[Libav-user] Per frame real time stamps

Timour Khanipov khanipov at gmail.com
Wed Nov 23 19:38:10 CET 2011

Thank you, Nicolas.

First of all, let me say a few more words about the camera. We are
recording video by ourselves (using libav) and we only get a sequence of
(bitmaps) from the camera (by the way, its GigE UI-5220SE). I know that in
its API there are functions for getting timestamps but at first glance they
have nothing to do with the video being recorded.

Speaking about the PTS I thought (after studying FFMpeg tutorial at
dranger.com) that these are only sequence numbers needed to correctly
display frames which should be decoded in a different order (B-frames).
After looking at the Wikipedia page about PTS I figured out that PTS may be
indeed linked with real time. Thank you for this particular clue.

Could you please mention which libav-functions should I look at to use
those arbitrary PTS?

And am I right that this stuff is somehow related to variable framerate
(VFR)?  I am curious because at the moment we are using constant frame rate
to record videos (we set it equal to camera framerate). This raised a tough
question for us even when we used a single camera: small inaccuracies in
from-camera frames timings would not be taken into account when recording
constant frame rate video. So using custom timestamps would be a panacea.

One last question is about the correct format for storing arbitrary
timestamps. In fact the format we are using now is AVI, so I would like to
ask you to suggest formats which are supported by libav* and are capable of
storing those timestamps?

Thanks a lot.
Timour Khanipov.

2011/11/23 Nicolas George <nicolas.george at normalesup.org>

> Le tridi 3 frimaire, an CCXX, Timour Khanipov a écrit :
> > In our application we are recording several video streams from different
> > cameras and we need to synchronize them at replay stage. Besides that we
> > have some events which should be linked with specific camera and specific
> > time moment. So it would be very useful if there were some sort of
> > functionality in libav  for writing real timestamps for each frame.
> The PTS is almost exactly that. And, depending on the kind of camera you
> are
> recording from, it may be already set to the timestamp recorded by the
> hardware or the driver.
> You just need to make sure you use a format that correctly stores arbitrary
> timestamps, unlike AVI for example.
> Regards,
> --
>  Nicolas George
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