FFmpeg函数avformat_find_stream_info()

摘要: avformat_find_stream_info

FFMPEG代码为3.2 release版本， 输入为flv文件。

获取流参数

/* If not enough info to get the stream parameters, we decode the
first frames to get it. (used in mpeg case for example) */
ret = avformat_find_stream_info(ic, opts);

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, *pkt;
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;

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) {
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);

for (i = 0; i < ic->nb_streams; i++) {
const AVCodec *codec;
AVDictionary *thread_opt = NULL;
st = ic->streams[i];
avctx = st->internal->avctx;

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;
}

/* 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->request_probe <= 0) {
st->parser = av_parser_init(st->codecpar->codec_id);
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);
if (ret < 0)
goto find_stream_info_err;
if (st->request_probe <= 0)
st->internal->avctx_inited = 1;

codec = find_probe_decoder(ic, st, st->codecpar->codec_id);

/* 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 av_find_stream_info\n");
}

// Try to just open decoders, in case this is enough to get parameters.
if (!has_codec_parameters(st, NULL) && st->request_probe <= 0) {
if (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 av_find_stream_info\n");
}
if (!options)
av_dict_free(&thread_opt);
}

for (i = 0; i < ic->nb_streams; i++) {
#if FF_API_R_FRAME_RATE
ic->streams[i]->info->last_dts = AV_NOPTS_VALUE;
#endif
ic->streams[i]->info->fps_first_dts = AV_NOPTS_VALUE;
ic->streams[i]->info->fps_last_dts  = AV_NOPTS_VALUE;
}

read_size = 0;
for (;;) {
int analyzed_all_streams;
if (ff_check_interrupt(&ic->interrupt_callback)) {
ret = AVERROR_EXIT;
av_log(ic, AV_LOG_DEBUG, "interrupted\n");
break;
}

/* check if one codec still needs to be handled */
for (i = 0; i < ic->nb_streams; i++) {
int fps_analyze_framecount = 20;

st = ic->streams[i];
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. */
if (av_q2d(st->time_base) > 0.0005)
fps_analyze_framecount *= 2;
if (!tb_unreliable(st->internal->avctx))
fps_analyze_framecount = 0;
if (ic->fps_probe_size >= 0)
fps_analyze_framecount = ic->fps_probe_size;
if (st->disposition & AV_DISPOSITION_ATTACHED_PIC)
fps_analyze_framecount = 0;
/* variable fps and no guess at the real fps */
if (!(st->r_frame_rate.num && st->avg_frame_rate.num) &&
st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
int count = (ic->iformat->flags & AVFMT_NOTIMESTAMPS) ?
st->info->codec_info_duration_fields/2 :
st->info->duration_count;
if (count < fps_analyze_framecount)
break;
}
if (st->parser && st->parser->parser->split &&
!st->internal->avctx->extradata)
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;
if (i == ic->nb_streams) {
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. */
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;
}
}
/* We did not get all the codec info, but we read too much data. */
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]->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). */
ret = read_frame_internal(ic, &pkt1);
if (ret == AVERROR(EAGAIN))
continue;

if (ret < 0) {
/* EOF or error*/
eof_reached = 1;
break;
}

pkt = &pkt1;

if (!(ic->flags & AVFMT_FLAG_NOBUFFER)) {
ret = add_to_pktbuf(&ic->internal->packet_buffer, pkt,
&ic->internal->packet_buffer_end, 0);
if (ret < 0)
goto find_stream_info_err;
}

st = ic->streams[pkt->stream_index];
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 find_stream_info_err;
st->internal->avctx_inited = 1;
}

if (pkt->dts != AV_NOPTS_VALUE && st->codec_info_nb_frames > 1) {
/* check for non-increasing dts */
if (st->info->fps_last_dts != AV_NOPTS_VALUE &&
st->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->info->fps_last_dts_idx,
st->info->fps_last_dts, st->codec_info_nb_frames,
pkt->dts);
st->info->fps_first_dts =
st->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->info->fps_last_dts != AV_NOPTS_VALUE &&
st->info->fps_last_dts_idx > st->info->fps_first_dts_idx &&
(pkt->dts - st->info->fps_last_dts) / 1000 >
(st->info->fps_last_dts     - st->info->fps_first_dts) /
(st->info->fps_last_dts_idx - st->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->info->fps_last_dts_idx,
st->info->fps_last_dts, st->codec_info_nb_frames,
pkt->dts);
st->info->fps_first_dts =
st->info->fps_last_dts  = AV_NOPTS_VALUE;
}

