Auto UNDERclock would be more appropriate since it reduces clock speed when the processor is idle.

20 hours? did you try a smaller sample to see if that crashes on that whole script? at least we'd know it's definitely the script. Just Trim(0, 10000) or something. Though if that passes it won't guarantee it's not avs fault on the larger file.

Well, I tried with smaller samples and they all were fine, that's why I needed to render a full episode to see it crush. So... after 20 hours rendering from that lossless encode, it seems that h264 no longer crashes... leading me to think it has something to do with the filtering. What I don't understand is that there are no error while compressing to lossless nor xvid and if I preview the avs script in virtualdub, it does not crash either (using that exact same script posted above). I've found a way around the initial problem so I no longer need assistance. On the other hand, I'd be glad to provide more information to diagnose this issue if it turns out it's a bug in h264 Many thanks for all your suggestions.

To take a small guess x264 does alot more intense calculations than a lossless conversion so it may just be doing too much at once, combined with overclocking could concieveably cause errors.

check the CPU temp while encoding.