RFC: Video file upload to HLS and MP3

[brandonhundt]

See the scope doc improve video support

Workflow:

• User uploads a video file in Feeder
• There's a call to Porter to create HLS and MP3 derivatives from the video file using ffmpeg
• Files start on Feeder > Dovetail CDN

RFC should:

• Figure out how to make multiple derivatives out of a single call to Porter
• Here’s my video, here’s my transcript, can we line them up?
• (I am sure there is more! We can discuss!)