forAudioChannelMask
s = MediaString::forAudioChannelMask(format.u.raw_audio.channel_mask);
s = MediaString::forAudioChannelMask(format.u.raw_audio.channel_mask);
s << (empty ? "" : " ") << "(" << forAudioChannelMask(format.channel_mask) << ")";
static BString forAudioChannelMask(