avformat_find_stream_info 的主要作用就是：解析媒体文件并获取相关的流信息
整体的逻辑如下图所示：
/**
* Read packets of a media file to get stream information. This
* is useful for file formats with no headers such as MPEG. This
* function also computes the real framerate in case of MPEG-2 repeat
* frame mode.
* The logical file position is not changed by this function;
* examined packets may be buffered for later processing.
*
* @param ic media file handle
* @param options If non-NULL, an ic.nb_streams long array of pointers to
* dictionaries, where i-th member contains options for
* codec corresponding to i-th stream.
* On return each dictionary will be filled with options that were not found.
* @return >=0 if OK, AVERROR_xxx on error
*
* @note this function isn't guaranteed to open all the codecs, so
* options being non-empty at return is a perfectly normal behavior.
*
* @todo Let the user decide somehow what information is needed so that
* we do not waste time getting stuff the user does not need.
*/
/**
* 从注释可知道，此方法通过读取若干 packet 包来获取流信息，这对于像 MPEG 这种没有 header 的格式比较有用。此函数也计算了像 MPEG-2 这种支持 repeat mode 的真实帧率
* 这个函数不会修改逻辑文件位置，所读取到的 packet 会缓存起来供后面使用。
*/
int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
{
int i, count = 0, ret = 0, j;
int64_t read_size;
AVStream *st;
AVCodecContext *avctx;
AVPacket pkt1;
int64_t old_offset = avio_tell(ic->pb);
// new streams might appear, no options for those
int orig_nb_streams = ic->nb_streams;
int flush_codecs;
int64_t max_analyze_duration = ic->max_analyze_duration;
int64_t max_stream_analyze_duration;
int64_t max_subtitle_analyze_duration;
int64_t probesize = ic->probesize;
int eof_reached = 0;
int *missing_streams = av_opt_ptr(ic->iformat->priv_class, ic->priv_data, "missing_streams");
flush_codecs = probesize > 0;
av_opt_set(ic, "skip_clear", "1", AV_OPT_SEARCH_CHILDREN);
max_stream_analyze_duration = max_analyze_duration;
max_subtitle_analyze_duration = max_analyze_duration;
if (!max_analyze_duration) {
//默认5*AV_TIME_BASE，针对flv和mpeg默认90*AV_TIME_BASE和7*AV_TIME_BASE
max_stream_analyze_duration =
max_analyze_duration = 5*AV_TIME_BASE;
max_subtitle_analyze_duration = 30*AV_TIME_BASE;
if (!strcmp(ic->iformat->name, "flv"))
max_stream_analyze_duration = 90*AV_TIME_BASE;
if (!strcmp(ic->iformat->name, "mpeg") || !strcmp(ic->iformat->name, "mpegts"))
max_stream_analyze_duration = 7*AV_TIME_BASE;
}
if (ic->pb)
av_log(ic, AV_LOG_DEBUG, "Before avformat_find_stream_info() pos: %"PRId64" bytes read:%"PRId64" seeks:%d nb_streams:%d\n",
avio_tell(ic->pb), ic->pb->bytes_read, ic->pb->seek_count, ic->nb_streams);
/**
* -----【第一次循环遍历流】-------
* 主要就是：初始化 avctx 的 time_base 等参数，初始化解析器，将编解码器的参数信息拷贝到编解码器上下文中，
* 查找解码器、打开解码器
*/
for (i = 0; i < ic->nb_streams; i++) {
const AVCodec *codec;
AVDictionary *thread_opt = NULL;
st = ic->streams[i];
avctx = st->internal->avctx;//获取编解码器上下文
if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO ||
st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE) {
/* if (!st->time_base.num)
st->time_base = */
if (!avctx->time_base.num)
avctx->time_base = st->time_base;//设置avctx->time_base
}
/* check if the caller has overridden the codec id */
#if FF_API_LAVF_AVCTX
