Re: [codec] draft-ietf-codec-oggopus and "album" gain

Ralph Giles <giles@thaumas.net> Mon, 25 August 2014 23:12 UTC

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Date: Mon, 25 Aug 2014 16:11:21 -0700
From: Ralph Giles <giles@thaumas.net>
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Subject: Re: [codec] draft-ietf-codec-oggopus and "album" gain
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On 2014-08-15 9:01 PM, Ron wrote:

> So the patch applied for this part is now:
> 
>> - If an encoder wishes to use R128 normalization, and the output gain is not
>> - otherwise constrained or specified, the encoder SHOULD write the R128 gain
>> - into the 'output gain' field and store a tag containing "R128_TRACK_GAIN=0".
>> - That is, it should assume that by default tools will respect the 'output gain'
>> - field, and not the comment tag.

I agree this part is confusing. I think it's too terse to offer good
guidance.

>>   If a tool modifies the ID header's 'output gain' field, it MUST also update or
>>   remove the R128_TRACK_GAIN and R128_ALBUM_GAIN comment tags if present.

This seems helpful in avoiding broken files.

>> + An encoder should assume that by default tools will respect the 'output gain'
>> + field, and not the comment tag.

I read this as a non-normative should. Would it be better:

"By default, implementations of this specification MUST respect the
'output gain' field, but MAY NOT respect the comments. Encoder authors
are advised to take this into account. For example, to produce R128
normalized files it's more reliable for post-processing application to
update the 'output gain' field and write a comment 'R128_TRACK_GAIN=0'
than to put the normalized value directly in the comment."

This removes the normative suggestion of 'should' while maintaining the
suggestion and rationale.

 -r