[mythtv] MythTV on AppleTV under Linux Ubuntu

Scott D. Davilla davilla at 4pi.com
Sun Sep 9 00:50:41 UTC 2007


I'm working on developing a mythtv frontend distribution running on 
the AppleTV under Ubuntu Edgy.

See 
http://forum.awkwardtv.org/viewtopic.php?f=23&t=167&hilit=&sid=bd94c51c9ef092d26d6d815933a9cdbb 
for progress over the past few months. I'm running kernel 2.6.21.5 
with several appletv specific patches. I'm about to migrate it to 
2.6.22 with ck1 patches for better thread scheduling.

Bottom line is the results are quite promising but still not 100 
percent solid regarding HD content decode. SD content is trivial.

Here's my issues;

  I was running svn #13716 until a week ago. With this version HD 
decode with nvidia was looking pretty good. Tickets 3690 and 3789 
were the main problem issues. 1080i decode was running 50-60 percent 
cpu, Xorg was less than 5 percent. The ffmpeg sync was painful but I 
was working toward tracking down the problems.

The Zap2it -> SD migration forced me to update my backend to svn 
#14374 which of course propagated a protocol change from 34 to 35. So 
mythtv frontend on the appletv was also updated to #14374.

Now on the AppleTV frontend, HD content is not possible. The removal 
of internal a52 to ac3 has pushed me over on cpu and both video and 
audio are stuttering badly.

Now comes the fun part. I've disabled the internal ac3 and am using 
external liba52 for audio decode. I've also pulled ffmpeg from svn as 
well as mplayer for comparison games.

The results;
a) mplayer (xvmc) + ffmpeg using liba52 -> 1080i HD content plays 
fine with less than 60 percent cpu and Xorg is less than 5 percent. 
Slight audio stutters which should be resolved with 2.6.22 with ck1 
patches.

b) mythtv (standard xvmc) + liba52 -> periodic video/audio skips, cpu 
close to 100 percent. OSD is gray.

c) mythtv (standard ffmpeg) + liba52 -> good video, slight audio 
stutters, cpu is about 88 percent. OSD is color. I suspect that the 
slight audio stutters will also be resolved with 2.6.22 with ck1 
patches.

I don't understand how c) mythtv with standard (ffmpeg) decoding can 
perform better than b) xvmc assisted decode. This should not be 
possible with HD content using the 1GHz pentium-m in the AppleTV.

Any suggestions about what is going on?

Also, I see that mythtv-vid branch has been merged into trunk. Since 
I'm working on the bleeding edge, are there any issues regarding 
pulling the current svn for frontend work or will I have to update my 
backend too?

I try to keep my backend stable as it's a production box recording 
2-4 shows a day from a dual pvr-150 setup connected to two dish 
network DP311 and the dual tuner HDHomeRun for HD content from 
off-the-air. Backend is 1.83GHz Intel Core 2 Due with 2.5TB of 
storage so plenty of ponies here.

Just for comparisons, my other HD content frontend is a Roku HD1000. 
Running MythRoku it always works without problems.

Thanks
Scott




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