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Quantizer?
Can anybody point me to a really good article on what exactly a quantizer is/does in terms of video compression/output?
Thanks a million!
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4 Replies
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Are you looking for a mathematical explaination about how it works, or merely a practical explaination about how it relates to video quality?
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Practical please. 🙂
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Many codecs, mostly those based on mpeg technology, use a thing called quantizers to determine the amount of compression that is applied to a frame. The larger the quantizer used, the more compression will be applied to the frame. Similarly, the larger the quantizer used, the lower the quality of the frame will be.
Usually, you don’t deal with quantizers directly. With most encoders, you will typically specify a bitrate or a filesize, and the encoder will automatically choose the quantizers for each frame that will allow the video to fit that bitrate. Some encoders may give you an option to encode at a constant quantizer though, or to cap the minimum or maximum quantizers that may be used. Generally, quantizers in the range of 2-4 provide a nice visual quality (although the visual quality can depend on other factors), though for low-bitrate material you might see quantizers more along the lines of 8-12, or even up in the 20s.
Don’t get quantizers confused with a “quantization matrix”. That is something completely different. Anything else you needed to know about them?
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Not really, but my brain is so full from work today I’ll have to read this later 🙂 Ty
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