ReadyTalk just announced beta availability of a new feature letting webinar hosts include prerecorded video clips as part of their session content. Video clips must be uploaded to the ReadyTalk server where they undergo a conversion process. The Quick Start Guide says that conversion can take up to two hours, and ReadyTalk recommends doing the conversion at least a day in advance and testing the converted output before the live session.
Once uploaded, videos can be played as part of a webinar session. Attendees hear any audio in the clip and the playback audio/video is included in the session archive recording.