The Poodll Subtitle Editor for Atto allows you create and edit audio and video captions directly from the HTML editor. Optionally combine its use with the Cloud Poodll for Atto, which can auto create subtitles and it forms a full subtitling solution.
Poodll Subtitle Editor Features

Edit Captions for Video
The editor resizes nicely to allow you to edit the subtitles alongside a preview of the video.

Edit Captions for Audio
The editor can also subtitle audio. The audio player displays above the subtitle editor tiles.

Intuitive Editor Interface
Because it has been designed to work in a popup dialog, the subtitle editor controls are compact and simple.