Subject: [Cellar] webm webvtt codec ids

From: Dave Rice <[email-masked]>
Date: Mon, 25 Sep 2017 19:49:23 -0400

Hi all,
I’ve found a few matroska files using the "D_WEBVTT/SUBTITLES” codec id. This isn’t defined in the Codec specs and the “D_” prefix isn’t either. I see this in both webm code and in libavformat. Does the “D_” prefix for codec mappings have any meaning worth defining? Do "D_WEBVTT/SUBTITLES” and "S_TEXT/WEBVTT” have the same meaning?
Dave Rice

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From: hubblec4 <[email-masked]>
Date: Tue, 26 Sep 2017 01:56:39 +0200

Hi Dave

> I’ve found a few matroska files using the "D_WEBVTT/SUBTITLES” codec id. This isn’t defined in the Codec specs and the “D_” prefix isn’t either. I see this in both webm code and in libavformat. Doe…

How old are the matroska files? WEBVTT subs have not been so long 
implemented in Matroska.

For the moment I would say this ID's are wrong.

Martin

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From: Hendrik Leppkes <[email-masked]>
Date: Tue, 26 Sep 2017 10:35:37 +0200

> I’ve found a few matroska files using the "D_WEBVTT/SUBTITLES” codec id. This isn’t defined in the Codec specs and the “D_” prefix isn’t either. I see this in both webm code and in libavformat. Doe…

This codec id is from the WebM spec, strictly speaking its only valid
in webm, not in Matroska.
https://www.webmproject.org/docs/container/#webvtt-guidelines

They use D_WEBVTT/<kind> for different content in WebVTT format.

PS:
Re-send to the list.
Can someone please configure this mailing list to properly set
Reply-To headers, so I don't keep messing up replying to the list?

- Hendrik

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From: Moritz Bunkus <[email-masked]>
Date: Tue, 26 Sep 2017 10:49:34 +0200

Hey,

>> I’ve found a few matroska files using the "D_WEBVTT/SUBTITLES” codec
>> id. This isn’t defined in the Codec specs and the “D_” prefix isn’t
>> either. I see this in both webm code and in libavformat. Does the “D_”
>> prefix for codec mappings have any meaning worth defining? Do
>> "D_WEBVTT/SUBTITLES” and "S_TEXT/WEBVTT” have the same meaning?

D_WEBVTT/… are CodecIDs from the WebM mapping for WebVTT[1]. However, back
when I implemented WebVTT for Matroska in March 2016 I noticed that the
WebM mapping was based on an older WebVTT spec and that it did not
represent best Matroska practices. Therefore we decided on a different
mapping in Matroska. See [2] for details.

So no, we should not define it (our official mapping is S_TEXT/WEBVTT), and
it is definitely not the same.

Kind regards,
mosu

[1]  http://wiki.webmproject.org/webm-metadata/temporal-metadata/webvtt-in-webm
[2]  https://lists.matroska.org/pipermail/matroska-devel/2016-March/005012.html

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From: Jerome Martinez <[email-masked]>
Date: Tue, 26 Sep 2017 10:54:29 +0200

> it is definitely not the same.

I suggest that we define D_WEBVTT/* in Matroska spec, as "reserved", + 
"SHOULD NOT use and MAY read it" wording and a link to WebM website, 
because files are there and WebM is a lot used, we need to avoid conflicts.
any luck that WebM moves to Matroska version in the future?