[FFmpeg-devel] [PATCH] Export mkv doctype via the metadata API

Michael Niedermayer michaelni
Wed Jul 28 15:18:24 CEST 2010


On Wed, Jul 28, 2010 at 08:41:57AM +0200, Anton Khirnov wrote:
> On Wed, Jul 28, 2010 at 07:51:24AM +0200, Reimar D?ffinger wrote:
> > On Wed, Jul 28, 2010 at 12:31:05AM -0400, Alex Converse wrote:
> > > We do something similar for mp4/mov.
> > > 
> > > If people think this is stupid then I won't put up much of a fuss.
> > 
> > I don't know. On the one hand it is useful, but it is stupid because
> > other formats will write it in their metadata.
> > Actually even the matroska muxer (if it supports/supported arbitrary metadata)
> > would write "doctype" literally into the new file when remuxing, which
> > does seem like not quite the intended behaviour...
> Same applies to some other tags we already export, e.g. "encoder", mp4
> brand stuff, etc. It seems we need a flag to mark these tags as
> nontransferrable.

There is metadata that describes a video bitstream like its encoder (ex: x264)
There is metadata that describes the video content like it being recorded
with cammera xyz
There is metadata that describes the content of timespans of all streams,
namely chapters with their title and whatever else
There is metadata that describes all streams content like movie title and
director
There is metadata that describes the binary data of the muxed file,
if you call that metadata

When what is described is being copied then it is correct to copy the
description too. Otherwise its not correct to copy. The problem just
starts when data about content and bitstream encodings is mixed by
sloppy or stuborn people.
The current metadata API is intended for content descriptions where
AVOption based structs take bitstream descriptions. Iam working on
extending AVOptions so they can easily be used to access fields in
the private context of codecs and (de)muxers.
AVOptions also come with default values and descriptions which can be
usefull for muxers and encoders for these fields. And allow available
fields to be listed and so on which the metadata api does not allow.
OTOH content descriptions have nothing to do th the format in which
they are being stored, a movie has a title no matter if its in avi
or mkv, some containers might not support storing it or require a
specific format like for data and time but its information that semantically
has nothing to do with the container. While things like doctype are
describing the container and belong to the context that describes
the container during demuxing

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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