Audio files are often accompanied by image files in the same directory containing cover art and such. Unfortunately, FFmpeg considers these to be video files and as a result ffmpegfs would try to convert these to the destination type, even if that destination type is an audio format.
These changes make it so that there must at least be some overlap in types of media between the two formats to be considered convertible, preventing this situation without being overly restrictive.
Audio files are often accompanied by image files in the same directory containing cover art and such. Unfortunately, FFmpeg considers these to be video files and as a result ffmpegfs would try to convert these to the destination type, even if that destination type is an audio format. These changes make it so that there must at least be some overlap in types of media between the two formats to be considered convertible, preventing this situation without being overly restrictive.