You can use the stream name alias package to work around the problem of not being able to put prefix with “:” That is one of the examples in the included Readme.html
Prepends mp4: and mp3: to files with common H.264/MP3 extensions
*.mp4=mp4:${Stream.Name}
*.mov=mp4:${Stream.Name}
*.m4v=mp4:${Stream.Name}
*.m4a=mp4:${Stream.Name}
*.f4v=mp4:${Stream.Name}
*.3gp=mp4:${Stream.Name}
*.3g2=mp4:${Stream.Name}
*.mp3=mp3:${Stream.Name}
*=${Stream.Name}
Richard