Make previews for a folder of .mov or .mp4 files that MacOS can open. Normalizes to 480x270 at 30fps and 96kbps audio.

make-video-previews.sh

#!/bin/bash

# Make previews for a folder of .mov or .mp4 files that MacOS can open.
# Normalizes to 480x270 at 30fps and 96kbps audio.

current_file=none

# Catch ctrl-c and stop the whole batch, otherwise ctrl-c just stops ffmpeg and the loop continues
trap ctrl_c INT
function ctrl_c() {
  echo "** aborting $current_file"
  if [ -e "$current_file.preview.mp4" ]
  then
    # Delete the current file since ffmpeg will have left it there after being interrupted
    rm "$current_file.preview.mp4"
  fi
  exit
}

for filename in `ls *.{MOV,MP4,mov,mp4}`
do
  # Check if the preview file already exists
  if [ -e "$filename.preview.mp4" ]
  then
    echo "$filename.preview.mp4 already exists"
  else
    # Don't convert .preview.mp4 files
    if [[ $filename != *.preview.mp4 ]]
    then
      current_file=$filename
      
      # ffmpeg flags
      # -c:v libx264 -- encode using h264
      # -b:a 96k     -- set audio to 96kbps
      # -s 480x270   -- scale video to 480x270 (1/4 of 1920x1080)
      # -r 30        -- set frame rate to 30fps
      # -movflags faststart  -- move the index to the beginning of the file
      # -pix_fmt yuv420p -- this is needed for the resulting video to be understood by some apps like Quicktime and Quick Look

      ffmpeg -i $filename -c:v libx264 -b:a 96k -s 480x270 -r 30 -movflags faststart -pix_fmt yuv420p $filename.preview.mp4
    fi
  fi
done