摄像头原始数据读取——V4L2(userptr模式,V4L2_MEMORY_USERPTR)

摄像头原始数据读取——V4L2(userptr模式,V4L2_MEMORY_USERPTR)

用户指针方式允许用户空间的应用程序分配内存，并将内存地址传递给内核中的驱动程序。驱动程序直接将数据填充到用户空间的内存中，从而避免了数据的拷贝过程。
流程：

1. 通过VIDIOC_REQBUFS ioctl请求内核分配视频数据缓冲区，在v4l2_requestbuffers里将memory字段设置成V4L2_MEMORY_USERPTR。
2. 通过VIDIOC_QUERYBUF ioctl获取内核已经分配好的视频数据缓冲区信息。
3. 应用程序分配内存，并将内存地址填充到已经分配好的视频缓冲区中。
4. 通过VIDIOC_QBUF ioctl将已经申请好的缓冲区放入数据缓存队列，将memory字段设置成V4L2_MEMORY_USERPTR。
5. 启动视频流后，使用poll或select函数等待设备缓冲区数据就绪。
6. 通过VIDIOC_DQBUF ioctl从队列中取出已填充的数据缓冲区并进行处理。
7. 处理完数据后，再次通过VIDIOC_QBUF ioctl将缓冲区放入输入队列，循环使用。

v4l2userptrmode.hpp

#ifndef _V4L2USERPTRMODE_H_
#define _V4L2USERPTRMODE_H_


#include <iostream>
#include <list>
#include <vector>
#include <utility>
#include <functional>
#include <mutex>
#include <thread>
#include <linux/videodev2.h>

//图像帧数据结构体
struct VideoBufferStruct
{
    std::string dev_name;   //video设备名
    unsigned int pixel_format; //当前使用的图像格式
    int width;     //图像宽度
    int height;   //图像高度
    unsigned long timestamp; //图像从内核读上来后的时间戳
    size_t data_len;  //图像数据长度
    void *data;   //图像数据
};

class V4L2CaptureVideoData
{
public:
    static bool m_keeprunning;

public:
    explicit V4L2CaptureVideoData();
    ~V4L2CaptureVideoData();

    void RegisterVideoDataProcessCallback(std::function<void(const VideoBufferStruct&)> func);
    bool OpenVideoDevice(std::string device_name);
    bool closeVideoDevice();
    bool QueryVideoDeviceCapability(const unsigned int capability);
    void RegisterVideoUserptr(std::vector<std::pair<unsigned long, unsigned int>> &video_userptr);
    void StartUserptrData();

