[MPlayer-users] Bug: av sync, bframes, dwStart issues

[Corey Hickey]

John Stebbins wrote:
>> What I was wondering, though, was whether the B-frame variation actually
>> affected A/V sync within the file, as you had indicated. Have you
>> observed this effect with any video players? I just ran a test with
>> mplayer and there wasn't a problem.
>>   
> There I go making bad/untrue assumptions.  Thanks for testing.

You're welcome.

> I guess
> the player has the video delay whether there are actually bframes
> present or not. So now I have to wonder how the player knows that
> bframes are suppose to be present.

In MPEG-4 ASP, the presence of B-frames is indicated by the low_delay 
flag. When low_delay==1, each frame can be presented immediately after 
being decoded; otherwise, I-frames and P-frames must (or "should"?) be 
delayed.

> And does a similar test with
> b-pyramid enabled sync correctly as well.

I wanted to do a test last night, but I don't see how to trick x264 
similarly. I may end up hacking the source.

> If this is the case, then the
> player could compensate for the sync because it knows in advance that it
> will be delaying video.

I can probably check for low_delay, but I'm not sure about h.264 and 
b_pyramid.

> I know this doesn't "fix" the problem for all
> the other players that exhibit this same problem, but I still believe
> this is something the player should be doing.

Well, we'll see. If I end up working on this and making a patch, you/we 
can make a case for applying it. I'm undecided as to whether it would be 
better.

-Corey