FF_DISABLE_DEPRECATION_WARNINGS
if (st->codec->codec_id != st->internal->orig_codec_id) {
st->codecpar->codec_id = st->codec->codec_id;
st->codecpar->codec_type = st->codec->codec_type;
st->internal->orig_codec_id = st->codec->codec_id;
}
FF_ENABLE_DEPRECATION_WARNINGS
#endif
// only for the split stuff
if (!st->parser && !(ic->flags & AVFMT_FLAG_NOPARSE) && st->internal->request_probe <= 0) {
st->parser = av_parser_init(st->codecpar->codec_id);//解析器为空则初始化解析器
if (st->parser) {
if (st->need_parsing == AVSTREAM_PARSE_HEADERS) {
st->parser->flags |= PARSER_FLAG_COMPLETE_FRAMES;
} else if (st->need_parsing == AVSTREAM_PARSE_FULL_RAW) {
st->parser->flags |= PARSER_FLAG_USE_CODEC_TS;
}
} else if (st->need_parsing) {
av_log(ic, AV_LOG_VERBOSE, "parser not found for codec "
"%s, packets or times may be invalid.\n",
avcodec_get_name(st->codecpar->codec_id));
}
}
if (st->codecpar->codec_id != st->internal->orig_codec_id)
st->internal->orig_codec_id = st->codecpar->codec_id;
ret = avcodec_parameters_to_context(avctx, st->codecpar);//参数拷贝
if (ret < 0)
goto find_stream_info_err;
if (st->internal->request_probe <= 0)
st->internal->avctx_inited = 1;
codec = find_probe_decoder(ic, st, st->codecpar->codec_id);//根据解码器id查找解码器
/* Force thread count to 1 since the H.264 decoder will not extract
* SPS and PPS to extradata during multi-threaded decoding. */
av_dict_set(options ? &options[i] : &thread_opt, "threads", "1", 0);
if (ic->codec_whitelist)
av_dict_set(options ? &options[i] : &thread_opt, "codec_whitelist", ic->codec_whitelist, 0);
/* Ensure that subtitle_header is properly set. */
if (st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE
&& codec && !avctx->codec) {
if (avcodec_open2(avctx, codec, options ? &options[i] : &thread_opt) < 0)
av_log(ic, AV_LOG_WARNING,
"Failed to open codec in %s\n",__FUNCTION__);
}
// Try to just open decoders, in case this is enough to get parameters.
// 在某些场景下，只需打开解码器，就能获取到编码层的参数
if (!has_codec_parameters(st, NULL) && st->internal->request_probe <= 0) {
if (codec && !avctx->codec)
if (avcodec_open2(avctx, codec, options ? &options[i] : &thread_opt) < 0)//打开解码器
av_log(ic, AV_LOG_WARNING,
"Failed to open codec in %s\n",__FUNCTION__);
}
if (!options)
av_dict_free(&thread_opt);
}
for (i = 0; i < ic->nb_streams; i++) {//-----【第二个循环】-------
#if FF_API_R_FRAME_RATE
ic->streams[i]->internal->info->last_dts = AV_NOPTS_VALUE;
#endif
ic->streams[i]->internal->info->fps_first_dts = AV_NOPTS_VALUE;
ic->streams[i]->internal->info->fps_last_dts = AV_NOPTS_VALUE;
}
// 对 stream 中的数据进行 probe，读取一定的数据到内存中
read_size = 0;
for (;;) {//-------------------------【第三个循环】------------------
const AVPacket *pkt;
int analyzed_all_streams;
// ff_check_interrupt 检测是否有用户层进行中断请求，
if (ff_check_interrupt(&ic->interrupt_callback)) {
ret = AVERROR_EXIT;
av_log(ic, AV_LOG_DEBUG, "interrupted\n");
break;
}
/* 再次对所有的 streams 进行一次遍历，检查 stream 中 codec 信息是否完整，
* 如果还有没解析出的，那么 break 跳出当前 stream 的遍历（此时还没有跳出 for(;;) 的大循环）
* 在确认了 has_codec 之后，根据各种可能出现的情况设置好 fps_analyze_framecount；之后，还有一系列判断是否应该 break 遍历。
*/
/* check if one codec still needs to be handled */
