对接USB摄像头

开发者套件支持接入UVC协议的USB摄像头，本节介绍如何接入并测试USB摄像头。

1. 将USB摄像头接入开发者套件任意一个空闲USB接口（USB 3.0 Type A）。
2. 以root用户登录开发者套件，执行命令，可以通过回显看到通过USB接口接入的摄像头。

   lsusb

   回显如下：

   Bus 005 Device 003: ID 0bda:9143 Realtek Semiconductor Corp. USB Camera

3. 开发者套件可自动检测USB摄像头接入并创建设备节点“/dev/video0”。用户可通过v4l2命令确认USB摄像头工作是否正常，执行以下命令。

   sudo v4l2-ctl -d /dev/video0 --all

   系统回显如下，包含摄像机帧率、分辨率等信息：

   Driver Info:
           Driver name      : uvcvideo
           Card type        : USB Camera: USB Camera
           Bus info         : usb-a5100000.usb_2-1
           Driver version   : 5.10.0
           Capabilities     : 0x84a00001
                   Video Capture
                   Metadata Capture
                   Streaming
                   Extended Pix Format
                   Device Capabilities
           Device Caps      : 0x04200001
                   Video Capture
                   Streaming
                   Extended Pix Format
   Media Driver Info:
           Driver name      : uvcvideo
           Model            : USB Camera: USB Camera
           Serial           : 200901010001
           Bus info         : usb-a5100000.usb_2-1
           Media version    : 5.10.0
           Hardware revision: 0x00002021 (8225)
           Driver version   : 5.10.0
   Interface Info:
           ID               : 0x03000002
           Type             : V4L Video
   Entity Info:
           ID               : 0x00000001 (1)
           Name             : USB Camera: USB Camera
           Function         : V4L2 I/O
           Flags            : default
           Pad 0x01000007   : 0: Sink
             Link 0x02000013: from remote pad 0x100000a of entity 'Realtek Extended Controls Unit' (Video Pixel Formatter): Data, Enabled, Immutable
   Priority: 2
   Video input : 0 (Camera 1: ok)
   Format Video Capture:
           Width/Height      : 1280/720
           Pixel Format      : 'MJPG' (Motion-JPEG)
           Field             : None
           Bytes per Line    : 0
           Size Image        : 1843200
           Colorspace        : sRGB
           Transfer Function : Rec. 709
           YCbCr/HSV Encoding: ITU-R 601
           Quantization      : Default (maps to Full Range)
           Flags             :
   Crop Capability Video Capture:
           Bounds      : Left 0, Top 0, Width 1280, Height 720
           Default     : Left 0, Top 0, Width 1280, Height 720
           Pixel Aspect: 1/1
   Selection Video Capture: crop_default, Left 0, Top 0, Width 1280, Height 720, Flags:
   Selection Video Capture: crop_bounds, Left 0, Top 0, Width 1280, Height 720, Flags:
   Streaming Parameters Video Capture:
           Capabilities     : timeperframe
           Frames per second: 30.000 (30/1)
           Read buffers     : 0