Re: [Cellar] ATRAC1 codec ID for Matroska

Sir68k <sir68k@gmail.com> Wed, 05 October 2022 06:58 UTC

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From: Sir68k <sir68k@gmail.com>
Date: Wed, 05 Oct 2022 08:58:00 +0200
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To: Jerome Martinez <jerome@mediaarea.net>
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Subject: Re: [Cellar] ATRAC1 codec ID for Matroska
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Kieran: Thank you!

Nick, you could take a look at
https://github.com/cybercase/netmd-js/blob/ada9272a6f670ff7813b4405fd8444809c5ceb67/src/utils.ts#L339,
it might be a good pointer regarding the header.

Moritz: Thanks for confirming that the scheme makes sense!

Jerome: Sony didn't make versioning easy, and introduced a lot of
complicated terminologies.

The original ATRAC codec, which we generally call ATRAC1, had several
revisions in terms of encoding and decoding silicon. What this means is
that if you have a device that supports ATRAC 3.5, they actually mean that
it records audio in ATRAC1, but with encoder v3.5, and playback with
decoder v3.5. You can play a MiniDisc recorded with a newer ATRAC1 version
on older devices, and typically you might even get better audio output as
well. Format-wise, nothing changes, it's just better bit allocation during
encoding and more accurate decoding.

Then Sony introduced ATRAC3, which is a different codec, but of course,
people confuse it with ATRAC1 encoder/decoder version 3.

>From the perspective of the container, there is no need at all to know
which version of ATRAC1 was used to encode the data.

We will send a PR as soon as possible!

Kind regards,
Sir68k


On Wed, Oct 5, 2022 at 8:32 AM Jerome Martinez <jerome@mediaarea.net> wrote:

> On 05/10/2022 00:07, Moritz Bunkus wrote:
>
> A_ATRAC/<something> has the advantage of being extensible with multiple
> versions.
>
>
> Skimming https://en.wikipedia.org/wiki/ATRAC I read:
> "ATRAC3 (not to be confused with version 3 of original ATRAC)"
>
> So it needs to be clear what "<something>" refers to.
>
> We already have for incompatible formats with same kind of name the
> version without a slash e.g. "V_MPEG1" and "V_MPEG2", so maybe V_ATRAC or
> V_ATRAC1 makes more sense here, with a number after the slash being the
> version of ATRAC1 if needed (incompatibility between versions of ATRAC1?)
>
> Sir68k, a PR on
> https://github.com/ietf-wg-cellar/matroska-specification/blob/master/codec_specs.md
> with implementation details would be great!
>
> Jérôme
>