Qt Multimedia Video not working on Nvidia Xavier and Orin platforms

We are developing a Linux EGLFS application using Qt QML that
runs on NVidia Xavier and Orin platforms.

When trying to playback a video file using QML Video items the
video did not play and the gstreamer log indicated that the
various gstreamer elements used failed to negotiate.
Some debugging later , we found that the playback pipeline using
the nvv4l2decoder element was lacking a conversion plugin to work
together with the "videosinkbin".

The default "videoconvert" plugin could not handle the NVidia formats
used.

As a workaround, the NVidia "nvvidconv" plugin was added to
QGstreamerVideoSink in a similar fashion as "imxvideoconvert_g2d"
had been added before.
 
This solved the issue. A patch containing this fix is attached
to this bug report.