Multichannel handling - nu774/qaac GitHub Wiki
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 | supported codec |
| 3ch* | FL FR FC | C L R | LC, ALAC |
| 4ch | FL FR FC BC | C L R Cs | LC, ALAC |
| 4ch * | FL FR BL BR | L R Ls Rs | LC, HE |
| 4ch | FL FR SL SR | L R Ls Rs | LC, HE |
| 5ch * | FL FR FC BL BR | C L R Ls Rs | LC, ALAC |
| 5ch | FL FR FC SL SR | C L R Ls Rs | LC, ALAC |
| 5.1ch * | FL FR FC LF BL BR | C L R Ls Rs LFE | LC, HE, ALAC |
| 5.1ch | FL FR FC LF SL SR | C L R Ls Rs LFE | LC, HE, ALAC |
| 6ch | FL FR FC BL BR BC | C L R Ls Rs Cs | LC |
| 6ch | FL FR FC BC SL SR | C L R Ls Rs Cs | LC |
| 6.1ch * | FL FR FC LF BL BR BC | C L R Ls Rs Cs LFE | LC, ALAC |
| 6.1ch | FL FR FC LF BC SL SR | C L R Ls Rs Cs LFE | LC, ALAC |
| 7ch | FL FR FC BL BR SL SR | C L R Ls Rs Rls Rrs | LC |
| 7.1ch front | FL FR FC LF BL BR FLC FRC | C Lc Rc L R Ls Rs LFE | LC, HE, ALAC |
| 7.1ch front | FL FR FC LF FLC FRC SL SR | C Lc Rc L R Ls Rs LFE | LC, HE, ALAC |
| 7.1ch rear* | FL FR FC LF BL BR SL SR | C L R Ls Rs Rls Rrs LFE | LC, HE |
| 8ch | FL FR FC BL BR BC SL SR | C L R Ls Rs Rls Rrs Cs | LC |
Some notes:
- 3ch AAC is supported since CoreAudioToolbox.dll version 7.9.8.1.
- 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:
- Front Left - FL, L
- Front Right - FR, R
- Front Center - FC, C
- Low Frequency - LF, LFE
- Back Left - BL
- Back Right - BR
- Front Left of Center - FLC, Lc
- Front Right of Center - FRC, Rc
- Back Center - BC
- Side Left - SL
- Side Right - SR
- Left Surround Direct - Lsd
- Right Surround Direct - Rsd
- Left Surround - Ls
- Right Surround - Rs
- Rear Left Surround - Rls
- Rear Right Surround - Rrs
- Center Surround - Cs