for (i = 0; i < ic->nb_streams; i++) {//-----------【第三个循环的第一个嵌套循环】---------------
int fps_analyze_framecount = 20;
int count;
st = ic->streams[i];
/**
* has_codec_parameters：此函数检查 codec 信息是否完整
*/
if (!has_codec_parameters(st, NULL))
break;
/* If the timebase is coarse (like the usual millisecond precision
* of mkv), we need to analyze more frames to reliably arrive at
* the correct fps. */
//如果时基比较粗略（例如 mkv 通常的毫秒精度），我们需要分析更多帧才能可靠地获得正确的 fps，fps_analyze_framecount * 2
if (av_q2d(st->time_base) > 0.0005)
fps_analyze_framecount *= 2;
if (!tb_unreliable(st->internal->avctx))//时间基不正常或不是 mpeg4/mpeg2/HEVC/AVC 影片，不需要分析，fps_analyze_framecount = 0
fps_analyze_framecount = 0;
if (ic->fps_probe_size >= 0)//设置了 fps_probe_size，则按 fps_probe_size
fps_analyze_framecount = ic->fps_probe_size;
if (st->disposition & AV_DISPOSITION_ATTACHED_PIC)//如果是音频文件附带的图片流或者是视频附带的信息流，就不需要估计帧率
fps_analyze_framecount = 0;
/* variable fps and no guess at the real fps */
// 可变 fps 并且无法猜测真实 fps
count = (ic->iformat->flags & AVFMT_NOTIMESTAMPS) ?
st->internal->info->codec_info_duration_fields/2 :
st->internal->info->duration_count;
//未找到帧率的视频帧，并且 count < fps_analyze_framecount，则退出循环去估算视频帧
if (!(st->r_frame_rate.num && st->avg_frame_rate.num) &&
st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
if (count < fps_analyze_framecount)
break;
}
// Look at the first 3 frames if there is evidence of frame delay
// but the decoder delay is not set.
//查看前 3 帧是否有帧延迟现象但未设置解码器延迟
if (st->internal->info->frame_delay_evidence && count < 2 && st->internal->avctx->has_b_frames == 0)
break;
if (!st->internal->avctx->extradata &&
(!st->internal->extract_extradata.inited ||
st->internal->extract_extradata.bsf) &&
extract_extradata_check(st))
break;
if (st->first_dts == AV_NOPTS_VALUE &&
!(ic->iformat->flags & AVFMT_NOTIMESTAMPS) &&
st->codec_info_nb_frames < ((st->disposition & AV_DISPOSITION_ATTACHED_PIC) ? 1 : ic->max_ts_probe) &&
(st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO ||
st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO))
break;
}
analyzed_all_streams = 0;
/* 如果循环能正常结束，说明流信息的探测完毕，此时 i == ic->nb_streams；
* 如果中间 break 了，说明某个流的信息还没有完全得到，此时 i < ic->nb_streams， 需继续探测
*/
if (!missing_streams || !*missing_streams)
if (i == ic->nb_streams) {// i == ic->nb_streams，说明所有的流都没问题了
analyzed_all_streams = 1;
/* NOTE: If the format has no header, then we need to read some
* packets to get most of the streams, so we cannot stop here. */
// 如果是像 MPEG 这种没有头的封装格式，需要解析更多的 packets; 否则 break
if (!(ic->ctx_flags & AVFMTCTX_NOHEADER)) {
/* If we found the info for all the codecs, we can stop. */
ret = count;
av_log(ic, AV_LOG_DEBUG, "All info found\n");
flush_codecs = 0;
break;
}
}
// 下面属于继续探测的流程
/* We did not get all the codec info, but we read too much data. */
//虽然流信息还没完全探测出来，但是 read_size >= probesize， 已读取到的大小超过了 probesize，则退出
if (read_size >= probesize) {
ret = count;
av_log(ic, AV_LOG_DEBUG,
"Probe buffer size limit of %"PRId64" bytes reached\n", probesize);
for (i = 0; i < ic->nb_streams; i++)
if (!ic->streams[i]->r_frame_rate.num &&
ic->streams[i]->internal->info->duration_count <= 1 &&
ic->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
strcmp(ic->iformat->name, "image2"))
