I'm having playback issues on a combined frontend/backend myth system. I've been using MythTV for about three years now with no playback issues. I've upgraded hardware several times, most recently replacing a single WD20EARS with an SSD for the system and a WD20EARX for videos. Now I get errors like this during video playback or while watching live TV:
Code:
Sep 29 21:40:22 mythtv mythfrontend[8385]: I Decoder ringbuffer.cpp:1086 (WaitForAvail) RingBuf(/second_drive/recordings/3130_20120103210000.mpg): Waited 2.0 seconds for data #012#011#011#011to become available... 0 < 32768
Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 3719ms for video buffers AAAAAAAAAAALff
Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 3823ms for video buffers AAAAAAAAAAALff
Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 3926ms for video buffers AAAAAAAAAAALff
Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 4029ms for video buffers AAAAAAAAAAALff
If a recording is being made while watching a different recording or live TV the problem is exacerbated.

Ubuntu 12.04.1 LTS (GNU/Linux 3.2.0-31-generic-pae i686)
MythTV Version : v0.25.2-15-g46cab93
MythTV Branch : fixes/0.25
Playback is set to VDPAU slim
Combined frontend/backend on
Intel i5-2400S
ASUS ENGT520 SL/DI/2GD3
Crucial CT64M4SSD2
Western Digital WD20EARX
I searched for related issues and found several threads, most nearly a year old, regarding various issues like playback from a NAS, using multiple frontends, etc. But none of the cases I've found represent my situation.

What might cause these issues?