| 摘要 |
A communication system includes a pool of multimedia players (MP) in communication with a multimedia server (MS), both the players and the server operating according to the IETF RTSP protocol independently of the used transport network. A new network element called streaming switching processor (SSP) is located between the players and the video-server/video-encoders (ME) for executing the switching of the streaming contents upon a command (NOTIFY) received from the player (MP). Alternatively, the SSP also embodies the funtionality of video server and video encoders. The SSP includes at least M buffers (ch-1,...,ch-M) for an equal number of independent streaming contents kept always on. This architecture enables the SSP while is processing the switching message (NOTIFY) to forward in parallel the switched streaming contents to the player. As a consequence, the player receives the new streaming contents in the context of the first RTSP session. The Switching Delay Time SDT is drastically reduced operating in this way because some typical delays overlap and others are contemporary to SDT. The multimedia contents can be derived from encoded real-time signals, such as satellite TV channels, or registered contents taken from archives. The player is programmed to flush the video/audio MPEG-4 frames out of its receiving buffer and fill up the emptied space with the frames of the relevant auxiliary buffer clocked faster. The further expedient to align the sending in correspondence of a Key-frame followed by a "secure" filled length prevents the artefacts on the displayed image. The switching message is sent by the player either on UDP or TCP; it includes at least the identifier of the request channel, the buffer status inside the Player. Alternatively, a new RTSP message is created including in its body these information fields described according to the RTSP presentation rules.
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