Creating transparent Movies for Keynote with ffmpeg

I wanted to integrate a transparent video into my master thesis presentation. Unfortunately Keynote requires special encoding to support transparency in video.

Encode the video #

Videos have to be encoded with qtrle. For a folder containing numbered xx.png files we can create the video in the following way:

ffmpeg -framerate 2 -i %02d.png -vcodec qtrle movie.mov

Generating transparent Images #

With imagemagick it is also possible to replace the background of white images to a transparent background:

mogrify -transparent white *.png

This will replace the white color in all images ending with .png with the alpha value 0. Imagemagick will also take a fuzz value -fuzz 2%. For more details see this stackoverflow post.

Note that convert will take a single file where as mogrify will apply these changes to multiple images.