[FFmpeg-devel] [PATCH] av_metadata_count()

[Aurelien Jacobs]

Michael Niedermayer wrote:

> 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

Oh, indeed. A negative genre could lead to a buffer overrun. Fixed.
The strcpy itself should be safe as all the strings in id3v1_genre_str[]
are less than 20 chars while dst is 512 bytes. But in case something
change in the future, I've now used av_strlcpy instead, for extra safety.

Aurel
-------------- next part --------------
A non-text attachment was scrubbed...
Name: md_mp3.diff
Type: text/x-patch
Size: 9927 bytes
Desc: not available
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20090201/a8ea681f/attachment.bin>