Match Core Audio channel layouts for FLAC

[sbooth]

The channel layouts for FLAC 4.0, 5.0, and 5.1 are possibly incorrect.

4 channels

ffmpeg uses the quad layout.

CoreAudio uses kAudioChannelLayoutTag_WAVE_4_0_B (L R Rls Rrs). This is the current behavior.

It might be more correct to use kAudioChannelLayoutTag_Quadraphonic (L R Ls Rs -- 90 degree speaker separation).

5 channels (5.0)

CoreAudio uses kAudioChannelLayoutTag_WAVE_5_0_A (L R C Ls Rs).

This differs from the current behavior which is kAudioChannelLayoutTag_WAVE_5_0_B (L R C Rls Rrs).

6 channels (5.1)

CoreAudio uses kAudioChannelLayoutTag_WAVE_5_1_A (L R C LFE Ls Rs).

This differs from the current behavior which is kAudioChannelLayoutTag_WAVE_5_1_B (L R C LFE Rls Rrs).

The Core Audio channel definitions are:

// Ls - left surround
// Rs - right surround
// Rls - rear left surround
// Rrs - rear right surround