[Matroska-devel] Tagging MKV files

Dan Hinsley danhi at cox.net
Sat Sep 15 17:17:20 CEST 2012

Let me add my support to having Secondary SeekHeads.  What I'm writing an
app to add/update tags/chapters/cover art.  What I don't want to have to do
is rewrite the entire (probably gigabyte plus) file just to do so.  It's
going to be common that the new SeekHead will not fit in the space provided
by the existing SeekHead, and relying on finding a Void that I can use, then
rewriting everything between the original SeekHead and the Void, is just not
reasonable.  Having a Secondary SeekHead removes the need to do this.

But I'm totally OK with only allowing one.  But I think all players should
support at least one.


-----Original Message-----
From: matroska-devel-bounces at lists.matroska.org
[mailto:matroska-devel-bounces at lists.matroska.org] On Behalf Of Steve Lhomme
Sent: Saturday, September 15, 2012 7:27 AM
To: Discussion about the current and future development of Matroska
Subject: Re: [Matroska-devel] Tagging MKV files

On Sat, Sep 1, 2012 at 10:36 PM, Moritz Bunkus <moritz at bunkus.org> wrote:
> Hey,
> On Sat, Sep 1, 2012 at 10:25 PM, Dan Hinsley <danhi at cox.net> wrote:
>> Now this file still plays, but when I run mkvalidator it tells me:
> Completely ignore mkvalidator in this case. It is buggy, doesn't take
> several situations into account that are perfectly valid (when you
> look at the Matroska specs at
> http://www.matroska.org/technical/specs/index.html then you'll see
> that SeekHeads are marked as "multiple", meaning it's more than valid
> to have more than one SeekHead inside a segment) etc etc. This
> situation is one of those that it doesn't account for. The first
> "warning" means that it doesn't parse the secondary seek head. All the
> other warnings are subsequent faults, of course, because those
> elements ARE referenced.
> Also: those things are WARNINGS. I've long argued with Steve Lhomme,
> author of mkvalidator, that even printing a warning for such issues is
> often mistaken by users to mean that a file is not valid. That is NOT
> the case! A warning issued by mkvalidator solely means that the file
> is not 100% over-the-top optimized. E.g. for playback situations in
> which no seeking is possible (in such cases the secondary seek head
> would not be parsable by a player). However, guess how often such a
> situation occurs nowadays... Again: ignore them.

I agree the wording "Unnecessary" in the warning is not good. Now I
never liked the idea of a secondary SeekHead in the first place. It is
marked in the spec as multiple to be repeated, not linked further. It
is not written anywhere that linked SeekHeads are OK. It's tolarated
for the case mentioned above. But in the end since it's not in the
specs, players are not required to handle it and may fail on it.

In practice it's probably rare noawdays to find a SeekHead without a
Void element around, so it can be rewritten in place to add a few
Level 1 links.

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