[mythtv-users] Can't Do HD ATSC Playback

Robert Current robert.current at gmail.com
Wed Apr 25 03:43:18 UTC 2007


My system completely falls over when I try to do HD ATSC playback.

Just got an antenna today, and started using my air2pc card for the
first time (in addition to my PVR-150).  Now I've learned that my
system can't handle "real" HDTV.  I was surprised, because it will
play what I thought were HD recordings, but not recordings of my
own...

Here is what I've managed to figure out, and why I think it might be a
video card issue:

I can record ATSC HDTV with the air2pc card, and record MPEG-2 encoded
standard definition shows from cable TV on the PVR-150, and play back
one of the standard definition shows, while doing 1-2 commercial flag
or transcode jobs, all at the same time without problem.

PBS broadcasts an ATSC "SD" channel, I watched it, and it seemed fine.
 I tried recording that to for testing.  File size was big, but it
managed to play that back fine.  It even plays that back while
recording two shows at once and doing a transcode job.

But, I can't watch live ATSC HDTV, I get pauses and jumps at about 1
per second.  The same thing happens when I try to watch a ATSC HDTV
recording.

When watching ATSC HDTV recordings, I ran top in an ssh session, and I
saw that the mythtvfrontend was using 75% to 90% of the CPU.  It only
uses about 25% for SD shows.  So, I started to feel confident it was
PLAYING the recording, not the encoding or recording of the file.

So, I ran a transcode on one of the ATSC HDTV recordings, hoping to
make it smaller, quicker to display, hoping I could watch that.
Unfortunately, the and the file size didn't reduce much, and I still
got the pause/skip thing happening.

Since my transcode experiment didn't help much, I just started
watching the same 5 seconds of a ATSC HDTV show over and over and
over.  I was trying to see if the skips were always in the same spots,
indicating a problem with the recorded file.  But, I'm fairly
confident the skips were not always the same, telling me the recording
was fine, but I couldn't play it back on my system.

Does this seem like a reasonable conclusion?  Does it sound like only
a playback issue, and not related to any other step?

And IF that seems to be the issue, what do I need to upgrade to watch ATSC HDTV?

I'm guessing the CPU, drive speeds, and RAM aren't the bottleneck,
because it can do so much I/O in the background if I'm not trying to
display the image... so I'm thinking video card only maybe?

My system is a Compaq Presario SR1500NX 2GHz Desktop, with AMD
SempronT processor 3000+ 2.0GHz processor, upgraded to 1GB RAM, 80GB
hard drive for /myth (recordings only) and 40G / (everything else),
DVD/CD-RW combo drive, 9-in-1 flash card reader, blah, blah, blah...
The video seems weak, I'm using the "Video Graphics Integrated
graphics with 64MB of shared video memory."

As near as I can tell, it's an ASUS A7V8X-LA motherboard, so it uses
"Via Unichrome KM400 graphics" but I'm not sure what that means.  It
does have one One AGP 8x/4x (1.5V) slot that I'm not using.  I'm
hoping I can just stick a card in there and move on?

Does this sound right?  If so, I'd like to get something that has DVI
out, and S-Video out, and is really inexpensive.  I don't really care
about noise, a fan is ok, this system makes a bit of noise anyway.
Any recommendations?

Thanks in advance,
Rob C.


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