I have noticed that in mason.sim.util.media.MovieEncoder.java:302-303:

        // i think my hacking begins here (dan)
        // get formats with current framerate, which should not matter
        Format format =
(Format)(ImageToBuffer.createBuffer(i,frameRate).getFormat());
        source = new MovieEncoderDataSource(format, frameRate);

The format that is passed by the constructor is not being used here, thus
causing errors when not passing the same format as the one that is
automatically selected here. So, in contrary to the comment, I do believe
that the format given here does matter. I have attached a patch with the
proposed change.

Thanks,
Jose Trigueros