V4L2抓取USB摄像头YUV视频数据代码

Posted 2022-02-07 柳鲲鹏

• 下载

V4L2 API Specification

• 编译

gcc -o test \\
    v4l2.c

• 测试

编译后运行。

然后使用YUV查看：菜单color-> yuyv，size->640x480

sourceforge-YUVplayer.zip-图像处理文档类资源-CSDN下载

• 源码

源码略有改动，定义了视频宽、高、格式三个常量。同时输出了一些信息。

/*
 *  V4L2 video capture example
 *
 *  This program can be used and distributed without restrictions.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>             /* getopt_long() */

#include <fcntl.h>              /* low-level i/o */
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#include <asm/types.h>          /* for videodev2.h */

#include <linux/videodev2.h>

#define CLEAR(x) memset (&(x), 0, sizeof (x))

#define LOG_HERE()    printf("%s-%d\\n", __func__, __LINE__)

typedef enum 
	IO_METHOD_READ, IO_METHOD_MMAP, IO_METHOD_USERPTR,
 io_method;

struct buffer 
	void * start;
	size_t length;
;

static char * dev_name = NULL;
static io_method g_ioMethod = IO_METHOD_MMAP;
static int g_fd = -1;
struct buffer * buffers = NULL;
static unsigned int n_buffers = 0;

FILE *fp;
char *filename = "test.yuv\\0";

static void errno_exit(const char * s) 
	fprintf(stderr, "%s error %d, %s\\n", s, errno, strerror(errno));

	exit(EXIT_FAILURE);


static int xioctl(int fd, int request, void * arg) 
	int r;

	do 
		r = ioctl(fd, request, arg);
	 while (-1 == r && EINTR == errno);

	return r;


static void process_image(const void * p, int size) 
	fwrite(p, size, 1, fp);


static int read_frame(int count) 
	struct v4l2_buffer buf;
	unsigned int i;

	switch (g_ioMethod) 
	case IO_METHOD_READ:
		if (-1 == read(g_fd, buffers[0].start, buffers[0].length)) 
			switch (errno) 
			case EAGAIN:
				return 0;

			case EIO:
				/* Could ignore EIO, see spec. */
				/* fall through */
			default:
				errno_exit("read");
			
		

		process_image(buffers[0].start, buffers[0].length);

		break;

	case IO_METHOD_MMAP:
		CLEAR(buf);

		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;

		if (-1 == xioctl(g_fd, VIDIOC_DQBUF, &buf)) 
			switch (errno) 
			case EAGAIN:
				return 0;

			case EIO:
				/* Could ignore EIO, see spec. */

				/* fall through */

			default:
				errno_exit("VIDIOC_DQBUF");
			
		

		assert(buf.index < n_buffers);

               LOG_HERE();
               printf("left=%d, length=%d\\n", count, buf.length);
		process_image(buffers[buf.index].start, buf.length);

		if (-1 == xioctl(g_fd, VIDIOC_QBUF, &buf))
			errno_exit("VIDIOC_QBUF");

		break;

	case IO_METHOD_USERPTR:
		CLEAR(buf);
		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_USERPTR;

		if (-1 == xioctl(g_fd, VIDIOC_DQBUF, &buf)) 
			switch (errno) 
			case EAGAIN:
				return 0;

			case EIO:
				/* Could ignore EIO, see spec. */

				/* fall through */

			default:
				errno_exit("VIDIOC_DQBUF");
			
		

		for (i = 0; i < n_buffers; ++i)
			if (buf.m.userptr == (unsigned long) buffers[i].start
					&& buf.length == buffers[i].length)
				break;

		assert(i < n_buffers);

		process_image((void *) buf.m.userptr, buf.length);

		if (-1 == xioctl(g_fd, VIDIOC_QBUF, &buf))
			errno_exit("VIDIOC_QBUF");

		break;
	

	return 1;


static void mainloop(void) 
	unsigned int count;

	count = 100;

	while (count-- > 0) 
		for (;;) 
			fd_set fds;
			struct timeval tv;
			int r;

			FD_ZERO(&fds);
			FD_SET(g_fd, &fds);

			/* Timeout. */
			tv.tv_sec = 2;
			tv.tv_usec = 0;

			r = select(g_fd + 1, &fds, NULL, NULL, &tv);

			if (-1 == r) 
				if (EINTR == errno)
					continue;

				errno_exit("select");
			

			if (0 == r) 
				fprintf(stderr, "select timeout\\n");
				exit(EXIT_FAILURE);
			

			if (read_frame(count))
				break;

			/* EAGAIN - continue select loop. */
		
	


static void stop_capturing(void) 
	enum v4l2_buf_type type;

	switch (g_ioMethod) 
	case IO_METHOD_READ:
		/* Nothing to do. */
		break;

	case IO_METHOD_MMAP:
	case IO_METHOD_USERPTR:
		type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

		if (-1 == xioctl(g_fd, VIDIOC_STREAMOFF, &type))
			errno_exit("VIDIOC_STREAMOFF");

		break;
	


static void start_capturing(void) 
	unsigned int i;
	enum v4l2_buf_type type;

	switch (g_ioMethod) 
	case IO_METHOD_READ:
		/* Nothing to do. */
		break;

	case IO_METHOD_MMAP:
		for (i = 0; i < n_buffers; ++i) 
			struct v4l2_buffer buf;

