[Libav-user] av_read_frame returns packets with AV_NOPTS_VALUE

[Yurii Monakov]

2018-05-12 12:03 GMT+03:00 Paul B Mahol <onemda at gmail.com>:

> On 5/12/18, Yurii Monakov <monakov.y at gmail.com> wrote:
> > Hi, FFmpeg users!
> >
> > I'm developing a stream recording application. So it takes arbitrary
> stream
> > and records it in chunks of approx 20 minutes, splitting input stream at
> > key frame boundaries.
> >
> > I'm using this stream for testing purposes (recording only video stream):
> > http://bitmovin-a.akamaihd.net/content/playhouse-vr/m3u8s/105560.m3u8
> > It initializes properly and first packets, including first key frame, are
> > good. I save them with output context without any problem.
> >
> > But when next key frames arrive their PTS/DTS are set to AV_NOPTS_VALUE.
> > av_interleaved_write_frame function expectedly complains about it and
> > produces garbled videos. This is strange, because av_read_frame function
> > states that
> >
> >  * 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).
> >
> > I've tried to open this stream by ffmpeg with '-fdebug t' option and it
> > also shows key frame packets  without PTS:
> >
> > $ ffmpeg -fdebug ts -i
> > http://bitmovin-a.akamaihd.net/content/playhouse-vr/m3u8s/105560.m3u8
> -an
> > -f null
> > ...
> > [hls,applehttp @ 0xe004e0] ff_read_packet stream=1, pts=NOPTS, dts=NOPTS,
> > size=464722, duration=3003, flags=1
> > [hls,applehttp @ 0xe004e0] read_frame_internal stream=1, pts=NOPTS,
> > dts=NOPTS, size=464722, duration=3003, flags=1
> > [hls,applehttp @ 0xe004e0] ff_read_packet stream=1, pts=1099098,
> > dts=1084083, size=223452, duration=3003, flags=0
> > [hls,applehttp @ 0xe004e0] read_frame_internal stream=1, pts=1099098,
> > dts=1084083, size=223452, duration=3003, flags=0
> > ...
> > As you can see, PTS/DTS are missing only in key frame (flags=1).
> >
> > Remuxing this stream to mp4 with ffmpeg gives no artifacts on the video
> and
> > no errors are shown in the output. So it fixes PTS/DTS somehow to
> maintain
> > their sequence.
> >
> > Now I simply keep track of previous packet PTS/DTS values and alter them
> > according to duration. But this approach can handle only PTS/DTS loss
> only
> > in presence of duration (which is not reliable also).
> >
> > So, what is the best way to fix input stream PTS/DTS returned from
> > av_read_frame?
> >
> > Yurii
> >
>
> Looks like the bug that should be reported.
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But FFmpeg somehow fixes these timestamps to provide consistent stream.

Another oddity I've discovered with this test stream - FFmpeg is unable to
create segmented files.
This command does not work:

ffmpeg -i
http://bitmovin-a.akamaihd.net/content/playhouse-vr/m3u8s/105560_video_1920_9000000.m3u8
-c copy -map 0 -f segment -segment_format mp4 -segment_time 10
-reset_timestamps 1 part%03d.mp4

it creates single file part000.mp4 and complains about missing PTS. But
playback is perfect with VLC/ffplay.

BTW, what is the best place to report this kind of bugs?

Yurii
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