I'm trying to concatenate multiple .avi files to run through mjpegtools (yes, I know lav2yuv supports multiple files, but not this many). I found on the internet that you can do cat *.avi > tmp.avi mencoder -forceidx -oac copy -ovc copy -o tmp2.avi tmp.avi However,when I run lav2yuv on these files, I get the following error: Not a JPEG file: starts with 0x1f 0x07 ++ WARN: [lav2yuv] Decoding of Frame 0 failed Does anyone know why? Thanks, Jon