Playback defaults in admin settings

[B-Interactive]

Currently playback options can be specified on a per-video basis. The code for this at the moment, is specific to shortcodes. The available options, with their current defaults are:

• controls = true
• autoplay = false
• loop = false
• preload = false
• muted = false

I propose providing these controls in the admin settings with these aims:

1. The user can specify and modify default playback options universally for all videos.
2. Videos can still override these defaults on a per-video basis.
3. Use of these defaults is no longer shortcode specific, but applies to blocks also.

This proposal is contingent on how blocks will be implemented, and whether they can dynamically access and optionally override these defaults.

The autoplay/muted options have the caveat that when autoplay is enabled, browsers will tend to force mute the video. Browsers such as Chrome will apparently adapt based on user behaviour, so it's not a definite rule, but it should be expected.

[davidmpurdy]

The more things come up, the more it seems to make sense to just have the blocks be fully dynamic, in which case the defaults can totally apply.

The biggest change will probably be changing the block inspector controls UI to reflect three states for the toggles instead of two (default/off/on replaces just off/on).