I'm trying to set a V4L2 camera's parameters according to the V4L2 API.
However, seems the API does not display the correct parameters as were set by the OS.
Can you suggest how to debug this issue to figure if the failure of the camera to show the correct parameters is a problem
Problem demonstration:
$ v4l2-ctl -d2 --set-fmt-video=width=424,height=240,pixelformat=1
$ v4l2-ctl -d2 --get-fmt-video | egrep 'Pixel Format|Width/Height'
Width/Height : 424/240
Pixel Format : 'UYVY'
$ python incorrect_pix_format.SO.py
>> device capabilities
Driver: uvcvideo
Camera: Intel(R) RealSense(TM) 410
video capture device? True
Supports read() call? False
Supports streaming? True
>> format parameters
pix_format.width: 0
pix_format.height: 0
pix_format.pixelformat: 0
>> Stop streaming
$ v4l2-ctl --list-formats-ext -d 2
ioctl: VIDIOC_ENUM_FMT
Index : 0
Type : Video Capture
Pixel Format: ''
Name : 00000032-0000-0010-8000-00aa003
Size: Discrete 424x240
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 480x270
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 640x360
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 640x480
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 848x480
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 1280x720
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Index : 1
Type : Video Capture
Pixel Format: 'UYVY'
Name : UYVY 4:2:2
Size: Discrete 424x240
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 480x270
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 640x360
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 640x480
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 848x480
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 1280x720
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Index : 2
Type : Video Capture
Pixel Format: 'Y8I '
Name : Greyscale 8 L/R (Y8I)
Size: Discrete 424x240
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 480x270
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 640x360
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 640x480
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 848x480
Interval: Discrete 0.011s (90.000 fps)
Interval: Discrete 0.017s (60.000 fps)
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 1280x720
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Interval: Discrete 0.167s (6.000 fps)
Size: Discrete 1920x1080
Interval: Discrete 0.033s (30.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Index : 3
Type : Video Capture
Pixel Format: 'Y12I'
Name : Greyscale 12 L/R (Y12I)
Size: Discrete 960x540
Interval: Discrete 0.040s (25.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Size: Discrete 1920x1080
Interval: Discrete 0.040s (25.000 fps)
Interval: Discrete 0.067s (15.000 fps)
Python code (mcve):
$ cat incorrect_pix_format.SO.py
#!/usr/bin/env python3
from __future__ import print_function
import fcntl
import v4l2
def get_capability(vd):
cp = v4l2.v4l2_capability()
fcntl.ioctl(vd, v4l2.VIDIOC_QUERYCAP, cp)
return cp
def show_capability(cp):
print("Driver:", cp.driver)
print("Camera:", cp.card)
print("video capture device?\t", bool(cp.capabilities & v4l2.V4L2_CAP_VIDEO_CAPTURE))
print("Supports read() call?\t", bool(cp.capabilities & v4l2.V4L2_CAP_READWRITE))
print("Supports streaming?\t", bool(cp.capabilities & v4l2.V4L2_CAP_STREAMING))
def show_format(vd):
fmt = v4l2.v4l2_format()
pix_format = v4l2.v4l2_pix_format()
print("pix_format.width:", pix_format.width)
print("pix_format.height:", pix_format.height)
print("pix_format.pixelformat:", pix_format.pixelformat)
if __name__ == "__main__":
vd = open('/dev/video2', 'rb+', buffering=0)
print(">> device capabilities")
cp = get_capability(vd)
show_capability(cp)
print(">> format parameters")
show_format(vd)
print(">> Stop streaming")
vd.close()
Environment:
OS: Ubuntu 16.04
V4L2 calls based on https://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec-single/v4l2.html
Seems my show_format() was incorrect. When I changed it to:
def show_format(vd):
fmt = v4l2.v4l2_format()
fmt.type = v4l2.V4L2_BUF_TYPE_VIDEO_CAPTURE
fcntl.ioctl(vd, v4l2.VIDIOC_G_FMT, fmt)
print("width:", fmt.fmt.pix.width)
print("height", fmt.fmt.pix.height)
print("pixelformat", fmt.fmt.pix.pixelformat)
I get the correct values.
$ cat incorrect_pix_format.SO.py
#!/usr/bin/env python3
from __future__ import print_function
import fcntl
import v4l2
def get_capability(vd):
cp = v4l2.v4l2_capability()
fcntl.ioctl(vd, v4l2.VIDIOC_QUERYCAP, cp)
return cp
def show_capability(cp):
print("Driver:", cp.driver)
print("Camera:", cp.card)
print("video capture device?\t", bool(cp.capabilities & v4l2.V4L2_CAP_VIDEO_CAPTURE))
print("Supports read() call?\t", bool(cp.capabilities & v4l2.V4L2_CAP_READWRITE))
print("Supports streaming?\t", bool(cp.capabilities & v4l2.V4L2_CAP_STREAMING))
def show_OS_format(vd, type, index):
fmtdesc = v4l2.v4l2_fmtdesc()
fmtdesc.type = type
fmtdesc.index = index
fcntl.ioctl(vd, v4l2.VIDIOC_ENUM_FMT, fmtdesc)
print("fmtdesc.description:", fmtdesc.description)
print("fmtdesc.pixelformat:", fmtdesc.pixelformat)
def show_format(vd):
fmt = v4l2.v4l2_format()
fmt.type = v4l2.V4L2_BUF_TYPE_VIDEO_CAPTURE
fcntl.ioctl(vd, v4l2.VIDIOC_G_FMT, fmt)
print("width:", fmt.fmt.pix.width)
print("height", fmt.fmt.pix.height)
print("pixelformat", fmt.fmt.pix.pixelformat)
if __name__ == "__main__":
vd = open('/dev/video2', 'rb+', buffering=0)
print(">> device capabilities")
cp = get_capability(vd)
show_capability(cp)
print(">> OS set format")
show_OS_format(vd, type=v4l2.V4L2_BUF_TYPE_VIDEO_CAPTURE, index=1)
print(">> format parameters")
show_format(vd)
print(">> Stop streaming")
vd.close()
$ python incorrect_pix_format.SO.py
>> device capabilities
Driver: uvcvideo
Camera: Intel(R) RealSense(TM) 410
video capture device? True
Supports read() call? False
Supports streaming? True
>> OS set format
fmtdesc.description: UYVY 4:2:2
fmtdesc.pixelformat: 1498831189
>> format parameters
width: 424
height 240
pixelformat 1498831189
>> Stop streaming