[FFmpeg-devel] Missing documentation of metadata keys

Michael Niedermayer michaelni
Wed Oct 21 13:46:04 CEST 2009

On Wed, Oct 21, 2009 at 12:27:43AM +0200, Stefano Sabatini wrote:
> On date Tuesday 2009-10-20 16:16:52 -0200, Ramiro Polla encoded:
> > Hi,
> > 
> > On Tue, Oct 20, 2009 at 3:30 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
> > > On Tue, Oct 20, 2009 at 1:10 PM, Bjoern Voigt <bjoern at cs.tu-berlin.de> wrote:
> > >> If I scanned the source code right, metadata keys are static. If they are
> > >> indeed more dynamic (dependent on compile options, libraries etc.), a more
> > >> dynamic approach (like a "-list-metadata-keys" option for ffmpeg) would
> > >> probably be a better idea.
> > >
> > > Regardless of static or not, this would be a good idea, IMHO.
> > > Introspection is a great thing.
> +1.
> > Attached patch should be a good starting point to list the conversion
> > tags from ffmpeg (and document its use in the manuals).
> Duplicating information and synching docs with the code is always
> brittle and leads to inaccurate / outdated documentation, I think is
> better to provide some mechanism to make the user ask the requested
> information directly to the program, either make the documentation
> generated by the code.

I think that something is overlooked here, metadata is just some key+value
string pairs and most containers can happily store arbitrary things there.
What you(plural) try to document here is not what can be stored because
anything can, but rather what are the standard tags.
In that respect iam not sure if this is that usefull. For example if i
have a video for which i know which lens was used to film it. then i
need to know what key to use and in what format i should provide the
value of the tag. But the question if my target format has a standarized
tag for such lens is less important, i would want to store the information
anyway (it does no harm and might be usefull to a human looking at the tags)

ffmpeg does the convertion from ffmpegs standard tag to the format specific
anyway so theres no need to know all standard tags for all formats. That
said we of course will need a way for people to bypass that convertion
and get their tags stored unchanged as they are. The discussion related
to ffmpeg filling in timetamp values have shown that some people want
things more raw ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you think the mosad wants you dead since a long time then you are either
wrong or dead since a long time.
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