Multichannel handling

In addition to mono/stereo, following channel layouts are supported for AAC and ALAC with slight variations. When channel layout is unknown, one of the layouts indicated by asterisk is assumed as default.

#	input layout	output layout
3ch*	FL FR FC	C L R
4ch	FL FR FC BC	C L R Cs
4ch	FC FLC FRC BC	C L R Cs
4ch *	FL FR BL BR	L R Ls Rs
4ch	FL FR SL SR	L R Ls Rs
5ch *	FL FR FC BL BR	C L R Ls Rs
5ch	FL FR FC SL SR	C L R Ls Rs
5.1ch *	FL FR FC LF BL BR	C L R Ls Rs LFE
5.1ch	FL FR FC LF SL SR	C L R Ls Rs LFE
6ch	FL FR FC BL BR BC	C L R Ls Rs Cs
6ch	FL FR FC BC SL SR	C L R Ls Rs Cs
6.1ch *	FL FR FC LF BL BR BC	C L R Ls Rs Cs LFE
6.1ch	FL FR FC LF BC SL SR	C L R Ls Rs Cs LFE
7ch	FL FR FC BL BR SL SR	C L R Ls Rs Rls Rrs
7.1ch front	FL FR FC LF BL BR FLC FRC	C Lc Rc L R Ls Rs LFE
7.1ch front	FL FR FC LF FLC FRC SL SR	C Lc Rc L R Ls Rs LFE
7.1ch rear*	FL FR FC LF BL BR SL SR	C Lc Rc L R Ls Rs LFE
8ch	FL FR FC BL BR BC SL SR	C L R Ls Rs Rls Rrs Cs

Some notes:

• 3ch AAC is supported since CoreAudioToolbox.dll version 7.9.8.1.
• 4ch(C L R Cs), 5ch, 6ch, 6.1ch, 7ch, 8ch are not supported by HE encoder. In other words, only 4ch(quad), 5.1ch, 7.1ch are supported.
• ALAC supports 3ch, 4ch(C L R Cs), 5ch, 5.1ch, 6.1ch, 7.1ch.
• AAC's standard 7.1ch layout is 7.1ch front (front 5ch + surround 2ch + LFE). 7.1ch rear (front 3ch + surround 2ch + rear surround 2ch + LFE) is not supported by Apple's encoder. However, since the latter is rather common, we accept it and map to 7.1ch front in the following way:
  FL, FR -> Lc, Rc
  SL, SR -> L, R
  BL, BR -> Ls, Rs
• Many more channel layout such as 1.1ch are supported as input, but they are not available for AAC/ALAC encoding. WAV output is OK. Maximum channel number is 8.
• Difference in input channel order is accepted as long as channel layout is the same. For example, "C L R" (used by ALAC) is not present in the table above as an input, but it differs from "FL FR FC" only in channel order, hence available. In Microsoft WAV format, channel order is always fixed for the same layout. AIFF and CAF allows many order variations. qaac automatically normalizes channel order to Microsoft order before processing, and finally reorder to AAC/ALAC order before encoding.
• When channel layout is not declared in the input file, you can force layout by --chanmask option. If channels are not ordered in the Microsoft WAV order, you will also need --chanmap option.
• QuickTime (and Adobe Audition) maps SL/SR to Lsd/Rsd, BL/BR to Ls/Rs. However, Ls/Rs and Rls/Rrs are more preferably used by Dolby (and QuickTime), and in their mapping Rls/Rrs have no corresponding in WAV. qaac tries to take care of these mapping issue.

Meaning of abbreviation:

1. Front Left - FL, L
2. Front Right - FR, R
3. Front Center - FC, C
4. Low Frequency - LF, LFE
5. Back Left - BL
6. Back Right - BR
7. Front Left of Center - FLC, Lc
8. Front Right of Center - FRC, Rc
9. Back Center - BC
10. Side Left - SL
11. Side Right - SR
12. Left Surround Direct - Lsd
13. Right Surround Direct - Rsd
14. Left Surround - Ls
15. Right Surround - Rs
16. Rear Left Surround - Rls
17. Rear Right Surround - Rrs
18. Center Surround - Cs