av_log(ic, AV_LOG_WARNING,
"Stream #%d: not enough frames to estimate rate; "
"consider increasing probesize\n", i);
break;
}
/* NOTE: A new stream can be added there if no header in file
* (AVFMTCTX_NOHEADER). */
// 读取 packet
ret = read_frame_internal(ic, &pkt1);
if (ret == AVERROR(EAGAIN))
continue;
if (ret < 0) {
/* EOF or error*/
eof_reached = 1;
break;
}
if (!(ic->flags & AVFMT_FLAG_NOBUFFER)) {
ret = avpriv_packet_list_put(&ic->internal->packet_buffer,
&ic->internal->packet_buffer_end,
&pkt1, NULL, 0);
if (ret < 0)
goto unref_then_goto_end;
pkt = &ic->internal->packet_buffer_end->pkt;
} else {
pkt = &pkt1;
}
st = ic->streams[pkt->stream_index];
//更新 read_size， read_size 用于下一轮判断是否已经超过 probesize
if (!(st->disposition & AV_DISPOSITION_ATTACHED_PIC))
read_size += pkt->size;
avctx = st->internal->avctx;
if (!st->internal->avctx_inited) {
ret = avcodec_parameters_to_context(avctx, st->codecpar);
if (ret < 0)
goto unref_then_goto_end;
st->internal->avctx_inited = 1;
}
if (pkt->dts != AV_NOPTS_VALUE && st->codec_info_nb_frames > 1) {
/* check for non-increasing dts */
if (st->internal->info->fps_last_dts != AV_NOPTS_VALUE &&
st->internal->info->fps_last_dts >= pkt->dts) {
av_log(ic, AV_LOG_DEBUG,
"Non-increasing DTS in stream %d: packet %d with DTS "
"%"PRId64", packet %d with DTS %"PRId64"\n",
st->index, st->internal->info->fps_last_dts_idx,
st->internal->info->fps_last_dts, st->codec_info_nb_frames,
pkt->dts);
st->internal->info->fps_first_dts =
st->internal->info->fps_last_dts = AV_NOPTS_VALUE;
}
/* Check for a discontinuity in dts. If the difference in dts
* is more than 1000 times the average packet duration in the
* sequence, we treat it as a discontinuity. */
if (st->internal->info->fps_last_dts != AV_NOPTS_VALUE &&
st->internal->info->fps_last_dts_idx > st->internal->info->fps_first_dts_idx &&
(pkt->dts - (uint64_t)st->internal->info->fps_last_dts) / 1000 >
(st->internal->info->fps_last_dts - (uint64_t)st->internal->info->fps_first_dts) /
(st->internal->info->fps_last_dts_idx - st->internal->info->fps_first_dts_idx)) {
av_log(ic, AV_LOG_WARNING,
"DTS discontinuity in stream %d: packet %d with DTS "
"%"PRId64", packet %d with DTS %"PRId64"\n",
st->index, st->internal->info->fps_last_dts_idx,
st->internal->info->fps_last_dts, st->codec_info_nb_frames,
pkt->dts);
st->internal->info->fps_first_dts =
st->internal->info->fps_last_dts = AV_NOPTS_VALUE;
}
/* update stored dts values */
if (st->internal->info->fps_first_dts == AV_NOPTS_VALUE) {
st->internal->info->fps_first_dts = pkt->dts;
st->internal->info->fps_first_dts_idx = st->codec_info_nb_frames;
}
st->internal->info->fps_last_dts = pkt->dts;
st->internal->info->fps_last_dts_idx = st->codec_info_nb_frames;
}
if (st->codec_info_nb_frames>1) {
int64_t t = 0;
int64_t limit;
//下面计算已经读取到的时间长度
//codec_info_duration：已经读取到的 packet 的总时长
if (st->time_base.den > 0)
t = av_rescale_q(st->internal->info->codec_info_duration, st->time_base, AV_TIME_BASE_Q);
//t = 已经读取到的帧数/帧率
if (st->avg_frame_rate.num > 0)
t = FFMAX(t, av_rescale_q(st->codec_info_nb_frames, av_inv_q(st->avg_frame_rate), AV_TIME_BASE_Q));
