Streaming media, commonly referred to as streaming, refers to the simultaneous transmission and playback of video and/or audio data via a computer network via a data stream. The program that is transmitted is referred to as a stream; if the transmitted content takes place in real time, as a live stream. In contrast to downloading, the goal of streaming is not to create a copy of the media for the user, but to output the media directly, then discard the data. Examples of streaming media include video streaming and audio streaming (e.g., web radio and music streaming). The content is often distributed via streaming portals and internet-based media libraries.
The playback of programmes via a live stream usually differs from traditional broadcasting. While broadcasting involves broadcasting to an indefinite number of receivers at the same time , streaming is usually a direct connection between the broadcaster’s server and the client of each individual user (unicast). Typical data transfer rates of the source data are:
- Audio: mostly in the two- to three-digit kbit/s range
- Video: a few hundred kbit/s to a few Mbit/s (for triple-play offers)
Since the playback of the data is to take place at the same time as the reception, a sufficient data transfer rate must be available. It is necessary that the data transfer rate available for the transmission is greater than the data transfer rate used for the streaming. The audio and video data to be sent is therefore always compressed. In most cases, the content is lossily compressed, as this is the only way to achieve a transferable amount of data per period of time; in addition, the compression factor is far higher than that of lossless compression, without any noticeable loss of quality.
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In order to compensate for different transit times of the data packets in the network and to prevent the associated delays, a buffer is used in the media player. That’s why the playback is also slightly delayed, typically by 2 to 6 seconds. If this buffer is not sufficient, some media players will dynamically increase it. Since video data usually has a higher data rate than audio data, much stronger compression is also required here.
On-Demand Streaming
- Data is transmitted from the server to the client over the network.
- Playback takes place during transmission.
- Intermediate buffering is necessary for seamless playback.
- Fast-forwarding, rewinding and pausing is possible in principle.
- Protocols: HTTP, FTP
Live Streaming
- Provision of the offer in real time
- Protocols: RTP, RTCP, RTSP, SIP, SRT, HLS, DASH
- Special form: Phonecast (distribution via telephone server)
- Fast-forwarding is possible up to the current live position; Pausing and rewinding is usually possible as in the on-demand stream.
Audio, Video Container Formats and Software
The formats are .3gp, Flash Video Streaming, Advanced Streaming Format (ASF), Audio Video Interleave (AVI), Flash Video (FLV)
FLAC, .MP3, .MP4, MPEG Transport Stream, Ogg, QuickTime, RealMedia, WebM, Windows Media and so on.
The known software used are Ampache, Cameleon, Catra Streaming Platform, dyne:bolic, FFserver, Helix Server, Icecast, Icecast2 (free software), Jinzora Broadcast server software, Kodi, nginx, Open Broadcaster Software (OBS), SHOUTcast, VideoLAN Server etc.
