Blocking after call VideoCapture set CV_CAP_PROP_POS_MSEC

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We use OpenCv to play a http url video.We use VideoCapture get a wrong frame number from video(possible my video format having problem). but when use VideoCapture set frame index for a wrong number. OpenCV will blocking. Please help me.

string m_strFilePath = szFilePath; //url  http://172.20.32.211:8080/123.avi
m_vidCapture.open(m_strFilePath);
double fTotalFrams = m_vidCapture.get(CV_CAP_PROP_FRAME_COUNT); //get wrong frame number
m_vidCapture.set(CV_CAP_PROP_POS_MSEC, nPosTime); // set wrong frame number rely on wrong total frames number,it will blocking for a long times