[FFmpeg-devel] [PATCH 2/3] avisynth: use AviSynth+'s frame properties to set various fields

[Steinar Apalnes]

tor. 25. aug. 2022 kl. 02:11 skrev Stephen Hutchinson <qyot27 at gmail.com>:

> On 8/24/22 1:04 PM, Steinar Apalnes wrote:
> > tir. 8. feb. 2022 kl. 12:03 skrev Stephen Hutchinson <qyot27 at gmail.com>:
> >
> >> * Field Order
> >> * Chroma Location
> >> * Color Transfer Characteristics
> >> * Color Range
> >> * Color Primaries
> >> * Matrix Coefficients
> >>
> >> The existing TFF/BFF detection is retained as a fallback for
> >> older versions of AviSynth that can't access frame properties.
> >> The other properties have no legacy equivalent to detect them.
> >>
> >> Signed-off-by: Stephen Hutchinson <qyot27 at gmail.com>
> >>
> > .......
> >   Hi Stephen,
> >
> > Would it be possible to add support for "_SARum" and "_SARDen" so that
> > ffmpeg could also recognize the sample aspect ratio in avs scripts?
> >
>
> I'm a bit hesitant to do so, namely because the _SARNum/Den properties
> are much more likely to need to have been changed due to operations
> in-script, and unless the user is studious about updating those
> properties after even just a basic resizing operation, then _SARNum/Den
> will still be set to the original values populated by the source filter,
> and will be wrong, leading to encodes ending up wrong and potentially
> bug reports to Trac which aren't actually the fault of the demuxer.
>
> This is partially coming from the fact that even the color-based
> properties that were already added have experienced some level of
> backlash because of the requirement for users to ensure the properties
> are correctly updated if they've done any changes to those factors
> (as best as I'm aware, the filters in the AviSynth+ core still only pass
> through the existing properties, but they don't update them if they
> pertain to that property's functionality; I believe some external
> filters do update them, however).  I would be fairly confident in
> betting that users resizing video is far more common than them doing
> color correction ops that would require updating the frameprops FFmpeg
> can currently read.
>
> One mitigation to that, IMO, would be to flag that as an experimental
> feature, making it to where FFmpeg won't read _SARNum/Den unless
> the -strict option has been used.
> _______________________________________________
>
>
If you think cherry picking what props to support under normal operation is
the way to go
then a -strict option to support *all* "scary" avs props would be very
welcome indeed.
Because as it is now we have nothing at all in regards to the SAR.

Thanks for your efforts :-)

-steinar