AnyStream - This company is perhaps a bit more focused on working with broadcasters on online video transcoding. It recent grew by M&A when it merged with Voxant [1].
Dilithium Networks - This Petaluma, Calif., vendor has a gateway and other solutions [2] supporting real-time video transcoding, with an emphasis on mobile-related transcoding needs.
Envivio - Envivio has been in encoding in support of SD and HD content [3] for a while now. The vendor played a big role in supporting China Central Television's encoding needs during the summer's 2008 Beijing Olympics.
Harmonic - The Sunnyvale, Calif., companies Rhozet business unit enables video encoding/transcoding, and just saw its solution picked up by 3 Italia for mobile DVB-H transcoding [4].
Links:
[1] http://www.fierceonlinevideo.com/story/anystream-and-voxant-merge/2008-09-22
[2] http://www.fiercewireless.com/press-releases/dilithium-unveils-content-adapter-real-time-mobile-video
[3] http://www.fierceiptv.com/story/also-noted-vendor-announcements-at-telcotv-and-much-more/2006-11-02
[4] http://www.harmonicinc.com/ah_press_release_text.cfm?ID=794
[5] http://www.fierceiptv.com/special-reports/fierceiptv-special-report-video-transcoding
[6] http://www.fierceiptv.com/special-reports/video-transcoding-companies-watch-0