Hello i wish if i could help you. please i need to send voice over network using tcp socket and i believe you can help me if you give me your code (server and client side both )i will be very thankful.thank you soo much in advance.

Don't think this is solved, uninstalling gst-plugins-vaapi is a workaround at best.

Bug:
Qt Multimedia GStreamer backend doesn't support HW-accelerated video decoding
https://bugreports.qt.io/browse/QTBUG-23761