Feature request: combining audio and video

**Is your feature request related to a problem? Please describe.**
I'm always frustrated when I need to combine audio and video together

**Describe the solution you'd like**
add a function to combine an audio track and a video together Example: ffmpeg.convert("audio.mp3", "video.mp4", "newname.mp4", "mediaTag")

**Describe alternatives you've considered**
I have consided a server that would do it but I dont want to wait for that and hope for a js lib to do this.

**Additional context**
none that is it.