Download ffmpegXbinaries here:
ffmpegXbinaries20060307.zip
Copy mencoder to /usr/local/bin
Terminal:
cat 1.avi 2.avi 3.avi > tmp.avi
mencoder -forceidx -oac copy -ovc copy tmp.avi -o output.avi
Source: SuperUser
Download ffmpegXbinaries here:
ffmpegXbinaries20060307.zip
Copy mencoder to /usr/local/bin
Terminal:
cat 1.avi 2.avi 3.avi > tmp.avi
mencoder -forceidx -oac copy -ovc copy tmp.avi -o output.avi
Source: SuperUser