Video playback performance is very bad on Apalix i.MX6

The playback performance for a 1080p mp4 video file is very bad on Qt 6.5.3 on Toradex Apalis i.MX6. The playback is very laggy with a low frame rate. The same video plays well on Qt5 or using gstreamer directly, using the KMS sink.

You can reproduce the issue with the mediaplayer example (Qt/Examples/Qt-6.5.3/demos/mediaplayer) with a 1080p mp4 file.

The following log output is resulted during the playback:

(MediaPlayerApp:933): GStreamer-CRITICAL **: 08:37:08.419: gst_element_message_full_with_details: assertion 'GST_IS_ELEMENT (element)' failed
qt.multimedia.player: Attempt to set an incorrect index 0 for the track type 1
qt.multimedia.player: Warning: "A lot of buffers are being dropped."