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USB摄像头

操作环境：

  • Newman USB Camera camera-NM13-4K
  • LPA3588
  • Ubuntu20.04

查找USB摄像头文件名​

插入USB摄像头后，内核日志如下：

neardi@LPA3588:~$ dmesg  
[ 2740.549384] usb 7-1.2: new high-speed USB device number 6 using xhci-hcd  
[ 2740.705306] usb 7-1.2: New USB device found, idVendor=1bcf, idProduct=0215, bcdDevice=34.07  
[ 2740.705328] usb 7-1.2: New USB device strings, Mfr=1, Product=2, SerialNumber=0  
[ 2740.705341] usb 7-1.2: Product: 4K AutoFocus Webcam  
[ 2740.705353] usb 7-1.2: Manufacturer: 4K AutoFocus Webcam  
[ 2740.775878] uvcvideo: Found UVC 1.00 device 4K AutoFocus Webcam (1bcf:0215)  
[ 2741.037436] usb 7-1.2: Warning! Unlikely big volume range (=4096), cval->res is probably wrong.  
[ 2741.037459] usb 7-1.2: [7] FU [Mic Capture Volume] ch = 1, val = 0/4096/1

您也可以使用lsusb命令列出所有USB��设备：

neardi@LPA3588:~$ lsusb  
Bus 006 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub  
Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub  
Bus 008 Device 003: ID 0bda:9210 Realtek Semiconductor Corp. Ugreen Storage Device  
Bus 008 Device 002: ID 05e3:0620 Genesys Logic, Inc. USB3.2 Hub  
Bus 008 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub  
Bus 007 Device 005: ID 046d:c534 Logitech, Inc. Unifying Receiver  
Bus 007 Device 006: ID 1bcf:0215 Sunplus Innovation Technology Inc. 4K AutoFocus Webcam  
Bus 007 Device 002: ID 05e3:0610 Genesys Logic, Inc. 4-port hub

ID为1bcf:0215的设备就是4K Newman USB摄像头。

使用v4l2-ctl命令列出所有视频设备：

neardi@LPA3588:~$ v4l2-ctl --list-devices  
......  
4K AutoFocus Webcam: 4K AutoFoc (usb-xhci-hcd.6.auto-1.2):  
	/dev/video23  
	/dev/video24  
	/dev/media2

这表明ID为1bcf:0215的USB摄像头的设备文件是/dev/video23和/dev/video24。

打开摄像头​

查看摄像头支持的格式、分辨率和帧率：

neardi@LPA3588:~/samba$ v4l2-ctl -d /dev/video23 --list-formats-ext  
ioctl: VIDIOC_ENUM_FMT  
	Type: Video Capture  
  
	[0]: 'MJPG' (Motion-JPEG, compressed)  
		Size: Discrete 1920x1080  
			Interval: Discrete 0.033s (30.000 fps)  
			Interval: Discrete 0.033s (30.000 fps)  
		Size: Discrete 1280x720  
			Interval: Discrete 0.033s (30.000 fps)  
	......  
	[1]: 'YUYV' (YUYV 4:2:2)  
		Size: Discrete 1920x1080  
			Interval: Discrete 0.200s (5.000 fps)  
			Interval: Discrete 0.200s (5.000 fps)  
		Size: Discrete 1280x720  
			Interval: Discrete 0.100s (10.000 fps)  
		Size: Discrete 1600x900  
			Interval: Discrete 0.200s (5.000 fps)  
		Size: Discrete 640x360  
			Interval: Discrete 0.033s (30.000 fps)  
	.....

使用GStreamer（推荐）​

实时视频预览

neardi@LPA3588:~$ gst-launch-1.0 v4l2src device=/dev/video23 ! image/jpeg,width=640,height=480,framerate=30/1 ! mppjpegdec ! videoconvert ! fpsdisplaysink

编码并保存为H.264文件

neardi@LPA3588:~$ neardi@LPA3588:~$ gst-launch-1.0 v4l2src device=/dev/video23 ! image/jpeg,width=640,height=480,framerate=30/1 ! mppjpegdec ! videoconvert ! mpph264enc ! h264parse ! filesink location=output.h264

将视频流编码为H.264并保存到output.h264。

使用V4l2工具​

neardi@LPA3588:~$ sudo apt update  
neardi@LPA3588:~$ sudo apt install qv4l2  
neardi@LPA3588:~$ qv4l2 -d /dev/video23

使用ffplay​

neardi@LPA3588:~$ ffplay /dev/video23

常见问题​

4K60FPS丢帧故障排除和优化​

当捕获高分辨率和高帧率视频（例如4K@60fps）时，您可能会遇到丢帧（报告为dropped buffers）。例如：

neardi@LPA3588:~# v4l2-ctl -d /dev/video41 --set-fmt-video=width=1280,height=720,pixelformat=YUYV --stream-mmap --stream-count=1000 --stream-skip=3  
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 59.95 fps, dropped buffers: 1  
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 59.95 fps, dropped buffers: 5  
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 59.95 fps, dropped buffers: 1  
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 59.95 fps, dropped buffers: 2  
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 59.95 fps, dropped buffers: 1  
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 59.95 fps, dropped buffers: 15  
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 59.95 fps, dropped buffers: 1

解决方案：启用性能模式

为了减少由CPU频率调节引起的丢帧，将系统切换到performance模式：

sudo -i;   
echo performance | tee $(find /sys/ -name *governor);