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

[Marton Balint <cus@passwd.hu>]

On Wed, 16 Mar 2022, Tomas Härdin wrote:

> 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@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.

I tried, but body partition count is the same for the last body partition 
and for the footer partition, both having different index tables...

So I still find it more starightforward to use index start position 
instead of some magic to find out the proper partition count, is it fine 
with you?

Thanks,
Marton
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