[FFmpeg-trac] #7596(undetermined:new): ffmpeg ignores v4l2 device prefs and selects a non-optimal format

[FFmpeg]

#7596: ffmpeg ignores v4l2 device prefs and selects a non-optimal format
-------------------------------------+-------------------------------------
             Reporter:  colemickens  |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary:

 1. Set a v4l2 format preference.
 2. Use ffmpeg or mpv to open the v4l2 device.
 3. ffmpeg will use the correct resolution, but incorrect pixelformat

 This results in a sub-optimal format being used, resulting in potentially
 highly unfortunate end-results for the user.

 Ideally:
 1. ffmpeg would respect the preferences set for the device in v4l2
 2. ffmpeg would choose the more optimal resolution/format for the best
 result

 In my case, since ffmpeg respects the resolution, but not the pixelformat,
 it winds up operating at the best 1080p YUYV profile, which is 5FPS.
 (compare to 1080p MJPEG which is 30FPS).

 {{{

 $ v4l2-ctl -d 4 --set-fmt-video=width=1920,height=1080,pixelformat=1

 $ v4l2-ctl -d 4 --get-fmt-video
 Format Video Capture:
         Width/Height      : 1920/1080
         Pixel Format      : 'MJPG' (Motion-JPEG)
         Field             : None
         Bytes per Line    : 0
         Size Image        : 4147200
         Colorspace        : sRGB
         Transfer Function : Default (maps to sRGB)
         YCbCr/HSV Encoding: Default (maps to ITU-R 601)
         Quantization      : Default (maps to Full Range)
         Flags             :

 $ mpv av://v4l2:/dev/video4
 Playing: av://v4l2:/dev/video4
  (+) Video --vid=1 (rawvideo 1920x1080 5.000fps)
 [autoconvert] Converting yuyv422 -> yuv422p
 VO: [gpu] 1920x1080 yuv422p
 V: 00:00:02 / 00:00:03 (87%)

 $ ffmpeg -f v4l2 -i /dev/video4 -c:v copy out.mkv

 ...
 Input #0, video4linux2,v4l2, from '/dev/video4':
   Duration: N/A, start: 23757.859585, bitrate: 165888 kb/s
     Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 1920x1080,
 165888 kb/s, 5 fps, 5 tbr, 1000k tbn, 1000k tbc
 ...

 $ ffmpeg -f v4l2 -input_format mjpeg -i /dev/video4 -c:v copy out.mkv

 Input #0, video4linux2,v4l2, from '/dev/video4':
   Duration: N/A, start: 23792.047911, bitrate: N/A
     Stream #0:0: Video: mjpeg, yuvj422p(pc, bt470bg/unknown/unknown),
 1920x1080, 30 fps, 30 tbr, 1000k tbn, 1000k tbc

 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/7596>
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