There are many videos on sites such as Youtube that simply contain album art and an audio track. This is easy to do with tools such as openshot or pitivi but it is time consuming. Is there a script or command that can be used to automate this process?
This may be helpful, even though it requires that you have the album art separate from the audio file. and that the audio be in .mp3 format, you could however, look at the command and alter it to suit other input and output formats.
At your terminal in a directory containing the image and audio files you could use ffmpeg like this:
This will take cover_art.jpg and test.mp3 and create a video out.avi with cover_art.jpg as the video and test.mp3 as the audio track of length the duration of the audio track.
ffmpeg may have to be compiled with restricted formats enabled.
A great automation would be to find something that can extract the art from the audio file and use that image with ffmpeg.