[FFmpeg-trac] #7507(avfilter:new): hwupload: missing device platform

[FFmpeg]

#7507: hwupload: missing device platform
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             Reporter:  msiders      |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  normal       |                Component:  avfilter
              Version:  unspecified  |               Resolution:
             Keywords:  hwupload,    |               Blocked By:
  hwaccel                            |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |
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Comment (by msiders):

 Hi oromit,

 This is my suggestion:

 - The vars "hw_device_ctx" and "hw_frames_ctx" are both AVBufferRef
 pointers.
 - And ANY filter/decoder/encoder only takes just one "hw_device_ctx".
 - So the pointers doesn't change!
 - The only difference would be that the new hwupload can point to a
 ''new'' context pointer.

 So, the basis are that the "hw_device_ctx" doesn't change for filters.

 See this overview example:

   INPUT --> DECODER A --> FILTER B --> HWDOWNLOAD --> FILTER C -->
 HWUPLOAD --> ENCODER D --> OUTPUT

 As you can note:

 - GPU platform X: applies to A,B & hwdownload.
 - System memory: C only .
 - GPU platform Y: hwupload & D.

 In this case, the "hw_device_ctx" is unique for filters and opaque to all.
 Just only the ffmpeg.c needs to initialize the different platforms when
 more than one is used. And the hwupload needs to select between the
 different available contexts inside the ffmpeg.c list.

 Does this sound good to you?

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Ticket URL: <https://trac.ffmpeg.org/ticket/7507#comment:4>
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