Upgraded to 2.13.2: 
Documentation of 3.5 Media code
#26870 Add (JSDoc)umentation to the Backbone-centric Media files
This is underway, with several commits already. Slow-and-steady approach. Have started with annotations, gradually adding top-level comments to all class methods. I have been using pseudo-code to map out each file: https://gist.github.com/staylor/10115a0f455e16c6eafd.
Start with identifying every piece of the tree, then making sure all methods have each piece of the documentation.
#26650 Replace media file type icons with Dashicons
These will replace the “crystal” icon set. For AV2, we are interested in replacing the icons that show up in the media list tables, and using the icons in the placeholders for Audio, Video, Playlist, and Video Playlist shortcodes in TinyMCE content.
#26864 Consolidate handling of object, audio and video tags in wpautop
PHP and JS versions of
wpautop() need to respect the inner elements of media HTML tags for media: <param>, <embed>, <track>, <source>
Initial patch – ongoing work from azaozz
#26628 Use the content of a video shortcode when provided – depends on ^
Placeholders (TinyMCE views) for Audio / Video shortcodes
Depends on: #26628
Chromeless YouTube via ME.js
#24764 Support mediaelement.js YouTube sources in the video shortcode
This has a patch: https://core.trac.wordpress.org/attachment/ticket/24764/24764.diff
I have just been letting it soak in the wild for a day.
Metadata Regeneration for audio/video
#26825 Add ability to generate metadata for audio / video files on-demand
This currently has 2 implementations.
- a button on the Edit Media page if your audio or video does not have a row in postmeta for
! isset(), not
- On the fly in
#1 requires the user to care
#2 IMO does not scale, as the media modal loads ALL of your media in one fell swoop upon being opened – let’s say you have 300 videos uploaded pre-3.6: there will be no metadata, so you might melt your filesystem by scanning and analyzing 300 files at once.
This is still in the exploratory phase – would love some UX thinking on this.
Playlist and Video Playlist shortcodes
#26631 Add a “playlist” shortcode
The TinyMCE view code can probably be merged into the wpaudiovideo TinyMCE plugin once #26628 goes in, which has its own dependencies. As I mentioned, Playlists and Video Playlists probably need their own identifying icons.
I have created a basic UI for playlists that inherits styles from your existing theme. The HTML and CSS is minimal and generic. Here are some screenshots of it in action: