Modification of Leanback Video Player UI

I want to modify the Leanback Video Player UI. There are two things I want to change:

1. The Seekbar in which I want to to be able to put the cue point markers for ads.
2. I want to change the positions of the buttons and the title and subtitle.

I tried extending the androidx.leanback.widget.SeekBar class and modifying it and overriding the lb_playback_transport_controls_row.xml file but that class has been marked as final. I already have the cue point locations and just need to modify the Seekbar.

I don't know which class to extend and modify and which layout file to override to put the poster in.

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