Add live transcoding

[erodozer]

After listening to some of my high quality audio, I've realized that streaming them directly might not always be a good option. Sent around 400mb over 2.4hrs, which is not friendly for streaming to a phone at all.

Look into adding transcoding with ffmpeg and sending over a generator. There's an example here that might need some additional tweaks. The biggest drawback is now we'll be serving data from flask instead of nginx, so that might hurt performance a bit.
https://stackoverflow.com/questions/3639604/html5-audio-video-and-live-transcoding-with-ffmpeg