[Flac] Spatial/Atmos on FLAC?

[Renatas Laužadis]

Hm,

"Atmos presumably has it's own lossy compression” – maybe. But what about Atmos in TrueHD or Atmos in LPCM?

Spatial audio:
https://developer.microsoft.com/en-us/windows/mixed-reality/spatial_sound
https://developer.microsoft.com/en-us/windows/mixed-reality/spatial_sound_in_directx

There is a set of HRTF functions - head-relative transfer functions
There are basically 3 major formats DTS:X, Atmos and Auro 3D.

One of the major obstacles for VR/AR headsets is the sound and proper positioning of sound. IMHO, this is one of the reasons why Microsoft is bringing Dolby Atmos to Windows platform. And this is one of the reasons Microsoft has implemented Windows Sonic at the same time. There are no popular mechanisms to position objects based audio in some kind unified way. Windows Sonic is now one such technology.

While Windows Sonic rendering exists there is now format for this kind of files, except Atmos and DTS:X. Sony does their own implementation.

So I thought maybe FLAC or Xiph.org has some plans for that...

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From: Brian Willoughby<mailto:brianw at audiobanshee.com>
Sent: 2017 m. rugpjūčio 12 d., šeštadienis 12:45
To: flac at xiph.org<mailto:flac at xiph.org>
Subject: Re: [Flac] Spatial/Atmos on FLAC?

On Aug 10, 2017, at 5:46 AM, Renatas Lau?adis <renatas at outlook.com> wrote:
> are there any plans for FLAC to implement spatial audio? Or maybe Atmos on FLAC?

FLAC is a multichannel audio format supporting up to 8 channels. There are advantages to compressing 2 channel (stereo) audio in terms of file size savings, but there is no compression advantage to other combinations.

Atmos supports up to 128 channels, 10-channel minimum, so it cannot be directly stored in FLAC due to the 8-channel limit. In addition, Atmos presumably has it's own lossy compression, so it would be pointless to use a lossless conversion for a lossy surround file. Atmos is also proprietary, or at least I assume we do not have the option of supporting it anyway.

I do not see any documentation of Spatial - is that a standard format? Is it an open format? Is it even intended to be distributed as a separate digital file?

In any event, archival and delivery for mastering of surround audio is generally done in individual mono files. Some surround projects are delivered on 8-channel digital audio tape with only 6 channels used in the case of 5.1 surround audio. Beyond 5.1, there must be various methods of delivering audio. There might be some advantage with FLAC to combine pairs in surround, such as front, side, rear, but otherwise I would say that it's a bad idea to try and place more than 2 channels in a single file. The audio frames become too large to compress well.

There's a difference between formats used for recording, mixing, and mastering versus formats used for delivery of the final product to consumers. Delivery formats like Dolby and DTS generally require licensed software compression tools, making it difficult to convert to FLAC in any case.

Perhaps you could explain more about what you hope to see?

Brian Willoughby

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