OpenCV / C ++：如何有效设置Raspberry Cam帧速率

Question

我最近开始使用OpenCV。 尽管我一开始取得了许多进步，但现在我似乎已经开始对看似简单的任务迷失了方向：使用Raspberry Pi cam录制简单的视频。 问题在于所产生的视频似乎是快进的，并且原因似乎是录制时实际上未写入一半必要的帧。

经过一个小时的尝试，对编解码器进行了实验并对代码进行了时间测量，以发现瓶颈，现在我发现问题似乎与OpenCV VideoCapture类有关，该类在我的代码中实际提供的帧比预期少得多。

因此，我写了一篇简单的文章，计算了VideoCapture在5秒钟内传送的帧数。 将捕获的属性设置为640x480x30fps可以正常工作，并提供约150帧。 但是，以高达1920x1080x30fps的速度拨号（根据规格，这是一种有效的相机模式，在其他应用程序中也可以正常使用），最终在5秒内只有15帧左右。

可能有一个非常明显的解决方案，但我完全空白。 谁能帮我？ 谢谢！

#include <iostream>
#include <opencv2/core.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>
#include <ctime>

float getElapsedCPUTime(std::clock_t begin){
    return float(clock() - begin)/CLOCKS_PER_SEC;
}

std::time_t getCurrentWallTime(){
    return std::time(nullptr);
}

int main (){ 
//  int cols(640);
//  int rows(480);
    int cols(1920);
    int rows(1080);
    cv::Mat currentFrame;

    // set capture properties
    cv::VideoCapture cap(0);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT, rows);
    cap.set(CV_CAP_PROP_FRAME_WIDTH, cols);
    cap.set(cv::CAP_PROP_FPS, 30);
    cap.set(cv::CAP_PROP_FOURCC, 0x21);

    // control capture properties
    int rows_c(cap.get(CV_CAP_PROP_FRAME_HEIGHT));
    int cols_c(cap.get(CV_CAP_PROP_FRAME_WIDTH));
    int fps(cap.get(cv::CAP_PROP_FPS));
    std::cout << "rows: " << rows_c << ", cols " << cols_c << ", fps " << fps << ", CPS: " << CLOCKS_PER_SEC << std::endl;

    int cnt(0);
    std::time_t loopExecution_begin(getCurrentWallTime());
    while(1){
        std::string msg("");

        // capture frame
        std::clock_t capture_begin(clock());
        cap >> currentFrame;
        float time_for_capture = getElapsedCPUTime(capture_begin);
        ++cnt;

        // get elapsed wall time
        std::time_t loopRunTime = getCurrentWallTime() - loopExecution_begin;

        // output message
        msg += "#: " + std::to_string(cnt);
        msg += "\tTicks begin: " + std::to_string(capture_begin);
        msg += "\tCapturetime: " + std::to_string(time_for_capture) + "s";
        msg += "\tLoop Runtime: " + std::to_string(loopRunTime) + "s";
        std::cout << msg << std::endl;

        // break after 5s
        if (loopRunTime > 5.0) break;

