FFmpeg源代码简单学习：avformat_find_stream_info()
参考博客：https://blog.csdn.net/leixiaohua1020/article/details/44084321
int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
{
int i, count, ret = 0, j;
int64_t read_size;
AVStream *st;
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_duration2;
int64_t probesize = ic->probesize2;
//最大分析时长处理
if (!max_analyze_duration)
max_analyze_duration = ic->max_analyze_duration;
//probesize处理
if (ic->probesize)
probesize = ic->probesize;
flush_codecs = probesize > 0;
av_opt_set(ic, "skip_clear", "1", AV_OPT_SEARCH_CHILDREN);
//最大分析时长处理
if (!max_analyze_duration) {
if (!strcmp(ic->iformat->name, "flv") && !(ic->ctx_flags & AVFMTCTX_NOHEADER)) {
max_analyze_duration = 10*AV_TIME_BASE;
} else
max_analyze_duration = 5*AV_TIME_BASE;
}
if (ic->pb)
av_log(ic, AV_LOG_DEBUG, "Before avformat_find_stream_info() pos: %"PRId64" bytes read:%"PRId64" seeks:%d\n",
avio_tell(ic->pb), ic->pb->bytes_read, ic->pb->seek_count);
for (i = 0; i < ic->nb_streams; i++) {
const AVCodec *codec;
AVDictionary *thread_opt = NULL;
st = ic->streams[i];
if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO ||
st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
/* if (!st->time_base.num)
st->time_base = */
if (!st->codec->time_base.num)
st->codec->time_base = st->time_base;
}
// only for the split stuff
if (!st->parser && !(ic->flags & AVFMT_FLAG_NOPARSE)) {
st->parser = av_parser_init(st->codec->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->codec->codec_id));
}
}
//寻找解码器
codec = find_decoder(ic, st, st->codec->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. */
//subtitle
if (st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE
&& codec && !st->codec->codec) {
//调用avcodec_open2解码器
if (avcodec_open2(st->codec, 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 && !st->codec->codec)
if (avcodec_open2(st->codec, 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;
}
count = 0;
read_size = 0;
for (;;) {
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->codec))
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->info->duration_count < fps_analyze_framecount &&
st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
break;
if (st->parser && st->parser->parser->split &&
!st->codec->extradata)
break;
if (st->first_dts == AV_NOPTS_VALUE &&
!(ic->iformat->flags & AVFMT_NOTIMESTAMPS) &&
st->codec_info_nb_frames < ic->max_ts_probe &&
(st->codec->codec_type == AVMEDIA_TYPE_VIDEO ||
st->codec->codec_type == AVMEDIA_TYPE_AUDIO))
break;
}
if (i == ic->nb_streams) {
/* 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. */
//未获取所有的码流信息
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]->codec->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). */
//读取帧数据--压缩帧数据
ret = read_frame_internal(ic, &pkt1);
if (ret == AVERROR(EAGAIN))
continue;
if (ret < 0) {
/* EOF or error*/
break;
}
//容错机制
if (ic->flags & AVFMT_FLAG_NOBUFFER)
free_packet_buffer(&ic->packet_buffer, &ic->packet_buffer_end);
{
pkt = add_to_pktbuf(&ic->packet_buffer, &pkt1,
&ic->packet_buffer_end);
if (!pkt) {
ret = AVERROR(ENOMEM);
goto find_stream_info_err;
}
if ((ret = av_dup_packet(pkt)) < 0)
goto find_stream_info_err;
}
st = ic->streams[pkt->stream_index];
if (!(st->disposition & AV_DISPOSITION_ATTACHED_PIC))
read_size += pkt->size;
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;
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 (t >= max_analyze_duration) {
av_log(ic, AV_LOG_VERBOSE, "max_analyze_duration %"PRId64" reached at %"PRId64" microseconds\n",
