最近想做一个 使用 video4linux2（注意不是 video4linux ）采集 usb 摄像头上的图像的程序，网上找了一个源码，运行成功，分享过程。
程序编译时直接使用 gcc -o test test.c就可以了。
本人运行时所带参数：./test -r 2
运行所生成的jpg图像文件：
程序源代码：
/* * V4L2 video capture example */ #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 <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)) 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 io = IO_METHOD_MMAP; /* can be V4L2_PIX_FMT_YUV420 or V4L2_PIX_FMT_PWC2 */ static int pixel_format = V4L2_PIX_FMT_YUV420; static int fd = -1; struct buffer *buffers = NULL; static unsigned int n_buffers = 0; static unsigned int width = 320; static unsigned int height = 240; static unsigned int count = 1; 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, ssize_t size) { unsigned char *bbuf=(unsigned char *)p;int ll; for ( ll= 1024 ; ll< 60000; ll++) if ((bbuf[ll] == 0xFF) && (bbuf[ll+1] == 0xD9)) break;FILE *fp2;fp2=fopen("xx.jpg","w");fwrite(bbuf, 1, ll+2, fp2); /* static int no_image = 0; char filename[1024]; int fd; ssize_t written = 0; snprintf(filename, sizeof(filename), "/tmp/webcam-%5.5d.%s", no_image++, pixel_format == V4L2_PIX_FMT_YUV420 ? "yuv" : "raw"); fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR); if (fd < 0) { fputc('*', stdout); fflush(stdout); return; } do { int ret; ret = write(fd, p + written, size - written); if (ret < 0) { fputc('+', stdout); fflush(stdout); return; } written += ret; } while (written < size); close(fd); fputc('.', stdout); fflush(stdout); */ } static int read_frame(void) { struct v4l2_buffer buf; unsigned int i; ssize_t read_bytes; unsigned int total_read_bytes; switch (io) { case IO_METHOD_READ: total_read_bytes = 0; do { read_bytes = read(fd, buffers[0].start, buffers[0].length); if (read_bytes < 0) { switch (errno) { case EIO: case EAGAIN: continue; default: errno_exit("read"); } } total_read_bytes += read_bytes; } while (total_read_bytes < buffers[0].length); 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(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); process_image(buffers[buf.index].start, buf.length); if (-1 == xioctl(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(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(fd, VIDIOC_QBUF, &buf)) errno_exit("VIDIOC_QBUF"); break; } return 1; } static void mainloop(void) { while (count-- > 0) { for (;;) { fd_set fds; struct timeval tv; int r; FD_ZERO(&fds); FD_SET(fd, &fds); /* Timeout. */ tv.tv_sec = 2; tv.tv_usec = 0; r = select(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()) break; /* EAGAIN - continue select loop. */ } } } static void stop_capturing(void) { enum v4l2_buf_type type; switch (io) { 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(fd, VIDIOC_STREAMOFF, &type)) errno_exit("VIDIOC_STREAMOFF"); break; } } static void start_capturing(void) { unsigned int i; enum v4l2_buf_type type; switch (io) { 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(fd, VIDIOC_QBUF, &buf)) errno_exit("VIDIOC_QBUF"); } type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == xioctl(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.m.userptr = (unsigned long) buffers[i].start; buf.length = buffers[i].length; if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) errno_exit("VIDIOC_QBUF"); } type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == xioctl(fd, VIDIOC_STREAMON, &type)) errno_exit("VIDIOC_STREAMON"); break; } } static void uninit_device(void) { unsigned int i; switch (io) { 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 = 1; req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; req.memory = V4L2_MEMORY_MMAP; if (-1 == xioctl(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(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 */ , 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; CLEAR(req); req.count = 4; req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; req.memory = V4L2_MEMORY_USERPTR; if (-1 == xioctl(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 = malloc(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(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"); } } //VIDIOC_QUERYCAP,VIDIOC_S_CROP,VIDIOC_CROPCAP if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) { fprintf(stderr, "%s is no video capture device/n", dev_name); exit(EXIT_FAILURE); } switch (io) { 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. */ cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) { /* Errors ignored. */ } crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; crop.c = cropcap.defrect; /* reset to default */ if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) { switch (errno) { case EINVAL: /* Cropping not supported. */ break; default: /* Errors ignored. */ break; } } CLEAR(fmt); fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; fmt.fmt.pix.width = width; fmt.fmt.pix.height = height; fmt.fmt.pix.pixelformat = pixel_format; fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; printf("%d %d /n",width,height); if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt)) errno_exit("VIDIOC_S_FMT"); /* Note VIDIOC_S_FMT may change width and height. */ width = fmt.fmt.pix.width; height = fmt.fmt.pix.height; printf("%d %d /n",width,height); switch (io) { 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(fd)) errno_exit("close"); 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); } fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, 0); if (-1 == fd) { fprintf(stderr, "Cannot open '%s': %d, %s/n", dev_name, errno, strerror(errno)); exit(EXIT_FAILURE); } } int main(int argc, char **argv) { dev_name = "/dev/video0"; printf("%d,%d,%d/n",VIDIOC_QUERYCAP,VIDIOC_S_CROP,VIDIOC_CROPCAP); open_device(); init_device(); start_capturing(); mainloop(); stop_capturing(); uninit_device(); close_device(); exit(EXIT_SUCCESS); return 0; }
（——仅供交流——）
大多数人想要改造这个世界，但却罕有人想改造自己。
