Patch by Anton Khirnov <wyskas gmail com>.
Originally committed as revision 22808 to svn://svn.ffmpeg.org/ffmpeg/trunk
mtag=NULL;
while((mtag=av_metadata_get(in_file->metadata, "", mtag, AV_METADATA_IGNORE_SUFFIX)))
- av_metadata_set(&out_file->metadata, mtag->key, mtag->value);
+ av_metadata_set2(&out_file->metadata, mtag->key, mtag->value, AV_METADATA_DONT_OVERWRITE);
av_metadata_conv(out_file, out_file->oformat->metadata_conv,
in_file->iformat->metadata_conv);
}