[mythtv] Problem with Via VLD XVMC display and DVB recordings in current CVS: Gaps in video and audio

[Terry Barnaby]

Terry Barnaby wrote:
> Hi,
> 
> The current MythTv CVS version of MythTV has a stange problem with 
> display on my Via M10K box which uses Via VLD XVMC hardware MPEG decode.
> The Via M10K box is a simple client with a separate server containg DVB 
> cards.
> 
> Myth CVS after 2005.03.30 has this problem.
> MythTV CVS before 2005.02.20 is Ok.
> 
> If I watch an old recording, all is fine.
> If I watch live TV or a new recording the video and audio seems to
> have continuous gaps (about 4 per second) resulting in unwatchable/
> unlistenable output. This results in a start/stop display.
> There are no special messages from mythfrontend.
> Watching using another system using software MPEG decode and Xv output
> all is fine.
> 
> Could some change to the DVB code have resulted in an MPEG stream that 
> the Via MPEG hardware cannot decode correctly ?
> 
> Any ideas ?
> 
> Terry
> 
> 
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I have been playing around with this and this is where I am:

1. The new DVB code's Autopid feature means that on channels where
	there are multiple Audio streams these are saved in the
	recording.

2. On a Via M10K box using VLD XVMC HW MPEG, this results in very
	jumpy display/audio with error messages:
"A/V diverged by 3.0873 frames, extending frame to keep audio in sync"

3. Using Xv output with software decoding is fine.

4. Not sending any IDCT data to the HW mpeg decoder has no effect on
	the problem.

In an example case the recording has a 2 channel audio stream and
a mono audio stream (possibly one for the hard of hearing). The
overall frame rate when playing this is about 14frames/s. It is almost
as if MythTv was trying to sync to the agregate of the two audio
streams .....

I would not have thought that using XvMC VLD video decoding would
have affected the audio decoding .....

Terry