[FFmpeg-devel] [PATCH] avformat/mxf: Establish register of local tags

[Tomas Härdin]

ons 2021-01-27 klockan 21:38 +0100 skrev Marton Balint:
> 
> On Wed, 27 Jan 2021, Tomas Härdin wrote:
> 
> > Hi
> > 
> > Ticket #9079 brought this about. This should prevent accidentally
> > adding local tags that are not registered in the primer. It also allows
> > us to omit tags that we know won't be used, in a manner that is more
> > elegant than the old code.
> > 
> > The actual meat of this patch is mxf_mark_tag_unused(),
> > mxf_write_primer_pack(), mxf_write_local_tag() and
> > ff_mxf_lookup_local_tag()
> 
> IMHO you should not move the local tags to mxf.c, because only encoding 
> uses them.
> 
> The only exception where sharing made sense is 
> ff_mxf_mastering_display_local_tags, but that is super ugly that you 
> now lookup them in mxfdec.c based on local tags we assign them for 
> encoding. Not to mention the linear search you use for each lookup...

We could sort them and use a binary search, but I wanted some feedback
on this idea before going further. There's not terribly many of them

I'd like to avoid having the full ULs twice in the code. The only way I
can see how to do that is with #defines

> So I suggest you simply duplicate the 4 UL-s to the single local tags 
> array you make and keep them in mxfenc.c, that way you also don't have to 
> specify the array size manually...

That might conflict with Andreas' deduplication efforts. But yeah, the
thought did occur to me

/Tomas