[mythtv-users] I just want to make a wife-friendly MythTV system

Raymond Wagner raymond at wagnerrp.com
Sun Nov 23 08:21:39 UTC 2008


Marc Barrett wrote:
> The documentation on the Hauppauge web page says that
> a 2Ghz dual-core would be sufficient to play back HD-PVR programs,
> but I have seen it said elsewhere that Linux has greater requirements
> (something about HD playback not being threaded on Linux, so a 
> faster core clock rate is needed).
>   
The h.264 codec has built in threading capability, in the form of 
'slices'.  The video is literally sliced into multiple domains, and 
these domains are encoded and decoded independently, allowing for 
multi-threaded operation.  This is available in both Linux and Windows 
decoders.  The HD-PVR outputs single sliced streams, meaning all 
decodes, Windows or Linux, will be single-threaded.  Single or dual core 
makes little difference.  A 2GHz Core2 will get you decoding of moderate 
bitrates out of the HD-PVR (maybe 10mbps), and a similarly clocked AMD 
chip will get you slightly less.  3GHz is really needed for smooth 
software decoding of the highest bitrates it will output.

The last several generations of both ATI and nVidia chips, since the 
switch to PCIe, have all supported at least partial offloading of h.264 
decoding (at least with proper decoders).  The last couple generations 
have offered complete offloading, requiring almost no CPU power for 
playback.  The 2GHz value seems to be arbitrarily chosen.
> I also saw mention, recently, about something called VDPAU.  With
> this, I could buy a slower system, stick in a fast nvidia card, and be
> happy.  Of course, all this would depend on how soon VDPAU could be
> supported by the MythTV development community.
>   
VDPAU was released somewhat of a surprise about a week and a half ago.  
It offers complete offloading of mpeg1/2, h.264, and WMV for 8000 series 
and better cards (and for some 9000 series, VC-1 as well).  This is 
still very beta grade.  While providing a functional patch for mplayer, 
it serves as more of a proof of concept, as well as a demo for 
developers to use for adding support in their own applications.  There 
is still work to be done in the driver, and considerable work to be done 
to get mplayer properly working.  Don't expect this to be in a release 
version of MythTV any time soon.


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