v4l2
介绍
v4l2 是 用户 从设备获取 音视频数据的方法。
用户通过 v4l2 可以知道 设备支持 哪些操作 和 支持 哪些数据格式。
通常使用 内存映射，传输数据。
用户预先建立多个内存映射，将空内存输队，等待kernel将数据填充到空内存块，装有数据的内存块出队，用户操作数据。
操作逻辑
- 设置设备数据格式等参数
- 申请内存块，并建立和应用空间的内存映射
- 开始捕获，并入队 内存块
- 出队内存块
- 处理数据
- 入队无用内存块
示例
V4L2_BUF_TYPE_VIDEO_CAPTURE
V4L2_BUF_TYPE_VIDEO_CAPTURE ： 一个内存块存储一帧数据的捕获模式
代码出处：https://www.jianshu.com/p/0ac427d267d4
/*v4l2_example.c*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <linux/videodev2.h>
#include <sys/mman.h>
#include <sys/time.h>
#define TRUE (1)
#define FALSE (0)
#define FILE_VIDEO "/dev/video0"
#define IMAGE "./img/demo"
#define IMAGEWIDTH 640
#define IMAGEHEIGHT 480
#define FRAME_NUM 4
int fd;
struct v4l2_buffer buf;
struct buffer
{
void * start;
unsigned int length;
long long int timestamp;
} *buffers;
int v4l2_init()
{
struct v4l2_capability cap;
struct v4l2_fmtdesc fmtdesc;
struct v4l2_format fmt;
struct v4l2_streamparm stream_para;
//打开摄像头设备
if ((fd = open(FILE_VIDEO, O_RDWR)) == -1)
{
printf("Error opening V4L interface\n");
return FALSE;
}
//查询设备属性
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1)
{
printf("Error opening device %s: unable to query device.\n",FILE_VIDEO);
return FALSE;
}
else
{
printf("driver:\t\t%s\n",cap.driver);
printf("card:\t\t%s\n",cap.card);
printf("bus_info:\t%s\n",cap.bus_info);
printf("version:\t%d\n",cap.version);
printf("capabilities:\t%x\n",cap.capabilities);
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE)
{
printf("Device %s: supports capture.\n",FILE_VIDEO);
}
if ((cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING)
{
printf("Device %s: supports streaming.\n",FILE_VIDEO);
}
}
//显示所有支持帧格式
fmtdesc.index=0;
fmtdesc.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
printf("Support format:\n");
while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc)!=-1)
{
printf("\t%d.%s\n",fmtdesc.index+1,fmtdesc.description);
fmtdesc.index++;
}
//检查是否支持某帧格式
struct v4l2_format fmt_test;
fmt_test.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt_test.fmt.pix.pixelformat=V4L2_PIX_FMT_RGB32;
if(ioctl(fd,VIDIOC_TRY_FMT,&fmt_test)==-1)
{
printf("not support format RGB32!\n");
}
else
{
printf("support format RGB32\n");
}
//查看及设置当前格式
printf("set fmt...\n");
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB32; //jpg格式
//fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;//yuv格式
fmt.fmt.pix.height = IMAGEHEIGHT;
fmt.fmt.pix.width = IMAGEWIDTH;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
printf("fmt.type:\t\t%d\n",fmt.type);
printf("pix.pixelformat:\t%c%c%c%c\n",fmt.fmt.pix.pixelformat & 0xFF, (fmt.fmt.pix.pixelformat >> 8) & 0xFF,(fmt.fmt.pix.pixelformat >> 16) & 0xFF, (fmt.fmt.pix.pixelformat >> 24) & 0xFF);
printf("pix.height:\t\t%d\n",fmt.fmt.pix.height);
printf("pix.width:\t\t%d\n",fmt.fmt.pix.width);
printf("pix.field:\t\t%d\n",fmt.fmt.pix.field);
if(ioctl(fd, VIDIOC_S_FMT, &fmt) == -1)
{
printf("Unable to set format\n");
return FALSE;
}
printf("get fmt...\n");
