camera的测试程序-预览的保存

最新推荐文章于 2025-04-26 10:29:28 发布

xiaojsj111

最新推荐文章于 2025-04-26 10:29:28 发布

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分类专栏： camera 文章标签： linux camera

本文链接：https://blog.youkuaiyun.com/xiaojsj111/article/details/38843605

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本文详细介绍了在Linux环境下，通过相机设备进行视频预览的步骤，包括打开设备、设置视频格式和帧率、分配缓冲区、映射缓冲区、启动流、获取并保存视频帧、停止流和关闭设备。重点讨论了视频帧的内存分配、映射到用户空间以及数据传输的过程。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

step1: 打开视频设备

static int video_open(const char *devname)
{
	struct v4l2_capability cap;
	int dev, ret;

	dev = open(devname, O_RDWR);
	if (dev < 0) {
		TestAp_Printf(TESTAP_DBG_ERR, "Error opening device %s: %d.\n", devname, errno);
		return dev;
	}

	memset(&cap, 0, sizeof cap);
	ret = ioctl(dev, VIDIOC_QUERYCAP, &cap);
	if (ret < 0) {
		TestAp_Printf(TESTAP_DBG_ERR, "Error opening device %s: unable to query device.\n",
			devname);
		close(dev);
		return ret;
	}
}

step2: Set the video format

static int video_set_format(int dev, unsigned int w, unsigned int h, unsigned int format)
{
	struct v4l2_format fmt;
	int ret;

	memset(&fmt, 0, sizeof fmt);
	fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	fmt.fmt.pix.width = w;
	fmt.fmt.pix.height = h;
	fmt.fmt.pix.pixelformat = format;
	fmt.fmt.pix.field = V4L2_FIELD_ANY;

	ret = ioctl(dev, VIDIOC_S_FMT, &fmt);
	if (ret < 0) {
		TestAp_Printf(TESTAP_DBG_ERR, "Unable to set format: %d.\n", errno);
		return ret;
	}

	TestAp_Printf(TESTAP_DBG_FLOW, "Video format set: width: %u height: %u buffer size: %u\n",
		fmt.fmt.pix.width, fmt.fmt.pix.height, fmt.fmt.pix.sizeimage);
	return 0;
}

step3: Set the frame rate

static int video_set_framerate(int dev, int framerate)
{
	struct v4l2_streamparm parm;
	int ret;

	memset(&parm, 0, sizeof parm);
	parm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	ret = ioctl(dev, VIDIOC_G_PARM, &parm);
	if (ret < 0) {
		TestAp_Printf(TESTAP_DBG_ERR, "Unable to get frame rate: %d.\n", errno);
		return ret;
	}

	TestAp_Printf(TESTAP_DBG_FLOW, "Current frame rate: %u/%u\n",
		parm.parm.capture.timeperframe.numerator,
		parm.parm.capture.timeperframe.denominator);

	parm.parm.capture.timeperframe.numerator = 1;
	parm.parm.capture.timeperframe.denominator = framerate;

	ret = ioctl(dev, VIDIOC_S_PARM, &parm);
	if (ret < 0) {
		TestAp_Printf(TESTAP_DBG_ERR, "Unable to set frame rate: %d.\n", errno);
		return ret;
	}

	ret = ioctl(dev, VIDIOC_G_PARM, &parm);
	if (ret < 0) {
		TestAp_Printf(TESTAP_DBG_ERR, "Unable to get frame rate: %d.\n", errno);
		return ret;
	}

	TestAp_Printf(TESTAP_DBG_FLOW, "Frame rate set: %u/%u\n",
		parm.parm.capture.timeperframe.numerator,
		parm.parm.capture.timeperframe.denominator);
	return 0;
}

step4：Allocate buffers.

static int video_reqbufs(int dev, int nbufs)
{
	struct v4l2_requestbuffers rb;
	int ret;

	memset(&rb, 0, sizeof rb);
	rb.count = nbufs;
	rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	rb.memory = V4L2_MEMORY_MMAP;

	ret = ioctl(dev, VIDIOC_REQBUFS, &rb);
	if (ret < 0) {
		TestAp_Printf(TESTAP_DBG_ERR, "Unable to allocate buffers: %d.\n", errno);
		return ret;
	}

	TestAp_Printf(TESTAP_DBG_FLOW, "%u buffers allocated.\n", rb.count);
	return rb.count;
}

对应的内核处理流程如下：