Proceedings of the 4th Gigabit Minijam of the Corporation for National Research Initiatives, January 1994.
Abstract:
In the ViewStation distributed multimedia system being developed at
MIT, media data is handled at the application level rather than in
dedicated hardware. This software-oriented approach has many benefits
including flexibility, scalability and portability among platforms.
One requirement of handling media in software is that the application
environment must be capable of controlling the data rate and quality
of media sources to contend with demands on the computational resources
of the host computer.
This talk describes a system for establishing a variable frame-rate video link between a capture board and a workstation over an ATM network. The video capture element of this system consists of a network-based video capture board designed for the ViewStation system called the Vidboard. The Vidboard has hardware support for the temporal decoupling of video from an analog television source. A closed-loop algorithm acting between the Vidboard and workstation is used for requesting video on a frame by frame basis. The rate of requests is then adjusted to vary the frame rate. Using this algorithm, an application is capable of varying the frame rate of the video stream to match the computational resources at its disposal, allowing for graceful degradation.
Within the local-scale ViewStation system, this technique has been used successfully for all video applications involving the Vidboard for the past year. Recently, it has been used within the Aurora testbed to ship video between MIT and a ViewStation node located at Bellcore.