max_analyze_duration,
t);
if (ic->flags & AVFMT_FLAG_NOBUFFER)
av_packet_unref(pkt);
break;
}
if (pkt->duration) {
st->info->codec_info_duration += pkt->duration;
st->info->codec_info_duration_fields += st->parser && st->need_parsing && st->codec->ticks_per_frame ==2 ? st->parser->repeat_pict + 1 : 2;
}
}
#if FF_API_R_FRAME_RATE
if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
ff_rfps_add_frame(ic, st, pkt->dts);
#endif
if (st->parser && st->parser->parser->split && !st->codec->extradata) {
int i = st->parser->parser->split(st->codec, pkt->data, pkt->size);
if (i > 0 && i < FF_MAX_EXTRADATA_SIZE) {
if (ff_alloc_extradata(st->codec, i))
return AVERROR(ENOMEM);
memcpy(st->codec->extradata, pkt->data,
st->codec->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 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 (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 */
//尝试解码帧数据
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->codec);
}
ff_rfps_calculate(ic);
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
if (st->codec->codec_id == AV_CODEC_ID_RAWVIDEO && !st->codec->codec_tag && !st->codec->bits_per_coded_sample) {
uint32_t tag= avcodec_pix_fmt_to_codec_tag(st->codec->pix_fmt);
if (avpriv_find_pix_fmt(avpriv_get_raw_pix_fmt_tags(), tag) == st->codec->pix_fmt)
st->codec->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 ( st->codec->time_base.den * (int64_t) st->time_base.num
<= st->codec->time_base.num * st->codec->ticks_per_frame * (int64_t) st->time_base.den) {
st->r_frame_rate.num = st->codec->time_base.den;
st->r_frame_rate.den = st->codec->time_base.num * st->codec->ticks_per_frame;
} else {
st->r_frame_rate.num = st->time_base.den;
st->r_frame_rate.den = st->time_base.num;
}
}
} else if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
if (!st->codec->bits_per_coded_sample)
st->codec->bits_per_coded_sample =
av_get_bits_per_sample(st->codec->codec_id);
// set stream disposition based on audio service type
switch (st->codec->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 (!has_codec_parameters(st, &errmsg)) {
char buf[256];
avcodec_string(buf, sizeof(buf), st->codec, 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);
find_stream_info_err:
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
if (ic->streams[i]->codec->codec_type != AVMEDIA_TYPE_AUDIO)
ic->streams[i]->codec->thread_count = 0;
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;
}
//---------------------------------------------
//find_decoder函数查找解码器
static const AVCodec *find_decoder(AVFormatContext *s, const AVStream *st, enum AVCodecID codec_id)
{
#if FF_API_LAVF_AVCTX
FF_DISABLE_DEPRECATION_WARNINGS
if (st->codec->codec)
return st->codec->codec;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
switch (st->codecpar->codec_type) {//codec_type指示类型
case AVMEDIA_TYPE_VIDEO://video类型
if (s->video_codec) return s->video_codec;
break;
case AVMEDIA_TYPE_AUDIO://audio类型
if (s->audio_codec) return s->audio_codec;
break;
case AVMEDIA_TYPE_SUBTITLE://字幕类型
if (s->subtitle_codec) return s->subtitle_codec;
break;
}
//如果codec已经存在，则不做处理，直接返回
//如果codec不存在，则调用avcodec_find_decoder函数进行解码器的查找
return avcodec_find_decoder(codec_id);
}
//------------------------------------
/* returns 1 or 0 if or if not decoded data was returned, or a negative error */
static int try_decode_frame(AVFormatContext *s, AVStream *st,
const AVPacket *avpkt, AVDictionary **options)
{//尝试解码帧数据
AVCodecContext *avctx = st->internal->avctx;
