[Libav-user] av_read_frame returns packets with AV_NOPTS_VALUE

[Yurii Monakov]

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
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