[mythtv-users] XvMC profile group playing MPEG4 videos?

[Paul Bender]

Johnny Russ wrote:
> I have an old PIII 1GHz box that I use to playback SD shows and also my 
> kids' videos. In 0.20 I used XvMC to playback my MPEG-2 shows and the 
> default settings (whatever they were) on the internal player worked fine 
> with my MPEG-4 videos. Since updating to 0.21 I haven't been able to get 
> my playback profile setup such that I can playback my MPEG-2 shows and 
> my MPEG-4 videos satisfactorily. With my hardware I can play the videos 
> with ffmpeg, but using this for my TV shows starts to get a little jumpy 
> if anything is going on (e.g. commercial flagging). However, if I use 
> XvMC my TV shows are great with minimal CPU usage, but my MPEG-4 videos 
> have issues (hanging, audio sync, choppy). I thought that XvMC would 
> only be used for MPEG-2 streams 
> (http://www.mythtv.org/wiki/index.php/Playback_profiles)? I set up my 
> playback profile such that XvMC would be used first, then ffmpeg would 
> be used second. I thought this would cause my MPEG-2 shows to use XvMC 
> and then everything else would use ffmpeg. However, with this setup my 
> videos have issues. If I remove the XvMC or change the order of the 
> profile groups then the videos are fine. It seems to me like my MPEG-4 
> videos are using the XvMC profile group instead of falling through to 
> the ffmpeg profile group. Am I mistaken about XvMC will only play MPEG-2 
> content? Since the content all has similar resolutions, I can't make 
> distinctions based on that criteria. Any ideas what is going on? Is 
> there a way to use XvMC for only my TV shows and not for my videos?

I believe that the issue is how the profiles are used. My understanding 
is that once it determines that the hardware supports the decoder and 
renderer for the specific video size, it uses it. However, if the codec 
does not support the selection it falls back to another selection 
without consulting the profile.

In your case, when it finds that it cannot use the xvmc-blit renderer to 
play MPEG4, it fall back to the xv-opengl renderer. If this is your 
problem, then you will see messages in console output from mythfrontend. 
Therefore, if you run mythfrontend in a terminal window, then you will 
see messages say that xvmc-blit is not supported by the codec and that 
it is using xv-opengl instead.

For MiniMyth, I created a patch so that xvmc-blit falls back to xv-blit 
(if present) and xvmc-opengl falls back to xv-opengl (if present).

There is a ticket (#4792) about this.