    /* VIDIOC_QUERYCAP 获取设备支持的操作*/
    bool GetVideoDeviceCapability(struct v4l2_capability &cap);
    /* VIDIOC_G_PRIORITY   获取设备操作的优先级*/
    bool GetVideoDevicePriority(unsigned int &priority);
    /* VIDIOC_S_PRIORITY   设置设备操作的优先级*/
    bool SetVideoDevicePriority(const unsigned int priority);
    /* VIDIOC_LOG_STATUS  获取关于视频设备当前状态的日志信息*/
    bool GetVideoDeviceLogStatus(void);
    /* VIDIOC_ENUM_FMT 列举设备所支持的视频格式*/
    bool EnumVideoDeviceFormat(std::list<struct v4l2_fmtdesc> &fmtdesc);
    /* VIDIOC_G_FMT 获取设备当前使用的视频像素格式*/
    bool GetVideoDeviceFormat(struct v4l2_format &fmt);
    /* VIDIOC_S_FMT 设置设备当前使用的视频像素格式*/
    bool SetVideoDeviceFormat(const struct v4l2_format &fmt);
    /* VIDIOC_TRY_FMT 尝试设置视频像素格式、用于判断设备是否支持该视频像素格式*/
    bool TrySetVideoDeviceFormat(const struct v4l2_format &fmt);
    /* VIDIOC_ENUM_FRAMESIZES 枚举设备支持的视频采集分辨率*/
    bool EnumVideoDeviceFrameSize(const unsigned int pixel_format, std::list<struct v4l2_frmsizeenum> &frmsize);
    /* VIDIOC_ENUM_FRAMEINTERVALS 枚举设备支持的视频采集帧率fps*/
    bool EnumVideoDeviceFrameIntervals(const unsigned int pixel_format, const unsigned int width, const unsigned int height, std::list<struct v4l2_frmivalenum> &frmivals);
    /*VIDIOC_STREAMON 启动视频采集*/
    bool StartVideoCapture(void);
    /*VIDIOC_STREAMOFF 停止视频采集*/
    bool StopVideoCapture(void);
    /*VIDIOC_REQBUFS  申请驱动分配视频帧缓冲区*/
    bool RequestVideoBuffer(const struct v4l2_requestbuffers &requestbuf);
    /*VIDIOC_QUERYBUF 查询视频缓冲区信息 struct v4l2_buffer*/
    bool GetVideoBuffer(const unsigned int memory_type, unsigned int index, v4l2_buffer &video_buffer);
    /*VIDIOC_QBUF 将申请的缓冲帧放入队列*/
    bool PushVideoBuffer(const struct v4l2_buffer &video_buffer);
    /*VIDIOC_DQBUF 采集的缓冲帧出队列*/
    bool PopVideoBuffer(const unsigned int memory_type, struct v4l2_buffer &video_buffer);

private:
    unsigned long getEpochTimeShiftus();

private:
    int m_video_fd;
    std::function<void(const VideoBufferStruct&)> m_video_data_callback;
    std::string m_video_device_name;
    std::vector<std::pair<unsigned long, unsigned int>> m_video_userptr;
};

#endif // _V4L2USERPTRMODE_H_

v4l2userptrmode.cpp

#include "v4l2userptrmode.hpp"

#include <iostream>
#include <thread>
#include <chrono>
#include <string>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <assert.h>
#include <signal.h>
#include <fcntl.h> 
#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 <linux/videodev2.h>

bool V4L2CaptureVideoData::m_keeprunning=true;

V4L2CaptureVideoData::V4L2CaptureVideoData()
{
    m_video_fd=-1;
    m_video_data_callback=nullptr;
    m_video_device_name.clear();
    m_video_userptr.clear();
}

V4L2CaptureVideoData::~V4L2CaptureVideoData()
{
    if(m_video_fd!=-1)
    {
        closeVideoDevice();
    }
}

void V4L2CaptureVideoData::RegisterVideoDataProcessCallback(std::function<void(const VideoBufferStruct&)> func)
{
    m_video_data_callback=func;
}

bool V4L2CaptureVideoData::OpenVideoDevice(std::string device_name)
{
    m_video_device_name=device_name;
    std::string device_head="/dev/video";
    if(m_video_device_name.compare(0, device_head.size(), device_head)!=0)
    {
        std::cerr<<m_video_device_name<<" is not camera device"<<std::endl;
        return false;
    }

    m_video_fd = open(m_video_device_name.c_str(), O_RDWR /* required */ | O_NONBLOCK, 0);
    if (-1 == m_video_fd) 
    {
        std::cerr<<"cannot open video device:"<<"device name="<<m_video_device_name<<",errno="<<errno<<",strerror="<<strerror(errno)<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::closeVideoDevice()
{
    if(m_video_fd<0)
    {
        return true;
    }
    if(close(m_video_fd)==-1)
    {
        std::cerr<<"close video device failed:"<<"errno="<<errno<<",strerror="<<strerror(errno)<<std::endl;
        m_video_fd=-1;
        return false;
    }

    m_video_fd=-1;
    return true;
}

bool V4L2CaptureVideoData::QueryVideoDeviceCapability(const unsigned int capability)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }

    v4l2_capability video_cap;
    if(GetVideoDeviceCapability(video_cap)==false)
    {
        return false;
    }

