[FFmpeg-devel] [PATCH] codec_desc: mark CFHD as intra-only

[Anton Khirnov]

Quoting James Almer (2020-06-10 14:46:21)
> On 6/10/2020 6:19 AM, Anton Khirnov wrote:
> > Quoting James Almer (2020-06-09 14:45:33)
> >> On 6/9/2020 6:06 AM, Anton Khirnov wrote:
> >>> I don't think this needs to be visible externally, since it's only
> >>> meaningful for internal use. I'm wondering if the presence of
> >>> update_thread_context() callback won't be sufficient for this.
> >>
> >> True, it could be a caps_internal. But take for example the possibility
> >> of an external library with a fully featured decoder getting a wrapper,
> >> this being a public capability would let the user choose it over the
> >> internal one, same as how it can choose a stable decoder over an
> >> experimental one, or a software one over an hybrid/hw one.
> > 
> > I don't see why this should be a criterium for the user to base any
> > decisions on. It's purely an internal implementation detail that's tied
> > to the way frame threading is currently implemented and can potentially
> > change later. So I don't see why it should be accessible through the
> > API.
> 
> An intra only decoder returns I frames only. A fully feature decoder
> would return I and P (and actually get you something other than a key
> frame slideshow). Or at least that's how i understood it.
> Giving the user a way to choose the best decoder for their needs is not
> too crazy. We already do with other implementation specific
> capabilities, as i mentioned above.
> 
> > 
> > Also, not sure if you saw but I have new patch fixing this problem in
> > another manner.
> 
> Yes, i saw. I'm arguing about this other approach because if it's done
> now, it can be done seamlessly (Just revert the change and pretend the
> flag was never deprecated). After 4.3 is effectively tagged, we would
> require to undo the deprecation with another API change, and it will
> look messy.
> 
> The flag was meaningless and a duplicate of the codec prop, but now we
> found a way to use it to actually convey information about a decoder, so
> why not do it?

It still seems to me that this is a solution in search of a problem. If
I understand you correctly, the case you have in mind is a codec where
there is an internal implementation that only supports intra frames
and an external implementation that also supports inter frames.
But that seems incredibly contrived to me. For one thing, I don't know
of any actual situations like this, now or in the past. For another, why
pick out specifically the ability to decode intra vs inter frames?
There is a huge number of codec features that may be potentially
unsupported by various implementations (see e.g. AAC) and there's no
sane way we can have capability flags for them all.

-- 
Anton Khirnov