[FFmpeg-trac] #7564(avfilter:new): hwdownload fails when size changes

[FFmpeg]

#7564: hwdownload fails when size changes
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             Reporter:  msiders     |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avfilter
              Version:  git-master  |               Resolution:
             Keywords:  hwdownload  |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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Comment (by oromit):

 To avoid such confusion, please provide the full uncut output like asked
 at the very beginning in the future.

 The outlink w/h parameters are set during config_props, where they are
 received from the hw_frames_ctx, which is created and set in the hwupload
 filter.
 Unfortunately that means in its current state both hwupload and hwdownload
 do not support dynamic size changes and cannot be easily changed to do so.

 hwupload is the much bigger issue here. It will keep using the original
 hw_frames_ctx, which after the size change either allocates too big(waste
 of space) of a buffer or even too small of a buffer(which probably results
 in a crash).

 Now it could be changed to monitor for input parameter changes, and then
 re-create a new hw_frames_ctx. But all downstream filters are already
 configured to the old context, and do not expect it to change at runtime.

 Support for runtime parameter changes is also very spotty with pure sw
 filtering. With a hw filter chain it would be a major undertaking
 affecting every single hw filter.

 So the conclusion here is, that without a lot of bigger changes, runtime
 parameter changes like this are unsupported with a filter chain that uses
 hardware frames.

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Ticket URL: <https://trac.ffmpeg.org/ticket/7564#comment:9>
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