[FFmpeg-devel] [PATCH] avformat/mov: export xml metadata

[wm4]

On Wed, 1 Feb 2017 13:31:46 +0100
Robert Krüger <krueger at lesspain.software> wrote:

> On Wed, Feb 1, 2017 at 1:07 PM, wm4 <nfxjfg at googlemail.com> wrote:
> 
> > On Wed,  1 Feb 2017 12:50:51 +0100
> > Paul B Mahol <onemda at gmail.com> wrote:
> >  
> > > Signed-off-by: Paul B Mahol <onemda at gmail.com>
> > > ---
> > >  libavformat/mov.c | 25 +++++++++++++++++++++++++
> > >  1 file changed, 25 insertions(+)
> > >
> > > diff --git a/libavformat/mov.c b/libavformat/mov.c
> > > index 9ae4f8c..75e1c9c60 100644
> > > --- a/libavformat/mov.c
> > > +++ b/libavformat/mov.c
> > > @@ -3764,6 +3764,25 @@ static int mov_read_keys(MOVContext *c,  
> > AVIOContext *pb, MOVAtom atom)  
> > >      return 0;
> > >  }
> > >
> > > +static int mov_read_xml(MOVContext *c, AVIOContext *pb, MOVAtom atom)
> > > +{
> > > +    uint8_t *xml;
> > > +
> > > +    if (atom.size < 5)
> > > +        return 0;
> > > +
> > > +    avio_skip(pb, 4);
> > > +    xml = av_calloc(atom.size - 4 + 1, sizeof(uint8_t));
> > > +    if (!xml)
> > > +        return AVERROR(ENOMEM);
> > > +
> > > +    avio_read(pb, xml, atom.size - 4);
> > > +    av_dict_set(&c->fc->metadata, "xml", xml, 0);
> > > +    av_free(xml);
> > > +
> > > +    return 0;
> > > +}
> > > +
> > >  static int mov_read_custom(MOVContext *c, AVIOContext *pb, MOVAtom atom)
> > >  {
> > >      int64_t end = avio_tell(pb) + atom.size;
> > > @@ -5280,6 +5299,12 @@ static int mov_read_default(MOVContext *c,  
> > AVIOContext *pb, MOVAtom atom)  
> > >              parse = mov_read_keys;
> > >          }
> > >
> > > +        if (!parse &&
> > > +            atom.type == MKTAG('m','e','t','a') &&
> > > +            a.type == MKTAG('x','m','l',' ')) {
> > > +            parse = mov_read_xml;
> > > +        }
> > > +
> > >          if (!parse) { /* skip leaf atoms data */
> > >              avio_skip(pb, a.size);
> > >          } else {  
> >
> > We had this discussion recently: the metadata AVDictionary should
> > probably only contain real tags, not other information that's contained
> > in the format but for which libavformat has no good way to export yet.
> >
> > There needs to be a concept for distinguishing user-visible tags and
> > other data.
> >
> > (You don't want to show a xml dump in a GUI that happens to use ffmpeg,
> > do you?)
> >
> >  
> I thought that was already the case for XMP (i.e. xml) metadata embedded in
> mov. I must look up how that was handled. I seem to remember there was a
> flag to suppress this on the command line. With the policy you propose,
> libavformat will be of a lot less use for api users. Not that I had a vote
> here. It's just 2c of an api user.

I'm not voting for removing it, just that there should be a separate
mechanism for this.

And I as API user are very bothered by irrelevant crap being dumped
in what should return user tags (that can be displayed to a user), or
the fact that these can even show up in remuxes.

Example: just what is the use of "crap" like MAJOR_BRAND or
COMPATIBLE_BRANDS in Matroska tags? Yeah, let's add some
meaningless XML garbage to produced files as well.