Alain Kelder is a Giant Dork

Script to calculate clip duration from start/stop times for trimming with mencoder or ffmpeg

To trim a video clip, mencoder and ffmpeg expect a start time in hh:mm:ss, but instead of end time, want duration:

$ mencoder -ss 00:02:55 -endpos 00:07:15 -oac copy -ovc copy in.avi -o out.avi
$ ffmpeg -ss 00:02:55 -t 00:07:15 -vcodec copy -acodec copy -i in.avi out.avi 

Video players make it easy to identify start/stop times, but difficult to figure out duration, so I wrote a little shell script that will calculate duration from start/stop times.

Update 2011-06-02: for those lazy like me, here's a script that calculates duration and trims the video. Gosh, could I make it any easier for ya? (Hint: the answer is "no").

Update 2014-06-17: here's an improved version of this script that fixes the limitations of this script, adds some functionality, and generally easier on the eye thanks to my improved scripting skills. 🙂

Usage example:

$ calc-duration 00:02:55 00:10:10
 
 Start: 00 hrs 02 min 55 sec
 Stop:  00 hrs 10 min 10 sec

 +----------------------+
 | duration is 00:07:15 |
 +----------------------+

Script:

#!/bin/bash
#============================================================#
# Calculates duration between start time and stop time
# USAGE: calc-duration 00:02:00 00:10:10
# Fix:
# 1. Currently expects start hour to be less than stop hour,
# so won't work for a clip that's longer than 24 hrs, not an
# issue for me as I don't have any of those... 😉
#============================================================#
starthh=$(echo $1 | awk -F: '{print$1}')
startmm=$(echo $1 | awk -F: '{print$2}')
startss=$(echo $1 | awk -F: '{print$3}')

stophh=$(echo $2 | awk -F: '{print$1}')
stopmm=$(echo $2 | awk -F: '{print$2}')
stopss=$(echo $2 | awk -F: '{print$3}')

echo
echo " Start:" $starthh hrs $startmm min $startss sec
echo " Stop: " $stophh hrs $stopmm min $stopss sec
echo

if   [[ $((10#$startmm)) -gt $((10#$stopmm)) && $((10#$startss)) -gt $((10#$stopss)) ]]; then
        # echo start mm and ss are greater than stop
	# start mm is greater than stop mm, so we add 60 to stop mm and
	# substract 1 from stop hh
	newstopmm1=$((10#$stopmm+10#60))
	newstophh=$((10#$stophh-10#1))
	# start ss is greater than stop ss, so we add 60 to stop ss and
        # substract 1 from stop mm
        newstopss=$((10#$stopss+10#60))
        newstopmm=$((10#$newstopmm1-10#1))
        # calculate differences
	diffhh=$((10#$newstophh-10#$starthh))
	diffmm=$((10#$newstopmm-10#$startmm))
	diffss=$((10#$newstopss-10#$startss))

elif [[ $((10#$startmm)) -gt $((10#$stopmm)) ]]; then
        # echo startmm is greater than stopmm
	# start mm is greater than stop mm, so we add 60 to stop mm and
        # substract 1 from stop hh
        newstopmm=$((10#$stopmm+10#60))
        newstophh=$((10#$stophh-10#1))
	# calculate differences
        diffhh=$((10#$newstophh-10#$starthh))
        diffmm=$((10#$newstopmm-10#$startmm))
        diffss=$((10#$stopss-10#$startss))

elif [[ $((10#$startss)) -gt $((10#$stopss)) ]]; then
        # echo startss is greater than stopss
        # start ss is greater than stop ss, so we add 60 to stop ss and
        # substract 1 from stop mm
        newstopss=$((10#$stopss+10#60))
        newstopmm=$((10#$stopmm-10#1))
        # calculate differences
        diffhh=$((10#$stophh-10#$starthh))
        diffmm=$((10#$newstopmm-10#$startmm))
        diffss=$((10#$newstopss-10#$startss))
else
	# echo all stop values are greater than start values
        # calculate differences
        diffhh=$((10#$stophh-10#$starthh))
        diffmm=$((10#$stopmm-10#$startmm))
        diffss=$((10#$stopss-10#$startss))
fi

# pad single digit results with a zero (if + signs contain a single digit, add a zero, then remove + signs)
pdiffhh=$(echo +$diffhh+ | sed 's/+\([0-9]\{1\}\)+/+0\1+/g;s/+//g')
pdiffmm=$(echo +$diffmm+ | sed 's/+\([0-9]\{1\}\)+/+0\1+/g;s/+//g')
pdiffss=$(echo +$diffss+ | sed 's/+\([0-9]\{1\}\)+/+0\1+/g;s/+//g')

echo " +----------------------+"
echo " | duration is" $pdiffhh:$pdiffmm:$pdiffss "|"
echo " +----------------------+"
echo