[mythtv-users] Looking for new DVB-S+CAM based backendhardwarerecommendations

[Phil Jordan]

Michael T. Dean wrote:
> On 08/29/2007 02:28 PM, Wim Fokkens wrote:
>> BBC HD seems to be encoded as H.264 at 1440x1080, at least on DVB-T from 
>> the Crystal Palace transmitter. I've tried recording and playing it, and 
>> it won't decode it in realtime, even on my Core2 Duo E6600. That's from 
>> mythfrontend or just playing the file in mplayer or xine. My guess is 
>> I've either messed up my config, my binaries aren't compiled right 
>> (packman for OpenSuse 10.2 x86_64) or libavcodec is just too 
>> inefficient. Have you had any luck with the HD stuff? 
> 
> H.264 decoding at HDTV resolutions is /very/ tough.
I gathered. I've had a good read through some documentation on it and
the decoding is somewhat more involved than, say, MPEG-2. I've had a
brief go at trying to understand the h264 code in libavcodec/ffmpeg, and
from the limited amount of time I've had with it, I can say there's a
lot going on. ;)

> You probably won't
> be able to do it with Myth until ffmpeg is updated to support
> multi-threaded decoding of H.264 and Janne integrates the updated ffmpeg
> into MythTV.  This process is in the works, so it will be done "soon"
> (i.e. within a couple of years ;).  If nothing else, it should be done
> before processor technology advances sufficiently that a single-core CPU
> can do the decoding in realtime.

Good to hear there's change afoot, although for me it won't make much of
a difference in practice - my main (living room) frontend is just a
Pentium M, and the backend is in more urgent need of an upgrade.

I have looked into offloading the later stages of the decoding (after
the dequantisation) onto the GPU, but it doesn't look like anyone has
attempted it on Linux. I sadly can't financially justify working on it
full time for 2 months or so. :) Someone should get a collection going. ;)

Seriously though, I do think it's very feasible even without special
driver support as long as you've got access to pixel+vertex shaders and
render-to-texture via OpenGL. Which we do, of course, for
nvidia/fglrx/intel. The main work would be integrating with
MythTV/ffmpeg and tuning it to be fast enough on lower-end GPUs and the
various quirky drivers.

~phil