如何打开相机:在终端(文本后,促使美元=命令我类型):_________________
$ ls /dev/video*
/dev/video0 /dev/video1
$ vlc v4l2:///dev/video0
VLC media player 2.0.8 Twoflower (revision 2.0.8a-0-g68cf50b)
[0x9f2d908] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface.
VLC开始播放摄像机输出。
在另一个新的终端中(BOLD =我键入的命令):
$ vlc v4l2:///dev/video1
VLC media player 2.0.8 Twoflower (revision 2.0.8a-0-g68cf50b)
[0x9b24908] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface.
[0xb0500960] v4l2 demux error: VIDIOC_STREAMON failed
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
[0xb0501188] v4l2 access error: cannot set input 0: Device or resource busy
[0xb0501188] v4l2 access error: cannot set input 0: Device or resource busy
[0xb5300618] main input error: open of `v4l2:///dev/video1' failed
没有视频播放，只有错误信息。
主要目标:我想在opencv (c++)中同时打开两个摄像头…得到类似的错误与opencv ..所以我使用VLC播放器来调试这个问题。使用c++ opencv同时打开两个摄像机时的错误(代码类似于https://code.ros.org/trac/opencv/browser/trunk/opencv/samples/cpp/starter_video.cpp?rev=4705)
e557822@e557822-T740:~/Desktop/Camera/starter_video2$ ls /dev/video*
/dev/video0 /dev/video1 /dev/video2
e557822@e557822-T740:~/Desktop/Camera/starter_video2$ ./starter_video2 0 1
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
press space to save a picture. q or esc to quit
init done
opengl support available
libv4l2: error turning on stream: No space left on device
VIDIOC_STREAMON: No space left on device
UPDATE 7/24:这个Ubuntu 12.04(32位)是一个运行在VMware Fusion上的客户操作系统。这里的主机操作系统是OSX 10.9.4，运行在Mac Pro计算机硬件上。
$ lsusb -t
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=uhci_hcd/2p, 12M
|__ Port 1: Dev 2, If 0, Class=HID, Driver=usbhid, 12M
|__ Port 2: Dev 3, If 0, Class=hub, Driver=hub/7p, 12M
|__ Port 1: Dev 4, If 0, Class='bInterfaceClass 0xe0 not yet handled', Driver=btusb, 12M
|__ Port 1: Dev 4, If 1, Class='bInterfaceClass 0xe0 not yet handled', Driver=btusb, 12M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci_hcd/6p, 480M
|__ Port 1: Dev 6, If 0, Class='bInterfaceClass 0x0e not yet handled', Driver=uvcvideo, 480M
|__ Port 1: Dev 6, If 1, Class='bInterfaceClass 0x0e not yet handled', Driver=uvcvideo, 480M
|__ Port 2: Dev 7, If 0, Class='bInterfaceClass 0x0e not yet handled', Driver=uvcvideo, 480M
|__ Port 2: Dev 7, If 1, Class='bInterfaceClass 0x0e not yet handled', Driver=uvcvideo, 480M
$
这是USB带宽问题，而不是VLC问题。
VIDIOC_STREAMON: No space left on device是USB带宽满时给出的消息。
大多数现代USB相机做高速，高密度图像输出。USB2限制在480Mbps，理论上是60兆字节/秒。在实践中，所有类型的开销将使用它的一半，而30mb/s是您可以获得的最大值。这意味着相机可以以30fps的速度发送1mb的图像。
所有你能做的就是得到主板与多个USB总线。所有的小型计算机往往只有一个。高端游戏主板有2..3USB2.0总线。你可以在linux下看到它:
$ lsusb -t
/: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
/: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M
|__ Port 4: Dev 2, If 0, Class=scard, Driver=usbfs, 12M
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci_hcd/2p, 480M
|__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/8p, 480M
|__ Port 5: Dev 3, If 0, Class='bInterfaceClass 0xe0 not yet handled', Driver=btusb, 12M
|__ Port 5: Dev 3, If 1, Class='bInterfaceClass 0xe0 not yet handled', Driver=btusb, 12M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci_hcd/2p, 480M
|__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/6p, 480M
|__ Port 3: Dev 3, If 0, Class=vend., Driver=rts5139, 480M
|__ Port 5: Dev 4, If 0, Class='bInterfaceClass 0x0e not yet handled', Driver=uvcvideo, 480M
|__ Port 5: Dev 4, If 1, Class='bInterfaceClass 0x0e not yet handled', Driver=uvcvideo, 480M
$
很可能两个摄像机连接到同一总线。
另一个选择是降低FPS速度或分辨率。但这并不总是有用，因为我见过相机保留80%的USB带宽。