> On Jul 6, 2022, at 12:09 PM, Gyan Doshi <ffm...@gyani.pro> wrote:
>
>
>
> On 2022-07-06 08:23 am, "zhilizhao(赵志立)" wrote:
>>
>>> On Jul 5, 2022, at 10:33 PM, Gyan Doshi <ffm...@gyani.pro> wrote:
>>>
>>>
>>>
>>> On 2022-07-05 07:05 pm, "zhilizhao(赵志立)" wrote:
>>>>> On Jul 5, 2022, at 8:07 PM, Gyan Doshi <ffm...@gyani.pro> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 2022-07-05 01:20 pm, Zhao Zhili wrote:
>>>>>> From: Zhao Zhili <zhiliz...@tencent.com>
>>>>>>
>>>>>> Streams with all zero sample_delta in 'stts' have all zero dts.
>>>>>> They have higher chance be chose by mov_find_next_sample(), which
>>>>>> leads to seek again and again.
>>>>>>
>>>>>> For example, GoPro created a 'GoPro SOS' stream:
>>>>>> Stream #0:4[0x5](eng): Data: none (fdsc / 0x63736466), 13 kb/s
>>>>>> (default)
>>>>>> Metadata:
>>>>>> creation_time : 2022-06-21T08:49:19.000000Z
>>>>>> handler_name : GoPro SOS
>>>>>>
>>>>>> With 'ffprobe -show_frames http://example.com/gopro.mp4', ffprobe
>>>>>> blocks until all samples in 'GoPro SOS' stream are consumed first.
>>>>>>
>>>>>> Signed-off-by: Zhao Zhili <zhiliz...@tencent.com>
>>>>>> ---
>>>>>> libavformat/mov.c | 14 ++++++++++++++
>>>>>> 1 file changed, 14 insertions(+)
>>>>>>
>>>>>> diff --git a/libavformat/mov.c b/libavformat/mov.c
>>>>>> index 88669faa70..2a4eb79f27 100644
>>>>>> --- a/libavformat/mov.c
>>>>>> +++ b/libavformat/mov.c
>>>>>> @@ -3062,6 +3062,20 @@ static int mov_read_stts(MOVContext *c,
>>>>>> AVIOContext *pb, MOVAtom atom)
>>>>>> st->nb_frames= total_sample_count;
>>>>>> if (duration)
>>>>>> st->duration= FFMIN(st->duration, duration);
>>>>>> +
>>>>>> + // All samples have zero duration. They have higher chance be chose
>>>>>> by
>>>>>> + // mov_find_next_sample, which leads to seek again and again.
>>>>>> + //
>>>>>> + // It's AVERROR_INVALIDDATA actually, but such files exist in the
>>>>>> wild.
>>>>>> + // So only mark data stream as discarded for safety.
>>>>>> + if (!duration && sc->stts_count &&
>>>>>> + st->codecpar->codec_type == AVMEDIA_TYPE_DATA) {
>>>>>> + av_log(c->fc, AV_LOG_WARNING,
>>>>>> + "All samples in data stream index:id [%d:%d] have zero
>>>>>> duration, "
>>>>>> + "discard the stream\n",
>>>>>> + st->index, st->id);
>>>>>> + st->discard = AVDISCARD_ALL;
>>>>>> + }
>>>>>> sc->track_end = duration;
>>>>>> return 0;
>>>>>> }
>>>>> So this will allow audio and video streams to be demuxed, but not data?
>>>>> That distinction seems arbitrary.
>>>> Disable audio/video streams may create regression. It’s unlikely for random
>>>> and broken data stream.
>>>>
>>>>> Print a warning and assign a duration to each sample. Either 1 or if not
>>>>> zero/Inf, st->duration/st->nb_frames.
>>>> Set sample_duration to 1 doesn’t work. Dts still far behind other streams.
>>>>
>>>> Set sample_duration st->duration/st->nb_frames works for me, but I prefer
>>>> current strategy for the following reasons:
>>>>
>>>> 1. AVDISCARD_ALL is more close to AVERROR_INVALIDDATA by giving up instead
>>>> of trying correction and hope it works, which may not, e.g., st->duration
>>>> is broken, or bad interleave even though we fixed sample_duration.
>>> It's not about hoping that it works. It's about not preventing the user
>>> from acquiring the stream payload.
>>>
>>> Can you test if setting -discard:d none -i INPUT allows reading the stream
>>> with your patch?
>> Yes it does allow reading the stream. ’stts’ box is parsed during
>> avformat_find_stream_info(), AVStream->discard flag can be modified
>> after that. The patch has no effect if user changed AVStream->discard
>> flag.
>
> What's the duration of the demuxed stream?
The demuxed data track has correct duration since there is a check
```
if (duration)
st->duration= FFMIN(st->duration, duration);
```
st->duration comes from ‘mdhd’ and not overwrite in this case.
Every packet has zero as timestamp, as expected:
./ffmpeg -debug_ts -discard:d none -i ~/tmp/gopro.mp4 -map 0:4 -c copy
-copy_unknown -f data /tmp/test
demuxer -> ist_index:4 type:data next_dts:0 next_dts_time:0 next_pts:0
next_pts_time:0 pkt_pts:0 pkt_pts_time:0 pkt_dts:0 pkt_dts_time:0 duration:0
duration_time:0 off:0 off_time:0
demuxer+ffmpeg -> ist_index:4 type:data pkt_pts:0 pkt_pts_time:0 pkt_dts:0
pkt_dts_time:0 duration:0 duration_time:0 off:0 off_time:0
muxer <- type:data pkt_pts:0 pkt_pts_time:0 pkt_dts:0 pkt_dts_time:0 duration:0
duration_time:0 size:16
>
> Regards,
> Gyan
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