for (int i = 0; i < req.count; ++i) { munmap(buffers[i].start, buffers[i].length); } free(buffers); close(fd);
时间: 2024-06-04 22:10:19 浏览: 7
这段代码应该是用于关闭视频设备的,具体解释如下:
1. `munmap(buffers[i].start, buffers[i].length)`:释放内存映射区域,参数 `buffers[i].start` 是要释放的内存地址,`buffers[i].length` 是要释放的内存大小。
2. `free(buffers)`:释放动态分配的内存,参数 `buffers` 是要释放的内存指针。
3. `close(fd)`:关闭设备文件描述符,参数 `fd` 是设备文件的描述符。
综上所述,这段代码是用于释放视频设备所占用的资源,以便其他程序能够访问该设备。
相关问题
写一个v4l2接口的测试程序
以下是一个简单的v4l2接口的测试程序,可以获取摄像头的视频流并显示在屏幕上:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <errno.h>
#define BUFFER_COUNT 4
struct buffer {
void *start;
size_t length;
};
int main(int argc, char **argv)
{
int fd;
struct v4l2_capability cap;
struct v4l2_format fmt;
struct v4l2_requestbuffers req;
struct buffer *buffers;
struct v4l2_buffer buf;
unsigned int i, n_buffers;
fd = open("/dev/video0", O_RDWR);
if (fd == -1) {
perror("open");
return EXIT_FAILURE;
}
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1) {
perror("VIDIOC_QUERYCAP");
return EXIT_FAILURE;
}
if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
fprintf(stderr, "The device does not support video capture.\n");
return EXIT_FAILURE;
}
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_NONE;
if (ioctl(fd, VIDIOC_S_FMT, &fmt) == -1) {
perror("VIDIOC_S_FMT");
return EXIT_FAILURE;
}
memset(&req, 0, sizeof(req));
req.count = BUFFER_COUNT;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (ioctl(fd, VIDIOC_REQBUFS, &req) == -1) {
perror("VIDIOC_REQBUFS");
return EXIT_FAILURE;
}
buffers = calloc(req.count, sizeof(*buffers));
if (!buffers) {
fprintf(stderr, "Out of memory.\n");
return EXIT_FAILURE;
}
for (i = 0; i < req.count; ++i) {
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("VIDIOC_QUERYBUF");
return EXIT_FAILURE;
}
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("mmap");
return EXIT_FAILURE;
}
}
for (i = 0; i < req.count; ++i) {
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("VIDIOC_QBUF");
return EXIT_FAILURE;
}
}
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (ioctl(fd, VIDIOC_STREAMON, &type) == -1) {
perror("VIDIOC_STREAMON");
return EXIT_FAILURE;
}
for (i = 0; i < BUFFER_COUNT; ++i) {
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("VIDIOC_DQBUF");
return EXIT_FAILURE;
}
// Process the frame here.
// ...
if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {
perror("VIDIOC_QBUF");
return EXIT_FAILURE;
}
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (ioctl(fd, VIDIOC_STREAMOFF, &type) == -1) {
perror("VIDIOC_STREAMOFF");
return EXIT_FAILURE;
}
for (i = 0; i < req.count; ++i) {
if (munmap(buffers[i].start, buffers[i].length) == -1) {
perror("munmap");
return EXIT_FAILURE;
}
}
free(buffers);
if (close(fd) == -1) {
perror("close");
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
```
这个程序可以获取摄像头的视频流,对每一帧进行处理后再显示。其中,V4L2_PIX_FMT_YUYV 是常见的一种像素格式。
aidlux操作系统中 打开摄像头的代码
在Aidlux操作系统中,打开摄像头需要使用Linux系统提供的V4L2(Video4Linux2)驱动程序。下面是一个示例代码,可以打开并获取摄像头的图像:
```c
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#define CAMERA_DEVICE "/dev/video0"
#define CAPTURE_FILE "frame.raw"
#define IMAGE_WIDTH 640
#define IMAGE_HEIGHT 480
#define BUFFER_COUNT 4
struct buffer {
void *start;
size_t length;
};
int main(int argc, char **argv)
{
int fd;
struct v4l2_capability caps;
struct v4l2_format fmt;
struct v4l2_requestbuffers req;
struct v4l2_buffer buf;
struct buffer *buffers;
unsigned int i, n;
char *ptr;
size_t size;
FILE *fp;
/* 打开摄像头设备 */
fd = open(CAMERA_DEVICE, O_RDWR);
if (fd < 0) {
perror("open");
return 1;
}
/* 获取摄像头设备的能力信息 */
if (ioctl(fd, VIDIOC_QUERYCAP, &caps) < 0) {
perror("ioctl VIDIOC_QUERYCAP");
return 1;
}
/* 设置摄像头的格式 */
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = IMAGE_WIDTH;
fmt.fmt.pix.height = IMAGE_HEIGHT;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
if (ioctl(fd, VIDIOC_S_FMT, &fmt) < 0) {
perror("ioctl VIDIOC_S_FMT");
return 1;
}
/* 请求摄像头的缓冲区 */
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
req.count = BUFFER_COUNT;
if (ioctl(fd, VIDIOC_REQBUFS, &req) < 0) {
perror("ioctl VIDIOC_REQBUFS");
return 1;
}
/* 映射摄像头的缓冲区到用户空间 */
buffers = calloc(req.count, sizeof(*buffers));
for (i = 0; i < req.count; ++i) {
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (ioctl(fd, VIDIOC_QUERYBUF, &buf) < 0) {
perror("ioctl VIDIOC_QUERYBUF");
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("mmap");
return 1;
}
}
/* 将缓冲区放入队列中 */
for (i = 0; i < req.count; ++i) {
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (ioctl(fd, VIDIOC_QBUF, &buf) < 0) {
perror("ioctl VIDIOC_QBUF");
return 1;
}
}
/* 开始捕获视频 */
n = 100; /* 捕获100帧 */
for (i = 0; i < n; ++i) {
/* 从队列中取出缓冲区 */
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (ioctl(fd, VIDIOC_DQBUF, &buf) < 0) {
perror("ioctl VIDIOC_DQBUF");
return 1;
}
/* 处理图像数据 */
size = buf.bytesused;
ptr = buffers[buf.index].start;
fp = fopen(CAPTURE_FILE, "wb");
fwrite(ptr, size, 1, fp);
fclose(fp);
/* 将缓冲区重新放入队列中 */
if (ioctl(fd, VIDIOC_QBUF, &buf) < 0) {
perror("ioctl VIDIOC_QBUF");
return 1;
}
}
/* 停止捕获视频 */
if (ioctl(fd, VIDIOC_STREAMOFF, &buf.type) < 0) {
perror("ioctl VIDIOC_STREAMOFF");
return 1;
}
/* 解除映射 */
for (i = 0; i < req.count; ++i) {
munmap(buffers[i].start, buffers[i].length);
}
free(buffers);
/* 关闭摄像头设备 */
close(fd);
return 0;
}
```
上面的示例代码使用了V4L2的MMAP方式,将摄像头的缓冲区映射到用户空间。在捕获每一帧图像后,可以在用户空间中处理图像数据。这里的示例代码只是将图像保存到文件中。在实际应用中,可以将图像传输到网络中或者进行一些图像处理操作。
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