You can create videos out of audio files.
Supported video from audio formats are: mp4, WebM and ogv.
This basically creates a video by combining the waveform and audio of our file and is useful if you want to play audio within a video player and wish to monetize audio files through video ads.
To create an mp4 video out of our original sample Railgun wav audio, format the URL as in:
Video from audio by changing .wav to .mp4