Use FFmpeg to generate a movie with alpha channel

Question

I have two movies: input_v.mp4 and input_k.mp4. input_v is the video fill, input_k is a black and white matte for keying.

I want to use FFmpeg to create output.mov in the Avid DNXHD codec, with input_v as the fill (RGB) video and the alpha (A) built from the luma values of input_k.

Is this possible?

Answer 1

If your looking for a movie format showing as a matte effect in Avid then this might work:

ffmpeg -i input_v.mp4 -i input_k.mp4 -filter_complex "[0:v][1:v]alphamerge" -shortest -c:v qtrle -an output.mov

As mulvya suggests Prores also supports an alpha channel.