This pull request is: an enhancement and a bug fix.
It's an enhancement because now tracks that report a "Piano" type contributor from the API will reflect that in the PERFORMER metadata tag. Also, tracks with the "Engineer" type contributor from the API will reflect that in the ENGINEER metadata tag.
It's a bug fix because the process of ensuring that tracks have audio stream first, video stream second (attached album cover) has been changed to copy the data to a temporary file first, and then use FFmpeg to order the streams in the desired final output file.
This pull request is: an enhancement and a bug fix.