Live Streaming Video

The Tuesday morning lecture or guest speaker is webcast live from room 317 in COM. Students may view it online at that time, or watch the video archive later in the week. The stream consists of a mix of full-motion video of the teacher, the students in the classroom, and the lecture slides, accompanied by the voice of the teacher. As much as possible, we try to communicate the visual and auditory environment of a classroom to the online students. The teacher uses a lectern, but also walks around through the class; the students listen, take notes, yawn, ask questions, and respond to the teacher's questions. Online students watching the live webcast can ask questions using the discussion board on the course web page.

We have found so far that few of our online students watch the video live, since most are working at 9:30 on Tuesdays. They watch is later in the day, or n Wednesday, through the archive.

Technical details

We mix three video sources for the webcast: two cameras in the classroom (Hi-8), and the output from the computer from which the teacher is presenting the lecture slides and demonstrations. A grad student in the Television program operates a video mixer to combine these as appropriate. Audio is fed to a mixer from a wireless microphone on the teacher, and from the computer that's doing the slide presentations and demos, many of which include sound.

The mixed audio and video stream is compressed and packetized by Sorenson Broadcaster software running on an Apple Macintosh G3 computer that sits in the portable lectern that we have built for this course. We have found that a 320x240 pixel video, at 12 to 20 frames per second, works well, giving a combination of quality and smoothness that works well for the online students, but is capable of being received through DSL and cable modem connections. The bandwidth of our webcast varies with the nature of its sources, but averages 315 kilobytes per second.

The video is compressed with the H.263 codec, the audio with IMA 4:1 compression. This seems to work best for us and our students. The compressed and packetized stream is sent from the lecture hall over the local area network (Ethernet) via unicast to a QuickTime Streaming server running on an Apple Macintosh G3 computer at the College of Communication. This server runs under the OSX version of the Unix operating system. The streaming video from this server is embedded in a web page on the course site, which can be received with both Netscape and Explorer on both Macintosh and Windows computers.