[vlc] How does VLC determine stream time for MPEG4 streams?

[John Sokol]

Cool company. I posted a link to it on my blog.
http://videotechnology.blogspot.com/2011/10/web-based-carrier-grade-video.html


After a seek you need to start on a GOP boundary and make sure you have an
Iframe. Also the PTS for a/v should be too far out of place from each other.

It would take some careful examination of packets which it looks like your
starting to do.

What are you using to examine packets. I just made a small tool to help me
with with just this issue on MPEG2, so unfortunately It's not going to help
you just yet, but want to add mpeg4 too.

1) pts cycles through the values 2-29 (in increments of 3) and repeats.
> 2) decoded_picture_number is incremented by 1 each packet
> 3) display_picture_number is a constant 0


These fields sound bogus, and not correctly populated.

Some mpeg decoders will not care and others will be very particular that
these fields have legitimate values.

What are you using for playback of streams?

John L. Sokol
videotechnology.com


On Mon, Oct 24, 2011 at 7:10 AM, Tomer Margalit <
tomer.margalit at videocells.com> wrote:

> Hi,
>
> I'm currently working on integrating an old (highly customized) video
> server that my company has.
> The old player was a custom built player as well, and the player and server
> were pretty much built one around the other.
> Now trying to integrate it with VLC, I see a lot of problems (particularly
> after a seek - since at that point everything seems to go out of sync).
>
> Sometimes (not always), after a seek the movie freezes - and when we use
> VLCJ to play it, the time change callback shows the time is not changing
> (but new packets are received).
> I have checked the rtp timestamps and have tried altering them many times,
> but nothing seems to work (actually the times in the callback are
> unaffected) - which implies the problem lies within the mpeg packets (pts?).
>
> I have looked at the times of the mpeg4 packets being released from the
> server (as an FFmpeg AVPacket) - pts, coded_picture_number,
> display_picture_number. The things I have noticed are that:
> 1) pts cycles through the values 2-29 (in increments of 3) and repeats.
> 2) decoded_picture_number is incremented by 1 each packet
> 3) display_picture_number is a constant 0
>
> I have two questions:
> 1) Does anyone know what the problem could be, or why the values are
> problematic for VLC?
> 2) What value does VLC use to determine the movie time? pts,
> decoded_picture_number, display_picture_number? A combination of the values?
> Some other values?
>
> Thanks,
>   Tomer
>
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