Timeline Item Position
This section covers the position dictionary returned by TimelineItem:GetPosition, and accepted by TimelineItem:SetPosition and Timeline:MoveItems.
The position dictionary contains the following keys:
trackType: string (options: "video", "audio", "subtitle". Returned by GetPosition; ignored by SetPosition and MoveItems)
trackIndex: int (1-based track index. Omit to retain the current track)
startFrame: float (frame number. Omit to retain the current frame)