v4l2 qt c++显示摄像头

要在Qt C++中显示摄像头，请使用Video for Linux 2（V4L2）API。

以下是显示摄像头的基本步骤：

1. 打开摄像头设备：

int fd = open("/dev/video0", O_RDWR);
if (fd == -1) {
    perror("Error opening device");
    return -1;
}

2. 查询摄像头设备的参数：

struct v4l2_capability cap;
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1) {
    perror("Error querying device capabilities");
    return -1;
}

3. 设置摄像头设备的参数，如图像格式、分辨率、帧率等：

struct v4l2_format fmt;
memset(&fmt, 0, sizeof(fmt));
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = 640;
fmt.fmt.pix.height = 480;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
if (ioctl(fd, VIDIOC_S_FMT, &fmt) == -1) {
    perror("Error setting device format");
    return -1;
}

4. 创建视频缓冲区：

struct v4l2_requestbuffers req;
memset(&req, 0, sizeof(req));
req.count = 4;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (ioctl(fd, VIDIOC_REQBUFS, &req) == -1) {
    perror("Error requesting buffers");
    return -1;
}

struct buffer {
    void *start;
    size_t length;
};
buffer *buffers = new buffer[req.count];
for (int i = 0; i < req.count; ++i) {
    v4l2_buffer buf;
    memset(&buf, 0, sizeof(buf));
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    buf.index = i;
    if (ioctl(fd, VIDIOC_QUERYBUF, &buf) == -1) {
        perror("Error querying buffer");
        return -1;
    }
    buffers[i].length = buf.length;
    buffers[i].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
    if (buffers[i].start == MAP_FAILED) {
        perror("Error mapping buffer");
        return -1;
    }
}

5. 开始视频采集：

for (int i = 0; i < req.count; ++i) {
    v4l2_buffer buf;
    memset(&buf, 0, sizeof(buf));
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    buf.index = i;
    if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {
        perror("Error queuing buffer");
        return -1;
    }
}

enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (ioctl(fd, VIDIOC_STREAMON, &type) == -1) {
    perror("Error starting stream");
    return -1;
}

6. 读取视频数据并显示：

while (true) {
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(fd, &fds);
    timeval tv = {0};
    tv.tv_sec = 2;
    int r = select(fd + 1, &fds, NULL, NULL, &tv);
    if (r == -1) {
        perror("Error waiting for frame");
        return -1;
    } else if (r == 0) {
        perror("Timeout waiting for frame");
        return -1;
    }
    v4l2_buffer buf;
    memset(&buf, 0, sizeof(buf));
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    if (ioctl(fd, VIDIOC_DQBUF, &buf) == -1) {
        perror("Error dequeuing buffer");
        return -1;
    }
    // buf.index is the index of the buffer that contains the captured frame
    // buffers[buf.index].start contains the frame data
    // buffers[buf.index].length contains the length of the frame data
    // Display the frame using Qt or other libraries
    if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {
        perror("Error queuing buffer");
        return -1;
    }
}

以上是基本的代码框架，你可以根据需要进行修改和优化。注意，这里没有包含错误处理和资源释放的代码，你需要自己添加。