Using ffmpeg for cutting media files

As simple as:

ffmpeg -ss start-time -t duration -i file-in file-out

Usually start-time/stop-time are given so duration have to be computed. Nothing difficult but the following bash script calculates duration for us:

#!/bin/bash
# cnt_sec function converts string `hh:mm:ss' to seconds, both
# `hh' and `mm' are optional
function cnt_sec () {
  echo $1 | awk -F":" '{ if (NF>2) { sec += 60*60 * $(NF-2) } ;
        if (NF>1) { sec += 60 * $(NF-1) } ;
        if (NF>0) { sec += $NF } ; 
        print sec }'
}

STRT_TIME=`cnt_sec $1`
STOP_TIME=`cnt_sec $2`

DURATION=$((STOP_TIME-STRT_TIME))
echo $DURATION
# cut from file $3 from $1 to $2 write to $4
# both $1 and $2 are time durations in `hh:mm:ss' format
ffmpeg  -ss $1 -t $DURATION -i $3 $4