[mythtv-users] Terrible LiveTV performance

[Paul Jara]

I used to be able to watch live TV with MythTV without much issue. I've 
got a P4 2.2 with 512MB RAM, and MPEG-4 480x480 live TV was quite 
smooth. However, for the best part of 4 months, I've been using MythTV 
solely to record shows and have been watching these recordings later. 
I've been upgrading MythTV in this time period. This past week I just 
got into using the live TV functionality again, and the performance is 
just terrible on my machine. There are a couple of issues. I've been 
using the RPMs but 3 times I've compiled from source and the problems 
still remain. Interestingly enough, they are often worse when compiling 
from source.

1) Slow-motion video after changing channels. When switching to live 
TV, the first channel is quite viewable and performance is great - the 
video is fluid with no dropped frames. Changing channels though causes 
the audio to drop out, and the video to continue in slow-motion. The 
only workaround is to exit out of live TV and restart it, at which 
point the cycle continues with the initial channel working as expected 
and subsequent channels not working properly.

2) Jerky video after changing channels. I've cleaned out and 
re-installed MythTV about half a dozen times. More often than not, this 
issue is the consistent one with issue 1) happening consistently with 
only 2 of those installs (1 being an RPM install and the other a build 
from source). Watching live TV is quite viewable with the initial 
channel, but changing the channel immediately results in a consistent 
dropping of frames. Consequently, the video appears jerky and the audio 
periodically pops. I can workaround this issue by pausing the video, 
building up a 5 second buffer, and resuming watching, at which point 
the video is as smooth as that produced by the initial channel.

I'm using RH9 with the latest kernel. I've got the ALSA drivers 
installed for my SBLive! Value. ALSA support is not compiled into the 
RPMs, but when building from source, I have compiled it in and as I 
said, the problems are actually worse (similar behaviour, but they are 
more exaggerated). Not sure if this is because of the ALSA support or 
some other variables in the build process that vary from the RPMs. I'm 
using an Nvidia GeForce 3 and have tried the two latest binary releases 
and the XFree86 open source drivers without resolving this issue. This 
problem happens when using MPEG-4 and RTjpeg as the live TV codec. 
Ditto with using uncompressed audio and MP3 audio. I've tried with 
Jitter reduction on/off, experimental AV sync on/off, aggressive 
soundcard buffering on/off, and the commercial skipping and flagging 
features on/off. None resolve the problem.

I'm sure lots has changed since April, but at one time I was able to 
watch live TV and it was great. I'm not sure where along the lines the 
problems started but I've also built a recent CVS version and the 
problems remain.

-Paul