			CLEAR(buf);

			buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
			buf.memory = V4L2_MEMORY_MMAP;
			buf.index = i;

			if (-1 == xioctl(g_fd, VIDIOC_QBUF, &buf))
				errno_exit("VIDIOC_QBUF");
		

		type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

		if (-1 == xioctl(g_fd, VIDIOC_STREAMON, &type))
			errno_exit("VIDIOC_STREAMON");

		break;

	case IO_METHOD_USERPTR:
		for (i = 0; i < n_buffers; ++i) 
			struct v4l2_buffer buf;

			CLEAR(buf);

			buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
			buf.memory = V4L2_MEMORY_USERPTR;
			buf.index = i;
			buf.m.userptr = (unsigned long) buffers[i].start;
			buf.length = buffers[i].length;

			if (-1 == xioctl(g_fd, VIDIOC_QBUF, &buf))
				errno_exit("VIDIOC_QBUF");
		

		type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

		if (-1 == xioctl(g_fd, VIDIOC_STREAMON, &type))
			errno_exit("VIDIOC_STREAMON");

		break;
	


static void uninit_device(void) 
	unsigned int i;

	switch (g_ioMethod) 
	case IO_METHOD_READ:
		free(buffers[0].start);
		break;

	case IO_METHOD_MMAP:
		for (i = 0; i < n_buffers; ++i)
			if (-1 == munmap(buffers[i].start, buffers[i].length))
				errno_exit("munmap");
		break;

	case IO_METHOD_USERPTR:
		for (i = 0; i < n_buffers; ++i)
			free(buffers[i].start);
		break;
	

	free(buffers);


static void init_read(unsigned int buffer_size) 
	buffers = calloc(1, sizeof(*buffers));

	if (!buffers) 
		fprintf(stderr, "Out of memory\\n");
		exit(EXIT_FAILURE);
	

	buffers[0].length = buffer_size;
	buffers[0].start = malloc(buffer_size);

	if (!buffers[0].start) 
		fprintf(stderr, "Out of memory\\n");
		exit(EXIT_FAILURE);
	


static void init_mmap(void) 
	struct v4l2_requestbuffers req;

	CLEAR(req);

	req.count = 4;
	req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_MMAP;

	if (-1 == xioctl(g_fd, VIDIOC_REQBUFS, &req)) 
		if (EINVAL == errno) 
			fprintf(stderr, "%s does not support "
					"memory mapping\\n", dev_name);
			exit(EXIT_FAILURE);
		 else 
			errno_exit("VIDIOC_REQBUFS");
		
	

	if (req.count < 2) 
		fprintf(stderr, "Insufficient buffer memory on %s\\n", dev_name);
		exit(EXIT_FAILURE);
	

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

	if (!buffers) 
		fprintf(stderr, "Out of memory\\n");
		exit(EXIT_FAILURE);
	

	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) 
		struct v4l2_buffer buf;

		CLEAR(buf);

		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;
		buf.index = n_buffers;

		if (-1 == xioctl(g_fd, VIDIOC_QUERYBUF, &buf))
			errno_exit("VIDIOC_QUERYBUF");

		buffers[n_buffers].length = buf.length;
		buffers[n_buffers].start = mmap(NULL /* start anywhere */, buf.length,
				PROT_READ | PROT_WRITE /* required */,
				MAP_SHARED /* recommended */, g_fd, buf.m.offset);

		if (MAP_FAILED == buffers[n_buffers].start)
			errno_exit("mmap");
	


static void init_userp(unsigned int buffer_size) 
	struct v4l2_requestbuffers req;
	unsigned int page_size;

	page_size = getpagesize();
	buffer_size = (buffer_size + page_size - 1) & ~(page_size - 1);

	CLEAR(req);

	req.count = 4;
	req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_USERPTR;

	if (-1 == xioctl(g_fd, VIDIOC_REQBUFS, &req)) 
		if (EINVAL == errno) 
			fprintf(stderr, "%s does not support "
					"user pointer i/o\\n", dev_name);
			exit(EXIT_FAILURE);
		 else 
			errno_exit("VIDIOC_REQBUFS");
		
	

	buffers = calloc(4, sizeof(*buffers));

	if (!buffers) 
		fprintf(stderr, "Out of memory\\n");
		exit(EXIT_FAILURE);
	

	for (n_buffers = 0; n_buffers < 4; ++n_buffers) 
		buffers[n_buffers].length = buffer_size;
		buffers[n_buffers].start = memalign(/* boundary */page_size,
				buffer_size);

		if (!buffers[n_buffers].start) 
			fprintf(stderr, "Out of memory\\n");
			exit(EXIT_FAILURE);
		
