This commit adds in supporting if a cover path is null. If this is the
case, we completely remove the video stream from the file, as the user
either:
a) uploaded a file with no video stream (so removing it is a no-op)
b) removed the cover in ABS, so we should respect that on merge
Added support for chapter metadata in #678, but completely missed that
coverart wasn't getting embedded in the embed metadata tool. This commit
adds that in
This commit resolves issue #676. The embed metadata tool was missing the
flag that tells ffmpeg to not only update the "top" metadata, but also
the chapter metadata.
