编辑：升级到OpenCV 2.4.2和FFMPEG 0.11.1似乎解决了所有错误和连接问题，但是仍然没有解决帧率下降的问题。
我在Ubuntu 12.04中使用默认的OpenCV软件包，我相信它是2.3.1版本。我连接到一个流MJPEG的Foscam FI8910W。我看到有人说最好的方法是使用opencv+libjpeg+curl，因为这比gstreamer解决方案更快。然而，我偶尔（50%的时间）可以从构建的OpenCV中连到相机并得到视频流。该视频流开始时约为30 fps，大约持续1秒钟，然后就会变慢到5-10 fps。我正在开发的项目需要有6个相机，最好以每秒15-30帧运行（速度越快越好）。
以下是我的问题：
- 这是否是在2.4.2中修复的问题，我应该升级？
- 如果不是，为什么我会得到短暂的突发然后变慢？
- 最佳解决方案仍然是使用curl+libjpeg吗？
- 我看到很多人说已经发布了解决方案，但是实际的解决方案链接很少。将所有实际解决方案（包括curl和gstreamer）引用在一个地方会非常方便，例如http://opencv-users.1802565.n2.nabble.com/IP-camera-solution-td7345005.html。
以下是我的代码：
VideoCapture cap;
cap.open("http://10.10.1.10/videostream.asf?user=test&pwd=1234&resolution=32");
Mat frame;
cap >> frame;
wr.open("test.avi", CV_FOURCC('P','I','M','1'), 29.92, frame.size(), true);
if(!wr.isOpened())
{
cout << "Video writer open failed" << endl;
return(-1);
}
Mat dst = Mat::zeros(frame.rows + HEADER_HEIGHT, frame.cols, CV_8UC3);
Mat roi(dst, Rect(0, HEADER_HEIGHT-1, frame.cols, frame.rows));
Mat head(dst, Rect(0,0,frame.cols, HEADER_HEIGHT));
Mat zhead = Mat::zeros(head.rows, head.cols, CV_8UC3);
namedWindow("test", 1);
time_t tnow;
tm *tS;
double t1 = (double)getTickCount();
double t2;
for(int i = 0; i>-1 ; i++) // infinite loop
{
cap >> frame;
if(!frame.data)
break;
tnow = time(0);
tS = localtime(&tnow);
frame.copyTo(roi);
std::ostringstream L1, L2;
L1 << tS->tm_year+1900 << " " << coutPrep << tS->tm_mon+1 << " ";
L1 << coutPrep << tS->tm_mday << " ";
L1 << coutPrep << tS->tm_hour;
L1 << ":" << coutPrep << tS->tm_min << ":" << coutPrep << tS->tm_sec;
actValueStr = L1.str();
zhead.copyTo(head);
putText(dst, actValueStr, Point(0,HEADER_HEIGHT/2), fontFace, fontScale, Scalar(0,255,0), fontThickness, 8);
L2 << "Frame: " << i;
t2 = (double)getTickCount();
L2 << " " << (t2 - t1)/getTickFrequency()*1000. << " ms";
t1 = (double)getTickCount();
actValueStr = L2.str();
putText(dst, actValueStr, Point(0,HEADER_HEIGHT), fontFace, fontScale, Scalar(0,255,0), fontThickness, 8);
imshow("test", dst);
wr << dst; // write frame to file
cout << "Frame: " << i << endl;
if(waitKey(30) >= 0)
break;
}
以下是程序正常运行时列出的错误信息：
Opening 10.10.1.10
Using network protocols without global network initialization. Please use avformat_network_init(), this will become mandatory later.
Using network protocols without global network initialization. Please use avformat_network_init(), this will become mandatory later.
[asf @ 0x701de0] max_analyze_duration reached
[asf @ 0x701de0] Estimating duration from bitrate, this may be inaccurate
[asf @ 0x701de0] ignoring invalid packet_obj_size (21084 656 21720 21740)
[asf @ 0x701de0] freeing incomplete packet size 21720, new 21696
[asf @ 0x701de0] ff asf bad header 0 at:1029744
[asf @ 0x701de0] ff asf skip 678 (unknown stream)
[asf @ 0x701de0] ff asf bad header 45 at:1030589
[asf @ 0x701de0] packet_obj_size invalid
[asf @ 0x701de0] ff asf bad header 29 at:1049378
[asf @ 0x701de0] packet_obj_size invalid
[asf @ 0x701de0] freeing incomplete packet size 21820, new 21684
[asf @ 0x701de0] freeing incomplete packet size 21684, new 21836
Using network protocols without global network initialization. Please use avformat_network_init(), this will become mandatory later.
Using network protocols without global network initialization. Please use avformat_network_init(), this will become mandatory later.
[asf @ 0x701de0] Estimating duration from bitrate, this may be inaccurate
Successfully opened network camera
[swscaler @ 0x8cf400] No accelerated colorspace conversion found from yuv422p to bgr24.
Output #0, avi, to 'test.avi':
Stream #0.0: Video: mpeg1video (hq), yuv420p, 640x480, q=2-31, 19660 kb/s, 90k tbn, 29.97 tbc
[swscaler @ 0x9d25c0] No accelerated colorspace conversion found from yuv422p to bgr24.
Frame: 0
[swscaler @ 0xa89f20] No accelerated colorspace conversion found from yuv422p to bgr24.
Frame: 1
[swscaler @ 0x7f7840] No accelerated colorspace conversion found from yuv422p to bgr24.
Frame: 2
[swscaler @ 0xb9e6c0] No accelerated colorspace conversion found from yuv422p to bgr24.
Frame: 3
有时在第一次“从比特率估计持续时间”语句之后出现挂起的情况。