[FFmpeg-devel] [PATCH] s302m: Add Channle Layout for 6 channels

[Michael Niedermayer]

On Fri, Apr 06, 2012 at 01:08:33PM +0100, Kieran Kunhya wrote:
> FWIW all of these channel maps are wrong imo. There is no implicit
> channel map in 302M.

after a bit of dicussion on IRC it appears the consensus is that these
set layouts in s302m.c are neither correct nor wrong but may be
convenient to the end user.

I did then research this issue further and found that there is possibly
a optional channel layout stored in the AES3 stream:
(this byte 3 is spread into the channel status bits of AES3 frames
 IIUC)
Note, i have not checked at all what actual streams store in these
bits, so i do not know if this would allow us to set the channel
layout more accurately or not
do we have a volunteer to implement this ?


Byte 3
                   bit           7        Multichannel mode
                                 0        Undefined multichannel mode (default).
                  state          1        Defined multichannel modes.
The definition of the remaining bit states depends on the state of bit 7.
                  bits      0 to 6 Channel number, when byte 3 bit 7 is 0.
                            The channel number is the numeric value of the byte, with bit 0 as the least
                 value
                            significant bit, plus one.
OR,
                  bits       4 5 6        Multichannel mode, when byte 3 bit 7 is 1.
                              0 0 0       Multichannel mode 0. The channel number is defined by bits 0
                                          to 3 of this byte.
                              1 0 0       Multichannel mode 1. The channel number is defined by bits 0
                                          to 3 of this byte.
                 states       0 1 0       Multichannel mode 2. The channel number is defined by bits 0
                 note:                    to 3 of this byte.
                  LSB         1 1 0       Multichannel mode 3. The channel number is defined by bits 0
                  first                   to 3 of this byte.
                              1 1 1       User-defined multichannel mode. The channel number is
                                          defined by bits 0 to 3 of this byte.
                            All other states of bits 4 to 6 are reserved and are not to be used until further
                            defined.
                  bits        0 to 3      Channel number, when byte 3 bit 7 is 1
                            The channel number is the numeric value of these four bits, with bit 0 as the
                 value
                            least significant bit, plus one.
NOTE 1 The defined multichannel modes identify mappings between channel numbers and function. The
standard mappings are under consideration. Some mappings may involve groupings of up to 32 channels by
combining two modes.
NOTE 2 For compatibility with equipment that is only sensitive to the channel status data in one subframe the
channel carried by subframe 2 may indicate the same channel number as channel 1. In that case it is implicit
that the second channel has a number one higher than the channel of subframe 1 except in single channel double
sampling frequency mode.
NOTE 3 When bit 7 is 1 the 4 bit channel number can be mapped to the channel numbering in bits 20 to 23 of
the consumer mode channel status defined in IEC 60958-3. In this case channel A of consumer mode maps to
channel 2, channel B maps to channel 3 and so on.

[...]
-- 
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