My antiquated old Pentium PC can't play some of the modern video file formats like H264 because the processor is too slow. In the past I've tried to convert those to Xvid with various programs but without much success. I recently came across a free universal video format converter which does everything perfectly.
45 minute program, framerate can stay as original and mp3 audio at 128 bitrate and 44100 sample rate will do nicely. Press convert and off it goes. Perfectly synced sound and video, no codecs to load, everything's built in. I've run 30 or more files through it and they all came out perfect. There's a professional version you can pay for but god knows what else you'd need it to do. The free one rocks.
Just thought I'd pass it on.