use ffmpeg binary instead of ffmpeg.js

[gr2m]

We have a proof-of-concept working using ffmpeg.js, but our memory usage jumpeg from ~70mb to ~700mb and it’s very slow. We now got the ffmpeg binary on our bluemix server, so we can use that directly.

For reference, converting webm to ogg is as simple as ffmpeg -i speech.webm funk.ogg.

On Mac, the ffmpeg we need can be installed using brew: brew install ffmpeg --with-opus

[gr2m]

see also #38

[gr2m]

closed via 39