[Libav-user] How to calculate pts/dts ???

[Paul B Mahol]

On Mon, Jan 2, 2023 at 3:13 PM wolverin via Libav-user <
libav-user at ffmpeg.org> wrote:

> *Output #0, rtsp, to 'rtsp://127.0.1.1:555 <http://127.0.1.1:555>':*
> *  Stream #0:0: Video: h264, yuv422p(tv, bt470bg/unknown/unknown),
> 1280x720, q=2-31, 500 kb/s, 15 tbr, 90k tbn*
>
>
> I compared such an approximate calculation of pts/dts in ffprobe for my
> code and ffmpeg and they match until the real fps becomes different from
> the calculated one, then I see either delays or frame losses in VLC.
>
>
> You can not use 15 from video frame rate to calculate PTS when video is
> variable frame rate.
>
>
> ok, but then how do I calculate the pts/dts of each frame correctly???
>

PTS is represented as relative time starting from 0 for start of file.

PTS is just a int64_t number that tells relative time.
To know time resolution one use timebase.num/den, so they are actually tied
together with pts timestamp.

If video is VFR than there are gaps e.g. non-monotonous increasing of pts
from older to newer ones.

Say time of frame is 5.5 seconds and timebase used is 1/90000 than time of
1 second would have value of 90000 stored in pts.
5.5 seconds would then be 5*90000 + 0.5*90000.

Hope that you can conclude from this demonstration how to solve your
problem.

To rescale PTS from one timebase resolution to another one use
av_rescale_q().



> I want my SoC ARM to provide maximum transcoding speed, this is especially
> important for a resolution of 1920x1080 when fps is 8-11
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