I've been playing around with these values and have discovered the following (I only have SD channels - none HD) when replaying recordings.
Setting engine.buffers.audio_num_buffers to 2300 (10x default) does help with the skips in audio - where under the default value (230) I intermittantly get 2-3 second jumps in audio.
#engine.buffers.video_num_buffers is left at the default of 500. If I set this any higher, fast forwarding or rewinding causes the video to jump about 90 seconds.
engine.buffers.video_num_frames (default 15) I've had to set to 60. Anything less than this seems to make the video jump 2-3 seconds, in line with the audio_num_buffers described above. With this set to 60, there's no lost audio but video/audio still gets out of sync, and it gets worse and worse for 20 seconds then the audio stops and the video catches up. Also with anything <60, I get PPPPPPPP on the vdr console when replaying recordings.
What video card/driver do you use? I know of another guy with similar problems but with my Nvidia 8400GS using vdpau it works fine with just default settings. I've never had to adjust anything.
Card is a NVIDIA GPU GeForce 8400 GS too, but I'm not using the vpdau - as I currently have no HD or H.264 content.
Do you think I should change to vpdau anyway??