QuickTime Streaming

Unicast Streaming

In a unicast, the client contacts the server to request a movie using RTSP (Real Time Streaming Protocol). The server then replies to the client over RTSP with information describing the movie as a streaming session . A streaming session consists of one or more streams of data, such as a video stream and an audio stream. The server tells the client how many streams to expect and gives details on each stream, such as the media type and codec. The actual streams are then sent to the client over RTP. When a QuickTime movie is streamed over RTP, each track in the movie is sent as a separate stream.

Figure 1 Unicast streaming using RTSP

A stream can contain live content, such as a stock ticker or a radio broadcast, or stored content, such as a video track from a QuickTime movie. When a client is receiving unicast streams from stored content, the client's movie controller includes a "thumb" that allows the user to jump to any point in the movie. This gives the client random access to long movies without having to download an entire movie or store it locally. The client simply asks the server to begin streaming the movie from a new point.

Figure 2 Movie controller with "thumb"

Note : RSTP uses TCP/IP transport, but RTP uses low-level UDP/IP transport. If the client is behind a firewall that doesn't pass UDP, the movie will set up without error, but no media will be displayed. RTSP Proxy servers for several operating systems are available from Apple to help resolve firewall problems.