[flac-dev] WAVEFORMATEXTENSIBLE_CHANNEL_MASK is not described

[lvqcl]

Martin Leese wrote:

>> It was more obvious that "where defined" means 1-6 channels, and 7 and
>> 8-channel
>> files have undefined channel assignment. Now all possible numbers of
>> channels have
>> defined channel map, so the text should be (IMHO):
>>
>> 0000-0111 : (number of independent channels)-1. The channel order follows
>> SMPTE/ITU-R recommendations. The assignments are as follows:
>
> Note that the channel order may not be defined.

IMHO it doesn't matter in this place of documentation (which describes
default channel assignments for FLAC).




> So the WAVEFORMATEXTENSIBLE channel
> mask is saved ONLY when the channel order
> does not follow SMPTE/ITU-R recommendations.

Not quite true.
I created two stereo (FL+FR) 24-bit wav files (one with WAVEFORMATEX
header, the other with WAVEFORMATEXTENSIBLE header), and encoded them to FLAC.

And FLAC creates WAVEFORMATEXTENSIBLE_CHANNEL_MASK tag for the 2nd file
(tested on FLAC 1.3.1, 1.2.1, 1.1.4).



> Having channel assignments in two different
> places is bad practice.  In the FLAC spec there
> is "1011-1111 : reserved".  Why not specify one
> of the reserved codes to mean "channel
> assignment is specified in the
> WAVEFORMATEXTENSIBLE channel mask; go
> look there".  The problem is how to now specify
> the number of channels.

The channel mask implicitly contains the number of channels;
but such files probably won't be compatible with all existing
decoders. What's better: a sound with incorrect channel assignment
or no sound at all?