Converting Video On The Command Line
I recently acquired an iPad for work purposes… so the most important thing to know is how to convert video to play on it. Use handbrake, done – short blog post.
But, that would be all too simple. Often I want to watch an entire season of a show that I have collected from various sources over the years and these often have widely varying sound levels. That is quite annoying if you set the season to play and then have to adjust the volume for every episode.
Here is a simple guide to convert your videos into a format suitable for the iPad with equalized volumes. I somewhat deliberately used a variety of tools for illustration purposes, but I think the one I selected tended to be the quickest for each step. The following code snippets assume that your videos have extension “.avi”. They also destroy source files, so make a backup.
Step 1. Extract the audio track using mplayer:
for i in *.avi; do
mplayer -dumpaudio "$i" -dumpfile "${i//avi}mp3"
done
Step 2. Make sure all audio is mp3 and convert using ffmpeg if not:
for i in *.mp3; do
if ! file "$i" | grep -q "layer III"; then
mv "$i" "$i.orig"
ffmpeg -i "$i.orig" "$i"
rm "$i.orig"
fi
done
Step 3. Normalize the audio levels using mp3gain:
mp3gain -r *.mp3
Step 4. Stick the adjusted audio back into the video file using mencoder (part of mplayer):
for i in *.avi; do
mv "$i" "$i.orig"
mencoder -audiofile "${i//avi}mp3" "$i.orig" -o "$i" -ovc copy -oac copy
rm "$i.orig" "${i//avi}mp3"
done
Step 5. Convert to iPad format using the command line version of handbrake:
for i in *.avi; do
HandBrakeCLI -i "$i" -o "${i//avi/m4v}" --preset="iPad"
rm "$i"
done
This is probably not the most efficient way of doing this and will become less so once handbrake can normalize volume levels by itself (which appears to be being somewhat worked on by its developers…). But when you have several seasons of a show, each with more than 50 episodes (only a few minutes each), you quickly become glad to be able to make a simple script to do the conversion automatically.