if(ioctl(fd, VIDIOC_G_FMT, &fmt) == -1)
{
printf("Unable to get format\n");
return FALSE;
}
{
printf("fmt.type:\t\t%d\n",fmt.type);
printf("pix.pixelformat:\t%c%c%c%c\n",fmt.fmt.pix.pixelformat & 0xFF, (fmt.fmt.pix.pixelformat >> 8) & 0xFF,(fmt.fmt.pix.pixelformat >> 16) & 0xFF, (fmt.fmt.pix.pixelformat >> 24) & 0xFF);
printf("pix.height:\t\t%d\n",fmt.fmt.pix.height);
printf("pix.width:\t\t%d\n",fmt.fmt.pix.width);
printf("pix.field:\t\t%d\n",fmt.fmt.pix.field);
}
//设置及查看帧速率，这里只能是30帧，就是1秒采集30张图
memset(&stream_para, 0, sizeof(struct v4l2_streamparm));
stream_para.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
stream_para.parm.capture.timeperframe.denominator = 30;
stream_para.parm.capture.timeperframe.numerator = 1;
if(ioctl(fd, VIDIOC_S_PARM, &stream_para) == -1)
{
printf("Unable to set frame rate\n");
return FALSE;
}
if(ioctl(fd, VIDIOC_G_PARM, &stream_para) == -1)
{
printf("Unable to get frame rate\n");
return FALSE;
}
{
printf("numerator:%d\ndenominator:%d\n",stream_para.parm.capture.timeperframe.numerator,stream_para.parm.capture.timeperframe.denominator);
}
return TRUE;
}
int v4l2_mem_ops()
{
unsigned int n_buffers;
struct v4l2_requestbuffers req;
//申请帧缓冲
req.count=FRAME_NUM;
req.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory=V4L2_MEMORY_MMAP;
if(ioctl(fd,VIDIOC_REQBUFS,&req)==-1)
{
printf("request for buffers error\n");
return FALSE;
}
// 申请用户空间的地址列
buffers = malloc(req.count*sizeof (*buffers));
if (!buffers)
{
printf ("out of memory!\n");
return FALSE;
}
// 进行内存映射
for (n_buffers = 0; n_buffers < FRAME_NUM; n_buffers++)
{
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffers;
//查询
if (ioctl (fd, VIDIOC_QUERYBUF, &buf) == -1)
{
printf("query buffer error\n");
return FALSE;
}
//映射
buffers[n_buffers].length = buf.length;
buffers[n_buffers].start = mmap(NULL,buf.length,PROT_READ|PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
if (buffers[n_buffers].start == MAP_FAILED)
{
printf("buffer map error\n");
return FALSE;
}
}
return TRUE;
}
int v4l2_frame_process()
{
unsigned int n_buffers;
enum v4l2_buf_type type;
char file_name[100];
char index_str[10];
long long int extra_time = 0;
long long int cur_time = 0;
long long int last_time = 0;
//入队和开启采集
for (n_buffers = 0; n_buffers < FRAME_NUM; n_buffers++)
{
buf.index = n_buffers;
ioctl(fd, VIDIOC_QBUF, &buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
ioctl(fd, VIDIOC_STREAMON, &type);
//出队，处理，写入yuv文件，入队，循环进行
int loop = 0;
while(loop < 15)
{
for(n_buffers = 0; n_buffers < FRAME_NUM; n_buffers++)
{
//出队
buf.index = n_buffers;
ioctl(fd, VIDIOC_DQBUF, &buf);
//查看采集数据的时间戳之差，单位为微妙
buffers[n_buffers].timestamp = buf.timestamp.tv_sec*1000000+buf.timestamp.tv_usec;
cur_time = buffers[n_buffers].timestamp;
extra_time = cur_time - last_time;
last_time = cur_time;
printf("time_deta:%lld\n\n",extra_time);
printf("buf_len:%d\n",buffers[n_buffers].length);
//处理数据只是简单写入文件，名字以loop的次数和帧缓冲数目有关
printf("grab image data OK\n");
memset(file_name,0,sizeof(file_name));
