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

[Tomas Härdin]

fre 2022-07-29 klockan 14:14 +0200 skrev Pierre-Anthony Lemieux:
> On Fri, Jul 29, 2022 at 6:15 AM Tomas Härdin <tjoppen at 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.
> 

> > > > 
> > > > > +    { {
> > > > > 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