The parameter missedFrames should, before encoding is started,
contain an array of the frame number of every frame that is
missing from the image file inFile.
It is necessary for the Sampler to have access to a SaveFileChooser,
because the Sampler needs to use the getNextFile() method both in
init() and in finished().
It is necessary for the ScreenGrabber to have access to a SaveFileChooser,
because the ScreenGrabber needs to use the getNextFile() method both in
init() and in finished().