Audio format conversion using Ffmpeg swresample.

EDIT3: Audio format conversion.  FFmpeg libswresample (or libavresample as a temporary workaround) is required.
I'm personally not very happy with the way ffmpeg's use is split between two files (which is partly my own fault). I think it would be better designed if the ffmpeg decoder for both audio and video was put into its own source or component, and the video player and sound decoder interfaces with that (opencs might want a sound decoder too, for previewing audio stuff).