Affects the ffmpeg post processors, if ‘--prefer-ffmpeg’ is given and both avconv and ffmpeg are installed, it will use ffmpeg. Otherwise it will follow the old behaviour.
On Windows and other systems, other encodings would break when trying to encode non-ASCII characters. Simply use UTF-8, like every sane system.
In particular, explicitly require NT before trying ADS, and do not try to parse process output that may be localized.