S/PDIF muxer

by Bartłomiej Wołowiec for FFmpeg

S/PDIF is mostly used to transmit compressed multichannel audio from a media player to an amplifier/receiver. It can be used with many compression format as defined by IEC 61937 (AC3, DTS, MPEG audio, PCM, AAC and WMApro). My goal is to write S/PDIF support for FFmpeg. It will make it possible to send multichannel audio to sound system in digital quality.