Webcast Services

This section describes the services listed in table 1 that we developed to produce the Berkeley MIG Seminar webcast. The Remote Video Capture service (rvc) controls a video capture device. This service is essentially a server version of the vic Mbone tool [12]. Rvc encodes analog video signals into RTP packets and provides format and bit-rate interface controls. For the MIG Seminar webcast, two rvc services are used to produce two streams. The studio classroom has two capture machines each connected to an AMX control system

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Table: Table of services with their line numbers and functionality.

Service	Lines	Functionality
rvc	1768	Capture Machine. Digitizes analog audio and/or video, compresses it, and frames the digital media into RTP packets. Provides controls for both the digitization process and the device(s) connected to the capture machine (e.g., camera, mixer, VCR).
room405	229	Room 405. Controls environment parameters in the room (e.g., light controls, screen raise/drop).
replay	320	Archival Playback Manager. Archive catalog interface and playback service management.
replayproxy	612	Archival Playback Service. Streams archived media into a session. It provides controls to play, pause, and seek in the video.
specialfx	365	Special Effects Manager. Effects system manger and interface for specifying effects services.
specialfxproxy	1402	Special Effects Service. Controls a particular effects service.
rtc	411	Trancoding Service. Transcodes media streams at different bit-rates and formats from one session to another.
null_service	202	Overhead needed by all services.

HREF="footnode.html#foot144"> and an audio/video matrix switcher. Audio/video devices are connected to the AMX system and the matrix switcher. Rvc uses an RPC interface to issue commands through the AMX system to the matrix switch and media devices. For example, the rvc service can send commands to the AMX system to switch the video feed from the VCR to the speaker camera and commands to move the speaker camera to the right.

The room405 service provides an interface to non-media services in the classroom that can be operated through the AMX system. The current services include: room lights, raising/lowering projection screens, and turning on/off an ``On-Air" indicator light outside the classroom.

The replay service manager and replayproxy services allow archived material to be played into a webcast. A short opening video segment (approximately 20 seconds) is played at the beginning of the webcast. To play this opening, the director contacts the replay service manager and specifies the video to be played. The replay service instantiates a replayproxy service which is responsible for controlling this particular video. We currently use the MARS multimedia archive system to archive and play stored material on-demand [18]. The replayproxy service starts a MARS playback process, connects to dc, and acts as a proxy between dc and the MARS server. The proxy implements the VCR controls presented in the replayproxy control interface.

The specialfx service manager and specialfxproxy services are similar to the replay service manager and replayproxy services except they control video effects processes. The specialfx service manager starts the specialfxproxy service that starts video-effects processes [10]. The proxy service acts as an intermediary between the client application and the processes that implement the special effect.

The rtc service is a transcoding service that is still under development. It will take streams from one multicast session, transcode them to different bit-rates and formats, and send them into another multicast session. Rtc is a server version of the rtpgw service [2].