    }   
}

编辑：这是输出：

rows: 1080, cols 1920, fps 30, CPS: 1000000
#: 1    Ticks begin: 362378 Capturetime: 0.055826s  Loop Runtime: 1s
#: 2    Ticks begin: 418543 Capturetime: 0.022631s  Loop Runtime: 1s
#: 3    Ticks begin: 441338 Capturetime: 0.022695s  Loop Runtime: 1s
#: 4    Ticks begin: 464196 Capturetime: 0.023302s  Loop Runtime: 2s
#: 5    Ticks begin: 487659 Capturetime: 0.022729s  Loop Runtime: 2s
#: 6    Ticks begin: 510551 Capturetime: 0.022631s  Loop Runtime: 2s
#: 7    Ticks begin: 533349 Capturetime: 0.022663s  Loop Runtime: 2s
#: 8    Ticks begin: 556176 Capturetime: 0.023194s  Loop Runtime: 3s
#: 9    Ticks begin: 579535 Capturetime: 0.022640s  Loop Runtime: 3s
#: 10   Ticks begin: 602337 Capturetime: 0.023267s  Loop Runtime: 3s
#: 11   Ticks begin: 625789 Capturetime: 0.022741s  Loop Runtime: 3s
#: 12   Ticks begin: 648694 Capturetime: 0.023210s  Loop Runtime: 3s
#: 13   Ticks begin: 672069 Capturetime: 0.022487s  Loop Runtime: 4s
#: 14   Ticks begin: 694721 Capturetime: 0.023162s  Loop Runtime: 4s
#: 15   Ticks begin: 718051 Capturetime: 0.022611s  Loop Runtime: 4s
#: 16   Ticks begin: 740822 Capturetime: 0.023602s  Loop Runtime: 4s
#: 17   Ticks begin: 764600 Capturetime: 0.022555s  Loop Runtime: 5s
#: 18   Ticks begin: 787321 Capturetime: 0.022532s  Loop Runtime: 5s
#: 19   Ticks begin: 810019 Capturetime: 0.022626s  Loop Runtime: 5s
#: 20   Ticks begin: 832813 Capturetime: 0.023161s  Loop Runtime: 5s
#: 21   Ticks begin: 856138 Capturetime: 0.022543s  Loop Runtime: 6s

Answer 1

似乎您想从相机获得h.264流。

当您想对摄像机框架进行一些处理时，OpenCV是无与伦比的，但是由于Pi具有硬件h.264编码器，我不确定会使用OpenCV来完成需要获取H.264的任务。在你的情况下。

为了将h.264输出输出到文件或将其流式传输到某个地方，您可以使用标准raspivid应用程序并将其输出通过管道传递到所需的位置，或者，如果需要更多控制，则可以获取其源代码并对其进行修改。

我懒了，做了前者。 下面的代码将H.264流传输到TCP套接字。 如果存在拥塞（即无法将数据足够快地写入套接字，则代码将关闭套接字，然后我的客户端重新连接）。 这种方法可能不是很优雅，但是我已经使用了一段时间了，而且看起来还可以。

#include "CameraRelay.h"
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <sys/select.h>
#include <poll.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <thread>
#include <mutex>
#include <memory>
#include <stdlib.h>
#include <signal.h>
#include <sys/wait.h>

#define READ 0
#define WRITE 1

pid_t popen2(const char *command, char * const args[], int *infp, int *outfp) {
  int p_stdin[2], p_stdout[2];
  pid_t pid;

  if (pipe(p_stdin) != 0 || pipe(p_stdout) != 0)
    return -1;

  pid = fork();

  if (pid < 0)
    return pid;
  else if (pid == 0)
  {
    close(p_stdin[WRITE]);
    dup2(p_stdin[READ], READ);
    close(p_stdout[READ]);
    dup2(p_stdout[WRITE], WRITE);

    execv(command, args);
    perror("execl");
    exit(1);
  }

  if (infp == NULL)
    close(p_stdin[WRITE]);
  else
    *infp = p_stdin[WRITE];

  if (outfp == NULL)
    close(p_stdout[READ]);
  else
    *outfp = p_stdout[READ];

  return pid;
}

namespace CameraRelay {
  static std::unique_ptr<std::thread> s_thread;
  static std::mutex s_startStopMutex;
  static bool s_bRun;
  int s_listensock = -1;

  void RelayThread() {
    signal(SIGPIPE, SIG_IGN);
    s_listensock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (s_listensock < 0) {
      perror("socket() for camera relay failed");
      return;
    }

    int on = 1;
    setsockopt(s_listensock, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof(on));
    ioctl(s_listensock, FIONBIO, (char *)&on);

    unsigned int bufsz = 1024; // small buffer to control latency
    setsockopt(s_listensock, SOL_SOCKET, SO_SNDBUF, (void *)&bufsz, sizeof(bufsz));

