CAF channel layouts

The chan chunk gives each channel a meaning. It is required when a file has more than two channels and their order matters. Without one, a mono file is one channel and a stereo file is left then right.

Fields

Offset	Size	Type	Name	Description
0	4	u32	`mChannelLayoutTag`	the layout, below
4	4	u32	`mChannelBitmap`	used with the bitmap tag
8	4	u32	`mNumberChannelDescriptions`	the number of descriptions that follow
12	20 each	record	`mChannelDescriptions`	used with the descriptions tag

A channel description:

Offset	Size	Type	Name	Description
0	4	u32	`mChannelLabel`	a label
4	4	u32	`mChannelFlags`	how to read the coordinates, below
8	12	f32[3]	`mCoordinates`	the speaker’s position, with label 100

Flag	Constant
0	`kCAFChannelFlags_AllOff`
bit 0	`kCAFChannelFlags_RectangularCoordinates`
bit 1	`kCAFChannelFlags_SphericalCoordinates`
bit 2	`kCAFChannelFlags_Meters`

Layout tags

A tag is a number in its high 16 bits and the channel count in its low 16 bits. In the tables, L is left, R right, C centre, LFE the low-frequency channel, Ls and Rs the surround channels, Cs centre surround, Lc and Rc left and right centre, Rls and Rrs rear surround, and Lt and Rt matrix-encoded left and right.

Number	Channels	Constant (after `kCAFChannelLayoutTag_`)	Order
0	0	`UseChannelDescriptions`	use the descriptions
1	0	`UseChannelBitmap`	use the bitmap
100	1	`Mono`	mono
101	2	`Stereo`	L R
102	2	`StereoHeadphones`	L R, for headphones
103	2	`MatrixStereo`	Lt Rt
104	2	`MidSide`	mid, side
105	2	`XY`	a coincident microphone pair
106	2	`Binaural`	left, right
107	4	`Ambisonic_B_Format`	W X Y Z
108	4	`Quadraphonic`	front L, front R, back L, back R
109	5	`Pentagonal`	L R, rear L, rear R, C
110	6	`Hexagonal`	L R, rear L, rear R, C, rear
111	8	`Octagonal`	front L, front R, rear L, rear R, front C, rear C, side L, side R
112	8	`Cube`	L R, rear L, rear R, top L, top R, top rear L, top rear R
113	3	`MPEG_3_0_A`	L R C
114	3	`MPEG_3_0_B`	C L R
115	4	`MPEG_4_0_A`	L R C Cs
116	4	`MPEG_4_0_B`	C L R Cs
117	5	`MPEG_5_0_A`	L R C Ls Rs
118	5	`MPEG_5_0_B`	L R Ls Rs C
119	5	`MPEG_5_0_C`	L C R Ls Rs
120	5	`MPEG_5_0_D`	C L R Ls Rs
121	6	`MPEG_5_1_A`	L R C LFE Ls Rs
122	6	`MPEG_5_1_B`	L R Ls Rs C LFE
123	6	`MPEG_5_1_C`	L C R Ls Rs LFE
124	6	`MPEG_5_1_D`	C L R Ls Rs LFE
125	7	`MPEG_6_1_A`	L R C LFE Ls Rs Cs
126	8	`MPEG_7_1_A`	L R C LFE Ls Rs Lc Rc
127	8	`MPEG_7_1_B`	C Lc Rc L R Ls Rs LFE
128	8	`MPEG_7_1_C`	L R C LFE Ls Rs Rls Rrs
129	8	`Emagic_Default_7_1`	L R Ls Rs C LFE Lc Rc
130	8	`SMPTE_DTV`	L R C LFE Ls Rs Lt Rt
131	3	`ITU_2_1`	L R Cs
132	4	`ITU_2_2`	L R Ls Rs
133	3	`DVD_4`	L R LFE
134	4	`DVD_5`	L R LFE Cs
135	5	`DVD_6`	L R LFE Ls Rs
136	4	`DVD_10`	L R C LFE
137	5	`DVD_11`	L R C LFE Cs
138	5	`DVD_18`	L R Ls Rs LFE
139	6	`AudioUnit_6_0`	L R Ls Rs C Cs
140	7	`AudioUnit_7_0`	L R Ls Rs C Rls Rrs
141	6	`AAC_6_0`	C L R Ls Rs Cs
142	7	`AAC_6_1`	C L R Ls Rs Cs LFE
143	7	`AAC_7_0`	C L R Ls Rs Rls Rrs
144	8	`AAC_Octagonal`	C L R Ls Rs Rls Rrs Cs
145	16	`TMH_10_2_std`	L R C Vhc Lsd Rsd Ls Rs Vhl Vhr Lw Rw Csd Cs LFE1 LFE2
146	21	`TMH_10_2_full`	TMH_10_2_std, then Lc Rc HI VI Haptic
147	0	`RESERVED_DO_NOT_USE`	reserved

