Convert AVI to MP4 with ffmpeg

Use this command:

ffmpeg -i input_file.avi -c:v libx264 -preset slow -crf 22 -c:a libfaac -b:a 128k output_file.mp4

How to truncate video using command line

Here are two method, using ffmpeg and mencoder. Choose which one you want:

$ ffmpeg -vcodec copy -acodec copy -i [inputfile] -ss [start] -t [duration] [outputfile]

or

$ mencoder -ss [start] -endpos [duration] -oac copy -ovc copy [inputfile] -o [outputfile]