Things you can add to query string:

video_url=[video url] (NOT optional) The url of the video to embed. [video url] be a youtube page url or a video file url.
null_widget=true (optional) When true, makes the widget in null sandbox.
debug_js=true (optional) When true, opens a Javascript debugging panel
subtitle_immediately=true (optional) When true, opens subtitling dialog as soon as widget loads.
translate_immediately=true (optional) When true, opens translation dialog as soon as widget loads.
base_state={language:"es",revision:0} (optional) start with a given language and/or revision. To start with original language, omit the language param. To start with latest revision, omit revision param. Warning: not very robust -- will not react well to nonexistent revisions, etc.

Examples

http://amara.org/widget_demo/?video_url=http://www.youtube.com/watch?v=MJRF8xGzvj4
http://amara.org/widget_demo/?video_url=http://videos.mozilla.org/firefox/3.5/switch/switch.ogv&null_widget=true&debug_js=true