	


static void init_device(void) 
	struct v4l2_capability cap;
	struct v4l2_cropcap cropcap;
	struct v4l2_crop crop;
	struct v4l2_format fmt;
	unsigned int min;

	if (-1 == xioctl(g_fd, VIDIOC_QUERYCAP, &cap)) 
		if (EINVAL == errno) 
			fprintf(stderr, "%s is no V4L2 device\\n", dev_name);
			exit(EXIT_FAILURE);
		 else 
			errno_exit("VIDIOC_QUERYCAP");
		
	

	if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) 
		fprintf(stderr, "%s is no video capture device\\n", dev_name);
		exit(EXIT_FAILURE);
	

	switch (g_ioMethod) 
	case IO_METHOD_READ:
		if (!(cap.capabilities & V4L2_CAP_READWRITE)) 
			fprintf(stderr, "%s does not support read i/o\\n", dev_name);
			exit(EXIT_FAILURE);
		

		break;

	case IO_METHOD_MMAP:
	case IO_METHOD_USERPTR:
		if (!(cap.capabilities & V4L2_CAP_STREAMING)) 
			fprintf(stderr, "%s does not support streaming i/o\\n", dev_name);
			exit(EXIT_FAILURE);
		

		break;
	

	/* Select video input, video standard and tune here. */

	CLEAR(cropcap);

	cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	if (0 == xioctl(g_fd, VIDIOC_CROPCAP, &cropcap)) 
		crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		crop.c = cropcap.defrect; /* reset to default */

		if (-1 == xioctl(g_fd, VIDIOC_S_CROP, &crop)) 
			switch (errno) 
			case EINVAL:
				/* Cropping not supported. */
				break;
			default:
				/* Errors ignored. */
				break;
			
		
	 else 
		/* Errors ignored. */
	

	CLEAR(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 (-1 == xioctl(g_fd, VIDIOC_S_FMT, &fmt))
		errno_exit("VIDIOC_S_FMT");

	/* Note VIDIOC_S_FMT may change width and height. */

	/* Buggy driver paranoia. */
	min = fmt.fmt.pix.width * 2;
	if (fmt.fmt.pix.bytesperline < min)
		fmt.fmt.pix.bytesperline = min;
	min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
	if (fmt.fmt.pix.sizeimage < min)
		fmt.fmt.pix.sizeimage = min;

	switch (g_ioMethod) 
	case IO_METHOD_READ:
		init_read(fmt.fmt.pix.sizeimage);
		break;

	case IO_METHOD_MMAP:
		init_mmap();
		break;

	case IO_METHOD_USERPTR:
		init_userp(fmt.fmt.pix.sizeimage);
		break;
	


static void close_device(void) 
	if (-1 == close(g_fd))
		errno_exit("close");

	g_fd = -1;


static void open_device(void) 
	struct stat st;

	if (-1 == stat(dev_name, &st)) 
		fprintf(stderr, "Cannot identify '%s': %d, %s\\n", dev_name, errno,
				strerror(errno));
		exit(EXIT_FAILURE);
	

	if (!S_ISCHR(st.st_mode)) 
		fprintf(stderr, "%s is no device\\n", dev_name);
		exit(EXIT_FAILURE);
	

	g_fd = open(dev_name, O_RDWR /* required */| O_NONBLOCK, 0);

	if (-1 == g_fd) 
		fprintf(stderr, "Cannot open '%s': %d, %s\\n", dev_name, errno,
				strerror(errno));
		exit(EXIT_FAILURE);
	


static void usage(FILE * fp, int argc, char ** argv) 
	fprintf(fp, "Usage: %s [options]\\n\\n"
			"Options:\\n"
			"-d | --device name   Video device name [/dev/video]\\n"
			"-h | --help          Print this message\\n"
			"-m | --mmap          Use memory mapped buffers\\n"
			"-r | --read          Use read() calls\\n"
			"-u | --userp         Use application allocated buffers\\n"
			"", argv[0]);


static const char short_options[] = "d:hmru";

static const struct option long_options[] =   "device", required_argument,
		NULL, 'd' ,  "help", no_argument, NULL, 'h' ,  "mmap", no_argument,
		NULL, 'm' ,  "read", no_argument, NULL, 'r' ,  "userp", no_argument,
		NULL, 'u' ,  0, 0, 0, 0  ;

int main(int argc, char ** argv) 
	dev_name = "/dev/video0";

	for (;;) 
		int index;
		int c;

		c = getopt_long(argc, argv, short_options, long_options, &index);

		if (-1 == c)
			break;

		switch (c) 
		case 0: /* getopt_long() flag */
			break;

		case 'd':
			dev_name = optarg;
			break;

		case 'h':
			usage(stdout, argc, argv);
			exit(EXIT_SUCCESS);

		case 'm':
			g_ioMethod = IO_METHOD_MMAP;
			break;

		case 'r':
			g_ioMethod = IO_METHOD_READ;
			break;

		case 'u':
			g_ioMethod = IO_METHOD_USERPTR;
			break;

		default:
			usage(stderr, argc, argv);
			exit(EXIT_FAILURE);
		
	

	open_device();

	init_device();

	start_capturing();

	fp = fopen(filename, "wa+");
	mainloop();
	fclose(fp);

	stop_capturing();

	uninit_device();

	close_device();

	exit(EXIT_SUCCESS);

	return 0;