[Bug 752850] matroskademux: Does not send user-supplied metadata tags from streamable files

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=752850

--- Comment #11 from Glen Diener <grd at loganmill.net> ---
Question: what, and where, is the matroska spec? I have primarily used this
src:

    http://matroska.org/technical/specs/index.html

However, the above states:

"  This document is not the real format specification. It's a simple draft to
work. (For a simplified diagram of the layout of a Matroska file, see the
Diagram page.) But since it's quite complete it is used as a reference for the
development of libmatroska. An alternate version of the specification can be
found here (PDF doc maintained by Alexander Noé -- may be outdated)."

The content of the link to the alternate specification mentioned in this quote
(http://matroska.org/files/matroska.pdf, titled  "Matroska File Format (under
construction!)" is,as noted out of date, i.e.. There, in a footnote, it refers
to the "official documentation"...but this link in turns points back to the
previously mentioned doc.  Is this is the closest to an "official spec" that we
can have, or is there another source out there somewhere?

FYIW, my reading of the doc suggests that there is not, in fact, any prescribed
order in which elements need to occur, but there are "recommended" orders:

"While in EBML there is no particular order for elements, in Matroska it is
necessary to make sure some elements are placed in a certain order for better
playback, seeking and editing efficiency".  For the placement of tags, the doc
suggests that they be placed either early or at the end of the stream,
depending on the use case.

gstreamer's matroska mux places the tags before the segment track, if run with
streamable=true, and it places the tags after the segment track element (in
fact, at the very end of the file, after all the Clusters and Cues) if run with
streamable=false.  From my reading of the docs, both are valid, so in either
case, I think that matroskamux is generating a valid stream.

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