[mythtv] sound + xvmc + livetv = problem, why?

Isaac Richards ijr at case.edu
Sun Jan 29 21:40:51 UTC 2006

On Sunday 29 January 2006 14:38, Daniel Kristjansson wrote:
> I've been looking at ticket #774 a little more closely since it
> seems to be effecting more users and it makes the EPIA pretty
> useless as a frontend in LiveTV mode.
> I'm not very familiar with how the audio decoding works in MythTV.
> But it seems that the audio buffers aren't getting filled quickly
> enough when you are in LiveTV and using XvMC. This causes the A/V
> sync routines then kick in to slow down the video to match the audio
> speed, which in the meantime plays a sample, mutes, plays a sample,
> mutes, etc.
> This does not happen when you playback a recording, and the CPU
> utilization is lower when you play the same stream in LiveTV vs.
> playing back the recording. What I did notice is that with XvMC,
> when you pause a playing recording the audio '-v audio' debug
> keeps going, but it stops when you pause in LiveTV. With XVideo
> output, it keeps going in either case.
> I've tried upping the ringbuffering and I'm using ChromaKey OSD
> so I don't think the problem is with video (and the CPU is at 40%
> in LiveTV on a 1080i stream, and 70% playing a 1080i recording).
> AFAICT Everything points to audio, but I don't understand how that
> would interact with LiveTV mode. (I even tried removing the avlock
> locking, to see if there was some lock contention, it had no effect.)
> Anyone have an idea what might be happening here?

Does pausing for a few seconds, then unpausing help at all?


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