In qml file ,after videoOutput anchors.fill:parent executed, video playing outside of player,why?

[jieliujas]

Develop Environment
Linux rk3399pro 4.4.167
arm board : rk3399 AARCH64
Qt version : 5.9.4 aarch64 gcc6.3.1 cross complied

Problem description
Using Quickwidget+qml to develop a video player, in qml file , the property videoOutput's "anchors.fill:parent" execution error, in result the video screen is not covered with the player window, but separated from the window ， it's should display and fill the player window very fine ,all right ?

can anyone help me to analysis why please , thanks so much!

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