/* update stored dts values */
if (st->info->fps_first_dts == AV_NOPTS_VALUE) {
st->info->fps_first_dts     = pkt->dts;
st->info->fps_first_dts_idx = st->codec_info_nb_frames;
}
st->info->fps_last_dts     = pkt->dts;
st->info->fps_last_dts_idx = st->codec_info_nb_frames;
}
if (st->codec_info_nb_frames>1) {
int64_t t = 0;
int64_t limit;

if (st->time_base.den > 0)
t = av_rescale_q(st->info->codec_info_duration, st->time_base, AV_TIME_BASE_Q);
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));

if (   t == 0
&& st->codec_info_nb_frames>30
&& st->info->fps_first_dts != AV_NOPTS_VALUE
&& st->info->fps_last_dts  != AV_NOPTS_VALUE)
t = FFMAX(t, av_rescale_q(st->info->fps_last_dts - st->info->fps_first_dts, st->time_base, AV_TIME_BASE_Q));

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;

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(pkt);
break;
}
if (pkt->duration) {
if (avctx->codec_type == AVMEDIA_TYPE_SUBTITLE && pkt->pts != AV_NOPTS_VALUE && pkt->pts >= st->start_time) {
st->info->codec_info_duration = FFMIN(pkt->pts - st->start_time, st->info->codec_info_duration + pkt->duration);
} else
st->info->codec_info_duration += pkt->duration;
st->info->codec_info_duration_fields += st->parser && st->need_parsing && avctx->ticks_per_frame ==2 ? st->parser->repeat_pict + 1 : 2;
}
}
#if FF_API_R_FRAME_RATE
if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
ff_rfps_add_frame(ic, st, pkt->dts);
#endif
if (st->parser && st->parser->parser->split && !avctx->extradata) {
int i = st->parser->parser->split(avctx, pkt->data, pkt->size);
if (i > 0 && i < FF_MAX_EXTRADATA_SIZE) {
avctx->extradata_size = i;
avctx->extradata      = av_mallocz(avctx->extradata_size +
AV_INPUT_BUFFER_PADDING_SIZE);
if (!avctx->extradata)
return AVERROR(ENOMEM);
memcpy(avctx->extradata, pkt->data,
avctx->extradata_size);
}
}

/* 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. */
try_decode_frame(ic, st, pkt,
(options && i < orig_nb_streams) ? &options[i] : NULL);

if (ic->flags & AVFMT_FLAG_NOBUFFER)
av_packet_unref(pkt);

st->codec_info_nb_frames++;
count++;
}

if (eof_reached) {
int stream_index;
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) {
if (avcodec_open2(avctx, codec, (options && stream_index < orig_nb_streams) ? &options[stream_index] : NULL) < 0)
av_log(ic, AV_LOG_WARNING,
"Failed to open codec in av_find_stream_info\n");
}
}

// 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);
}
}
}

if (flush_codecs) {
AVPacket empty_pkt = { 0 };
int err = 0;
av_init_packet(&empty_pkt);

for (i = 0; i < ic->nb_streams; i++) {

st = ic->streams[i];

/* flush the decoders */
if (st->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);
}
}
}
}

// close codecs which were opened in try_decode_frame()
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
avcodec_close(st->internal->avctx);
}

