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

[Thierry Foucu]

On Fri, Apr 6, 2012 at 7:45 AM, Michael Niedermayer <michaelni at gmx.at>wrote:

> 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.
>
>
We did check some files containing S302M and we could not find out the
channel layout using the C bit.

Does any one have a valid file, which will contain such information? I will
be ok to write such parser if we found it is valid.


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