Background to the streaming problem

What is streaming?

Streaming is the process of transferring data via a channel to its destination, where it is decoded and consumed via the user or device in real time, that is, as the data is being delivered. It differs from non-streaming processes because it doesn't require the data to be fully downloaded before it can be seen or used. Streaming is not the property of the data that is being delivered, but is an attribute of the distribution channel. This means, technically, that most media can be streamed.

HTTP and RTSP

HTTP and RTSP are application-level protocols that allow remote retrieval of data. So why can't you use HTTP for streaming media content? The truth is, you can. When you click on a Web page link to play an audio file, in most cases the media data is streamed to your machine. However, streaming content over HTTP is inherently inefficient. This is because HTTP is based on the Transmission Control Protocol (TCP), which makes sure that media packets are delivered to their destination reliably without worrying about when they are delivered. On the other hand, RTSP can be based on both User Datagram Protocol (UDP), which is a connectionless protocol ensuring faster delivery over reliability, and on TCP. Besides, RTSP has control mechanisms built in that allow random access to the media data, allowing you to seek, pause, and play.

Making sense of RTSP, RTP, and RTCP

There is a lot of confusion among newcomers over the acronyms RTSP, RTP, and RTCP. All three represent different protocols related to streaming of media content. An RTSP session initiates both Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) sessions. RTSP is only the control protocol, a bit like a remote control for a DVD player, in that it allows you to start, stop, resume, and seek data remotely. The actual data delivery is done via RTP, and RTCP is a partner protocol to RTP providing feedback to both the sender and receiver on the quality of media data that is being transferred.