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Video Codecs 101

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If you watch videos on the web, you use video codecs. [galloping hooves] But what exactly is a video codec? Codecs reduce large videos to more manageable sizes. This is called compression. Without codecs, serving video on the web would be almost impossible. Uncompressed, or raw video, simply requires too much data to transmit, over even the fastest networks. For example a 5 minute mobile video without compression, uses over 3 gigabytes of data. A 5 minute HD video uses over 25 gigabytes. Files this large would take many hours to download to your computer for playback. On a mobile connection, they'd take weeks. So, how does a codec shrink all that data, to something that you can play on your device in seconds? Codecs use sophisticated algorithms to work their magic. But you don't need to know what a discreet cosign transform, or entropy encoder is, to understand the basics. The first thing to keep in mind is that digital videos are sequences of pictures, called "frames". Much like the frames in conventional movie film. In most web video, there are about 30 frames per second of video. Because there are so many pictures per second of video, the picture in each frame varies only slightly from the frames before it, and those after it. Codecs work by removing similarities in the uncompressed frames, keeping only the differences, and encoding the differences as symbols. After all the redundancies are removed, the resulting data, called the "encoded bitstream", uses far less data than the original uncompressed source. There are 2 parts to a codec - an encoder and a decoder. The encoder compresses the video stream into a binary encoded bitstream. The decoder restores the encoded bitstream back into sequential pictures, or frames, for playback. The encoding process results in some loss of the original video's quality. One test of a codec's quality, is measuring the size of that loss. On the decoding side, simplicity and speed are perhaps the most important qualities of a codec. After all, a decoder isn't much use if no one's computer is powerful enough to run it. So, that's a brief introduction to the world of video codecs. Next time you watch a video on the web, you'll know something about the amazing technology that makes it possible. [Captions by]

Video Details

Duration: 2 minutes and 29 seconds
Country: United States
Language: English
Views: 179
Posted by: ccwebguy on Nov 27, 2011


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