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From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
To: ffmpeg-devel@ffmpeg.org
Cc: Dave Rice <dave@dericed.com>
Subject: Re: [FFmpeg-devel] [PATCH 1/3] avformat/matroska: Support JPEG2000 for demuxing
Date: Mon, 26 May 2025 01:50:42 +0200
Message-ID: <GV1P250MB0737255E8BC47162604C7A248F9AA@GV1P250MB0737.EURP250.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <20250525125342.0000613a@hawaiiantel.net>

compn:
> On Sun, 25 May 2025 05:50:54 +0200, Andreas Rheinhardt wrote:
> 
>> Patches attached.
>>
>> - Andreas
> 
> looks ok but i wonder if anyone is using the vfw ffv1 mkv in the
> archiving universe on purpose. should we include a way to -vfw-codec-id
> manual for those systems? maybe is unimportant but it would be good to
> ask the ffv1 specification crowd about this change to mkv muxing. and
> maybe resend patch separately from jpeg2000 decoding subject. hiding an
> ffv1 change under jpeg2000 subj is weird.

Why should the FFV1 specification crowd object to us writing FFV1 files
in the way they have been intended to be written since February 2017
(since
https://github.com/ietf-wg-cellar/matroska-specification/commit/51a600106bfa66f58a7f2c8e05fab091ab059ebd)?
Anyway, I cc'ed Dave Rice, the author of the aforementioned commit.

> 
> said another another way, this change would change the checksums of
> files if people tried to recreate their mkv. which is something that
> archivists do sometimes.

That's generally what happens when you update your FFmpeg, not only for
the Matroska muxer, but for any component that is under active
development. We don't give guarantees that the output stays the same
when using different git snapshots.
Specifically for Matroska, there have been multiple commits changing the
output of basically every Matroska file created by our muxer (often by
using fewer bytes to write length fields); see e.g. git log
tests/ref/fate/matroska-flac-extradata-update
(Btw: The second patch in this set shows that simply remuxing is
dangerous for FFV1 in VFW-mode.)

- Andreas

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  reply	other threads:[~2025-05-25 23:50 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-05-25  3:50 Andreas Rheinhardt
2025-05-25 22:53 ` compn
2025-05-25 23:50   ` Andreas Rheinhardt [this message]
2025-05-27 14:06     ` Dave Rice
2025-05-27 23:09     ` compn
2025-05-28  0:33       ` Andreas Rheinhardt
2025-05-27 11:50 ` Andreas Rheinhardt

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