Script to concatenate a directory of mp4 files into one

ffmpeg-concat.zsh

#!/bin/zsh

# requires ffmpeg: https://ffmpeg.org/download.html

# clear the file list
echo "" > ./output.txt

# recursively find all mp4 files in the current directory and subdirectories
# (will preserve alphabetical order by full path)
for entry in ./**/*.mp4
do
  # ...and write them to a source file in the format ffmpeg expects
  echo "file '$entry'" >> ./output.txt
done

# this simpler approach yielded a "Could not find tag for codec pcm_alaw" error locally...
#ffmpeg -f concat -safe 0 -i output.txt -c copy output.mp4
# ...so I'm forcing the audio output to AAC:
ffmpeg -f concat -safe 0 -i output.txt -c:v copy -c:a aac output.mp4