//根据 fps_last_dts - fps_first_dts 来计算
if ( t == 0
&& st->codec_info_nb_frames>30
&& st->internal->info->fps_first_dts != AV_NOPTS_VALUE
&& st->internal->info->fps_last_dts != AV_NOPTS_VALUE)
t = FFMAX(t, av_rescale_q(st->internal->info->fps_last_dts - st->internal->info->fps_first_dts, st->time_base, AV_TIME_BASE_Q));
// 如果所有流都探测完
if (analyzed_all_streams) limit = max_analyze_duration;
else if (avctx->codec_type == AVMEDIA_TYPE_SUBTITLE) limit = max_subtitle_analyze_duration;
else limit = max_stream_analyze_duration;
// 当前读取到的 packet 总时长 >= limit，则 break
if (t >= limit) {
av_log(ic, AV_LOG_VERBOSE, "max_analyze_duration %"PRId64" reached at %"PRId64" microseconds st:%d\n",
limit,
t, pkt->stream_index);
if (ic->flags & AVFMT_FLAG_NOBUFFER)
av_packet_unref(&pkt1);
break;
}
// 更新已经读取到的 packet 的总时长
if (pkt->duration) {
if (avctx->codec_type == AVMEDIA_TYPE_SUBTITLE && pkt->pts != AV_NOPTS_VALUE && st->start_time != AV_NOPTS_VALUE && pkt->pts >= st->start_time) {
st->internal->info->codec_info_duration = FFMIN(pkt->pts - st->start_time, st->internal->info->codec_info_duration + pkt->duration);
} else
st->internal->info->codec_info_duration += pkt->duration;
st->internal->info->codec_info_duration_fields += st->parser && st->need_parsing && avctx->ticks_per_frame ==2 ? st->parser->repeat_pict + 1 : 2;
}
}
if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
#if FF_API_R_FRAME_RATE
ff_rfps_add_frame(ic, st, pkt->dts);
#endif
if (pkt->dts != pkt->pts && pkt->dts != AV_NOPTS_VALUE && pkt->pts != AV_NOPTS_VALUE)
st->internal->info->frame_delay_evidence = 1;
}
if (!st->internal->avctx->extradata) {
ret = extract_extradata(st, pkt);
if (ret < 0)
goto unref_then_goto_end;
}
/* If still no information, we try to open the codec and to
* decompress the frame. We try to avoid that in most cases as
* it takes longer and uses more memory. For MPEG-4, we need to
* decompress for QuickTime.
*
* If AV_CODEC_CAP_CHANNEL_CONF is set this will force decoding of at
* least one frame of codec data, this makes sure the codec initializes
* the channel configuration and does not only trust the values from
* the container. */
// 在某些场景下，打开解码器还获取不到编码层参数，就需要尝试解码，通过解码来获取到流的解码器信息
try_decode_frame(ic, st, pkt,
(options && i < orig_nb_streams) ? &options[i] : NULL);
if (ic->flags & AVFMT_FLAG_NOBUFFER)
av_packet_unref(&pkt1);
//已经探测的帧数 + 1，count 总数 + 1
st->codec_info_nb_frames++;
count++;
}
// 是否已经到达文件尾部
if (eof_reached) {
int stream_index;
// 再遍历一次流，检查编码器参数，如果参数完整会再次调用 avcodec_open2
for (stream_index = 0; stream_index < ic->nb_streams; stream_index++) {
st = ic->streams[stream_index];
avctx = st->internal->avctx;
if (!has_codec_parameters(st, NULL)) {
const AVCodec *codec = find_probe_decoder(ic, st, st->codecpar->codec_id);
if (codec && !avctx->codec) {
AVDictionary *opts = NULL;
if (ic->codec_whitelist)
av_dict_set(&opts, "codec_whitelist", ic->codec_whitelist, 0);
if (avcodec_open2(avctx, codec, (options && stream_index < orig_nb_streams) ? &options[stream_index] : &opts) < 0)
av_log(ic, AV_LOG_WARNING,
"Failed to open codec in %s\n",__FUNCTION__);
av_dict_free(&opts);
}
}
// EOF already reached while reading the stream above.
