[webvtt] Suggest edits to the "cue overlap avoidance" portion of the specification

guohuideng has just created a new issue for https://github.com/w3c/webvtt:

== Suggest edits to the "cue overlap avoidance" portion of the specification ==
under session 6.1,  under clause
"If cue’s WebVTT cue snap-to-lines flag is false", the "step 4" deals with cue overlap/cutoff avoidance. below is the text from the specification.

"If there is a position to which the boxes in boxes can be moved while maintaining the relative positions of the boxes in boxes to each other such that none of the boxes in boxes would overlap any of the boxes in output, and all the boxes in boxes would be within the video’s rendering area, then move the boxes in boxes to the closest such position to their current position, and then jump to the step labeled done positioning below. If there are multiple such positions that are equidistant from their current position, use the highest one amongst them; if there are several at that height, then use the leftmost one amongst them."

////
The text has a few problems. 1. it's vague and it could be more concise. 2. it actually only suggests actions on "cut off" case, but not the case of cues overlapping with one another. 3. It could state "video safe area" instead of "rendering area". because of overscan the cue can still be cut off if placed too close to the boundary. Therefore it is common practice to put the cue in "save area".4. it put too much restricts on how the feature should be implemented. The specification should define syntax and semantics of the webvtt, and leave spaces to developers to improve the functionality.

Therefore my suggestion is to replace the text above with something like the below.
"
If the cues placement suffers from one or more problems listed here, then efforts could be made to mitigate or eliminate such problem(s)  by moving some cue boxes or all the cue boxes: 1. Any cue box is not placed in video safe area 2. Two or even more cue boxes overlap each other (one another).
"

/// With such text in specification, developers can also implement the feature incrementally, or keep improving this feature in the future. 





Please view or discuss this issue at https://github.com/w3c/webvtt/issues/441 using your GitHub account

Received on Thursday, 26 April 2018 18:27:24 UTC