    if(!(video_cap.capabilities & capability))
    {
        std::cerr<<m_video_device_name<<" not support this capability="<<capability<<std::endl;
        return false;
    }

    return true;
}

void V4L2CaptureVideoData::RegisterVideoUserptr(std::vector<std::pair<unsigned long, unsigned int>> &video_userptr)
{
    m_video_userptr=video_userptr;
}

void V4L2CaptureVideoData::StartUserptrData()
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return;
    }
    
    if(QueryVideoDeviceCapability(V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING)==false)
    {
        return;
    }

    if(m_video_userptr.size()==0)
    {
        std::cerr<<"not input already allocated memory block for v4l2 using in userptr mode"<<std::endl;
        return;
    }

    struct v4l2_format video_format;
    GetVideoDeviceFormat(video_format);

    struct VideoBufferStruct  data_buffer;
    data_buffer.dev_name=m_video_device_name;
    data_buffer.pixel_format=video_format.fmt.pix.pixelformat;
    data_buffer.width=video_format.fmt.pix.width;
    data_buffer.height=video_format.fmt.pix.height;

    unsigned int video_req_buffer_cnt=m_video_userptr.size();
    struct v4l2_requestbuffers video_req_buffer;
    memset(&video_req_buffer,'\0',sizeof(video_req_buffer));
    video_req_buffer.count = video_req_buffer_cnt;
    video_req_buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    video_req_buffer.memory = V4L2_MEMORY_USERPTR;
    if(RequestVideoBuffer(video_req_buffer)==false)
    {
        return;
    }

    for(int index=0;index<video_req_buffer_cnt;index++)
    {
        struct v4l2_buffer tmp_video_buffer;
        tmp_video_buffer.index=index;
        tmp_video_buffer.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        tmp_video_buffer.memory = V4L2_MEMORY_USERPTR;
        tmp_video_buffer.m.userptr = m_video_userptr[index].first;
        tmp_video_buffer.length =m_video_userptr[index].second;
        if(PushVideoBuffer(tmp_video_buffer)==false)
        {
            return;
        }
    }

    if(StartVideoCapture()==false)
    {
        return;
    }

    fd_set fds;
    struct timeval tv;
    int ret;
    while(m_keeprunning==true)
    {
        FD_ZERO (&fds);
        FD_SET (m_video_fd, &fds);
        tv.tv_sec = 3;
        tv.tv_usec = 0;

        ret = select (m_video_fd + 1, &fds, NULL, NULL, &tv);
        if (-1 == ret) 
        {
            if (EINTR == errno)
            {
                continue;
            }
            else
            {
                std::cerr<<"select failed:"<<"errno="<<errno<<",strerror="<<strerror(errno)<<std::endl;
                break;
            }
        }
        else if (0 == ret) 
        {
            std::cerr<<"select timeout no data available."<<std::endl;
            break;
        }
        else
        {
            struct v4l2_buffer video_buffer_data;
            if(PopVideoBuffer(V4L2_MEMORY_USERPTR,video_buffer_data)==false)
            {
                break;
            }
            
            data_buffer.data=(void*)m_video_userptr[video_buffer_data.index].first;
            data_buffer.data_len=video_buffer_data.bytesused;
            data_buffer.timestamp=video_buffer_data.timestamp.tv_sec*1000000+video_buffer_data.timestamp.tv_usec+getEpochTimeShiftus();
            m_video_data_callback(data_buffer);
            
            if(PushVideoBuffer(video_buffer_data)==false)
            {
                return;
            }
            std::this_thread::sleep_for(std::chrono::milliseconds(10));
        }
    }