// So continue with reoordering DTS with whatever delay we have.
if (ic->internal->packet_buffer && !has_decode_delay_been_guessed(st)) {
update_dts_from_pts(ic, stream_index, ic->internal->packet_buffer);
}
}
}
/*
* 刷新解码器
* 有一些帧可能在缓存区，需要 flush
*/
if (flush_codecs) {
AVPacket empty_pkt = { 0 };
int err = 0;
av_init_packet(&empty_pkt);
for (i = 0; i < ic->nb_streams; i++) {//------【第四个循环】-------
st = ic->streams[i];
/* flush the decoders */
if (st->internal->info->found_decoder == 1) {
do {
err = try_decode_frame(ic, st, &empty_pkt,
(options && i < orig_nb_streams)
? &options[i] : NULL);
} while (err > 0 && !has_codec_parameters(st, NULL));
if (err < 0) {
av_log(ic, AV_LOG_INFO,
"decoding for stream %d failed\n", st->index);
}
}
}
}
ff_rfps_calculate(ic);
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
avctx = st->internal->avctx;
if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
if (avctx->codec_id == AV_CODEC_ID_RAWVIDEO && !avctx->codec_tag && !avctx->bits_per_coded_sample) {
uint32_t tag= avcodec_pix_fmt_to_codec_tag(avctx->pix_fmt);
if (avpriv_find_pix_fmt(avpriv_get_raw_pix_fmt_tags(), tag) == avctx->pix_fmt)
avctx->codec_tag= tag;
}
/* estimate average framerate if not set by demuxer */
if (st->internal->info->codec_info_duration_fields &&
!st->avg_frame_rate.num &&
st->internal->info->codec_info_duration) {
int best_fps = 0;
double best_error = 0.01;
AVRational codec_frame_rate = avctx->framerate;
if (st->internal->info->codec_info_duration >= INT64_MAX / st->time_base.num / 2||
st->internal->info->codec_info_duration_fields >= INT64_MAX / st->time_base.den ||
st->internal->info->codec_info_duration < 0)
continue;
av_reduce(&st->avg_frame_rate.num, &st->avg_frame_rate.den,
st->internal->info->codec_info_duration_fields * (int64_t) st->time_base.den,
st->internal->info->codec_info_duration * 2 * (int64_t) st->time_base.num, 60000);
/* Round guessed framerate to a "standard" framerate if it's
* within 1% of the original estimate. */
for (j = 0; j < MAX_STD_TIMEBASES; j++) {
AVRational std_fps = { get_std_framerate(j), 12 * 1001 };
double error = fabs(av_q2d(st->avg_frame_rate) /
av_q2d(std_fps) - 1);
if (error < best_error) {
best_error = error;
best_fps = std_fps.num;
}
if (ic->internal->prefer_codec_framerate && codec_frame_rate.num > 0 && codec_frame_rate.den > 0) {
error = fabs(av_q2d(codec_frame_rate) /
av_q2d(std_fps) - 1);
if (error < best_error) {
best_error = error;
best_fps = std_fps.num;
}
}
}
if (best_fps)
av_reduce(&st->avg_frame_rate.num, &st->avg_frame_rate.den,
best_fps, 12 * 1001, INT_MAX);
}
if (!st->r_frame_rate.num) {
if ( avctx->time_base.den * (int64_t) st->time_base.num
<= avctx->time_base.num * avctx->ticks_per_frame * (uint64_t) st->time_base.den) {
av_reduce(&st->r_frame_rate.num, &st->r_frame_rate.den,
avctx->time_base.den, (int64_t)avctx->time_base.num * avctx->ticks_per_frame, INT_MAX);
} else {
st->r_frame_rate.num = st->time_base.den;
st->r_frame_rate.den = st->time_base.num;
}
}
