packet_buffer; if (pktl) { *pkt = pktl->pkt; st = s->streams[pkt->stream_index]; if (s->raw_packet_buffer_remaining_size <= 0) if ((err = probe_codec(s, st, NULL)) < 0) return err; if (st->request_probe <= 0) { s->raw_packet_buffer = pktl->next; s->raw_packet_buffer_remaining_size += pkt->size; av_free(pktl); return 0; } } pkt->data = NULL; pkt->size = 0; av_init_packet(pkt); //关键：读取Packet ret = s->iformat->read_packet(s, pkt); if (ret < 0) { if (!pktl || ret == AVERROR(EAGAIN)) return ret; for (i = 0; i < s->nb_streams; i++) { st = s->streams[i]; if (st->probe_packets) if ((err = probe_codec(s, st, NULL)) < 0) return err; av_assert0(st->request_probe <= 0); } continue; } if ((s->flags & AVFMT_FLAG_DISCARD_CORRUPT) && (pkt->flags & AV_PKT_FLAG_CORRUPT)) { av_log(s, AV_LOG_WARNING, "Dropped corrupted packet (stream = %d)\n", pkt->stream_index); av_free_packet(pkt); continue; } if (pkt->stream_index >= (unsigned)s->nb_streams) { av_log(s, AV_LOG_ERROR, "Invalid stream index %d\n", pkt->stream_index); continue; } st = s->streams[pkt->stream_index]; if (update_wrap_reference(s, st, pkt->stream_index, pkt) && st->pts_wrap_behavior == AV_PTS_WRAP_SUB_OFFSET) { // correct first time stamps to negative values if (!is_relative(st->first_dts)) st->first_dts = wrap_timestamp(st, st->first_dts); if (!is_relative(st->start_time)) st->start_time = wrap_timestamp(st, st->start_time); if (!is_relative(st->cur_dts)) st->cur_dts = wrap_timestamp(st, st->cur_dts); } pkt->dts = wrap_timestamp(st, pkt->dts); pkt->pts = wrap_timestamp(st, pkt->pts); force_codec_ids(s, st); /* TODO: audio: time filter; video: frame reordering (pts != dts) */ if (s->use_wallclock_as_timestamps) pkt->dts = pkt->pts = av_rescale_q(av_gettime(), AV_TIME_BASE_Q, st->time_base); if (!pktl && st->request_probe <= 0) return ret; add_to_pktbuf(&s->raw_packet_buffer, pkt, &s->raw_packet_buffer_end); s->raw_packet_buffer_remaining_size -= pkt->size; if ((err = probe_codec(s, st, pkt)) < 0) return err; }}ff_read_packet()中最关键的地方就是调用了AVInputFormat的read_packet()方法。AVInputFormat的read_packet()是一个函数指针，指向当前的AVInputFormat的读取数据的函数。在这里我们以FLV封装格式对应的AVInputFormat为例，看看read_packet()的实现函数是什么样子的。
FLV封装格式对应的AVInputFormat的定义位于libavformat\flvdec.c，如下所示。
AVInputFormat ff_flv_demuxer = { .name = "flv", .long_name = NULL_IF_CONFIG_SMALL("FLV (Flash Video)"), .priv_data_size = sizeof(FLVContext), .read_probe = flv_probe, .read_header = flv_read_header, .read_packet = flv_read_packet, .read_seek = flv_read_seek, .read_close = flv_read_close, .extensions = "flv", .priv_class = &flv_class,};从ff_flv_demuxer的定义可以看出，read_packet()对应的是flv_read_packet()函数。在看flv_read_packet()函数之前，我们先回顾一下FLV封装格式的结构，如下图所示。
从图中可以看出，FLV文件体部分是由一个一个的Tag连接起来的（中间间隔着Previous Tag Size）。每个Tag包含了Tag Header和Tag Data两个部分。Tag Data根据Tag的Type不同而不同：可以分为音频Tag Data，视频Tag Data以及Script Tag Data。下面简述一下音频Tag Data和视频Tag Data。
Audio Tag Data
Audio Tag在官方标准中定义如下。第1个字节的前4位的数值表示了音频数据格式：
0 = Linear PCM, platform endian第1个字节的第5-6位的数值表示采样率：0 = 5.5kHz，1 = 11KHz，2 = 22 kHz，3 = 44 kHz。
1 = ADPCM
2 = MP3
3 = Linear PCM, little endian
4 = Nellymoser 16-kHz mono
5 = Nellymoser 8-kHz mono
6 = Nellymoser
7 = G.711 A-law logarithmic PCM
8 = G.711 mu-law logarithmic PCM
9 = reserved
10 = AAC
14 = MP3 8-Khz
15 = Device-specific sound
第1个字节的第7位表示采样精度：0 = 8bits，1 = 16bits。
