How to get frame from video by using vlc-qt - c++

Question

I`m using vlc-qt for decode h264 video stream but I need every frame from video (stream) for further processing. I found this link that describes the solution :
https://discuss.tano.si/t/how-to-get-frame-from-video/253
I made a class that inherits from VlcVideoStream class and re-implement frameUpdated() function as bellow :
void MyVideoStream::frameUpdated() {
qDebug() << "frame" ;
int rows, cols, matType;
// convert to shared pointer to const frame to avoid crash
std::shared_ptr<const VlcYUVVideoFrame> frame = std::dynamic_pointer_cast<const VlcYUVVideoFrame>(renderFrame());
if (!frame) {
return; // LCOV_EXCL_LINE
}
rows = frame->height + frame->height/2;
cols = frame->width;
}
and declared my class as :
MyVideoStream *_stream ;
_stream = new MyVideoStream(Vlc::YUVFormat,ui->video) ;
_stream->init(_player) ;
where _player is a VlcMediaPlayer object reference. but when I ran the program nothing happened. I don`t know what is the problem.

Answer 1

when you subclass the VlcVideoStream and re-implement frameUpdated(), you have access to YUV frame every time it is updated.
if you are familiar with Opencv , just add these code to frameUpdated() function, then you can see the gray image :
void MyVideoStream::frameUpdated()
{
std::shared_ptr<const VlcYUVVideoFrame> frame= std::dynamic_pointer_cast<const VlcYUVVideoFrame>(renderFrame());
if (!frame) {
return; // LCOV_EXCL_LINE
}
int width = frame->width;
int height = frame->height;
cv::Mat result = cv::Mat(height, width, CV_8UC1, (void*)frame->frameBuffer.data());
imshow("result", result);
waitKey(2);
}