if (st->internal->display_aspect_ratio.num && st->internal->display_aspect_ratio.den) {
AVRational hw_ratio = { avctx->height, avctx->width };
st->sample_aspect_ratio = av_mul_q(st->internal->display_aspect_ratio,
hw_ratio);
}
} else if (avctx->codec_type == AVMEDIA_TYPE_AUDIO) {
// 对于音频流，基于音频流服务类型初始化 disposition
if (!avctx->bits_per_coded_sample)
avctx->bits_per_coded_sample =
av_get_bits_per_sample(avctx->codec_id);
// set stream disposition based on audio service type
switch (avctx->audio_service_type) {
case AV_AUDIO_SERVICE_TYPE_EFFECTS:
st->disposition = AV_DISPOSITION_CLEAN_EFFECTS;
break;
case AV_AUDIO_SERVICE_TYPE_VISUALLY_IMPAIRED:
st->disposition = AV_DISPOSITION_VISUAL_IMPAIRED;
break;
case AV_AUDIO_SERVICE_TYPE_HEARING_IMPAIRED:
st->disposition = AV_DISPOSITION_HEARING_IMPAIRED;
break;
case AV_AUDIO_SERVICE_TYPE_COMMENTARY:
st->disposition = AV_DISPOSITION_COMMENT;
break;
case AV_AUDIO_SERVICE_TYPE_KARAOKE:
st->disposition = AV_DISPOSITION_KARAOKE;
break;
}
}
}
// 计算时间相关参数
if (probesize)
estimate_timings(ic, old_offset);
av_opt_set(ic, "skip_clear", "0", AV_OPT_SEARCH_CHILDREN);
if (ret >= 0 && ic->nb_streams)
/* We could not have all the codec parameters before EOF. */
ret = -1;
for (i = 0; i < ic->nb_streams; i++) {
const char *errmsg;
st = ic->streams[i];
/* if no packet was ever seen, update context now for has_codec_parameters */
if (!st->internal->avctx_inited) {
if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO &&
st->codecpar->format == AV_SAMPLE_FMT_NONE)
st->codecpar->format = st->internal->avctx->sample_fmt;
ret = avcodec_parameters_to_context(st->internal->avctx, st->codecpar);
if (ret < 0)
goto find_stream_info_err;
}
if (!has_codec_parameters(st, &errmsg)) {
char buf[256];
avcodec_string(buf, sizeof(buf), st->internal->avctx, 0);
av_log(ic, AV_LOG_WARNING,
"Could not find codec parameters for stream %d (%s): %s\n"
"Consider increasing the value for the 'analyzeduration' (%"PRId64") and 'probesize' (%"PRId64") options\n",
i, buf, errmsg, ic->max_analyze_duration, ic->probesize);
} else {
ret = 0;
}
}
ret = compute_chapters_end(ic);
if (ret < 0)
goto find_stream_info_err;
// 更新 stream 各个结构的数据
/* update the stream parameters from the internal codec contexts */
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
if (st->internal->avctx_inited) {
int orig_w = st->codecpar->width;
int orig_h = st->codecpar->height;
ret = avcodec_parameters_from_context(st->codecpar, st->internal->avctx);
if (ret < 0)
goto find_stream_info_err;
ret = add_coded_side_data(st, st->internal->avctx);
if (ret < 0)
goto find_stream_info_err;
#if FF_API_LOWRES
// The decoder might reduce the video size by the lowres factor.
if (st->internal->avctx->lowres && orig_w) {
st->codecpar->width = orig_w;
st->codecpar->height = orig_h;
}
#endif
}
#if FF_API_LAVF_AVCTX
FF_DISABLE_DEPRECATION_WARNINGS
ret = avcodec_parameters_to_context(st->codec, st->codecpar);
if (ret < 0)
goto find_stream_info_err;
#if FF_API_LOWRES
// The old API (AVStream.codec) "requires" the resolution to be adjusted
// by the lowres factor.