第1个字节的第8位表示音频类型：0 = sndMono，1 = sndStereo。
其中，当音频编码为AAC的时候，第一个字节后面存储的是AACAUDIODATA，格式如下所示。
Video Tag Data
Video Tag在官方标准中的定义如下。第1个字节的前4位的数值表示帧类型（FrameType）：
1: keyframe (for AVC, a seekableframe)（关键帧）第1个字节的后4位的数值表示视频编码ID（CodecID）：
2: inter frame (for AVC, a nonseekableframe)
3: disposable inter frame (H.263only)
4: generated keyframe (reservedfor server use only)
5: video info/command frame
1: JPEG (currently unused)其中，当音频编码为AVC（H.264）的时候，第一个字节后面存储的是AVCVIDEOPACKET，格式如下所示。
2: Sorenson H.263
3: Screen video
4: On2 VP6
5: On2 VP6 with alpha channel
6: Screen video version 2
7: AVC
了解了FLV的基本格式之后，就可以看一下FLV解析Tag的函数flv_read_packet()了。
flv_read_packet()
flv_read_packet()的定义位于libavformat\flvdec.c，如下所示。
static int flv_read_packet(AVFormatContext *s, AVPacket *pkt){ FLVContext *flv = s->priv_data; int ret, i, type, size, flags; int stream_type=-1; int64_t next, pos, meta_pos; int64_t dts, pts = AV_NOPTS_VALUE; int av_uninit(channels); int av_uninit(sample_rate); AVStream *st = NULL; /* pkt size is repeated at end. skip it */ for (;; avio_skip(s->pb, 4)) { pos = avio_tell(s->pb); //解析Tag Header========== //Tag类型 type = (avio_r8(s->pb) & 0x1F); //Datasize数据大小 size = avio_rb24(s->pb); //Timstamp时间戳 dts = avio_rb24(s->pb); dts |= avio_r8(s->pb) << 24; av_dlog(s, "type:%d, size:%d, dts:%"PRId64" pos:%"PRId64"\n", type, size, dts, avio_tell(s->pb)); if (avio_feof(s->pb)) return AVERROR_EOF; //StreamID avio_skip(s->pb, 3); /* stream id, always 0 */ flags = 0; //======================== if (flv->validate_next < flv->validate_count) { int64_t validate_pos = flv->validate_index[flv->validate_next].pos; if (pos == validate_pos) { if (FFABS(dts - flv->validate_index[flv->validate_next].dts) <= VALIDATE_INDEX_TS_THRESH) { flv->validate_next++; } else { clear_index_entries(s, validate_pos); flv->validate_count = 0; } } else if (pos > validate_pos) { clear_index_entries(s, validate_pos); flv->validate_count = 0; } } if (size == 0) continue; next = size + avio_tell(s->pb); if (type == FLV_TAG_TYPE_AUDIO) { //Type是音频 stream_type = FLV_STREAM_TYPE_AUDIO; //Tag Data的第一个字节 flags = avio_r8(s->pb); size--; } else if (type == FLV_TAG_TYPE_VIDEO) { //Type是音频 stream_type = FLV_STREAM_TYPE_VIDEO; //Tag Data的第一个字节 flags = avio_r8(s->pb); size--; if ((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_VIDEO_INFO_CMD) goto skip; } else if (type == FLV_TAG_TYPE_META) { stream_type=FLV_STREAM_TYPE_DATA; if (size > 13 + 1 + 4 && dts == 0) { // Header-type metadata stuff meta_pos = avio_tell(s->pb); if (flv_read_metabody(s, next) <= 0) { goto skip; } avio_seek(s->pb, meta_pos, SEEK_SET); } } else { av_log(s, AV_LOG_DEBUG, "Skipping flv packet: type %d, size %d, flags %d.\n", type, size, flags);skip: avio_seek(s->pb, next, SEEK_SET); continue; } /* skip empty data packets */ if (!size) continue; /* now find stream */ for (i = 0; i < s->nb_streams; i++) { st = s->streams[i]; if (stream_type == FLV_STREAM_TYPE_AUDIO) { if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO && (s->audio_codec_id || flv_same_audio_codec(st->codec, flags))) break; } else if (stream_type == FLV_STREAM_TYPE_VIDEO) { if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO && (s->video_codec_id || flv_same_video_codec(st->codec, flags))) break; } else if (stream_type == FLV_STREAM_TYPE_DATA) { if (st->codec->codec_type == AVMEDIA_TYPE_DATA) break; } } if (i == s->nb_streams) { static const enum AVMediaType stream_types[] = {AVMEDIA_TYPE_VIDEO, AVMEDIA_TYPE_AUDIO, AVMEDIA_TYPE_DATA}; av_log(s, AV_LOG_WARNING, "Stream discovered after head already parsed\n"); st = create_stream(s, stream_types[stream_type]); if (!st) return AVERROR(ENOMEM); } av_dlog(s, "%d %X %d \n", stream_type, flags, st->discard); if ((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_KEY || stream_type == FLV_STREAM_TYPE_AUDIO) av_add_index_entry(st, pos, dts, size, 0, AVINDEX_KEYFRAME); if ( (st->discard >= AVDISCARD_NONKEY && !((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_KEY || (stream_type == FLV_STREAM_TYPE_AUDIO))) ||(st->discard >= AVDISCARD_BIDIR && ((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_DISP_INTER && (stream_type == FLV_STREAM_TYPE_VIDEO))) || st->discard >= AVDISCARD_ALL ) { avio_seek(s->pb, next, SEEK_SET); continue; } break; } // if not streamed and no duration from metadata then seek to end to find // the duration from the timestamps if (s->pb->seekable && (!s->duration || s->duration == AV_NOPTS_VALUE) && !flv->searched_for_end) { int size; const int64_t pos = avio_tell(s->pb); // Read the last 4 bytes of the file, this should be the size of the // previous FLV tag. Use the timestamp of its payload as duration. int64_t fsize = avio_size(s->pb);retry_duration: avio_seek(s->pb, fsize - 4, SEEK_SET); size = avio_rb32(s->pb); // Seek to the start of the last FLV tag at position (fsize - 4 - size) // but skip the byte indicating the type. avio_seek(s->pb, fsize - 3 - size, SEEK_SET); if (size == avio_rb24(s->pb) + 11) { uint32_t ts = avio_rb24(s->pb); ts |= avio_r8(s->pb) << 24; if (ts) s->duration = ts * (int64_t)AV_TIME_BASE / 1000; else if (fsize >= 8 && fsize - 8 >= size) { fsize -= size+4; goto retry_duration; } } avio_seek(s->pb, pos, SEEK_SET); flv->searched_for_end = 1; } if (stream_type == FLV_STREAM_TYPE_AUDIO) { int bits_per_coded_sample; channels = (flags & FLV_AUDIO_CHANNEL_MASK) == FLV_STEREO ? 2 : 1; sample_rate = 44100 << ((flags & FLV_AUDIO_SAMPLERATE_MASK) >> FLV_AUDIO_SAMPLERATE_OFFSET) >> 3; bits_per_coded_sample = (flags & FLV_AUDIO_SAMPLESIZE_MASK) ? 16 : 8; if (!st->codec->channels || !st->codec->sample_rate || !st->codec->bits_per_coded_sample) { st->codec->channels = channels; st->codec->channel_layout = channels == 1 ? AV_CH_LAYOUT_MONO : AV_CH_LAYOUT_STEREO; st->codec->sample_rate = sample_rate; st->codec->bits_per_coded_sample = bits_per_coded_sample; } if (!st->codec->codec_id) { flv_set_audio_codec(s, st, st->codec, flags & FLV_AUDIO_CODECID_MASK); flv->last_sample_rate = sample_rate = st->codec->sample_rate; flv->last_channels = channels = st->codec->channels; } else { AVCodecContext ctx = {0}; ctx.sample_rate = sample_rate; ctx.bits_per_coded_sample = bits_per_coded_sample; flv_set_audio_codec(s, st, &ctx, flags & FLV_AUDIO_CODECID_MASK); sample_rate = ctx.sample_rate; } } else if (stream_type == FLV_STREAM_TYPE_VIDEO) { size -= flv_set_video_codec(s, st, flags & FLV_VIDEO_CODECID_MASK, 1); } //几种特殊的格式 if (st->codec->codec_id == AV_CODEC_ID_AAC || st->codec->codec_id == AV_CODEC_ID_H264 || st->codec->codec_id == AV_CODEC_ID_MPEG4) { //对应AACPacketType或者AVCPacketType int type = avio_r8(s->p给我老师的人工智能教程打call！http://blog.csdn.net/jiangjunshow
