Unsolved qmlvideo flickering on video playing
this is my first time into QT forums, so sorry if I made a mistake in section choice, or if this is an already-answered question (I found nothing similar).
I'm developing an embedded board based on iMX6SX SOC (that does not have VPU) with a 7" integrated LCD.
On this board I sucessfully configured, built and installed a minimal Linux image using Yocto project at rocko release, without graphical server (X11 nor wayland) but directly on framebuffer, with the OpenGL ES support.
This image integrates also meta-qt5 layer (version 5.9.6 at last commit on rocko branch) to develop applications using eglfs platform.
I'm trying to run qmlvideo example on this board, but reproducing a sample video (h264 software-decoded by libav, 720x480, 25fps) I have a heavy flickering: it seems that video went decoded well, but went overlapped by some black frames, generating a "stroboscopic" effect with flickering frequency changing between each reproduction (I can provide a video if needed, here on forum I cannot upload it).
If I reporduce the same video using GStreamer from command-line, video is shown right (again I can provide a video).
CPU load is approximately the same (about 50%, due to SW decoding) both with qmlvideo and gstreamer.
I already tried to set QT_EGLFS_IMX6_NO_FB_MULTI_BUFFER=1 to disable multi-buffering, but without result.
I set GST_DEBUG environment variable, and logs regarding video stream are quite the same, and without errors (qmlvideo log reports also some rows regarding audio stream, because audio peripheral is disabled on our board).
What could be the problem? Could the problem be on the NXP side of the SW chain (something about OpenGL, gstreamer or other)? I googled for a solution, but I haven't found anything.
Thanks in advance, regards.