Advantech Wireless manufactures broadcast and satellite equipment that enables jitter-free streaming for all your multimedia and video broadcasts.

Multimedia is often associated with large volumes of data. Users wishing to access multimedia over the internet must, ultimately, have that data transferred to them. If traditional downloading methods were employed then significant delays could be incurred before users could view, or listen to, the media they requested.

As the volume of data increases, with longer playing or higher quality media, then this prospect becomes increasingly undesirable. For the live or continuous broadcast of events, where there is no clearly defined end to the media, then traditional downloading becomes untenable.

Streaming provides a solution to these problems. Streaming may be defined as…

“…a continuous connection over a network between server and client wherein media sent by the server is processed and displayed by the client [nearly] as soon as it is received.”

“Nearly” simply means that small buffer of data may be used to guard against network timing jitter. Since streaming plays out the media almost as soon as it arrives, each packet of data must arrive in the correct sequence and there is little or no opportunity for the correction of lost or damaged packets. Consequently streaming uses sophisticated encoding and decoding strategies to minimize the effects of lost packets and jitter.

It should be noted that streaming is not the same as a progressive download, where packets can arrive asynchronously and may be replaced if damaged. A further important difference between streaming and progressive downloading is that streamed data is not written to disk. This helps the distributor retain control over the copyright of the media.

Streaming Formats

The format of a stream refers to the particular compression CODEC used (e.g. Sorenson, RealVideo8, etc.), and to the file format (.mov, .asf, .rm etc.), and to the application layer protocols that are used (e.g. RTSP or other proprietary protocols.) Different vendors of streaming software use different combinations of compression CODEC and file format.

One difficulty faced by streaming is ensuring that the encoding rate is always low enough for the available bandwidth. For some streaming formats, such as QuickTime, if the bandwidth drops too low then the stream will stall. Some of the more sophisticated formats, such as RealNetwork’s SureStream, allow a player to dynamically switch between different encoding rates, to ensure that the show always goes on even under to most difficult bandwidth conditions.

At the transport layer the use of UDP/IP provides the best performance for streaming. This is because streaming requires a high data throughput and can make little use of retransmitted packets. However, it is not always possible to establish a UDP/IP transport between a server and client. This may happen, for example, if a Network Address Translator (NAT) or firewall lies in the network between the server and the client, and blocks UDP packets.

Streaming software tackles the problem of UDP/IP blocking by resorting to the use of TCP/IP where necessary. The use of often TCP/IP mitigates the problems associated with streaming through NATs and firewalls, but also incurs a performance penalty. Since, TCP/IP is a connection oriented protocol that incorporates a request-response cycle, unless a performance enhancement proxy (PEP) is implemented.

This compromise may lead to reduced quality of the media.

Streaming Software Example

The RealOne Player from RealNetworks is a versatile media player that is capable of playing most of the streaming formats that exist today, including RealMedia, WindowsMedia, and QuickTime. The RealOne player will allow the playing all of the media clips that are included on this page.

The RealOne Player can be obtained for free.

When streaming, the best performance results when UDP/IP is used as the transport protocol. However, if a NAT or firewall is present between the server and the player, then the use of UDP/IP can be problematic. Under such conditions it is necessary to use TCP/IP. The use of TCP/IP is somewhat of a compromise and can result in reduced quality.

By default the RealOne Player should first attempt to connect to the server using UDP/IP. If this fails, then the player will, by default, attempt to establish a TCP/IP connection. Thus, it is not normally necessary for the user to be concerned with TCP or UDP selection. However, if the RealOne player has difficulties in establishing a connection, or the playout of the media is unsatisfactory, then it is worth checking to see if the default setup has been modified.