Re: [codec] OggOpus: Rational for excluding replaygain tags?

Ralph Giles <giles@thaumas.net> Wed, 07 November 2012 17:22 UTC

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Date: Wed, 07 Nov 2012 09:22:02 -0800
From: Ralph Giles <giles@thaumas.net>
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Subject: Re: [codec] OggOpus: Rational for excluding replaygain tags?
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On 12-11-07 9:03 AM, Calvin Walton wrote:

> I would suggest that instead of simply saying that the OggOpus file
> SHOULD NOT contain the replaygain tags, it should say that they MAY be
> present, and should specify how they are interpreted and applied (This
> mainly would concern their relation to the stream "output gain").

I think the idea was to encourage adoption of the R128 methods along
with Opus, since R128 is both technically superiour and more officially
standardized. I agree it would be useful to describe what to do if
multiple tags are present, even if it remains SHOULD NOT.

I would say, "The R128 tag overrides any REPLAYGAIN tag which is
present. Player MAY choose to apply REPLAYGAIN values, combined with the
output gain from the OpusHead packet, if no R128 tag is present."

> I would however recommend that the files still SHOULD NOT have the
> REPLAYGAIN_{TRACK,ALBUM}_PEAK tags, as Opus does not have a bit-accurate
> decoder specified, and the peak values will also vary based on the
> sample rate selected for decoding.

That's a useful distinction to maintain. I agree.

The other issue is what encoders are doing. Are any of the applications
you tested *setting* REPLAYGAIN tags on files they encode? Or is it just
that you want some level equalization and your player doesn't currently
support the R128 scheme during playback? The question is whether we have
some hope of acheiving compliance with the idea as opposed, or if it's
too late for that already.

 -r