These constants have the same value as the layout on the right:

Constant	Same as
`MPEG_1_0`, `ITU_1_0`, `DVD_0`	`Mono`
`MPEG_2_0`, `ITU_2_0`, `DVD_1`	`Stereo`
`ITU_3_0`, `DVD_7`	`MPEG_3_0_A`
`ITU_3_1`, `DVD_8`, `DVD_13`	`MPEG_4_0_A`
`ITU_3_2`, `DVD_9`, `DVD_14`	`MPEG_5_0_A`
`ITU_3_2_1`, `DVD_12`, `DVD_17`, `AudioUnit_5_1`	`MPEG_5_1_A`
`ITU_3_4_1`, `AudioUnit_7_1`	`MPEG_7_1_C`
`DVD_2`	`ITU_2_1`
`DVD_3`	`ITU_2_2`
`DVD_15`	`DVD_10`
`DVD_16`	`DVD_11`
`DVD_19`, `AudioUnit_5_0`	`MPEG_5_0_B`
`DVD_20`	`MPEG_5_1_B`
`AudioUnit_4`, `AAC_Quadraphonic`	`Quadraphonic`
`AudioUnit_5`	`Pentagonal`
`AudioUnit_6`	`Hexagonal`
`AudioUnit_8`	`Octagonal`
`AudioUnit_6_1`	`MPEG_6_1_A`
`AAC_4_0`	`MPEG_4_0_B`
`AAC_5_0`	`MPEG_5_0_D`
`AAC_5_1`	`MPEG_5_1_D`
`AAC_7_1`	`MPEG_7_1_B`

Channel bitmap

With the bitmap tag, each set bit in mChannelBitmap is one channel, in order from the lowest bit up. The WAV column gives WAV’s name for the same speaker, where Apple’s specification notes one.

Bit	Constant (after `kCAFChannelBit_`)	WAV name
0	`Left`
1	`Right`
2	`Center`
3	`LFEScreen`
4	`LeftSurround`	Back Left
5	`RightSurround`	Back Right
6	`LeftCenter`
7	`RightCenter`
8	`CenterSurround`	Back Center
9	`LeftSurroundDirect`	Side Left
10	`RightSurroundDirect`	Side Right
11	`TopCenterSurround`
12	`VerticalHeightLeft`	Top Front Left
13	`VerticalHeightCenter`	Top Front Center
14	`VerticalHeightRight`	Top Front Right
15	`TopBackLeft`
16	`TopBackCenter`
17	`TopBackRight`

Channel labels

Value	Constant (after `kCAFChannelLabel_`)	Note
`0xFFFFFFFF`	`Unknown`
0	`Unused`
100	`UseCoordinates`	the position is in `mCoordinates`
1	`Left`
2	`Right`
3	`Center`
4	`LFEScreen`
5	`LeftSurround`	WAV: Back Left
6	`RightSurround`	WAV: Back Right
7	`LeftCenter`
8	`RightCenter`
9	`CenterSurround`	WAV: Back Center, or plain Rear Surround
10	`LeftSurroundDirect`	WAV: Side Left
11	`RightSurroundDirect`	WAV: Side Right
12	`TopCenterSurround`
13	`VerticalHeightLeft`	WAV: Top Front Left
14	`VerticalHeightCenter`	WAV: Top Front Center
15	`VerticalHeightRight`	WAV: Top Front Right
16	`TopBackLeft`
17	`TopBackCenter`
18	`TopBackRight`
33	`RearSurroundLeft`
34	`RearSurroundRight`
35	`LeftWide`
36	`RightWide`
37	`LFE2`
38	`LeftTotal`	matrix encoded
39	`RightTotal`	matrix encoded
40	`HearingImpaired`
41	`Narration`
42	`Mono`
43	`DialogCentricMix`
44	`CenterSurroundDirect`	back centre, not diffuse
200	`Ambisonic_W`
201	`Ambisonic_X`
202	`Ambisonic_Y`
203	`Ambisonic_Z`
204	`MS_Mid`
205	`MS_Side`
206	`XY_X`
207	`XY_Y`
301	`HeadphonesLeft`
302	`HeadphonesRight`
304	`ClickTrack`
305	`ForeignLanguage`

.CAF File Format – Channel layout

Fields

Layout tags

Channel bitmap

Channel labels