有可能在c++中使用树莓派v4l2相机获得良好的FPS吗

我正试图使用带有Raspberry Pi相机的官方V4L2驱动程序在Raspberrry Pi上播放视频，该驱动程序来自raspbian上的C++(2015-02版本)，但我遇到了低FPS问题。

目前，我只是创建一个窗口并将缓冲区复制到屏幕上(大约需要30ms)，而select()大约需要140ms(总共5-6 fps)。我还试着睡100毫秒，它将select()时间减少了类似的量(导致相同的fps)。CPU负载约为5-15%。

我还尝试从控制台(或system())更改驱动程序的fps，但它只能向下工作(例如，如果我将驱动程序fps设置为1fps，我会得到1fps；但如果我将其设置为90fps，即使驱动程序确认将其设置成90fps也会得到5-6fps)。此外，当查询FPS模式中使用的分辨率时，我得到90fps。

我包括了与V4L2相关的代码部分(不同部分之间省略了代码)：

//////////////////
// Open device
//////////////////
mFD = open(mDevName, O_RDWR | O_NONBLOCK, 0);
if (mFD == -1) ErrnoExit("Open device failed");
//////////////////
// Setup format
//////////////////
struct v4l2_format fmt;
memset(&fmt, 0, sizeof(fmt));
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
Xioctl(VIDIOC_G_FMT, &fmt);
mImgWidth = fmt.fmt.pix.width;
mImgHeight = fmt.fmt.pix.height;
cout << "width=" << mImgWidth << " height=" << mImgHeight << "nbytesperline=" << fmt.fmt.pix.bytesperline << " sizeimage=" << fmt.fmt.pix.sizeimage << "n";
// For some reason querying the format always sets pixelformat to JPEG
//  no matter the input, so set it back to YUYV
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
if (Xioctl(VIDIOC_S_FMT, &fmt) == -1)
{
cout << "Set video format failed : " << strerror(errno) << "n";
}
//////////////////
// Setup streaming
//////////////////
struct v4l2_requestbuffers req;
memset(&req, 0, sizeof(req));
req.count = 20;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (-1 == Xioctl(VIDIOC_REQBUFS, &req))
{
ErrnoExit("Reqbufs");
}
if (req.count < 2)
throw "Not enough buffer memory !";
mNBuffers = req.count;
mBuffers = new CBuffer[mNBuffers];
if (!mBuffers) throw "Out of memory !";
for (unsigned int i = 0; i < mNBuffers; i++)
{
struct v4l2_buffer buf;
memset(&buf, 0, sizeof(buf));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (-1 == Xioctl(VIDIOC_QUERYBUF, &buf))
ErrnoExit("Querybuf");
mBuffers[i].mLength = buf.length;
mBuffers[i].pStart = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, mFD, buf.m.offset);
if (mBuffers[i].pStart == MAP_FAILED)
ErrnoExit("mmap");
}
//////////////////
// Start streaming
//////////////////
unsigned int i;
enum v4l2_buf_type type;
struct v4l2_buffer buf;
for (i = 0; i < mNBuffers; i++)
{
memset(&buf, 0, sizeof(buf));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (-1 == Xioctl(VIDIOC_QBUF, &buf))
ErrnoExit("QBUF");
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1==Xioctl(VIDIOC_STREAMON, &type))
ErrnoExit("STREAMON");

主循环中的最后两部分：

//////////////////
// Get frame
//////////////////
FD_ZERO(&fds);
FD_SET(mFD, &fds);
tv.tv_sec = 3;
tv.tv_usec = 0;
struct timespec t0, t1;
clock_gettime(CLOCK_REALTIME, &t0);
// This line takes about 140ms which I don't get
r = select(mFD + 1, &fds, NULL, NULL, &tv);
clock_gettime(CLOCK_REALTIME, &t1);
cout << "select time : " << ((float)(t1.tv_sec - t0.tv_sec))*1000.0f + ((float)(t1.tv_nsec - t0.tv_nsec))/1000000.0f << "n";
if (-1 == r)
{
if (EINTR == errno)
continue;
ErrnoExit("select");
}
if (r == 0)
throw "Select timeoutn";
// Read the frame
//~ struct v4l2_buffer buf;
memset(&mCurBuf, 0, sizeof(mCurBuf));
mCurBuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
mCurBuf.memory = V4L2_MEMORY_MMAP;
// DQBUF about 2ms
if (-1 == Xioctl(VIDIOC_DQBUF, &mCurBuf))
{
if (errno == EAGAIN) continue;
ErrnoExit("DQBUF");
}
clock_gettime(CLOCK_REALTIME, &mCaptureTime);
// Manage frame in mBuffers[buf.index]
mCurBufIndex = mCurBuf.index;
break;
}
//////////////////
// Release frame
//////////////////
if (-1 == Xioctl(VIDIOC_QBUF, &mCurBuf))
ErrnoExit("VIDIOC_QBUF during mainloop");