[FFmpeg-devel] [PATCH v2 1/5] avutil/hwcontext_d3d11va: fix the uninitialized texture bindflag

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Hendrik Leppkes
> Sent: Sunday, May 1, 2022 5:54 PM
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH v2 1/5] avutil/hwcontext_d3d11va:
> fix the uninitialized texture bindflag
> 
> On Sun, May 1, 2022 at 5:48 PM Hendrik Leppkes <h.leppkes at gmail.com>
> wrote:
> >
> > On Sun, May 1, 2022 at 7:09 AM Soft Works <softworkz at hotmail.com>
> wrote:
> > > I think that's what Hendrik wanted to point out as far as I
> understood.
> > >
> >
> > Basically, I want explicit behavior, not implicit defaults. Anytime
> a
> > hwcontext is created, something should tell it what its going to be
> > used for, so we can determine which flags make sense (or ideally, it
> > should just specify the flags).
> >
> > This patch creates an implicit default for one use-case, is this
> going
> > to work with all others? No, of course not, because it has to know
> > what flags to set. Thats why explicitly setting those flags is
> > important, instead of just fixing one implicit case.

I said I agree with you - basically, just that we need to differentiate
between the use case:

1. Use via API
   => No defaults should be applied, caller is responsible for specifying
      the flags

2. Use via ffmpeg cli
   => Applying the render target flag would be safe here.
      We could require this to set via parameter, but there won't ever
      be a case to specify something different than the render target flag

Why? Let's look at the possible flags:

D3D11_BIND_DECODER
In all decoding cases, this flag is set explicitly, so it overrides
any default we would set

D3D11_BIND_VIDEO_ENCODER
Set explicitly when required, so it overrides any default we would set

D3D11_BIND_RENDER_TARGET
All other cases require this flag (e.g. video processing)

No Flag
Dead end, texture would be unusable for any kind of video processing


> On that note, the example commandline it fixes just does hwupload and
> nothing else - does that even require render target to be flagged?
> From what I can tell it uses a simple
> ID3D11DeviceContext::CopySubresourceRegion to copy from the staging
> texture, which should not require any particular bind flags. Bind
> Flags in turn would then depend on what you are actually trying to do
> with the texture (shader input, etc), in this example... nothing?

We are still in the context of ffmpeg cli - you know that there are
no shaders or 3d operations and no etc.

But at this point, you can derive to another context or you can hwmap.
For all of those things, you need D3D11_BIND_RENDER_TARGET.


Summary

As mentioned I see two possibilities:

1. Use D3D11_BIND_RENDER_TARGET as a default when used in context of
   ffmpeg cli, otherwise no default flags

2. Require a device initialization parameter in the command line
   (but it would always be about setting the render target flag
   and there's no case where you would NOT want to set it)

Let me know what you think.

Best regards
softworkz