1416143 - [webvtt] region scroll up functionality.

Status: NEW

(Core :: Audio/Video: Playback, enhancement, P3)

Description

[Benjamin Chen [:bechen]]

https://www.w3.org/TR/webvtt1/#introduction-other-features example 10.

We need some works to make the cue in region scroll up.

Comment 1

[Benjamin Chen [:bechen]]

"Smooth scroll up" is: 
We set the css for regionNode "display:inline-flex". If there are 2 lines in the region, when we append 3 cues in the region, the first cue should scroll up until disappeared, and the second cue should scroll up to the position of first cue(first line), then the third cue should scroll up to the second line. That's why we set the css "transitionProperty = top; 
transitionDuration = 0.433s" for the child of regionNode. 

To achieve smooth scroll up,
1. The layout mechanism for the "inline-flex" will change the top attribute for thier child, and here we need to insert the animation
2. vtt.jsm might need to modify the processCues() function.