嵌入式linux v4l2应用原理及代码解析

最新推荐文章于 2025-07-06 14:34:23 发布

弹簧xj

最新推荐文章于 2025-07-06 14:34:23 发布

阅读量505

点赞数 6

CC 4.0 BY-SA版权

文章标签： linux 运维服务器

本文链接：https://blog.youkuaiyun.com/weixin_45711878/article/details/138963990

原理

1、初始化v4l2

打开设备、buf初始化、设置格式、放入空闲列表



static int V4l2InitDevice(char *strDevName, PT_VideoDevice ptVideoDevice)
{
    int i;
    int iFd;
    int iError;
    struct v4l2_capability tV4l2Cap;
	struct v4l2_fmtdesc tFmtDesc;
    struct v4l2_format  tV4l2Fmt;
    struct v4l2_requestbuffers tV4l2ReqBuffs;
    struct v4l2_buffer tV4l2Buf;

    int iLcdWidth;
    int iLcdHeigt;
    int iLcdBpp;
	
	//1、打开设备节点/dev/videox
    iFd = open(strDevName, O_RDWR);
    if (iFd < 0)
    {
        DBG_PRINTF("can not open %s\n", strDevName);
        return -1;
    }
    ptVideoDevice->iFd = iFd;

	//2、VIDIOC_QUERYCAP 查询能力：是否为捕获设备（能否把图像收集传输）、是否支持mmap（内存映射），还是只支持read/write（v4l2的另一种采集图像方式）；
    iError = ioctl(iFd, VIDIOC_QUERYCAP, &tV4l2Cap);
    memset(&tV4l2Cap, 0, sizeof(struct v4l2_capability));
    iError = ioctl(iFd, VIDIOC_QUERYCAP, &tV4l2Cap);
    if (iError) {
    	DBG_PRINTF("Error opening device %s: unable to query device.\n", strDevName);
    	goto err_exit;
    }
	
	//2.1、判断是否支持 捕获能力
    if (!(tV4l2Cap.capabilities & V4L2_CAP_VIDEO_CAPTURE))
    {
    	DBG_PRINTF("%s is not a video capture device\n", strDevName);
        goto err_exit;
    }

	//2.2 判断是否支持流媒体的输入输出（支持mmap）
	if (tV4l2Cap.capabilities & V4L2_CAP_STREAMING) {
	    DBG_PRINTF("%s supports streaming i/o\n", strDevName);
	}

	//2.3 判断是否支持mmap还是只支持read/write
	if (tV4l2Cap.capabilities & V4L2_CAP_READWRITE) {
	    DBG_PRINTF("%s supports read i/o\n", strDevName);
	}

	memset(&tFmtDesc, 0, sizeof(tFmtDesc));
	tFmtDesc.index = 0;
	tFmtDesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	//3、枚举支持的格式（是否支持yuyv，mjpeg，rgb）
	while ((iError = ioctl(iFd, VIDIOC_ENUM_FMT, &tFmtDesc)) == 0) {
        if (isSupportThisFormat(tFmtDesc.pixel