Does exactly what I need it to do, does it flexibly, and does it as quickly as my computer can handle. What's particularly nice about this app is the responsiveness of the developer. When I started using the app to burn in subtitles I noticed that it wasn't adding line breaks when a chunk of text grew too large and overran the borders of the image. In under three hours the developer has responded to my email about the matter, addressed the issue, and mailed me a link to a version which fixed the problem. I have since used this software to output 1200 video files with burned-in titles and it has been stable, fast, and quick. I recommend Submerge wholeheartedly.