[FFmpeg-devel] [PATCH] av_metadata_count()

[Michael Niedermayer]

On Sun, Feb 01, 2009 at 06:36:44PM +0100, Aurelien Jacobs wrote:
> On Sun, 1 Feb 2009 02:06:21 +0100
> Michael Niedermayer <michaelni at gmx.at> wrote:
> 
> > On Sun, Feb 01, 2009 at 02:00:12AM +0100, Aurelien Jacobs wrote:
> > > On Fri, 30 Jan 2009 17:33:02 +0100
> > > Michael Niedermayer <michaelni at gmx.at> wrote:
> > > 
> > > > On Fri, Jan 30, 2009 at 01:43:34AM +0100, Aurelien Jacobs wrote:
> > > > > Hi,
> > > > > 
> > > > > Attached patch adds a new metadata API func to get the number of
> > > > > available tags among a list of keys. This func will be useful
> > > > > at least for the following muxers: asf, mov, mp3.
> > > > > It can also be quite handy for a user application.
> > > > 
> > > > i cant see this to be that usefull, please first show the code
> > > > that would benefit from this.
> > > 
> > > OK. As an example, here is a snipet from movenc:
> > >     // only save meta tag if required
> > >     if (s->title[0] || s->author[0] || s->album[0] || s->year ||
> > >         s->comment[0] || s->genre[0] || s->track) {
> > > It could be replaced by something very ugly:
> > >     // only save meta tag if required
> > >     if (av_metadata_get(s->metadata, "title"  , NULL, 0) ||
> > >         av_metadata_get(s->metadata, "author" , NULL, 0) ||
> > >         av_metadata_get(s->metadata, "album"  , NULL, 0) ||
> > >         av_metadata_get(s->metadata, "year"   , NULL, 0) ||
> > >         av_metadata_get(s->metadata, "comment", NULL, 0) ||
> > >         av_metadata_get(s->metadata, "genre"  , NULL, 0) ||
> > >         av_metadata_get(s->metadata, "track"  , NULL, 0)) {
> > > Or by something simpler like:
> > >     static const char const *mov_tags[] = {
> > >         "title", "author", "album", "year", "copyright", "comment",
> > >         "genre", "track", NULL
> > >     };
> > >     // only save meta tag if required
> > >     if (av_metadata_count(s->metadata, mov_tags, 0)) {
> > > 
> > > We have something similar in the mp3 muxer, except that it currently
> > > only check the presence of title to deceide whether it should mux
> > > metadata or not (this is wrong and it should really check for the
> > > presence of any supported tag).
> > > Attached is a patch to use new metadata API in mp3 (de)muxer, which
> > > make use of av_metadata_count(). (I have not yet finalized patch
> > > for the mov muxer, but it will use something similar, twice)
> > 
> > url_open_dyn_buf(&bc)
> > write title
> > write author
> > ...
> > 
> > if bc is not empty write it out
> 
> That's not as simple as "bc is not empty", because some data is written
> in the metadata header anyway, so bc won't ever be empty. But still,
> it's possible to do something like this by counting the number of tag
> which are actually written in the buffer.
> 
> So attached is a new patch to upgrade the mp3 (de)muxer to the new
> metadata API without using av_metadata_count().
> 
> Aurel

> Index: libavformat/mp3.c
> ===================================================================
> --- libavformat/mp3.c	(revision 16909)
> +++ libavformat/mp3.c	(working copy)
> @@ -167,18 +167,15 @@
>      return v;
>  }
>  
> -static void id3v2_read_ttag(AVFormatContext *s, int taglen, char *dst, int dstlen)
> +static void id3v2_read_ttag(AVFormatContext *s, int taglen, const char *key)
>  {
> -    char *q;
> -    int len;
> +    char *q, dst[512];
> +    int genre, len, dstlen = sizeof(dst)-1;
>  
> -    if(dstlen > 0)
> -        dst[0]= 0;
>      if(taglen < 1)
>          return;
>  
>      taglen--; /* account for encoding type byte */
> -    dstlen--; /* Leave space for zero terminator */
>  
>      switch(get_byte(s->pb)) { /* encoding type */
>  
> @@ -196,7 +193,18 @@
>          get_buffer(s->pb, dst, len);
>          dst[len] = 0;
>          break;
> +
> +    default:
> +        dst[0] = 0;
> +        break;
>      }
> +

> +    if (!strcmp(key, "genre") &&
> +        sscanf(dst, "(%d)", &genre) == 1 && genre <= ID3v1_GENRE_MAX)
> +        strcpy(dst, id3v1_genre_str[genre]);

sechole

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct awnser.
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