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Re: [Cellar] On the multiplicity of Info elements

Dave Rice <dave@dericed.com> Fri, 15 January 2016 06:47 UTC

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From: Dave Rice <dave@dericed.com>
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To: Moritz Bunkus <moritz@bunkus.org>
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Cc: cellar@ietf.org
Subject: Re: [Cellar] On the multiplicity of Info elements
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> On Jan 12, 2016, at 8:36 AM, Moritz Bunkus <moritz@bunkus.org> wrote:
> 
> Hey,
> 
>> From a sample set of 59,881 Matroska files uploaded to archive.org
>> only 119 of them include CRC-32 Elements. Almost 0.2%! Additionally
>> the webm Document Type lists the CRC-32 Element as unsupported. So I
>> think it’s true that it’s rarely bothered with. The implementation of
>> CRC-32 Elements does add many complications and perhaps demand has
>> been too low to resolve them. Moritz may have comments here.
> 
> That's pretty much spot on. The CRC32 element was added comparatively
> late; a lot of muxers had already been created by that time.
> 
> Most requests I've received where more concerned with error recovery
> than with error detection. This is something that CRC32 wasn't meant
> for; additionally CRC32 elements weren't meant to be written in the
> cluster elements which make up the bulk of a Matroska file's data.

There are certainly Matroska files that use CRC-32 within Clusters.

See: http://archive.org/download/WC14UruVsCost/FIFA.World.Cup.2014.Uruguay.Vs.Costa.Rica.SDTV-WDTeam_1st.mkv
Muxing App Haali DirectShow Matroska Muxer 1.13.138.14
Writing App gdsmux

Or http://archive.org/download/aawqws/Covert.Affairs.S01E05.mkv
Muxing App libebml-0.7.5 & libmatroska-0.7.7
Writing App VirtualDubMod 1.5.10.2 (build 2540/release)

Or http://archive.org/download/archive_actu1_Lara/Lara.S01.E24.mkv
Muxing App libebml v0.7.8 + libmatroska v0.8.1
Writing App Cyberlink Matroska Muxer v1.0.0

That last example uses CRC-32 Elements only within the Cluster Element and not elsewhere.

> Yes, there is a feature request[1] for adding support in mkvmerge and
> mkvinfo. It has been created in 2010, but except for those two people
> mentioned in the bug I haven't really received any other requests for
> such a functionality.
> 
> Kind regards,
> mosu
> 
> [1] https://github.com/mbunkus/mkvtoolnix/issues/543
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