[英]v4l2 documentation's sample code as is (with open as 'rw')?
我刚刚开始在Ubuntu 16.04.
上使用v4l2
(适用于Python 3
) Ubuntu 16.04.
我正在尝试从v4l2 Python文档运行示例,即:
$ cat demo4SO.py
#!/usr/bin/env python3
import v4l2
import fcntl
vd = open('/dev/video0', 'rw')
#vd = open('/dev/video0', 'r')
cp = v4l2.v4l2_capability()
fcntl.ioctl(vd, v4l2.VIDIOC_QUERYCAP, cp)
print("driver:",cp.driver)
print("card:",cp.card)
但是正在得到:
$ python3 demo4SO.py
Traceback (most recent call last):
File "demo4SO.py", line 6, in <module>
vd = open('/dev/video0', 'rw')
ValueError: must have exactly one of create/read/write/append mode
即使使用sudo.
运行,我也会遇到相同的错误sudo.
尝试以“ w +”(或“ r +”)打开,我得到:
$ python3 demo4SO.py
Traceback (most recent call last):
File "demo4SO.py", line 8, in <module>
vd = open('/dev/video0', "w+")
io.UnsupportedOperation: File or stream is not seekable.
如果我将“ rw”(或“ w +”或“ r +”)更改为“ r”,则代码将按预期工作。
$ cat demo4SO.py
#!/usr/bin/env python3
import v4l2
import fcntl
#vd = open('/dev/video0', 'rw')
vd = open('/dev/video0', 'r')
cp = v4l2.v4l2_capability()
fcntl.ioctl(vd, v4l2.VIDIOC_QUERYCAP, cp)
print("driver:",cp.driver)
print("card:",cp.card)
$ python3 demo4SO.py
driver: b'uvcvideo'
card: b'Intel(R) RealSense(TM) 410'
我的用户名属于视频设备的组,因此该问题似乎与权限无关:
$ groups
openstack root sudo video staff
$ ls -ls /dev/video0
0 crw-rw----+ 1 root video 81, 0 פבר 14 11:31 /dev/video0
知道为什么我不能按原样(使用'rw')运行文档的示例代码吗?
改变中
vd = open('/dev/video0', 'rw')
至
vd = open('/dev/video0', 'rb+', buffering=0)
启用具有O_RDWR权限的文件。
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