[FFmpeg-trac] #2305(avdevice:new): v4l2 user control configuration mechanism

[FFmpeg]

#2305: v4l2 user control configuration mechanism
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             Reporter:  elkq         |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  wish         |                Component:  avdevice
              Version:  git-master   |               Resolution:
             Keywords:  v4l2         |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by dronus):

 I think using v4l2-ctl before ffmpeg would be ok if it would work.

 Currently ffmpeg does a mess on the settings made by v4l2-ctl. The pixel
 format is not honored, but must be set by -pixel_format. Doing so it seems
 tend to reset other parameters, eg. exposure settings or something on some
 cameras. As those cannot be controlled by ffmpeg, they must be reapplied
 by v4l2-ctl after starting the capture, a need which renders the first
 seconds of the capture useless.

 So ffmpeg should either provide the full range of controls like cehoyos
 suggested (much work to do) or just keep whats set up and honor it. As
 v4l2.c matches up libav and v4l2 pixel formats it may be tricky to keep
 the already set v4l2 format and honor it, however ffmpeg could fail if no
 support is possible and suggest a compatible format to be set with
 v4l2-ctl.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2305#comment:4>
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