    if(StopVideoCapture()==false)
    {
        return;
    }

    closeVideoDevice();
}

bool V4L2CaptureVideoData::GetVideoDeviceCapability(v4l2_capability &cap)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_QUERYCAP, &cap);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_QUERYCAP failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    std::cout<<"camera v4l2_capability {"<<std::endl
             <<"       driver = "<<cap.driver<<std::endl
             <<"         card = "<<cap.card<<std::endl
             <<"     bus_info = "<<cap.bus_info<<std::endl
             <<"      version = "<<cap.version<<std::endl
             <<" capabilities = "<<cap.capabilities<<std::endl
             <<"  device_caps = "<<cap.device_caps<<std::endl
             <<"}"<<std::endl;

    return true;
}

bool V4L2CaptureVideoData::GetVideoDevicePriority(unsigned int &priority)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_G_PRIORITY, &priority);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_G_PRIORITY failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    std::cout<<"video device get priority = "<<priority<<std::endl;

    return true;
}

bool V4L2CaptureVideoData::SetVideoDevicePriority(const unsigned int priority)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    unsigned int bk_priority=priority;
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_S_PRIORITY, &bk_priority);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_S_PRIORITY failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    if(bk_priority!=priority)
    {
        std::cerr<<"actual video device priority set "<<bk_priority<<" not input value "<<priority<<std::endl;
        return false;
    }

    std::cout<<"video device set priority = "<<priority<<std::endl;

    return true;
}

bool V4L2CaptureVideoData::GetVideoDeviceLogStatus()
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_LOG_STATUS, NULL);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_LOG_STATUS failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::EnumVideoDeviceFormat(std::list<struct v4l2_fmtdesc> &fmtdesc)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    fmtdesc.clear();
    struct v4l2_fmtdesc tmp_fmtdesc;
    tmp_fmtdesc.index = 0;
    tmp_fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    int ret=0;
    while(!((ret == -1) && (errno != EINTR) && (errno != EAGAIN)))
    {
        ret=ioctl(m_video_fd,VIDIOC_ENUM_FMT,&tmp_fmtdesc);
        if(ret==0)
        {
            fmtdesc.push_back(tmp_fmtdesc);
            std::cout<<"camera v4l2_fmtdesc {"<<std::endl
                     <<"       index = "<<tmp_fmtdesc.index<<std::endl
                     <<"        type = "<<tmp_fmtdesc.type<<std::endl
                     <<"       flags = "<<tmp_fmtdesc.flags<<std::endl
                     <<" description = "<<tmp_fmtdesc.description<<std::endl
                     <<" pixelformat = "<<std::hex<<tmp_fmtdesc.pixelformat<<std::dec<<std::endl
                     <<"}"<<std::endl;
            tmp_fmtdesc.index++;
        } 
    }

    if(fmtdesc.size()==0)
    {
        std::cerr<<"get video format cout is 0"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::GetVideoDeviceFormat(v4l2_format &fmt)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    fmt.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_G_FMT, &fmt);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_G_FMT failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    std::cout<<"camera v4l2_format {"<<std::endl
             <<"                          type = "<<fmt.type<<std::endl
             <<"         v4l2_pix_format.width = "<<fmt.fmt.pix.width<<std::endl
             <<"        v4l2_pix_format.height = "<<fmt.fmt.pix.height<<std::endl
             <<"   v4l2_pix_format.pixelformat = "<<std::hex<<fmt.fmt.pix.pixelformat<<std::dec<<std::endl
             <<"         v4l2_pix_format.field = "<<fmt.fmt.pix.field<<std::endl
             <<"  v4l2_pix_format.bytesperline = "<<fmt.fmt.pix.bytesperline<<std::endl
             <<"     v4l2_pix_format.sizeimage = "<<fmt.fmt.pix.sizeimage<<std::endl
             <<"    v4l2_pix_format.colorspace = "<<fmt.fmt.pix.colorspace<<std::endl
             <<"          v4l2_pix_format.priv = "<<fmt.fmt.pix.priv<<std::endl
             <<"         v4l2_pix_format.flags = "<<fmt.fmt.pix.flags<<std::endl
             <<"}"<<std::endl;

