[ivtv-users] Status of the B-Frame issue ?

[Levente Novák]

On Mon, 2008-11-10 at 23:00 +0100, Hans Verkuil wrote:
> On Monday 10 November 2008 09:24:44 Alexander Pipelka wrote:
> > Hi,
> >
> > Are there any news on the B-Frame issue.
> > I sent a status log ~ 3 weeks ago.
> 
> Hi Alex,
> 
> I looked at it today and I could reproduce it. I also found what the 
> difference is between the old and current ivtv driver. When you pass 
> the B-frames to the card the API says that you should pass B+frames + 1 
> to the card. So if there are 0 B-frames, then the number should be 0+1 
> = 1. However, for some reason that does not seem to work for a 
> cx2584x-based card. If I put in 0 instead of 1, then it works again.
> 
> What I don't know is if that really produces a stream without B-frames. 
> Applying the attached patch should fix the problem you have, but I 
> wonder if you can also test the presence of B/I/P frames and check that 
> you get the right results (i.e. really 0 B-frames). I can also test it, 
> but not easily and not until after two weeks from now.
> 

Tested the patch on a PVR-150 MCE. Here are the observations:

B-frames requested    B-frames got    Remark
-------------------------------------------------------------
0                     1               Plays normally
1                     1               Plays normally
2                     2               Plays normally
3                     3               Choppy
4                     4               Choppy and plays at faster speed

So in conclusion: the patch did something but not quite what it was
expected to. At least now with B-frames set to 0 it does save a stream
which however has not 0 but 1 B-frame per P frame. At the higher B-frame
ratios, the video is unusable due to choppiness and/or faster replay
speeds (GOP at 12 frames except at 4 B-frames where it was set to 15 by
qv4l2). The audio seemed normal though.

Levente