1、前言

在查看攝像頭類型時，大致可以分為兩類：Video Capture 和 Video Capture Multiplanar。

本次應用程序主要針對類型為Video Capture Multiplanar的相機。

2、環境介紹

rk3566 + ov8858

3、步驟

應用程序編寫主要分為以下幾個步驟：

1、打開設備節點。

2、查詢設備能力。

3、枚舉支持的視頻格式。

4、設置格式。

5、請求buffer。

6、buffer入隊列。

7、打開相機。

8、buffer出隊列。

9、保存為yuv文件。

10、buffer重新入隊列。

11、關閉相機。

4、應用程序編寫

完整的應用程序如下：

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <linux/types.h>          
#include <linux/videodev2.h>
#include <poll.h>
#include <sys/mman.h>
#include <jpeglib.h>
#include <linux/fb.h>#define FRAME_SIZE_X    640
#define FRAME_SIZE_Y    480int main(int argc, char **argv)
{int fd;int ret;void *buffers[VIDEO_MAX_FRAME][VIDEO_MAX_PLANES];int type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;int buffer_cnt;struct pollfd fds[1];int i;int num_planes;char filename[32];int file_cnt = 0;if (argc != 2){printf("Usage: %s </dev/videoX>\n", argv[0]);return -1;}/* 1. open /dev/video* */fd = open(argv[1], O_RDWR);if (fd < 0){printf("can not open %s\n", argv[1]);goto _err;}/* 2. query capability */struct v4l2_capability cap;memset(&cap, 0, sizeof(struct v4l2_capability));if (0 == ioctl(fd, VIDIOC_QUERYCAP, &cap)){        if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE_MPLANE) == 0) {fprintf(stderr, "Error opening device %s: video capture mplane not supported.\n", argv[1]);goto _ioc_querycap_err;}if(!(cap.capabilities & V4L2_CAP_STREAMING)) {fprintf(stderr, "%s does not support streaming i/o\n", argv[1]);goto _ioc_querycap_err;}}else{printf("can not get capability\n");goto _ioc_querycap_err;}/* 3. enum formt */struct v4l2_fmtdesc fmtdesc;struct v4l2_frmsizeenum fsenum;int fmt_index = 0;int frame_index = 0;while (1){fmtdesc.index = fmt_index;  fmtdesc.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;  if (0 != ioctl(fd, VIDIOC_ENUM_FMT, &fmtdesc))break;// printf("format %s:\n", fmtdesc.description);frame_index = 0;while (1){memset(&fsenum, 0, sizeof(struct v4l2_frmsizeenum));fsenum.pixel_format = fmtdesc.pixelformat;fsenum.index = frame_index;if (ioctl(fd, VIDIOC_ENUM_FRAMESIZES, &fsenum) == 0){// printf("\t%d: %d x %d\n", frame_index, fsenum.discrete.width, fsenum.discrete.height);}else{break;}frame_index++;}fmt_index++;}/* 4. set formt */struct v4l2_format fmt;memset(&fmt, 0, sizeof(struct v4l2_format));fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;fmt.fmt.pix.width = FRAME_SIZE_X;fmt.fmt.pix.height = FRAME_SIZE_Y;fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_NV21;fmt.fmt.pix.field = V4L2_FIELD_ANY;if (0 == ioctl(fd, VIDIOC_S_FMT, &fmt)){num_planes = fmt.fmt.pix_mp.num_planes;printf("the final frame-size has been set : %d x %d\n", fmt.fmt.pix.width, fmt.fmt.pix.height);}else{printf("can not set format\n");goto _ioc_sfmt_err;}/* 5. require buffer */struct v4l2_requestbuffers rb;memset(&rb, 0, sizeof(struct v4l2_requestbuffers));rb.count = 32;rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;rb.memory = V4L2_MEMORY_MMAP;if (0 == ioctl(fd, VIDIOC_REQBUFS, &rb)){buffer_cnt = rb.count;for(i = 0; i < rb.count; i++) {struct v4l2_buffer buf;struct v4l2_plane planes[num_planes];memset(&buf, 0, sizeof(struct v4l2_buffer));memset(&planes, 0, sizeof(planes));buf.index = i;buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;buf.memory = V4L2_MEMORY_MMAP;buf.m.planes = planes;buf.length = num_planes;if (0 == ioctl(fd, VIDIOC_QUERYBUF, &buf)){for (int j = 0; j < num_planes; j++){buffers[i][j] = mmap(NULL, buf.m.planes[j].length, PROT_READ | PROT_WRITE, MAP_SHARED,fd, buf.m.planes[j].m.mem_offset);if (buffers[i][j] == MAP_FAILED) {printf("Unable to map buffer\n");goto _err;}}}else{printf("can not query buffer\n");goto _err;}            }}else{printf("can not request buffers\n");goto _ioc_reqbufs_err;}/* 6. queue buffer */for(i = 0; i < buffer_cnt; ++i) {struct v4l2_buffer buf;struct v4l2_plane planes[num_planes];memset(&buf, 0, sizeof(struct v4l2_buffer));memset(&planes, 0, sizeof(planes));buf.index = i;buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;buf.memory = V4L2_MEMORY_MMAP;buf.m.planes = planes;buf.length = num_planes;if (0 != ioctl(fd, VIDIOC_QBUF, &buf)){perror("Unable to queue buffer");goto _ioc_qbuf_err;}}/* start camera */if (0 != ioctl(fd, VIDIOC_STREAMON, &type)){printf("Unable to start capture\n");goto _err;}printf("start camera ...\n");while (1){/* poll */memset(fds, 0, sizeof(fds));fds[0].fd = fd;fds[0].events = POLLIN;if (1 == poll(fds, 1, -1)){/* dequeue buffer */struct v4l2_buffer buf;struct v4l2_plane planes[num_planes];memset(&buf, 0, sizeof(struct v4l2_buffer));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;buf.memory = V4L2_MEMORY_MMAP;buf.m.planes = planes;buf.length = num_planes;if (0 != ioctl(fd, VIDIOC_DQBUF, &buf)){printf("Unable to dequeue buffer\n");goto _ioc_dqbuf_err;}/* save as file */sprintf(filename, "video_raw_data_%04d.yuv", file_cnt++);int fd_file = open(filename, O_RDWR | O_CREAT, 0666);if (fd_file < 0){printf("can not create file : %s\n", filename);}printf("capture to %s\n", filename);for (int i = 0; i < num_planes; i++)write(fd_file, buffers[buf.index][i], buf.m.planes[i].bytesused);close(fd_file);/* queue buffer */if (0 != ioctl(fd, VIDIOC_QBUF, &buf)){printf("Unable to queue buffer");goto _ioc_qbuf_err;}}}/* close camera */if (0 != ioctl(fd, VIDIOC_STREAMOFF, &type)){printf("Unable to stop capture\n");goto _ioc_streamoff_err;}close(fd);return 0;_ioc_qbuf_err:
_ioc_reqbufs_err:
_ioc_sfmt_err:
_ioc_querycap_err:
_ioc_streamoff_err:
_ioc_dqbuf_err:
_err:return -1;
}

5、測試

5.1、編譯應用程序

如果你使用的buildroot系統，需要交叉編譯。

這里測試所使用的板子跑的是ubuntu，執行如下命令直接編譯：

sudo gcc -o mipi_to_yuv mipi_to_yuv.c 

5.2、運行應用程序

sudo ./mipi_to_yuv /dev/video0

在windows下使用yuv播放器打開任意一張圖片：

6、總結

參考文章：

Camera | 4.瑞芯微平臺MIPI攝像頭應用程序編寫_瑞芯微-CSDN專欄

源碼gitee倉庫：

倉庫主頁：
https://gitee.com/cattle_l/v4l2_app.git
直接拉取：
git clone https://gitee.com/cattle_l/v4l2_app.git