[FFmpeg-devel] [PATCH 2/2] avformat/mxfenc: do not write index tables with the same InstanceUID

[Tomas Härdin]

mån 2022-03-14 klockan 21:44 +0100 skrev Marton Balint:
> 
> 
> On Mon, 14 Mar 2022, Tomas Härdin wrote:
> 
> > mån 2022-03-14 klockan 20:54 +0100 skrev Marton Balint:
> > > 
> > > 
> > > On Mon, 14 Mar 2022, Tomas Härdin wrote:
> > > 
> > > > mån 2022-03-14 klockan 19:49 +0100 skrev Marton Balint:
> > > > > Only index tables repeating previous index tables should use
> > > > > the
> > > > > same
> > > > > InstaceUID. Use the index start position when generating the
> > > > > InstanceUID to fix
> > > > > this.
> > > > > 
> > > > > Signed-off-by: Marton Balint <cus at passwd.hu>
> > > > > ---
> > > > >  libavformat/mxfenc.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
> > > > > index ba8e7babfb..5b972eadaa 100644
> > > > > --- a/libavformat/mxfenc.c
> > > > > +++ b/libavformat/mxfenc.c
> > > > > @@ -1757,7 +1757,7 @@ static void
> > > > > mxf_write_index_table_segment(AVFormatContext *s)
> > > > >  
> > > > >      // instance id
> > > > >      mxf_write_local_tag(s, 16, 0x3C0A);
> > > > > -    mxf_write_uuid(pb, IndexTableSegment, 0);
> > > > > +    mxf_write_uuid(pb, IndexTableSegment, mxf-
> > > > > > last_indexed_edit_unit);
> > > > 
> > > > Two things: yes, it is good that this fixes the same
> > > > InstanceUID
> > > > being
> > > > reused. But more importantly, we should not be writing files
> > > > with
> > > > over
> > > > 65536 partitions!
> > > 
> > > last_indexed_edit_unit is frame based not partition based, so it
> > > can 
> > > overflow 65536 realtively easily, that is why I submitted patch
> > > 1.
> > 
> > Right. But we could use the partition number instead.
> 
> Well, we could use mxf->body_partitions_count but it is not trivial
> to see 
> that it will work for all cases.

I don't see why not. But upping to 32-bit is easy anyways.

> For simple indexes, we rewrite the index 
> table in the footer when writing the mxf header, opatom may follow
> another 
> layout, so it just felt less error-prone to use actually the start
> offset 
> of the index.

We only need to do this for frame wrapping. And yeah that can be a
separate patch.

/Tomas