thanks for the quick reply
I considered upgrading (a fresh install, actually) the server to run ubuntu 11.04 or newer, but you don't think it will have any impact? I will try upgrading mythbackend to 0.24.1 again to see if I can make any progress
Here is the new log from xbmc (with extra info enabled, sorry I thought I already had this option on the first time)
http://static.6amsoftware.com/misc/xbmc.log (I hope you don't mind that it's not on pastebin - but it wouldn't let me post anything over 500kb, and I wanted to include any information from the time xbmc started up, in case it's useful)
The capture cards I have on the server are 2 Hauppauge HD-PVRs, which both work properly with 0.23.1, but while I've been trying to get live tv to work with 0.24.0 I have disabled one of them (it's currently turned off), so right now there is only the 1 HD-PVR enabled, which is getting video through the component input and audio through SPDIF (although I have also tried using the analog input, but no change)
The exact version of MythBackend that I'm running right now is: 0.24.0+fixes.20120110.294968b-0ubuntu2 (on a 64-bit machine)
I tried googling for a solution (before I posted here, of course!) but only came up with very few posts about it, but a couple of posts (about the 0 byte file being created) seemed to think it was related to compiling mythtv against a kernel after 2.6.32-38, apparently something to do with the ivtv driver being removed from the kernel, but that doesn't seem like it should be an issue because the kernel my server is running right now is: 2.6.32-30-generic
I've also tried completely deleting the mythconverg database and starting over, since mythbackend was upgraded from 0.23.1 to 0.24.0 I thought there might be some weirdness there, but even with a new database the result was the same.
Thanks for having a look into this and let me know if there's any more info that might be helpful!