memset(index_str,0,sizeof(index_str));
sprintf(index_str,"%d",loop*4+n_buffers);
strcpy(file_name,IMAGE);
strcat(file_name,index_str);
strcat(file_name,".jpg");
//strcat(file_name,".yuv");
FILE *fp2 = fopen(file_name, "wb");
if(!fp2)
{
printf("open %s error\n",file_name);
return(FALSE);
}
fwrite(buffers[n_buffers].start, IMAGEHEIGHT*IMAGEWIDTH*2,1,fp2);
fclose(fp2);
printf("save %s OK\n",file_name);
//入队循环
ioctl(fd, VIDIOC_QBUF, &buf);
}
loop++;
}
return TRUE;
}
int v4l2_release()
{
unsigned int n_buffers;
enum v4l2_buf_type type;
//关闭流
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
ioctl(fd, VIDIOC_STREAMON, &type);
//关闭内存映射
for(n_buffers=0;n_buffers<FRAME_NUM;n_buffers++)
{
munmap(buffers[n_buffers].start,buffers[n_buffers].length);
}
//释放自己申请的内存
free(buffers);
//关闭设备
close(fd);
return TRUE;
}
/*int v4l2_video_input_output()
{
struct v4l2_input input;
struct v4l2_standard standard;
//首先获得当前输入的index,注意只是index，要获得具体的信息，就的调用列举操作
memset (&input,0,sizeof(input));
if (-1 == ioctl (fd, VIDIOC_G_INPUT, &input.index)) {
printf("VIDIOC_G_INPUT\n");
return FALSE;
}
//调用列举操作，获得 input.index 对应的输入的具体信息
if (-1 == ioctl (fd, VIDIOC_ENUMINPUT, &input)) {
printf("VIDIOC_ENUM_INPUT \n");
return FALSE;
}
printf("Current input %s supports:\n", input.name);
//列举所有的所支持的 standard，如果 standard.id 与当前 input 的 input.std 有共同的
//bit flag，意味着当前的输入支持这个 standard,这样将所有驱动所支持的 standard 列举一个
//遍，就可以找到该输入所支持的所有 standard 了。
memset(&standard,0,sizeof (standard));
standard.index = 0;
while(0 == ioctl(fd, VIDIOC_ENUMSTD, &standard)) {
if (standard.id & input.std){
printf ("%s\n", standard.name);
}
standard.index++;
}
// EINVAL indicates the end of the enumeration, which cannot be empty unless this device falls under the USB exception.
if (errno != EINVAL || standard.index == 0) {
printf("VIDIOC_ENUMSTD\n");
return FALSE;
}
}*/
int main(int argc, char const *argv[])
{
printf("begin....\n");
sleep(10);
v4l2_init();
printf("init....\n");
sleep(10);
v4l2_mem_ops();
printf("malloc....\n");
sleep(10);
v4l2_frame_process();
printf("process....\n");
sleep(10);
v4l2_release();
printf("release\n");
sleep(20);
return TRUE;
}
V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE ： 多个内存块存储一帧数据
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <linux/videodev2.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <assert.h>
#include "display.h"
#define TRUE (1)
#define FALSE (0)
#define FILE_VIDEO "/dev/video0"
#define IMAGE "./img/demo"
#define IMAGEWIDTH 1080
#define IMAGEHEIGHT 720
#define FRAME_NUM 4
#define CLEAR(item) memset(item, 0x0, sizeof(*(item)))
int fd;
#define FMT_NUM_PLANES 1
struct v4l2_requestbuffers reqbuf;
/* Our current format uses 3 planes per buffer */
struct {
void *start[FMT_NUM_PLANES];
size_t length[FMT_NUM_PLANES];
} *buffers;
struct v4l2_buffer buffer;
int v4l2_init()
{
struct v4l2_capability cap;
struct v4l2_fmtdesc fmtdesc;
struct v4l2_format fmt;
if ((fd = open(FILE_VIDEO, O_RDWR)) == -1)
{
