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Multichannel handling

nu774 edited this page · 17 revisions

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:

  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
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