posterCanvas use is ambiguous for audio only

[azaroth42]

Should the audio of the poster be played while the main content is buffering, or should it be played as ambient content while the user interacts with the main canvases?

Seems like we need a behavior on the canvas? Or ( 😖 ) two separate properties?

[zimeon]

Hmm... and should a video poster repeat, etc.? I note that this would seem to be an exception to any idea of inheritance of behaviors in #1612 if resolution of #1602 ended up with timeMode rolled into behavior

[azaroth42]

After the call on 2018-06-26, my feeling is now that we should have two properties (with all the 😖 that results in).

Rationale:

• We have agreed that both pre-play or during-play use cases are in scope (image while buffering, background music while playing) so can't solve it by saying it's one or the other alone
• If we solve it with a behavior on the canvas, then
  • posterCanvas needs to be an array for the situation when there's both ...
  • If the behaviors aren't present, then either there would need to be a default or an exception handling routine. This seems complicated
  • If the same behavior is present in multiple canvases, a client would need to distinguish which to use somehow based on other metadata ... in a presentation driven environment. This seems very difficult, if not impossible.
• If we solve it with multiple properties, we document two relationships each of which can be present and has exactly one Canvas. That seems cleaner for everyone.

[tomcrane]

placeholderCanvas and accompanyingCanvas...

with sensible observations or rules about where each of these make sense.

[tomcrane]

And clearly showing through recipes the difference between accompanyingCanvas and the together behavior.

[zimeon]

Discussed on 2018-08-29 Technical Community Call - noted that proposal #1605 (comment) was outcome of A/V group discussion. Consensus in favor of using placeholderCanvas and accompanyingCanvas, with good explanation and recipes

[azaroth42]

Closed by #1658

[zimeon]

Approved by TRC, already merged into image-prezi-rc2.