if (st->internal->avctx->lowres && st->internal->avctx->width) {
st->codec->lowres = st->internal->avctx->lowres;
st->codec->width = st->internal->avctx->width;
st->codec->height = st->internal->avctx->height;
}
#endif
if (st->codec->codec_tag != MKTAG('t','m','c','d')) {
st->codec->time_base = st->internal->avctx->time_base;
st->codec->ticks_per_frame = st->internal->avctx->ticks_per_frame;
}
st->codec->framerate = st->avg_frame_rate;
if (st->internal->avctx->subtitle_header) {
st->codec->subtitle_header = av_malloc(st->internal->avctx->subtitle_header_size);
if (!st->codec->subtitle_header)
goto find_stream_info_err;
st->codec->subtitle_header_size = st->internal->avctx->subtitle_header_size;
memcpy(st->codec->subtitle_header, st->internal->avctx->subtitle_header,
st->codec->subtitle_header_size);
}
// Fields unavailable in AVCodecParameters
st->codec->coded_width = st->internal->avctx->coded_width;
st->codec->coded_height = st->internal->avctx->coded_height;
st->codec->properties = st->internal->avctx->properties;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
st->internal->avctx_inited = 0;
}
find_stream_info_err:
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
if (st->internal->info)
av_freep(&st->internal->info->duration_error);
avcodec_close(ic->streams[i]->internal->avctx);
av_freep(&ic->streams[i]->internal->info);
av_bsf_free(&ic->streams[i]->internal->extract_extradata.bsf);
av_packet_free(&ic->streams[i]->internal->extract_extradata.pkt);
}
if (ic->pb)
av_log(ic, AV_LOG_DEBUG, "After avformat_find_stream_info() pos: %"PRId64" bytes read:%"PRId64" seeks:%d frames:%d\n",
avio_tell(ic->pb), ic->pb->bytes_read, ic->pb->seek_count, count);
return ret;
unref_then_goto_end:
av_packet_unref(&pkt1);
goto find_stream_info_err;
}
// 检查当前的音视频流信息是否完整
static int has_codec_parameters(AVStream *st, const char **errmsg_ptr)
{
AVCodecContext *avctx = st->internal->avctx;
#define FAIL(errmsg) do { \
if (errmsg_ptr) \
*errmsg_ptr = errmsg; \
return 0; \
} while (0)
if ( avctx->codec_id == AV_CODEC_ID_NONE
&& avctx->codec_type != AVMEDIA_TYPE_DATA)
FAIL("unknown codec");
switch (avctx->codec_type) {
case AVMEDIA_TYPE_AUDIO://音频的需要检测frame_size、sample_fmt、sample_rate、channels等
if (!avctx->frame_size && determinable_frame_size(avctx))
FAIL("unspecified frame size");
if (st->internal->info->found_decoder >= 0 &&
avctx->sample_fmt == AV_SAMPLE_FMT_NONE)
FAIL("unspecified sample format");
if (!avctx->sample_rate)
FAIL("unspecified sample rate");
if (!avctx->channels)
FAIL("unspecified number of channels");
if (st->internal->info->found_decoder >= 0 && !st->internal->nb_decoded_frames && avctx->codec_id == AV_CODEC_ID_DTS)
FAIL("no decodable DTS frames");
break;
case AVMEDIA_TYPE_VIDEO://视频的需要检测width、pix_fmt、sample_aspect_ratio等
if (!avctx->width)
FAIL("unspecified size");
if (st->internal->info->found_decoder >= 0 && avctx->pix_fmt == AV_PIX_FMT_NONE)
FAIL("unspecified pixel format");
if (st->codecpar->codec_id == AV_CODEC_ID_RV30 || st->codecpar->codec_id == AV_CODEC_ID_RV40)
if (!st->sample_aspect_ratio.num && !st->codecpar->sample_aspect_ratio.num && !st->codec_info_nb_frames)
FAIL("no frame in rv30/40 and no sar");
break;
case AVMEDIA_TYPE_SUBTITLE:
if (avctx->codec_id == AV_CODEC_ID_HDMV_PGS_SUBTITLE && !avctx->width)
FAIL("unspecified size");
break;
case AVMEDIA_TYPE_DATA:
if (avctx->codec_id == AV_CODEC_ID_NONE) return 1;
}
return 1;
}
