A webcast is a broadcast that – unlike a web video – is broadcast live (livestreaming) over the Internet. A broadcast may be pre-recorded. Webcasts use streaming media. A webcast that only hears sound is called audio webcast.
A webcast requires: a camera or video signal, an encoder, an on-site Internet connection and a streaming server. The encoder is often a powerful PC with firewire input, or a special video capture card, to which a video source can be connected. Streaming tracking software runs on the computer.
QuickTime Broadcaster is available for free for the Mac and can be coded live in the QuickTime format, MPEG-4 format and 3GPP format (for mobile phones). Windows Media encoder is available for free for Windows XP and can be encoded live in the Windows Media format.
Because the on-site Internet connection is in virtually no way fast enough to control multiple viewers, the stream, which comes from the encoder, is reflected via a streaming server. This can be done by means of a PUSH or in some cases by means of a PULL. In a push, the encoder initiates the stream to the server. QuickTime Broadcaster sets the server’s IP address, as well as the audio and video port on the server. The user then generates a Session Description Protocol (. SDP) file and places it on the streaming server. In Windows Media encoder, the user specifies the name of the server and their name and password.
Depending on the audience to be reached, there is a difference between a broadcast, multicast, narrowcasting, unicast and atnycast. This influences the choice of certain techniques.