1

I have a directory tracks with 3 files track1.mp3, track2.mp3, track3.mp3. I want to select a random chunk of 10 seconds from each file and combine these chunks into a new file called sample.mp3. How do I do this using ffmpeg?

I am pretty new to ffmpeg and all I managed to do so far is splitting a file into chunks

ffmpeg -i track1.mp3 -f segment -segment_time 10 -c copy out%03d.mp3

Someone, please help. I am on Mac OSX high sierra and bash shell

Tony Vincent
  • 113

1 Answers1

3

You can use the following bash script:

numFiles=3
maxStart=10
idx=1
for randomStart in $(jot -r $numFiles 0 $maxStart); do
    ffmpeg -y -ss "$randomStart" -i "track${idx}.mp3" -t 10 -c:a copy "track${idx}-chunk.mp3"
    idx=$((idx + 1))
done

Here, you have to specify the number of files (track1 through track3) and the maximum start position (e.g., if your files are only 20 seconds long, you should at most start from 00:00:10).

The jot utility is used to create random numbers between 0 and $maxStart (i.e., 10 in the above example). On Linux, jot is not available; instead use shuf -n $numFiles -i 0-$maxStart.

Then, concatenate the chunks (see the FFmpeg Wiki entry):

ffmpeg -f concat -safe 0 -i <(for f in ./*-chunk.mp3; do echo "file '$PWD/$f'"; done) -c copy output.mp3

It uses special shell syntax to construct a temporary concatenation file. This will copy the bitstreams, so no re-encoding is done.

slhck
  • 235,242