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->info->codec_info_duration_fields &&
!st->avg_frame_rate.num &&
st->info->codec_info_duration) {
int best_fps      = 0;
double best_error = 0.01;

if (st->info->codec_info_duration        >= INT64_MAX / st->time_base.num / 2||
st->info->codec_info_duration_fields >= INT64_MAX / st->time_base.den ||
st->info->codec_info_duration        < 0)
continue;
av_reduce(&st->avg_frame_rate.num, &st->avg_frame_rate.den,
st->info->codec_info_duration_fields * (int64_t) st->time_base.den,
st->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 (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 * (int64_t) st->time_base.den) {
st->r_frame_rate.num = avctx->time_base.den;
st->r_frame_rate.den = avctx->time_base.num * avctx->ticks_per_frame;
} else {
st->r_frame_rate.num = st->time_base.den;
st->r_frame_rate.den = st->time_base.num;
}
}
if (st->display_aspect_ratio.num && st->display_aspect_ratio.den) {
AVRational hw_ratio = { avctx->height, avctx->width };
st->sample_aspect_ratio = av_mul_q(st->display_aspect_ratio,
hw_ratio);
}
} else if (avctx->codec_type == AVMEDIA_TYPE_AUDIO) {
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;
}
}
}

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' and 'probesize' options\n",
i, buf, errmsg);
} else {
ret = 0;
}
}

compute_chapters_end(ic);

/* 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;
// The decoder might reduce the video size by the lowres factor.
if (av_codec_get_lowres(st->internal->avctx) && orig_w) {
st->codecpar->width = orig_w;
st->codecpar->height = orig_h;
}
}

#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;

// The old API (AVStream.codec) "requires" the resolution to be adjusted
// by the lowres factor.
if (av_codec_get_lowres(st->internal->avctx) && st->internal->avctx->width) {
av_codec_set_lowres(st->codec, av_codec_get_lowres(st->internal->avctx));
st->codec->width = st->internal->avctx->width;
st->codec->height = st->internal->avctx->height;
}

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->info)
av_freep(&st->info->duration_error);
av_freep(&ic->streams[i]->info);
}
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;
}

从内部buffer中获取packet数据

/* NOTE: A new stream can be added there if no header in file
* (AVFMTCTX_NOHEADER). */

static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
{
int ret = 0, i, got_packet = 0;
AVDictionary *metadata = NULL;

av_init_packet(pkt);

while (!got_packet && !s->internal->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];
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];

/* update context if required */
if (st->internal->need_context_update) {
if (avcodec_is_open(st->internal->avctx)) {
av_log(s, AV_LOG_DEBUG, "Demuxer context update while decoder is open, closing and trying to re-open\n");
avcodec_close(st->internal->avctx);
st->info->found_decoder = 0;
}

ret = avcodec_parameters_to_context(st->internal->avctx, st->codecpar);
if (ret < 0)
return ret;

#if FF_API_LAVF_AVCTX
FF_DISABLE_DEPRECATION_WARNINGS
/* update deprecated public codec context */
ret = avcodec_parameters_to_context(st->codec, st->codecpar);
if (ret < 0)
return ret;
FF_ENABLE_DEPRECATION_WARNINGS
#endif

st->internal->need_context_update = 0;
}

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=%"PRId64", 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->codecpar->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->codecpar->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, AV_NOPTS_VALUE, AV_NOPTS_VALUE);
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;
st->codecpar->sample_rate = st->internal->avctx->sample_rate;
st->codecpar->bit_rate = st->internal->avctx->bit_rate;
st->codecpar->channels = st->internal->avctx->channels;
st->codecpar->channel_layout = st->internal->avctx->channel_layout;
st->codecpar->codec_id = st->internal->avctx->codec_id;
} else {
/* free packet */
av_packet_unref(&cur_pkt);
}
if (pkt->flags & AV_PKT_FLAG_KEY)
st->skip_to_keyframe = 0;
if (st->skip_to_keyframe) {
av_packet_unref(&cur_pkt);
if (got_packet) {
*pkt = cur_pkt;
}
got_packet = 0;
}
}

if (!got_packet && s->internal->parse_queue)
ret = read_from_packet_buffer(&s->internal->parse_queue, &s->internal->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->start_skip_samples && (pkt->pts == 0 || pkt->pts == RELATIVE_TS_BASE))
st->skip_samples = st->start_skip_samples;
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 / discard %d\n", st->skip_samples, discard_padding);
}
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 FF_API_LAVF_AVCTX
update_stream_avctx(s);
#endif

