Re: [Cellar] Last call on FLAC specification

[Martin Leese <[e-mail]>]

On 9/29/22, Martijn van Beurden <[e-mail]> wrote:
> Op do 29 sep. 2022 om 17:42 schreef Martin Leese <
...
>> 2.  Section 9.6.2, Table 7, Page 20.  FLAC files do not
>>     necessarily contain speaker feeds.  Examples of such
>>     files are a collection of audio stems or an Ambisonic
>>     B-Format recording.  Could we therefore please include
>>     a Channel description of SPEAKER_NONE with:
>>     WAVEFORMATEXTENSIBLE_CHANNEL_MASK=0x0
>>
>>     Given the way Table 7 is organised, It is not immediately
>>     clear to me how to include this.
>
> I don't know what the FLAC reference implementation or ffmpeg do in this
> regard, but the channel mask is copied directly from Microsoft's
> WAVEFORMATEXTENSIBLE structure. See here:
> https://learn.microsoft.com/en-us/previous-versions/windows/hardware/design/dn653308(v=vs.85)
>
> It says
>
>> If, for example in a multi-channel audio authoring application,
>> no speaker location is desired on any of the mono streams, the
>> dwChannelMask should explicitly be set to 0. A dwChannelMask of
>> 0 tells the audio device to render the first channel to the
>> first port on the device, the second channel to the second port
>> on the device, and so on. This also means that if the device
>> doesn't know how to process the raw audio streams, it should
>> not accept the multi-channel stream with a dwChannelMask of
>> 0. A device like a digital mixer or a digital audio storage
>> device (hard disk, ADAT, and so on) might want to accept
>> formats without particular speaker locations.
>
> Perhaps this and other comments about the channel mask should be added to
> the FLAC specification, rephrased.

Yes, that would address my concern.

Note also that the Microsoft document you
reference above contains:
#define SPEAKER_RESERVED  0x80000000

In the RF64 spec this is changed to:
#define SPEAKER_ALL               0x80000000

You might also want to consider including this
(in addition to SPEAKER_NONE 0x0).  In
truth, I am not clear what SPEAKER_ALL
actually means.

Regards,
Martin
-- 
Martin J Leese
E-mail: martin.leese  stanfordalumni.org
Web: http://members.tripod.com/martin_leese/