    return true;
}

bool V4L2CaptureVideoData::SetVideoDeviceFormat(const v4l2_format &fmt)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    v4l2_format tmp_fmt;
    memcpy(&tmp_fmt,&fmt,sizeof(tmp_fmt));
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_S_FMT, &tmp_fmt);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_S_FMT failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    if((tmp_fmt.fmt.pix.width==fmt.fmt.pix.width) && 
       (tmp_fmt.fmt.pix.height==fmt.fmt.pix.height) && 
       (tmp_fmt.fmt.pix.pixelformat==fmt.fmt.pix.pixelformat))
    {
        std::cout<<"camera set v4l2_format {"<<std::endl
             <<"                          type = "<<fmt.type<<std::endl
             <<"         v4l2_pix_format.width = "<<fmt.fmt.pix.width<<std::endl
             <<"        v4l2_pix_format.height = "<<fmt.fmt.pix.height<<std::endl
             <<"   v4l2_pix_format.pixelformat = "<<std::hex<<fmt.fmt.pix.pixelformat<<std::dec<<std::endl
             <<"}"<<std::endl;
        return true;
    }
    else
    {
        std::cerr<<"camera actual set v4l2_format {"<<std::endl
             <<"                          type = "<<tmp_fmt.type<<std::endl
             <<"         v4l2_pix_format.width = "<<tmp_fmt.fmt.pix.width<<std::endl
             <<"        v4l2_pix_format.height = "<<tmp_fmt.fmt.pix.height<<std::endl
             <<"   v4l2_pix_format.pixelformat = "<<std::hex<<tmp_fmt.fmt.pix.pixelformat<<std::dec<<std::endl
             <<"}"<<std::endl;
        return false;
    }
}

bool V4L2CaptureVideoData::TrySetVideoDeviceFormat(const v4l2_format &fmt)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    std::cout<<"camera try set v4l2_format {"<<std::endl
             <<"                          type = "<<fmt.type<<std::endl
             <<"         v4l2_pix_format.width = "<<fmt.fmt.pix.width<<std::endl
             <<"        v4l2_pix_format.height = "<<fmt.fmt.pix.height<<std::endl
             <<"   v4l2_pix_format.pixelformat = "<<std::hex<<fmt.fmt.pix.pixelformat<<std::dec<<std::endl
             <<"         v4l2_pix_format.field = "<<fmt.fmt.pix.field<<std::endl
             <<"}"<<std::endl;

    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_TRY_FMT, &fmt);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_TRY_FMT failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::EnumVideoDeviceFrameSize(const unsigned int pixel_format,std::list<struct v4l2_frmsizeenum> &frmsize)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    frmsize.clear();
    struct v4l2_frmsizeenum tmp_frmsize;
    tmp_frmsize.index=0;
    tmp_frmsize.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    tmp_frmsize.pixel_format = pixel_format;
    int ret=0;
    while(!((ret == -1) && (errno != EINTR) && (errno != EAGAIN)))
    {
        ret=ioctl(m_video_fd,VIDIOC_ENUM_FRAMESIZES,&tmp_frmsize);
        if(ret==0)
        {
            frmsize.push_back(tmp_frmsize);
            std::cout<<"camera v4l2_frmsizeenum {"<<std::endl
                     <<"                        index = "<<tmp_frmsize.index<<std::endl
                     <<"                         type = "<<tmp_frmsize.type<<std::endl
                     <<"                 pixel_format = "<<std::hex<<tmp_frmsize.pixel_format<<std::dec<<std::endl
                     <<"  v4l2_frmsize_discrete.width = "<<tmp_frmsize.discrete.width<<std::endl
                     <<" v4l2_frmsize_discrete.height = "<<tmp_frmsize.discrete.height<<std::endl
                     <<"}"<<std::endl;
            tmp_frmsize.index++;
        } 
    }

