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，原因似乎是录制时实际上没有写入一半必要的帧。
在尝试了一个小时的编解码器和时间测量我的代码以发现瓶颈之后，我现在发现问题似乎与OpenCV VideoCapture类有关，该类在我的代码中的实际提供的内容要少得多帧超出预期。
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），最终只能在5秒内显示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
答案 0 :(得分：0)
您似乎想从相机获得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，因此我不确定将它用于需要H.264的任务，因此我不确定在您的情况下会用到。
要获取h.264输出到文件或将其流式传输到某个地方，可以使用标准raspivid应用程序并将其输出通过管道传输到所需的位置，或者，如果需要更多控制，则可以使用其源代码并修改它。
我懒了，做了前者。下面的代码将H.264流传输到TCP套接字。 如果出现拥塞（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）。这种方法可能并不十分优雅，但我已经使用了一段时间，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();
}
};