Evaluations of Existing HTML5 VIdeo Players

VideoJS

http://videojs.com/
uses flow player for flash support http://flowplayer.org/documentation/index.html
uses Video for Everybody http://camendesign.com/code/video_for_everybody
GPL 3
includes an event system based on Resig's
has a bunch of commented out stuff that messes with Array.prototype
cleanly written and well documented - easy to read
has an options block similar to jquery
appears to have a strategy for adding and removing behaviour but not on a per instance basis
markup and strings are hardcoded in a private function

mediaelement.js

http://mediaelementjs.com/
https://github.com/johndyer/mediaelement
License: GPLv2/MIT
polyfill: mimics the HTML5 MediaElement API for browsers that don't support HTML5
CSS nicely namespaced
The player uses hard-coded HTML with no means for customization
Player broken out nicely into features
claims to support <track> element

JW Player

http://www.longtailvideo.com/players/
http://developer.longtailvideo.com/trac/browser/trunk/fl5
commercial license for commercial use (free for non-commercial use)
plugin architecture
includes plugins for captions and audio descriptions
includes a Flash player (requires Flex SDK to build)
does pseudo-streaming
appears to do bitrate switching
supports dynamic resizing via JavaScript
good keyboard a11y

J-media element

http://protofunc.com/jme/index.html
http://html5video.org/wiki/JMediaelement
https://github.com/aFarkas/jMediaelement/
License: GPL2/MIT
jQuery plugin
includes a copy of JW Player and Cortada (Java)
not compatible with mobile platforms
demo shows resizable mp4 in a dialog (i.e. resizes with dialog - mp4 only?)

Kaltura

http://www.kaltura.org/project/HTML5_Video_Player (MIT licence)
http://www.kaltura.org/project/HTML5_Video_Media_JavaScript_Library (GPLv2 licence)
http://code.html5video.org/projects/html5video/repository/show/trunk/mwEmbed
MediaWiki plugin
skins hard-code HTML markup
skins pluggable - could write a skin that doesn't hard-code markup

jPlayer

http://jplayer.org/
https://github.com/happyworm/jPlayer
http://plugins.jquery.com/project/jPlayer
License: GPL/MIT
Flash-first, HTML5 as fall-back
integrator doesn't write the <video> tag, the jPlayer plug-in does that
seems quite skinnable (one demo shows a text-only audio player)
infusion-style overridable selectors for all controls, feedback, etc.
plugin figures out whether to use html or flash, and then for every action (play, seek, etc) calls the right function
nothing built-in for the <track> element (for captions or subtitles)
basic kbd a11y in place
could use improvements (e.g. enter activates buttons, but not spacebar)
skin doesn't include visual feedback of kbd focus
volume slider itself not kbd-a11y (only mute/unmute)

Video for Everybody

http://camendesign.com/code/video_for_everybody

basically:

<video>
    <object>
        <img title="instructions to use the download link below">
    </object>
</video>
<a src="downloadable version of video"/>

Pseudo-streaming

http://www.longtailvideo.com/support/jw-player/jw-player-for-flash-v4/12207/video-delivery-http-pseudo-streaming

OSM Player

http://www.mediafront.org/project/osmplayer

Projekktor

http://www.projekktor.com/

Captionator

https://github.com/cgiffard/Captionator
License: completely open ("You may copy and use this library as you see fit (including commercial use) and modify it, as long as you retain my attribution comment...")
closed-captioning polyfill for HTML5: implements support for <track> element
support for WebVTT, SRT, SBV, and SUB caption/subtitle formats
namespaced to "captionator"
can provide your own render function for the captions
claims non-standard support for use of <track> for audio and video
- small bug in video, but can get something to work
- haven't been able to get audio to work
bug: Captionator somehow interferes with native volume control?