[mythtv-users] overlay mode available?

Joseph A. Caputo jcaputo1 at comcast.net
Mon Nov 3 09:27:26 EST 2003


On Sunday 02 November 2003 10:40, abo wrote:
> Hi,
>
> is there an overlay mode to use with mythtv?
> I can watch fullscreen tv with xawtv without any problems (because
> xawtv uses overlay)
> If I try to do this with mythtv, a have a lot of framedrops.
>
> Is overlay not possible or do I have to switch it on?

The likely reason that you're seeing frame drops has nothing to do with 
'overlay' mode, but is more likely because you're pegging your CPU.  
Xawtv has low resource requirements because it merely overlays/blits 
the live video feed directly from the TV card to the display card.  It 
doesn't have to encode or decode anything.  MythTV, however, is a true 
PVR with timeshifting capabilities -- meaning when you're watching 
LiveTV, what it's really doing is encoding the TV stream to disk 
(RTjpeg, MPEG-4 or HW MPEG-2), then decoding it and playing the decoded 
stream.  The decoded stream must be scaled for playback, i.e., if 
you're recording at 640x480 but your display resolution is 800x600, the 
video must be scaled up to 800x600.  This scaling is very CPU 
intensive, but is supposed to be hardware-assisted by the Xv extensions 
to XFree86 that work with your video card.

So, what does all this mean for you?  Well, 2 possibilities:  (1) your 
encoding (recording) parameters are set too high for your CPU to handle 
without dropping frames, especially if you're doing simultaneous 
playback (LiveTV), (2) Xv is not enabled/working/available on your 
video card/X11 setup, so playback is consuming a lot of resources to do 
the scaling.

Maybe if you posted some information about your hardware and your 
recording profile settings, someone might be able to diagnose your 
problem...

-JAC



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