python - 为什么 V4L2 API 不显示正确的像素格式/宽度/高度参数？

Question

我正在尝试根据V4L2 API设置V4L2 相机的参数。 但是，似乎 API 没有显示操作系统设置的正确参数。

您能否建议如何调试此问题以确定相机无法显示正确参数是否是一个问题

用我的代码，
用相机，
还是使用API？

问题演示：

$ 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代码（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()

环境：

OS: Ubuntu 16.04
V4L2 calls based on https://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec-single/v4l2.html

score 1 · Accepted Answer

似乎我的 show_format() 不正确。当我将其更改为：

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)

我得到正确的值。

$ 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

python - 为什么 V4L2 API 不显示正确的像素格式/宽度/高度参数？

1 回答 1

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