[FFmpeg-devel] avformat/mxfenc: SMPTE RDD 48:2018 Amd 1:2022 (FFV1 in MXF) support

[Tomas Härdin]

sön 2023-01-29 klockan 11:36 -0500 skrev Dave Rice:
> 
> 
> > On Jan 20, 2023, at 10:17 AM, Tomas Härdin <git at haerdin.se> wrote:
> > 
> > ons 2023-01-18 klockan 15:15 +0100 skrev Jerome Martinez:
> > > On 18/01/2023 14:40, Tomas Härdin wrote:
> > > > Creating a new subthread because I just noticed something
> > > 
> > > I am a bit lost there because the line of code below is not part
> > > of
> > > this 
> > > FFV1 patch.
> > > Additionally, none on my patches (FFV1 of MXF
> > > stored/sampled/displayed 
> > > fix) modifies the discussed behavior (FFmpeg behavior would be
> > > same 
> > > before and after this patch for MPEG-2 and AVC), so should not
> > > block
> > > any 
> > > of them, and a potential fix for that should have its own patch
> > > as it
> > > would be a separate issue.
> > 
> > True, it doesn't need to hold up this patch. But some discussion is
> > warranted I think. I might create a separate patchset for this.
> > 
> > > 
> > > Anyway:
> > > 
> > > 
> > > > 
> > > > > +    //Stored height
> > > > >       mxf_write_local_tag(s, 4, 0x3202);
> > > > >       avio_wb32(pb, stored_height>>sc->interlaced);
> > > > > 
> > > > Won't this be incorrect for files whose dimensions are
> > > > multiples of
> > > > 16
> > > > but not multiples of 32? Isn't each field stored separately
> > > > with
> > > > dimensions a multiple of 16? So while for 1080p we'll have
> > > > 
> > > >    StoredHeight = 1088
> > > >    SampledHeight = 1080
> > > > 
> > > > and 1080i:
> > > > 
> > > >    StoredHeight = 544
> > > >    SampledHeight = 540
> > > > 
> > > > Where 544 is a multiple of 16, for say 720p we have
> > > > 
> > > >    StoredHeight = 720
> > > >    SampledHeight = 720
> > > > 
> > > > but for a hypothetical 720i we'd get
> > > > 
> > > >    StoredHeight = 360
> > > >    SampledHeight = 360
> > > > 
> > > > whereas the correct values should be
> > > > 
> > > >    StoredHeight = 368
> > > >    SampledHeight = 360
> > > 
> > > AFAIK, it would depend about if the stream has a
> > > picture_structure
> > > frame 
> > > (16x16 applies to the frame?) of field (16x16 applies to the
> > > field?),
> > > but I really don't know enough there for having a relevant
> > > opinion.
> > > 
> > > I can just say that I don't change the behavior of FFmpeg in your
> > > use
> > > case, I found the issues when I tried a random width and height
> > > of
> > > FFV1 
> > > stream then checked with MPEG-2 Video and the sampled width was
> > > wrong
> > > for sure e.g. sampled width of 1920 for a stream having a width
> > > of
> > > 1912, 
> > > with current FFmpeg code, and for your use case I am sure about
> > > nothing 
> > > so I don't change the behavior with my patch, IMO if there is an
> > > issue 
> > > with 720i MPEG-2 Video it should be in a separate topic and patch
> > > as
> > > it 
> > > would modify the "stored_height = (st->codecpar-
> > > >height+15)/16*16" 
> > > current code (in my patch I just move this code), unless we are
> > > sure
> > > of 
> > > what should be changed on this side and apply a fix on the way.
> > > Better 
> > > to fix 1 issue and let 1 open with no change than fixing no issue
> > > because we wouldn't be sure for 1 of the 2.
> > 
> > I suspect we are lucky because 720i doesn't really exist in the
> > real
> > world, and 576i and 480i are both multiples of 32.
> > 
> > IMO mxfenc shouldn't lie, but looking at S377m StoredWidth/Height
> > are
> > "best effort" and thus shall be encoded. Their values will depend
> > on
> > FrameLayout which in turn depends on what you say - how exactly the
> > interlacing is done.
> > 
> > TL;DR: this patchset doesn't need to be held up by this.
> 
> I'm just nudging on the consideration of merging this patch. I've
> been testing it over the last week with ffv1/mxf content and have
> found this demuxing support very helpful.

Surely you mean muxing?

Some FATE tests would be nice.

/Tomas