This has been an annoyance for sometime, when encoding anything with mencoder, but specifically ts files from recorded TV. Mencoder would start off fine and then freeze the PC completely or Seg Fault, not necessarily in the same place. Other PCs I have would encode fine using the same settings.
I found the solution today on the mplayerusers email list. About 18 months ago I had overclocked my machine, up from 1.7 to 1.9 mhz and increased the FSB. Apparently mencoder doesn’t like overclocked PCs, even though the writer with the solution said it wasn’t mencoder’s fault! So I put my settings back to “Optimal” / “Auto”, and everything is now rosy in the garden, just a tad slower than before I can live with that!