if (s->debug & FF_FDEBUG_TS)
av_log(s, AV_LOG_DEBUG,
"read_frame_internal stream=%d, pts=%s, dts=%s, "
"size=%d, duration=%"PRId64", flags=%d\n",
pkt->stream_index,
av_ts2str(pkt->pts),
av_ts2str(pkt->dts),
pkt->size, pkt->duration, pkt->flags);

return ret;
}

读取packet数据

int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
{
int ret, i, err;
AVStream *st;

for (;;) {
AVPacketList *pktl = s->internal->raw_packet_buffer;

if (pktl) {
*pkt = pktl->pkt;
st   = s->streams[pkt->stream_index];
if (s->internal->raw_packet_buffer_remaining_size <= 0)
if ((err = probe_codec(s, st, NULL)) < 0)
return err;
if (st->request_probe <= 0) {
s->internal->raw_packet_buffer                 = pktl->next;
s->internal->raw_packet_buffer_remaining_size += pkt->size;
av_free(pktl);
return 0;
}
}

pkt->data = NULL;
pkt->size = 0;
av_init_packet(pkt);
ret = s->iformat->read_packet(s, pkt);
if (ret < 0) {
/* Some demuxers return FFERROR_REDO when they consume
data and discard it (ignored streams, junk, extradata).
We must re-call the demuxer to get the real packet. */
if (ret == FFERROR_REDO)
continue;
if (!pktl || ret == AVERROR(EAGAIN))
return ret;
for (i = 0; i < s->nb_streams; i++) {
st = s->streams[i];
if (st->probe_packets || st->request_probe > 0)
if ((err = probe_codec(s, st, NULL)) < 0)
return err;
av_assert0(st->request_probe <= 0);
}
continue;
}

if (!pkt->buf) {
AVPacket tmp = { 0 };
ret = av_packet_ref(&tmp, pkt);
if (ret < 0)
return ret;
*pkt = tmp;
}

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_packet_unref(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;

err = add_to_pktbuf(&s->internal->raw_packet_buffer, pkt,
&s->internal->raw_packet_buffer_end, 0);
if (err)
return err;
s->internal->raw_packet_buffer_remaining_size -= pkt->size;

if ((err = probe_codec(s, st, pkt)) < 0)
return err;
}
}

其中s->iformat->read_packet(s, pkt)回调函数flv_read_packet(AVFormatContext *s, AVPacket *pkt)

flv格式解析流信息耗时部分：

函数avformat_find_stream_info()

/* check if one codec still needs to be handled */
for (i = 0; i < ic->nb_streams; i++) {
int fps_analyze_framecount = 20;

st = ic->streams[i];
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. */
if (av_q2d(st->time_base) > 0.0005)
fps_analyze_framecount *= 2;
if (!tb_unreliable(st->internal->avctx))
fps_analyze_framecount = 0;
if (ic->fps_probe_size >= 0)
fps_analyze_framecount = ic->fps_probe_size;
if (st->disposition & AV_DISPOSITION_ATTACHED_PIC)
fps_analyze_framecount = 0;
/* variable fps and no guess at the real fps */
if (!(st->r_frame_rate.num && st->avg_frame_rate.num) &&
st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
int count = (ic->iformat->flags & AVFMT_NOTIMESTAMPS) ?
st->info->codec_info_duration_fields/2 :
st->info->duration_count;
if (count < fps_analyze_framecount)
break;
}
if (st->parser && st->parser->parser->split &&
!st->internal->avctx->extradata)
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;
}

对于flv，time_base中分子是1，分母是1000，所以fps_analyze_framecount的值会是初始定义的两倍。

因为st->r_frame_rate.num 和st->avg_frame_rate.num值均为0，并且ic->iformat->flags为0，所以会判断st->info->duration_count和fps_analyze_framecount的值，而每解析一个视频tag，st->info->duration_count的值加1.也就是说需要解析四十个视频tag，才能跳出avformat_find_stream_info()函数的for循环。too long:)