How to make video with fixed duration

Question

I have videos:

video1 - 923 seconds

video2 - 1457 seconds

video3 - 860 seconds

I need to cut these videos and fix its duration - 600 seconds. But the difficulty is that I need to cut them under the scheme

Where :

1. blue segments is always 120 seconds (fixed);

2. red segments I should to cut;

3. green segments I shouldn't cut.

After that I need to join blue and green segments in new 600 seconds video, example

As the video1, video2, video3 have a different duration, then the red and green segments must have different duration, they must be in equal proportion to the duration of the video.

I need pure ffmpeg (avconv) command or bash script. I have no ideas how to make it.

Answer 1

probably the simples way to do this is to create an edit decision list (EDL), that you can then use to write your final video. i don't know of ffmpeg/avconv, but mplayer/mencoder will handle those quite will, see the docs.

to create the EDL, use a function like:

make_edl() {
 DUR=$1
 PRE=$2
 SLICES=$3
 POST=$4
 ## get the duration of the cut-up pieces
 SNIPPET=$(((DUR-PRE-POST)/SLICES))
 START=$PRE
 STOP=$((DUR-POST))

 curr=$START

 while [ $curr -lt $STOP ]; do
   currstop=$((cur+SNIPPET))
   if [ $currstop -gt $STOP ]; then
     currstop=$STOP
   fi
   echo "${curr} $((curr+SNIPPET)) 0"
   curr=$((curr+2*SNIPPET))
 done
}

# ...

## the following create an EDL for a 923sec movie,
## where we have 120sec of intro, than 31 alternating slices
## and 120sec of outro
make_edl 923 120 31 120 > myedl.txt

## apply the EDL
mencoder -edl myedl.txt input923.mov -o output923.mov

due to the limitations of bash arithmetic (integer only), this not be very precies