Watching Movie 9
Streaming technology has made listening to music or watching movies on the net as easy as turning on the radio or TV. Here's how the technology works.
The very first music and movie files you can find via the internet were just short clips because you had to download the whole file prior to deciding to could play it. Currently, conversely, you may start playing the file as soon as the first bytes begin to arrive... due to streaming.
This immediacy is possible because streaming doesn't send files over the internet the same as many other files are sent. It uses a different protocol.
A protocol is a set of rules defining how two computers connect with each other and the way they send each other data.
Most data which 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 so 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 look for errors.
If one packet gets damaged when downloading will be controlled by TCP, downloading will be suspended while that packet is resent. That way, after the download has been completed, you can make certain that you have the entire data file.
When you are streaming files, on the other hand, UDP allows packets to get lost now and then without interrupting the downloading. This is fine because, when an occasional packet is lost, you are unlikely to notice any interruption to the music or movie streaming. But if everything froze very briefly while a lost packet was being resent, you probably would notice the interruption.
With streaming technology, you should not have to wait for files to be downloaded entirely before you can begin listening to audio or watching a video. You can listen to a concert on the other side of the world in real time, make a video call or watch a film just like on tv.
Streaming video works in a similar way to streaming audio, except that the video must be separated into its separate audio and video components when it really is in the buffer in the RAM.
The server that holds the video for streaming shall have a video capture expansion card that can capture either a live feed from a video camera or a pre-recorded video. The capture board turns the analogue signals it receives into digital data and compresses it.
At the exact same time, it employs a trick to prevent having to capture more data than it needs so that you can make transmission easier.
In the event the camera used to record the video is stationary, ie, it really is not panning, the amount of data created can 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 offer the illusion of continuous movement. The rate can be 30 frames a second which gives the video a smooth look.
The compression system reduces 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 exactly what the background looks like.
As long as the camera remains still, only the changes in the frame, such as the movement of the actors, have to be transmitted. The background only must be transmitted again after the camera starts to pan and 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 into a small buffer in RAM as it does for audio.
At this point the signals are split into separate video and audio components which are sent to the video card and sound card respectively, whence they can be output to your monitor and speakers so you can watch the film and hear the sound-track.
