In Debian / Ubuntu, use avconv.

avconv -i input.mp4 -b 64k -s hd720 -strict experimental output.mp4

This command uses avconv, where..

-i input.mp4 = the input file name
-b 64k = down sample the audio channel to 64k – should be fine.
-s hd720 = reduce the video from hd1020 to the 720 format
-strict experimental = Allows mp4 output
output.mp4 = the output file.

If you haven’t got avconv installed, use

sudo apt-get install avconv

and follow instructions.