printf("Error opening V4L interface\n");
return FALSE;
}
// 查看设备支持的功能
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1)
{
printf("Error opening device %s: unable to query device.\n",FILE_VIDEO);
return FALSE;
}
else
{
printf("driver:\t\t%s\n",cap.driver);
printf("card:\t\t%s\n",cap.card);
printf("bus_info:\t%s\n",cap.bus_info);
printf("version:\t%d\n",cap.version);
printf("capabilities:\t%x\n",cap.capabilities);
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE)
{
printf("Device %s: supports capture.\n",FILE_VIDEO);
}
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE_MPLANE) == V4L2_CAP_VIDEO_CAPTURE_MPLANE)
{
printf("Device %s: supports mplane capture.\n",FILE_VIDEO);
}
if ((cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING)
{
printf("Device %s: supports streaming.\n",FILE_VIDEO);
}
}
// 枚举支持的所有图层格式
fmtdesc.index = 0;
fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
printf("Support format:\n");
while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc)!=-1)
{
printf("\t%d.%s,%d\n",fmtdesc.index+1,fmtdesc.description,
fmtdesc.flags);
fmtdesc.index++;
}
// 显示当前的图层格式
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
printf("get fmt...\n");
if(ioctl(fd, VIDIOC_G_FMT, &fmt) == -1) {
printf("Unable to get format\n");
perror("VIDIOC_G_FMT");
return FALSE;
}
else {
printf("fmt.type:\t\t%d\n",fmt.type);
printf("pix.pixelformat:\t%c%c%c%c\n",fmt.fmt.pix_mp.pixelformat & 0xFF, (fmt.fmt.pix_mp.pixelformat >> 8) & 0xFF,(fmt.fmt.pix_mp.pixelformat >> 16) & 0xFF, (fmt.fmt.pix_mp.pixelformat >> 24) & 0xFF);
printf("pix.height:\t\t%d\n",fmt.fmt.pix_mp.height);
printf("pix.width:\t\t%d\n",fmt.fmt.pix_mp.width);
printf("pix.field:\t\t%d\n",fmt.fmt.pix_mp.field);
}
fmt.fmt.pix_mp.pixelformat = V4L2_PIX_FMT_YUV420;
fmt.fmt.pix_mp.width = IMAGEWIDTH;
fmt.fmt.pix_mp.height = IMAGEHEIGHT;
if(ioctl(fd, VIDIOC_S_FMT, &fmt) == -1)
{
printf("Unable to set format\n");
return FALSE;
}
return TRUE;
}
int v4l2_mem_ops()
{
unsigned int i, j;
memset(&reqbuf, 0, sizeof(reqbuf));
reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
reqbuf.memory = V4L2_MEMORY_MMAP;
reqbuf.count = 4;
if (ioctl(fd, VIDIOC_REQBUFS, &reqbuf) < 0) {
if (errno == EINVAL)
printf("Video capturing or mmap-streaming is not supported\\n");
else
perror("VIDIOC_REQBUFS");
exit(EXIT_FAILURE);
}
/* We want at least five buffers. */
if (reqbuf.count < 2) {
/* You may need to free the buffers here. */
printf("Not enough buffer memory\\n");
exit(EXIT_FAILURE);
}
buffers = calloc(reqbuf.count, sizeof(*buffers));
assert(buffers != NULL);
for (i = 0; i < reqbuf.count; i++) {
struct v4l2_plane planes[FMT_NUM_PLANES];
memset(&buffer, 0, sizeof(buffer));
buffer.type = reqbuf.type;
buffer.memory = V4L2_MEMORY_MMAP;
buffer.index = i;
/* length in struct v4l2_buffer in multi-planar API stores the size
* of planes array. */
buffer.length = FMT_NUM_PLANES;
buffer.m.planes = planes;
if (ioctl(fd, VIDIOC_QUERYBUF, &buffer) < 0) {