    if(frmsize.size()==0)
    {
        std::cerr<<"get video frame size cout is 0"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::EnumVideoDeviceFrameIntervals(const unsigned int pixel_format,const unsigned int width,const unsigned int height,std::list<struct v4l2_frmivalenum> &frmivals)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    frmivals.clear();
    struct v4l2_frmivalenum tmp_frmival;
    tmp_frmival.index = 0;
    tmp_frmival.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    tmp_frmival.pixel_format = pixel_format;
    tmp_frmival.width = width;
    tmp_frmival.height = height;
    int ret=0;
    while(!((ret == -1) && (errno != EINTR) && (errno != EAGAIN)))
    {
        ret=ioctl(m_video_fd, VIDIOC_ENUM_FRAMEINTERVALS, &tmp_frmival);
        if(ret==0)
        {
            frmivals.push_back(tmp_frmival);
            std::cout<<"Frame interval<"<<tmp_frmival.discrete.denominator / tmp_frmival.discrete.numerator<<"fps>"<<std::endl;
            std::cout<<"camera v4l2_frmivalenum {"<<std::endl
                     <<"                  index = "<<tmp_frmival.index<<std::endl
                     <<"                   type = "<<tmp_frmival.type<<std::endl
                     <<"           pixel_format = "<<std::hex<<tmp_frmival.pixel_format<<std::dec<<std::endl
                     <<"                  width = "<<tmp_frmival.width<<std::endl
                     <<"                 height = "<<tmp_frmival.height<<std::endl
                     <<"   v4l2_fract.numerator = "<<tmp_frmival.discrete.numerator<<std::endl
                     <<" v4l2_fract.denominator = "<<tmp_frmival.discrete.denominator<<std::endl
                     <<"  numerator/denominator = "<<tmp_frmival.discrete.denominator / tmp_frmival.discrete.numerator<<" fps"<<std::endl
                     <<"}"<<std::endl;
            tmp_frmival.index++;
        }
    }

    if(frmivals.size()==0)
    {
        std::cerr<<"get video frame intervals cout is 0"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::StartVideoCapture()
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_STREAMON, &type);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_STREAMON failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::StopVideoCapture()
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_STREAMOFF, &type);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_STREAMOFF failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::RequestVideoBuffer(const v4l2_requestbuffers &requestbuf)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    if(ioctl(m_video_fd, VIDIOC_REQBUFS, &requestbuf)==-1)
    {
        std::cerr<<"ioctl VIDIOC_REQBUFS failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::GetVideoBuffer(const unsigned int memory_type,unsigned int index,struct v4l2_buffer &video_buffer)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    video_buffer.index = index;
    video_buffer.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    video_buffer.memory = memory_type;
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_QUERYBUF, &video_buffer);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));

    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_QUERYBUF failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    std::cout<<"camera v4l2_buffer {"<<std::endl
                     <<"   index = "<<video_buffer.index<<std::endl
                     <<"    type = "<<video_buffer.type<<std::endl
                     <<"   flags = "<<video_buffer.flags<<std::endl
                     <<"  memory = "<<video_buffer.memory<<std::endl
                     <<"  length = "<<video_buffer.length<<std::endl
                     <<"  offset = "<<std::hex<<video_buffer.m.offset<<std::dec<<std::endl
                     <<"      fd = "<<std::hex<<video_buffer.m.fd<<std::dec<<std::endl
                     <<" userptr = "<<std::hex<<video_buffer.m.userptr<<std::dec<<std::endl
                     <<"}"<<std::endl;

    return true;
}

bool V4L2CaptureVideoData::PushVideoBuffer(const v4l2_buffer &video_buffer)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_QBUF, &video_buffer);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_QBUF failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    return true;
}

bool V4L2CaptureVideoData::PopVideoBuffer(const unsigned int memory_type,struct v4l2_buffer &video_buffer)
{
    if(m_video_fd==-1)
    {
        std::cerr<<"not open video device,must open first"<<std::endl;
        return false;
    }
    
