See Movie 7
Streaming technology has made listening to music or watching movies on the web as easy as turning on the radio or TV. Here is how the technology works.
The first music and movie files you can find on the web were just short clips because you had to download the whole file before you could play it. Nowadays, however, you may start playing the file as soon as the very first bytes begin to arrive... thanks to streaming.
This immediacy is possible because streaming doesn't send files via the internet the same way because so many other files are sent. It uses another protocol.
A protocol is a set of rules defining how two computers connect with each other and just how they send each other data.
Most data that is sent over the internet is first broken up into packets (small blocks of data). The packets are sent separately and are the rejoined at their destination in order that the receiver gets the entire file.
The sending of most data on the net is governed by a set of rules called the Transmission Control Protocol (TCP). Streaming however uses the User Database Protocol (UDP).
Both of these protocols are quite different. The crucial difference is in how they check for errors.
If one packet gets damaged when downloading has been controlled by TCP, downloading will be suspended while that packet is resent. That way, in the event the download has been completed, you can make certain that you have the entire data file.
Whenever you are streaming files, on the other hand, UDP allows packets to get lost now and after that without interrupting the downloading. This really is fine because, when an occasional packet is lost, you are unlikely to notice any interruption to the music or movie. But if everything froze very briefly while a lost packet was being resent, you probably would notice the interruption.
With streaming technology, you don't have to wait for files to be downloaded entirely before you can begin listening to audio or watching movies online a video. You can listen to a concert on another side of the world in real time, make a video call or watch a film just like on television.
Streaming video works in a similar way to streaming audio, except that the video has to be separated into its separate audio and video components when it's within the buffer within the RAM.
The server that holds the video for streaming may have a video capture expansion card which can capture either a live feed from a video camera or perhaps a pre-recorded video. The capture board turns the analogue signals it receives into digital data and compresses it.
At the same time, it employs a trick to prevent having to capture more data than it needs in order to make transmission easier.
When the camera used to record the video is stationary, ie, it is not panning, the amount of data created may be reduced. This could be done because all moving images are made up of a series of frames (still images) that change in rapid succession to give the illusion of continuous movement. The rate is frequently 30 frames a second which gives the video a smooth look.
The compression system lessens the range of frames needed by comparing adjacent frames and only taking account of pixels that change from one frame to another. It does this by establishing what the background looks like.
As long as the camera remains however, only the changes within the frame, such as the movement of the actors, have to be transmitted. The background only has to be transmitted again once the camera starts to pan as well as the background changes.
Video streaming may also skip frames when your Internet link is slow, which may make the video jerky. Thus the faster your connection, the smoother the video will be.
When your computer receives the video signals, it shall decompress them and load them in to a small buffer in RAM as it does for audio.
At this point the signals are split into separate video and audio components that are sent to the video card and sound card respectively, whence they are output to your monitor and speakers so you may watch the movie and hear the sound-track.
