I'm new to wikis, but I'd like to share my experience with this issue. My frontend hardware:
Shuttle barebones system: AthlonXP 3000+ Barton core 1 GB DDR400? RAM geforce 4200 ti (128mb agp 8x) onboard sound nforce2 (Realtek) Mythbuntu 8.0 1280x1024@60 on 17inch LCD monitor
Using "High Quality" as a starting point, approximately every second in HD playback I would receive prebuffering messages. Normal playback was fine. Using Xvmc aggravated this problem, causing many prebuffering pauses to occur per second. This problem did not occur at all when playing back content that was not broadcast in HD. This problem was specific to this frontend on the network.
Things that had little to no effect: -fully enabling real time priority threads -sound buffering (or sound settings in general) -standard (ffmpeg) vs ligmpeg2 (since it is an amd system) -enabling always stream from backend
What ended up solving my problem: -increasing FSB from 100 to 133 -even better FSB from 133 to 166 -system unstable at FSB 200
I'd like to note that this is the 2nd frontend that I've set up on my network, the first frontend has significantly faster specs so I did not see this issue at all once the proprietary nvidia drivers were enabled.
Why was HVR-1600 section removed?
I'm using Mythbuntu 9.04 with an HVR-1600, and was suffering from regular prebuffering pause errors when viewing live tv. It turns out that Mythbuntu 9.04 is still shipping with version 1.0.1 of the cx18 driver, but the installation guide for the HVR 1600 on this wiki claims that version 1.0.1 is sufficient and this page no longer has a section on the HVR-1600. Only after much head-banging did I find the clue in the history of this page that version 1.0.4 of the driver fixes the error for that particular hardware. I was then able to follow the instructions for manually installing the cx18 drivers, which upgraded me to version 1.2.0 and fixed the problem.
I'd suggest either replacing the HVR-1600 section here with a recommendation of updating the cx18 driver and/or updating the HVR-1600 installation guide to recommend manual install if the driver version is less than 1.0.4.
Cpufrequtils cause prebuffering errors
I've got a MythTV installation with a dedicated backend and 1 frontend currently since 1 year. Playback of SD material (mpeg 2) worked fine, now I started to record HD as well. During playback I experience sound drop outs and sometimes a stuttering video as well. I turned out that this was caused by using the "Ondemand" governor of the cpufrequtils. Until now I activated it by default at startup, but obviously this caused interruptions in the audio and video stream although the CPU load wasn't significant during playback (below 40% with VDPAU normal, Audio upmixing "Best"). After loading the "performance" governor everything worked fine.
Configuration of my frontend: Asus M3N78-EM Athlon X2 5050e Mythbuntu 10.04 with MythTV 0.23 with VDPAU 46" LCD-TV connected over HDMI 1.3, sound over HDMI