How to convert video to ogv and webm versions with a high quality result? What is the best software for mac to convert video to ogv and webm versions with a high quality result?

I have adobe media encoder, is there is a setting or plugin available to do so in there? or another software that lets me control the quality of the final video to get the best quality possible. Many of the conversion programs I have tried are not providing a good quality output. The video is mp4 or mov H.264 1920 x 1080 and over 10 mins in length. Thank you.
I have Premiere/Media Encoder plugins for WebM and Theora (OGV) on GitHub. Check the ReadMe for download links. They're currently in beta.

Brendan