[mythtv-users] AppleTV with Linux

Scott D. Davilla davilla at 4pi.com
Fri Feb 8 08:05:49 UTC 2008

>Mostly in response to davilla at 4pi's posting re: appletv...
>So, does a straight linux install w/MythFrontend actually net usable
>1080i HD playback? I am willing to forego the Apple software and use
>straight linux.
>Anyone else do this and have some data to share? $229 and some legwork
>sounds great for another HD-capable mythfrontend. Heck, even an
>SD-only front end might be fine for the bedroom to replace my aging

1080i mpeg2 HD content is quite usable, I'm watching LiveTV at 1080i 
right now (testing subtle changes). cpu usage is around 72 percent. 
OSD overlay at 1080i will start glitching the audio. I run 720p with 
software decode. This is current svn as of r15831. MPlayer of the 
same 1080i content is around 55 percent cpu. Mytht was also in the 55 
percent range about six months ago but it been creeping up since the 
ffmpeg sync.

If I manually disable the continuous CC decode (if I'm not viewing 
CC, why spend the cpu cycles), cpu drops to about 65 percent. I've 
studied the code and there is way too much QString parsing and 
comparisons during realtime routines. QStrings are handly but costly. 
String handling and comparisons are slow. OSD key handler is a big 
offender. Once svn settles down again, I will submit a big 
ticket/patch. Right now, I'm busy with solving two issues and new 

There are two issues that I'm tracking. 1) random frontend hang. 2) 
nvidia green macro block corruption. The first you have to kill 
mythfrontend. The second you exit viewing and return and it's fixed. 
Both are random. For example, had an hang this morning about 1.5 
hours after tuning to LiveTV (I leave it on LiveTV for testing). 
However, right now it's been 4 hours straight with no hangs. I've 
seen that before so until it can last two days straight on LiveTV, I 
don't trust it yet.

I've been hammering at this for several months. I also happen to have 
an ITX motherboard with similar chipset but 1.7 GHz pentium-m. When I 
reduce the clock to 1GHz, performance is similar to the AppleTV. The 
one thing is that I've never seen on the ITX based system is a hang 
or have video corruption (but 6800 vs 7300 nvidia chipsets).

One big difference is EFI vs BIOS. Regarding linux this related to 
the console framebuffer and how the initial memory map is defined. 
I've eliminated the memory map difference by crafting a new 
bootloader that can load a traditional linux kernel. The console 
framebuffer still has to be a patched imacfb to get console output 
before X loads. I'm suspicious about the patched imacfb and 
interactions with the nvidia driver and it's something I'm looking at.

The take home message is, right now about 85-95 percent there. If you 
want something to deploy and forget, not quite there.

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