Re: [FFmpeg-devel] [PATCH 1/3] avformat/mxfdec: SMPTE RDD 48:2018 support

[Pierre-Anthony Lemieux <pal@sandflow.com>]

On Fri, Jul 29, 2022 at 4:19 PM Tomas Härdin <tjoppen@acc.umu.se> wrote:
>
> fre 2022-07-29 klockan 14:14 +0200 skrev Pierre-Anthony Lemieux:
> > On Fri, Jul 29, 2022 at 6:15 AM Tomas Härdin <tjoppen@acc.umu.se>
> > wrote:
> > >
> > > fre 2022-07-29 klockan 01:18 +0200 skrev Michael Niedermayer:
> > > > On Tue, Jul 19, 2022 at 03:48:59PM +0200, Tomas Härdin wrote:
> > > > > mån 2022-07-11 klockan 23:44 +0200 skrev Michael Niedermayer:
> > > > > >
> > > > > > +    { {
> > > > > > 0x06,0x0e,0x2b,0x34,0x04,0x01,0x01,0x0D,0x04,0x01,0x02,0x02,0
> > > > > > x03,
> > > > > > 0x09
> > > > > > ,0x01,0x00 }, 15,       AV_CODEC_ID_FFV1 }, /*FFV1 V0 */
> > > > > > +    { {
> > > > > > 0x06,0x0e,0x2b,0x34,0x04,0x01,0x01,0x0D,0x04,0x01,0x02,0x02,0
> > > > > > x03,
> > > > > > 0x09
> > > > > > ,0x02,0x00 }, 15,       AV_CODEC_ID_FFV1 }, /*FFV1 V1 */
> > > > > > +    { {
> > > > >
> > > > > Double-checked, these are correct
> >
> > I recommend the draft SMPTE metadata registry at the following as the
> > reference for ULs:
> >
> > https://registry.smpte-ra.org/apps/pages/
> >
> > The registry is kept up-to-date, machine readable and free to access.
>
> Neato. I actually have a tool for parsing ULs that I call wtful. For
> now it parses relevant RP spreadsheets, but it's kinda shitty. Maybe I
> can improve and publish it.

The canonical format for the SMPTE registers is XML. The data (and
corresponding XSDs) can also be found at:

https://registry.smpte-ra.org/apps/pages/draft/

("draft" registries are 99% correct. "published" are 99.9% correct but
lag by about 6 months.)

The following are Java bindings for folks that are into that :)

https://github.com/sandflow/regxmllib/tree/master/src/main/java/com/sandflow/smpte/register

> >
>
> > > > >
> > > > > > +    { {
> > > > > > 0x06,0x0e,0x2b,0x34,0x02,0x53,0x01,0x01,0x0d,0x01,0x01,0x01,0
> > > > > > x01,
> > > > > > 0x01
> > > > > > ,0x81,0x03 }, mxf_read_ffv1_sub_descriptor,
> > > > > > sizeof(MXFFFV1SubDescriptor), FFV1SubDescriptor },
> > > > >
> > > > > The spec says 0x7F not 0x53. 0x53 is used in groups with 2-byte
> > > > > tags
> > > >
> > > > If i put 0x7F with no other change there, it will break demuxing
> > > > the
> > > > files i have
> > > > I guess i must have copied this from the files without noticing
> > > > it
> > > > mismatches
> > > > the spec
> > >
> > > Yeah I would expect it to break with 0x7F. Perhaps this will change
> > > when the spec becomes official. If you have contact with the people
> > > involved in this then I suggest asking them about this. It could
> > > also
> > > be a typo in the spec.
> >
> > Byte 6 of Group ULs is set by convention to the wildcard value 0x7F
> > to
> > indicate that the encoding of the Group is not limited to 0x53 (local
> > set with 2-byte local tags and length field). See the following:
> >
> >
> > https://registry.smpte-ra.org/view/draft/docs/Submissions%20Overview/Document-Editors-Information--Style-Guide/#groups-ul
> >
> > MXF restricts header metadata to local sets with 2-byte local tags
> > and
> > 2-byte or BER lengths, so byte 6 can be 0x13 or 0x53.
>
> Alright, then it's fine. Maybe at some point we'll need to implement
> BER lengths in local sets, but not now
>
> /Tomas
>
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