linux系统下查看相机支持信息

linux系统下可以通过v4l2-ctl相关命令查询当前有哪些相机，以及相机支持的相关参数

1. 查看有多少相机

v4l2-ctl --list-devices
-------------------------------------------------------
Video Capture 3 (usb-0000:05:00.0-2):
    /dev/video0
    /dev/video1

2. 查看指定相机的输出图像格式及对应分辨率

v4l2-ctl --list-formats-ext -d /dev/video0
----------------------------------------------------------
ioctl: VIDIOC_ENUM_FMT
    Type: Video Capture

    [0]: 'MJPG' (Motion-JPEG, compressed)
        Size: Discrete 1280x720
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 320x180
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 320x240
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 352x288
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 424x240
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 640x360
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 640x480
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 848x480
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 960x540
            Interval: Discrete 0.033s (30.000 fps)
    [1]: 'YUYV' (YUYV 4:2:2)
        Size: Discrete 1280x720
            Interval: Discrete 0.100s (10.000 fps)
        Size: Discrete 320x180
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 320x240
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 352x288
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 424x240
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 640x360
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 640x480
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 848x480
            Interval: Discrete 0.050s (20.000 fps)
        Size: Discrete 960x540
            Interval: Discrete 0.067s (15.000 fps)

此信息意味着，当你选择输出格式为yuyv422时候默认会以帧率为10返回数据，图像会较卡顿，如果想以30帧率返回图像，可以酌情设置降低分辨率，或者直接设置输出图像格式为mpeg。