linux下怎样进行摄像头编程？

在linux下所有设备都是文件。所以对摄像头的操作其实就是对文件的操作。USB摄像头的设备文件就是在/dev目录下的video0(假如只有一个摄像头)。在linux下操作摄像头就是使用v4l2对摄像头进行的操作，操作步骤如下

打开设备文件。

int fd=open(”/dev/video0″,O_RDWR);

2. 取得设备的capability，看看设备具有什么功能，比如是否具有输入,或者音频输入输出等。VIDIOC_QUERYCAP,struct v4l2_capability

v4l2_std_id std;

do {

ret= ioctl(fd, VIDIOC_QUERYSTD, std);

} while (ret == -1 errno == EAGAIN);

switch (std) {

case V4L2_STD_NTSC:

//……

case V4L2_STD_PAL:

//……

}

3. 选择输入，一个设备可以有多个输入。VIDIOC_S_INPUT,struct v4l2_input(可不要)

4. 设置的制式和帧格式，制式包括PAL，NTSC，帧的格式个包括宽度和高度等。

VIDIOC_S_STD,VIDIOC_S_FMT,struct v4l2_std_id,struct v4l2_format

struct v4l2_format fmt;

memset ( fmt, 0, sizeof(fmt) );

fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

fmt.fmt.pix.width = 320;

fmt.fmt.pix.height = 240;

fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_JPEG;

if (ioctl(fd, VIDIOC_S_FMT, fmt) < 0）

{

printf(“set format failedn”);

//return 0;

}

5. 向驱动申请帧缓冲，一般不超过5个。struct v4l2_requestbuffers

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(“VIDIOC_REQBUFS error n”);

//return -1;

}

6.申请物理内存

将申请到的帧缓冲映射到用户空间，这样就可以直接操作采集到的帧了，而不必去复制。将申请到的帧缓冲全部入队列，以便存放采集到的数据.VIDIOC_QBUF,struct v4l2_buffer

VideoBuffer* buffers = calloc( req.count, sizeof(VideoBuffer) );

printf(“sizeof(VideoBuffer) is %dn”,sizeof(VideoBuffer));

struct v4l2_buffer buf;

for (numBufs = 0; numBufs < req.count; numBufs++)

{

memset( buf, 0, sizeof(buf) );

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

buf.memory = V4L2_MEMORY_MMAP;

buf.index = numBufs;

if (ioctl(fd, VIDIOC_QUERYBUF, buf) < 0)

{

printf(“VIDIOC_QUERYBUF errorn”);

//return -1;

}

printf(“buf len is %dn”,sizeof(buf));

//内存映射

buffers.length = buf.length;

buffers.offset = (size_t) buf.m.offset;

buffers.start = mmap (NULL, buf.length,PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);

printf(“buffers.length = %d,buffers.offset = %d ,buffers.start = %dn”,buffers.length,buffers.offset,buffers.start);

printf(“buf2 len is %dn”,sizeof(buffers.start));

if (buffers.start == MAP_FAILED)

{

perror(“buffers errorn”);

//return -1;

}

if (ioctl (fd, VIDIOC_QBUF, buf) < 0)

{

printf(“VIDIOC_QBUF errorn”);

//return -1;

}

}

7. 开始的采集。

enum v4l2_buf_type type;

type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

if (ioctl (fd, VIDIOC_STREAMON, type) < 0)

{

printf(“VIDIOC_STREAMON errorn”);

// return -1;

}

8. 出队列以取得已采集数据的帧缓冲，取得原始采集数据。VIDIOC_DQBUF, 将缓冲重新入队列尾,这样可以循环采集。VIDIOC_QBUF

if (ioctl(fd, VIDIOC_DQBUF, buf) < 0)

{

perror(“VIDIOC_DQBUF failed.n”);

//return -1;

}

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

buf.memory = V4L2_MEMORY_MMAP;

unsigned char *ptcur = buffers.start;

DEBUG(“buf.bytesused = %d n”,buf.bytesused);

int i1;

for(i1=0; i1<buf.bytesused; i1++)

{

if((buffers.start == 0xFF) (buffers.start == 0xC4))

{

DEBUG(“huffman table finded! nbuf.bytesused = %dnFFC4 = %d n”,buf.bytesused,i1);

break;

}

}

if(i1 == buf.bytesused)printf(“huffman table don’t exist! n”);

int i;

for(i=0; i<buf.bytesused; i++)

{

if((buffers.start == 0xFF) (buffers.start == 0xD8)) break;

ptcur++;

}

DEBUG(“i=%d,FF=%02x,D8=%02xn”,i,buffers.start,buffers.start);

int imagesize =buf.bytesused – i;

DEBUG(“buf.bytesused = %d n”,buf.bytesused);

DEBUG (“imagesize = %d n”,imagesize);

9. 停止的采集。VIDIOC_STREAMOFF

10. 关闭设备。close(fd);