Source of FFmpeg/Swscale

- What is lib Swscale used for by ffmpeg programers?
--  http://stackoverflow.com/questions/3367187/what-is-lib-swscale-used-for-by-ffmpeg-programers
 - Swscale is mainly used for players, not encoding/decoding
 - at a different pixel size/aspect ratio,  colorspace conversion between various RGB and YUV color formats
 - no faster software implementation presently exists for any of them, at least on x86 and x86_64