[FFmpeg-trac] #8396(undetermined:new): hwdownload always use 0th device (hwaccel_device 0)

FFmpeg trac at avcodec.org
Mon Nov 25 00:59:17 EET 2019

#8396: hwdownload always use 0th device (hwaccel_device 0)
             Reporter:  darn         |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:
             Keywords:  nvenc        |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |

Comment (by oromit):

 hwdownload copies frames _from_ the device, and thus uses the context of
 the frames it gets as input. The outcoming frames are in system RAM and
 not tied to any device.

 The second CUDA context on the default device (0) you are seeing is nvenc
 getting fed non-CUDA frames, which triggers it to create its own CUDA
 context to re-uploads the frames on.
 nvenc has its own option (-gpu) controlling on which device it creates
 that context.

 But really, why even download in the first place, just for nvenc to re-
 upload immediately?

Ticket URL: <https://trac.ffmpeg.org/ticket/8396#comment:2>
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