[mythtv-users] Unreasonably high CPU usage when playing HD content? Suggestions?

[Michael T. Dean]

On 04/06/2008 09:47 PM, Rick Hudson wrote:
> Michael T. Dean wrote:
>>> I think some of the info on http://www.mythtv.org/wiki/index.php/XvMC is 
>>> relevant to me where it says that many GPUs only support XV up to 1024x1024.
>>>       
>> Find out with:
>>
>> xvinfo | grep 'maximum XvImage size'
>>     
> Ah. Thanks for that tip! It says:
>
> maximum XvImage size: 1024 x 1088
>
> Interesting that it's 1088 rows instead of 1024 which tends to suggest it's 
> designed to handle 1080i video. However the 1024 width does appear to be a 
> problem. :-(
>   

Yeah, even "every HDTV channel in 1080i" DirecTV uses 1280x1080. 
(Question:  How has there not been a lawsuit or a smack-down by the FCC
or some advertising standards commission for their ads?  If Seagate gets
sued for using the proper terminology because it confuses consumers, how
can DirecTV get away with calling 1280x1080 "1080i"?  OK, it's possible
that their new DirecTV-10 and 11 satellites may be using 1920x1080
(unconfirmed), but they were running those commercials long before the
July 7, 2007 launch of DirecTV-10, and I'm pretty sure that they're
still sending HD-Lite on many of the channels (if not all, at least
those on other satellites).)

>> Unless you have some of the old, broken Intel drivers, I doubt this is
>> the problem.  (I'm thinking the i810 driver is garbage and the new intel
>> driver works, but don't quote me on that.)
>>     
> What would that not be the problem? Is the XvImage size a restriction of the 
> driver and not the hardware?
>   

As I understand it, there was a bug in some of the drivers that
specified a value that was significantly lower than what the hardware
actually supported.  I don't use any of the Intel GPU's, so I don't know
details.  Searching the list for posts by others (I think Jarod Wilson
knows/has mentioned the issue) would give you a lot more info than I have.

>>> What I don't understand though is that my screen size is 1280x720 so I would 
>>> have though it could play that resolution without scaling at all. There is 
>>> obviously something about GPU data transfer I'm missing. Maybe there's a 
>>> playback profile suitable for this unscaled situation that I haven't found yet.
>>>       
>> For 720p, display on a 720p TV should be unscaled unless you've
>> specified overscan in Myth and are using GUI size for playback or you're
>> running Myth in a window or something--i.e. not displaying video at
>> 1280x720.
>>     
> So you're saying that playing an unscaled video should be possible regardless 
> of whether it's bigger than the maximum XvImage size? I guess I need to find 
> out if mythtv is indeed trying to scale the video to something else for some 
> reason.

It would be unscaled, but it wouldn't be able to use Xv to render the
video.  While Xv does scaling "for free," it also does a lot
more--including allowing fast transfer of video data to the graphics
device.  Without Xv, you're stuck with other much-less-efficient
mechanisms, so your CPU usage would go way up compared to rendering with
Xv--exactly as you're seeing.

I'm glad to hear you got the 720p working, but if you are using the i810
drivers (and IIRC that they're older and broken and the intel drivers
are newer and working), you may still want to switch so you can actually
get Xv support and drop your CPU usage even more.

Mike