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

[Robert Krüger]

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.