在使用 OpenCV 的 Gstreamer API 之前,我们需要一个使用 Gstreamer 命令行工具的工作管道.
发送方: OP 使用 JPEG 编码,因此此管道将使用相同的编码.
gst-launch-1.0 -v v4l2src
! video/x-raw,format=YUY2,width=640,height=480
! jpegenc
! rtpjpegpay
! udpsink host=127.0.0.1 port=5000
Receiver:rtpjpegdepay的接收器caps需要匹配rtpjpegpay的srccaps 发送方管道.
gst-launch-1.0 -v udpsrc port=5000
! application/x-rtp, media=video, clock-rate=90000, encoding-name=JPEG, payload=26
! rtpjpegdepay
! jpegdec
! xvimagesink sync=0
现在我们有用于发送方和接收方的工作管道,我们可以将它们移植到 OpenCV.
发件人:
void sender()
{
// VideoCapture: Getting frames using 'v4l2src' plugin, format is 'BGR' because
// the VideoWriter class expects a 3 channel image since we are sending colored images.
// Both 'YUY2' and 'I420' are single channel images.
VideoCapture cap("v4l2src ! video/x-raw,format=BGR,width=640,height=480,framerate=30/1 ! appsink",CAP_GSTREAMER);
// VideoWriter: 'videoconvert' converts the 'BGR' images into 'YUY2' raw frames to be fed to
// 'jpegenc' encoder since 'jpegenc' does not accept 'BGR' images. The 'videoconvert' is not
// in the original pipeline, because in there we are reading frames in 'YUY2' format from 'v4l2src'
VideoWriter out("appsrc ! videoconvert ! video/x-raw,format=YUY2,width=640,height=480,framerate=30/1 ! jpegenc ! rtpjpegpay ! udpsink host=127.0.0.1 port=5000",CAP_GSTREAMER,0,30,Size(640,480),true);
if(!cap.isOpened() || !out.isOpened())
{
cout<<"VideoCapture or VideoWriter not opened"<<endl;
exit(-1);
}
Mat frame;
while(true) {
cap.read(frame);
if(frame.empty())
break;
out.write(frame);
imshow("Sender", frame);
if(waitKey(1) == 's')
break;
}
destroyWindow("Sender");
}
接收方:
void receiver()
{
// The sink caps for the 'rtpjpegdepay' need to match the src caps of the 'rtpjpegpay' of the sender pipeline
// Added 'videoconvert' at the end to convert the images into proper format for appsink, without
// 'videoconvert' the receiver will not read the frames, even though 'videoconvert' is not present
// in the original working pipeline
VideoCapture cap("udpsrc port=5000 ! application/x-rtp,media=video,payload=26,clock-rate=90000,encoding-name=JPEG,framerate=30/1 ! rtpjpegdepay ! jpegdec ! videoconvert ! appsink",CAP_GSTREAMER);
if(!cap.isOpened())
{
cout<<"VideoCapture not opened"<<endl;
exit(-1);
}
Mat frame;
while(true) {
cap.read(frame);
if(frame.empty())
break;
imshow("Receiver", frame);
if(waitKey(1) == 'r')
break;
}
destroyWindow("Receiver");
}
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