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

[Tomas Härdin]

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!

This has been bugging me for quite some time. Honestly I don't know why
the decision was taken initially to write indices every 10 seconds. In
any use-case where seeks are moderately expensive working with files
produced by mxfenc is a nightmare. Prime example being HTTP.

If we do still need to keep writing partitions this way, can we repeat
the IndexTableSegments in the footer so the entire file doesn't have to
be scanned?

/Tomas