perror("VIDIOC_QUERYBUF");
exit(EXIT_FAILURE);
}
/* Every plane has to be mapped separately */
for (j = 0; j < FMT_NUM_PLANES; j++) {
buffers[i].length[j] = buffer.m.planes[j].length; /* remember for munmap() */
buffers[i].start[j] = mmap(NULL, buffer.m.planes[j].length,
PROT_READ | PROT_WRITE, /* recommended */
MAP_SHARED, /* recommended */
fd, buffer.m.planes[j].m.mem_offset);
if (MAP_FAILED == buffers[i].start[j]) {
/* If you do not exit here you should unmap() and free()
the buffers and planes mapped so far. */
perror("mmap");
exit(EXIT_FAILURE);
}
}
}
printf("Success to test mem\n");
return EXIT_FAILURE;
}
int v4l2_frame_process()
{
unsigned int n_buffers;
enum v4l2_buf_type type;
char file_name[100];
char index_str[10];
long long int extra_time = 0;
long long int cur_time = 0;
long long int last_time = 0;
printf("count = : %d\n", reqbuf.count);
//入队和开启采集
int i;
for (i = 0; i < reqbuf.count; i++) {
buffer.index = i;
if (ioctl(fd, VIDIOC_QBUF, &buffer) < 0) {
printf("failed enqueue buffer\n");
perror("VIDIOC_QBUF");
return EXIT_FAILURE;
}
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
if (ioctl(fd, VIDIOC_STREAMON, &type) < 0) {
printf("failed start stream\n");
perror("VIDIOC_STREAMON");
return EXIT_FAILURE;
}
printf("Success to start stream\n");
display_t dp = {0};
if (display_init(&dp, IMAGEWIDTH,
IMAGEHEIGHT, SDL_IYUV_OVERLAY) < 0) {
printf("Failed to init display\n");
return -1;
}
//出队，处理，写入yuv文件，入队，循环进行
int loop = 3;
while(1)
{
for(i = 0; i < reqbuf.count; i++)
{
//出队
buffer.index = i;
if (ioctl(fd, VIDIOC_DQBUF, &buffer) < 0) {
printf("failed to dequeue\n");
perror("ioctl");
return EXIT_FAILURE;
}
//处理数据只是简单写入文件，名字以loop的次数和帧缓冲数目有关
printf("grab image data OK\n");
memset(file_name, 0, sizeof(file_name));
memset(index_str, 0, sizeof(index_str));
sprintf(index_str, "%d", loop * 4 + i);
strcpy(file_name, IMAGE);
strcat(file_name, index_str);
strcat(file_name,".yuv");
FILE *fp2 = fopen(file_name, "wb");
if(!fp2)
{
printf("open %s error\n",file_name);
return EXIT_FAILURE;
}
int j;
for (j = 0; j < FMT_NUM_PLANES; j++) {
fwrite(buffers[i].start[j], buffers[i].length[j],1,fp2);
}
fclose(fp2);
printf("save %s OK\n",file_name);
//入队循环
ioctl(fd, VIDIOC_QBUF, &buffer);
}
}
return TRUE;
}
int v4l2_release()
{
enum v4l2_buf_type type;
//关闭流
type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
ioctl(fd, VIDIOC_STREAMOFF, &type);
int i, j;
/* Cleanup. */
for (i = 0; i < reqbuf.count; i++)
for (j = 0; j < FMT_NUM_PLANES; j++)
munmap(buffers[i].start[j], buffers[i].length[j]);
//关闭设备
close(fd);
return TRUE;
}
int main(int argc, char const *argv[])
{
printf("begin....\n");
sleep(1);
v4l2_init();
printf("init....\n");
sleep(1);
v4l2_mem_ops();
printf("malloc....\n");
sleep(1);
v4l2_frame_process();
printf("process....\n");
sleep(1);
v4l2_release();
printf("release\n");
return TRUE;
}
资料推荐
http://100ask.net/pages/cfba84/#_7-2-v4l2视频采集原理
https://www.kernel.org/doc/html/v4.10/media/kapi/v4l2-intro.html