    video_buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    video_buffer.memory = memory_type;
    int ret=0;
    do
    {
        ret=ioctl(m_video_fd, VIDIOC_DQBUF, &video_buffer);
    } while (ret == -1 && ((errno == EINTR) || (errno == EAGAIN)));
    
    if(ret!=0)
    {
        std::cerr<<"ioctl VIDIOC_DQBUF failed:("<<"errno="<<errno<<",strerror="<<strerror(errno)<<")"<<std::endl;
        return false;
    }

    return true;
}

unsigned long V4L2CaptureVideoData::getEpochTimeShiftus()
{
    struct timeval epochtime;
    struct timespec  vsTime;

    gettimeofday(&epochtime, NULL);
    clock_gettime(CLOCK_MONOTONIC, &vsTime);

    unsigned long uptime_us = vsTime.tv_sec*1000000+(long)round(vsTime.tv_nsec/ 1000.0);
    unsigned long epoch_us =  epochtime.tv_sec*1000000+epochtime.tv_usec;
    return epoch_us - uptime_us;
}

测试代码test.cpp

#include "v4l2userptrmode.hpp"
#include <iostream>
#include <string>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>

//信号绑定，绑定Ctrl+C
static void sig_handler(int sig) 
{
    if (sig == SIGINT) 
    {
        V4L2CaptureVideoData::m_keeprunning = false;
    }
}

// save picture to file
static int id_index = 0;
//视频帧数据处理函数
void VideoDataFunc(const VideoBufferStruct &video_data)
{
    std::cout << "device name:" << video_data.dev_name << ",timestamp:" << video_data.timestamp << ",width:" << video_data.width << ",height:" << video_data.height << ",data length:" << video_data.data_len << std::endl;
    std::string filename = "pictures_yuv/test" + std::to_string(id_index) + ".yuv";
    int file_fd = open(filename.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0777);
    write(file_fd, video_data.data, video_data.data_len);
    close(file_fd);
    id_index++;
}

int main(int, char **)
{
    signal(SIGINT, sig_handler); 
    V4L2CaptureVideoData camera_read;
    //注册回调函数
    camera_read.RegisterVideoDataProcessCallback(VideoDataFunc);
    //打开视频设备
    if(camera_read.OpenVideoDevice("/dev/video0")==false)
    {
        return -1;
    }

    struct v4l2_format video_fmt;
    memset(&video_fmt, '\0', sizeof(video_fmt));
    //获取当前视频设备的格式
    if(camera_read.GetVideoDeviceFormat(video_fmt)==false)
    {
        return -1;
    }

//设置视频设备的格式
    video_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    video_fmt.fmt.pix.width = 1280;
    video_fmt.fmt.pix.height = 720;
    video_fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    video_fmt.fmt.pix.field = V4L2_FIELD_ANY;
    if(camera_read.SetVideoDeviceFormat(video_fmt)==false)
    {
        return -1;
    }

//申请用户空间内存
    std::vector<std::pair<unsigned long, unsigned int>> video_userptr_block;
    void *userptr_databuffer[4];
    for (int index = 0; index < 4; index++)
    {
        userptr_databuffer[index] = malloc(video_fmt.fmt.pix.sizeimage);
        video_userptr_block.push_back(std::make_pair((unsigned long)userptr_databuffer[index], video_fmt.fmt.pix.sizeimage));
    }
    //注册用户空间内存，用以接收图像数据
    camera_read.RegisterVideoUserptr(video_userptr_block);
    //开始采集数据
    camera_read.StartUserptrData();
    //释放用户空间申请的内存
    for (int index = 0; index < 4; index++)
    {
        free(userptr_databuffer[index]);
        userptr_databuffer[index]=NULL;
    }
    return 0;
}

测试结果：

原文地址：https://blog.csdn.net/qq_33232152/article/details/143884253

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