[FFmpeg-devel] [PATCH] specify a name/description per stream

[Michael Niedermayer]

On Thu, Aug 28, 2008 at 03:34:41AM +0200, Aurelien Jacobs wrote:
> Michael Niedermayer wrote:
> 
> > On Wed, Aug 27, 2008 at 09:04:32PM +0200, Aurelien Jacobs wrote:
> > > Michael Niedermayer wrote:
> > > 
> > > > On Wed, Aug 27, 2008 at 08:04:13PM +0200, Aurelien Jacobs wrote:
> > > > [...]
> > > > > > > [...]
> > > > > > >  
> > > > > > > Index: libavformat/avformat.h
> > > > > > > ===================================================================
> > > > > > > --- libavformat/avformat.h	(revision 14980)
> > > > > > > +++ libavformat/avformat.h	(working copy)
> > > > > > > @@ -409,6 +409,8 @@
> > > > > > >       * - decoding: Set by libavformat.
> > > > > > >       */
> > > > > > >      AVRational sample_aspect_ratio;
> > > > > > > +
> > > > > > > +    char *name;  /**< name/description of the track */
> > > > > > >  } AVStream;
> > > > > > 
> > > > > > Maybe char name[1024] is preferrable, like all other metadata in
> > > > > > AVFormatContext ?
> > > > > 
> > > > > I tried to be consistent with other fields in AVStream, such as
> > > > > filename. If an array is really preferred I can change it.
> > > > > Any other opinion about this.
> > > > 
> > > > a more generic metadata API may be interresting
> > > > Especially with user specified keys instead of "name" "author", ...
> > > > the current system would break down.
> > > 
> > > I agree that a more generic metadata API would be useful.
> > > But you should note that my current patch is not about adding
> > > a new metadata field in AVFormatContext. It's about adding a
> > > specific field in AVStream.
> > > Well, I guess that a generic metadata API could also be used
> > > per stream, but I wonder if this wouldn't be overkill. 
> > 
> > per stream, per chapter, per program, per file, ...
> 
> Well, I see the picture.
> 
> > > I doubt
> > > that any muxer could really fully benefit from it.
> > 
> > nut would have no problem with it :)
> 
> BTW: matroska support some kind off recursive metadata.
> eg:
>      ALBUM: stupid name
>      COMPOSER: Mr. X
>          EMAIL: x at x.com
>          PHONE: 00000
>      LEAD_PERFORMER: Mr. Y
>          EMAIL: y at y.com
>          PHONE: 11111
> 
> So a tag can apply to stream, chapter, etc...
> But a tag can also apply to another tag.
> 
> Would nut support such kind of nested tags ? (yes, sure, nut supports
> everything one can imagine, and even what no one can imagine)

info packets in nut are flat, not nested.
This has the large advantage of being simple

Above example could be handled in various ways, though this hasnt come
up yet on the nut ML thus there is no standard way defined on how to
do it. 

One way would be:

"Composer"      , "Mr. X"
"Composer/EMAIL", "x at x.com"
"Composer/Phone", "00000"


> 
> Is it worth to try to support such kind of nested tags in a
> generic metadata API ?

If its easy then yes


> 
> > > So do you place the generic metadata API as a strong requirement
> > > to export the stream name, or would my patch be an acceptable way
> > > to do it, at least in the mean time ?
> > 
> > generic metadata is not a strong requirement but things slowly become
> > messy without it
> 
> Agree.
> 
> > char [1024] vs char * being one, and iam in favor of char * i think
> 
> I'm also in favor of char *.
> 
> > Or
> > how much metadata is lost when remuxing currently?
> 
> many
> 
> > Or
> > What language is the metadata in
> 
> In matroska, each tag can have its language specified individualy.
> 
> > Besides, iam not sure if i just missed it when reading the thread but
> > what exactly is a name of a stream ? Also iam curious about some
> > examples about what value it would have before approving this ...
> 
> This is a random string describing the stream. Some people use it
> to put the name of the movie in the video track, some use it to
> add a full description of the codec and encoding parameters, some
> use it to add the full name of the language...
> Here are some examples for different kind of tracks:
> 
> == Video ==
> kurenai - 06: The Light is Shining Above You
> 1280x528 @ 23.98 fps 4392 kb/s
> Matrix Reloaded Trailer XviD 1.0 Beta1
> Neon Genesis Evangelion Renewal 01: Angel Attack
> 
> == Audio ==
> 2ch Vorbis
> English EAC3 48000Hz  640 kb/s tot , 3/2: L+C+R+SL+SR
> 5.1 HE-AAC
> HE-AAC 50-70
> 
> == Subtitles ==
> Styled Subtitles
> Czech subtitles
> Portuguese
> 
> So it is nothing more than a full text description of the stream,
> supposed to help people 

seems like "description" is a better description for it than "name"

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

Democracy is the form of government in which you can choose your dictator
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