Re: [FFmpeg-devel] [PATCH 2/5] vulkan_decode: use the new AVHWFramesContext.opaque field

[Anton Khirnov <anton@khirnov.net>]

Quoting Lynne (2023-06-13 14:53:35)
> Jun 13, 2023, 14:29 by anton@khirnov.net:
> 
> > Quoting Lynne (2023-06-13 06:19:34)
> >
> >> This depends on the previous patch, and allows moving the codec
> >> profile to the new AVHWFramesContext.opaque field.
> >>
> >> Patch attached.
> >>
> >>
> >> From f992905250062711fab7522906a573ff8ab5f716 Mon Sep 17 00:00:00 2001
> >> From: Lynne <dev@lynne.ee>
> >> Date: Tue, 13 Jun 2023 06:10:20 +0200
> >> Subject: [PATCH 2/5] vulkan_decode: use the new AVHWFramesContext.opaque field
> >>
> >> ---
> >>  libavcodec/vulkan_decode.c | 56 +++++++++++++++++++++++---------------
> >>  libavcodec/vulkan_decode.h |  6 ++--
> >>  2 files changed, 37 insertions(+), 25 deletions(-)
> >>
> >
> > This will not work, because the callers are not required to call
> > avcodec_get_hw_frames_parameters() and can create the frames context
> > themselves.
> >
> 
> Indeed they are. This commit doesn't break this.
> 
> 
> > The decoder is then not allowed to make any assumptions about the opaque
> > field.
> >
> 
> Exactly. This is just for the case that the user calls avcodec_get_hw_frames_parameters.
> Then, we need somewhere to put the profile.
> The opaque field is only set, it is never read in this particular case.
> Since it's libavcodec creating the frames context in this case, and since the user
> explicitly asked for frames parameters to be set, I don't think it's a problem
> to set a public field, much the same way the width, height and sw_format
> values are set.
> 
> If the user doesn't call avcodec_get_hw_frames_parameters, the rest
> of the code wouldn't notice. The rest of the decoder code gets the profile
> via the create_pnext chain (where the pointers to the profile structs must be).
> So users can attach their own profile, and store it wherever, including
> the opaque field.
> 
> This commit also fixes the situation where a users calls
> avcodec_get_hw_frames_parameters, gets a frame parameters.
> destroys the decode context, and uses the same frames context
> which was created for another decoder.

Why can't you use the existing user_opaque field?

-- 
Anton Khirnov
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