Structural metadata with undefined sections causes odd behavior for lil' scrub

[mschnaars]

Description

For items with structural metadata, when the defined spans don't cover the entirety of the item duration--but leaves areas of the item undefined--lil' scrub displays odd behavior.

Behavior 1: when playback is in an undefined section, lil' scrub moves in proportion to the entire item.

Behavior 2: when playback is in a defined section, lil' scrub moves in proportion to the defined section.

Disparity: playing from, clicking from, or dragging the timestamp from an undefined section into a defined section causes an abrupt switch from Behavior 1 to Behavior 2.

Steps to Reproduce

Go to Spruce.
Find the item "My Lunchroom".
Toggle Lil' Scrub.
Play the video.
Drag lil' scrub from 0 to 2:30 - moves in proportion to entire video.
Drag lil' scrub from 2:30 into 2:45-2:50 range - lil scrub now moves in proportion to a 3-second section.

Environment

Spruce, Avalon 6.4.3, Chrome

Expected Behavior

Seems like one of these should occur:

1. Structural metadata should not allow for undefined sections, i.e. undefined sections would throw an error and require definition.

2. Undefined sections would generate a defined but invisible span by default; i.e. lil' scrub would magnify the defined span but the span would be invisible to the user in the structural navigation.