    struct sockaddr_in sa;
    memset((char *)&sa, 0, sizeof(sa));
    sa.sin_family = AF_INET;
    sa.sin_addr.s_addr = htonl(INADDR_ANY);
    sa.sin_port = htons(7124);
    if (bind(s_listensock, (struct sockaddr *)&sa, sizeof(struct sockaddr)) < 0) {
      perror("bind() for camera relay failed");
      return;
    }
    bufsz = 1024; // small buffer to control latency
    setsockopt(s_listensock, SOL_SOCKET, SO_SNDBUF, (void *)&bufsz, sizeof(bufsz));
    if (listen(s_listensock, 1)) {
      perror("listen() for camera relay failed");
      return;
    }
    while (s_bRun) {
      sockaddr_in sa;
      memset((char *)&sa, 0, sizeof(sa));
      socklen_t len = sizeof(sa);
      struct pollfd pfd;
      memset(&pfd, 0, sizeof(pfd));
      pfd.fd = s_listensock;
      pfd.events = POLLIN;
      int ret = poll(&pfd, 1, 500);
      if (ret > 0) {        
        int sock = accept(s_listensock, (struct sockaddr *)&sa, &len);
        unsigned int bufsz = 16384; // small buffer to control latency
        setsockopt(sock, SOL_SOCKET, SO_SNDBUF, (void *)&bufsz, sizeof(bufsz));
        fcntl(sock, F_SETFL, fcntl(sock, F_GETFL, 0) | O_NONBLOCK);
        printf("camera relay socket got new connection.\n");
        char buffer[512];
        std::string cmd = "/usr/bin/raspivid";
        const char *args[] = { "/usr/bin/raspivid", "-o", "-", "-n" , "-s", "-t" ,"0", "-fl", "-hf", "-b", "5000000", "-w", "1280", "-h",  "720", "-fps", "25", nullptr };
        int pin = 0;
        int pout = 0;
        pid_t pid = popen2(cmd.c_str(), const_cast<char **>(args), &pin, &pout);
        if (pid <= 0) {
          perror("popen() failed!");
          break;
        }
        fcntl(pout, F_SETPIPE_SZ, 1024); // small buffer to control latency
        bool bFailed = false;
        int nWait = 0;
        while (s_bRun && !bFailed) {
          struct pollfd pfd2[2];
          memset(&pfd2, 0, sizeof(pfd2));
          pfd2[0].fd = sock;
          pfd2[0].events = POLLIN;
          pfd2[1].fd = pout;
          pfd2[1].events = POLLIN;
          poll(pfd2, 2, 500);

          if (pfd2[0].revents) {
            char rcv;
            if (recv(sock, &rcv, 1, 0)) {
            }
          }

          if (pfd2[1].revents) {
            int nRead = read(pout, buffer, sizeof(buffer));
            if (nRead <= 0) {
              break;
            }
            int nSent = 0;
            while (nSent < nRead) {
              int ret = send(sock, buffer + nSent, nRead - nSent, 0);
              if ((ret < 0 && errno != EWOULDBLOCK) || !s_bRun) {
                perror("camera relay send() failed");
                bFailed = true;
                break;
              }
              if (!nSent && ret == nRead) {
                nWait = 0;
              }
              nSent += ret;
              if (nSent < nRead) {
                memset(&pfd, 0, sizeof(pfd));
                pfd.fd = sock;
                pfd.events = POLLOUT;                
                poll(&pfd, 1, 500);
                nWait++;
                if (nWait > 2) {
                  bFailed = true;
                  break;
                }
              } 
            }
          }
        }
        if (pout > 0)
          close(pout);
        if (pin > 0)
          close(pin);
        if (pid > 0) {                    
          printf("Killing raspivid child process %d with SIGKILL...\n", pid);
          kill(pid, SIGINT);
          sleep(1);
          kill(pid, SIGKILL);
          int status = 0;
          printf("Waiting for process to end...\n");
          waitpid(pid, &status, 0);
          printf("Killed raspivid child process\n");
        }
        if (sock > 0)
          close(sock);        
      }
    }    
  }

  bool Open() {
    if (s_thread)
      return false;
    system("killall raspivid");
    s_bRun = true;
    s_thread = std::unique_ptr<std::thread>(new std::thread(RelayThread));
    return true;
  }

  void Close() {
     if (!s_thread)
      return;
    s_bRun = false;
    s_thread->join();
  }
};