const AVCodec *codec;
int got_picture = 1, ret = 0;
AVFrame *frame = av_frame_alloc();
AVSubtitle subtitle;
AVPacket pkt = *avpkt;
int do_skip_frame = 0;
enum AVDiscard skip_frame;
//！frame
if (!frame)
return AVERROR(ENOMEM);
//判断解码器是否打开&其他的判断
if (!avcodec_is_open(avctx) &&
st->internal->info->found_decoder <= 0 &&
(st->codecpar->codec_id != -st->internal->info->found_decoder || !st->codecpar->codec_id)) {
AVDictionary *thread_opt = NULL;
//调用find_probe_decoder函数进行查找
codec = find_probe_decoder(s, st, st->codecpar->codec_id);
if (!codec) {
st->internal->info->found_decoder = -st->codecpar->codec_id;
ret = -1;
goto fail;
}
/* Force thread count to 1 since the H.264 decoder will not extract
* SPS and PPS to extradata during multi-threaded decoding. */
//线程设置为1
av_dict_set(options ? options : &thread_opt, "threads", "1", 0);
/* Force lowres to 0. The decoder might reduce the video size by the
* lowres factor, and we don't want that propagated to the stream's
* codecpar */
//lowres设置为0
av_dict_set(options ? options : &thread_opt, "lowres", "0", 0);
if (s->codec_whitelist)
av_dict_set(options ? options : &thread_opt, "codec_whitelist", s->codec_whitelist, 0);
ret = avcodec_open2(avctx, codec, options ? options : &thread_opt);
if (!options)
av_dict_free(&thread_opt);
if (ret < 0) {
st->internal->info->found_decoder = -avctx->codec_id;
goto fail;
}
st->internal->info->found_decoder = 1;
} else if (!st->internal->info->found_decoder)
st->internal->info->found_decoder = 1;
if (st->internal->info->found_decoder < 0) {
ret = -1;
goto fail;
}
if (avpriv_codec_get_cap_skip_frame_fill_param(avctx->codec)) {
do_skip_frame = 1;
skip_frame = avctx->skip_frame;
avctx->skip_frame = AVDISCARD_ALL;
}
while ((pkt.size > 0 || (!pkt.data && got_picture)) &&
ret >= 0 &&
//has_codec_parameters()函数被用来判断AVStream中的成员变量是否都已经设置完毕
(!has_codec_parameters(st, NULL) || !has_decode_delay_been_guessed(st) ||
(!st->codec_info_nb_frames &&
(avctx->codec->capabilities & AV_CODEC_CAP_CHANNEL_CONF)))) {
got_picture = 0;
//如果是视频/音频类型
if (avctx->codec_type == AVMEDIA_TYPE_VIDEO ||
avctx->codec_type == AVMEDIA_TYPE_AUDIO) {
ret = avcodec_send_packet(avctx, &pkt);
if (ret < 0 && ret != AVERROR(EAGAIN) && ret != AVERROR_EOF)
break;
if (ret >= 0)
pkt.size = 0;
ret = avcodec_receive_frame(avctx, frame);
if (ret >= 0)
got_picture = 1;
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
ret = 0;
//如果是字幕类型
} else if (avctx->codec_type == AVMEDIA_TYPE_SUBTITLE) {
ret = avcodec_decode_subtitle2(avctx, &subtitle,
&got_picture, &pkt);
if (got_picture)
avsubtitle_free(&subtitle);
if (ret >= 0)
pkt.size = 0;
}
if (ret >= 0) {
if (got_picture)
st->internal->nb_decoded_frames++;
ret = got_picture;
}
}
if (!pkt.data && !got_picture)
ret = -1;
fail:
if (do_skip_frame) {
avctx->skip_frame = skip_frame;
}
av_frame_free(&frame);
return ret;
}
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)
//未知类型
if ( avctx->codec_id == AV_CODEC_ID_NONE
&& avctx->codec_type != AVMEDIA_TYPE_DATA)
FAIL("unknown codec");
//switch实现判断
switch (avctx->codec_type) {
case AVMEDIA_TYPE_AUDIO://音频类型
if (!avctx->frame_size && determinable_frame_size(avctx))
FAIL("unspecified frame size");//帧尺寸
if (st->internal->info->found_decoder >= 0 &&
avctx->sample_fmt == AV_SAMPLE_FMT_NONE)
FAIL("unspecified sample format");//格式
if (!avctx->sample_rate)
FAIL("unspecified sample rate");//码率
if (!avctx->channels)
FAIL("unspecified number of channels");//声道
if (st->internal->info->found_decoder >= 0 && !st->internal->nb_decoded_frames && avctx->codec_id == AV_CODEC_ID_DTS)
FAIL("no decodable DTS frames");//DTS帧
break;
case AVMEDIA_TYPE_VIDEO://视频
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;
}
static void estimate_timings(AVFormatContext *ic, int64_t old_offset)
{
int64_t file_size;
/* get the file size, if possible */
if (ic->iformat->flags & AVFMT_NOFILE) {
file_size = 0;
} else {
file_size = avio_size(ic->pb);
file_size = FFMAX(0, file_size);
}
if ((!strcmp(ic->iformat->name, "mpeg") ||
!strcmp(ic->iformat->name, "mpegts")) &&
file_size && (ic->pb->seekable & AVIO_SEEKABLE_NORMAL)) {
/* get accurate estimate from the PTSes */
//从PTSes进行精确评估
estimate_timings_from_pts(ic, old_offset);
ic->duration_estimation_method = AVFMT_DURATION_FROM_PTS;
} else if (has_duration(ic)) {
/* at least one component has timings - we use them for all
* the components */
//如果一个元素有timings,则将其应用于所有的
fill_all_stream_timings(ic);
/* nut demuxer estimate the duration from PTS */
//从PTS估算时间 nut解封转
if(!strcmp(ic->iformat->name, "nut"))
ic->duration_estimation_method = AVFMT_DURATION_FROM_PTS;
else
ic->duration_estimation_method = AVFMT_DURATION_FROM_STREAM;//流
} else {
/* less precise: use bitrate info */
//低精度：使用比特率信息
estimate_timings_from_bit_rate(ic);
ic->duration_estimation_method = AVFMT_DURATION_FROM_BITRATE;
}
update_stream_timings(ic);
for (unsigned i = 0; i < ic->nb_streams; i++) {
AVStream *st = ic->streams[i];
if (st->time_base.den)
av_log(ic, AV_LOG_TRACE, "stream %u: start_time: %s duration: %s\n", i,
av_ts2timestr(st->start_time, &st->time_base),
av_ts2timestr(st->duration, &st->time_base));
}
av_log(ic, AV_LOG_TRACE,
"format: start_time: %s duration: %s (estimate from %s) bitrate=%"PRId64" kb/s\n",
av_ts2timestr(ic->start_time, &AV_TIME_BASE_Q),
av_ts2timestr(ic->duration, &AV_TIME_BASE_Q),
duration_estimate_name(ic->duration_estimation_method),
(int64_t)ic->bit_rate / 1000);
}
//-----------------------------------------------
static void estimate_timings_from_bit_rate(AVFormatContext *ic)
{
int64_t filesize, duration;
int i, show_warning = 0;
AVStream *st;
/* if bit_rate is already set, we believe it */
//比特率
if (ic->bit_rate <= 0) {
int64_t bit_rate = 0;
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
if (st->codecpar->bit_rate <= 0 && st->internal->avctx->bit_rate > 0)
st->codecpar->bit_rate = st->internal->avctx->bit_rate;
if (st->codecpar->bit_rate > 0) {
if (INT64_MAX - st->codecpar->bit_rate < bit_rate) {
bit_rate = 0;
break;
}
bit_rate += st->codecpar->bit_rate;//累加
} else if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO && st->codec_info_nb_frames > 1) {
// If we have a videostream with packets but without a bitrate
// then consider the sum not known
bit_rate = 0;
break;
}
}
ic->bit_rate = bit_rate;
}
/* if duration is already set, we believe it */
//duration
if (ic->duration == AV_NOPTS_VALUE &&
ic->bit_rate != 0) {
filesize = ic->pb ? avio_size(ic->pb) : 0;
if (filesize > ic->internal->data_offset) {
filesize -= ic->internal->data_offset;
for (i = 0; i < ic->nb_streams; i++) {
st = ic->streams[i];
if ( st->time_base.num <= INT64_MAX / ic->bit_rate
&& st->duration == AV_NOPTS_VALUE) {
//计算duration
//av_rescale所实现的功能是什么？计算的细节？
duration = av_rescale(filesize, 8LL * st->time_base.den,
ic->bit_rate *
(int64_t) st->time_base.num);
st->duration = duration;
show_warning = 1;
}
}
}
}
if (show_warning)
av_log(ic, AV_LOG_WARNING,
"Estimating duration from bitrate, this may be inaccurate\n");
}
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