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I'm must admit however that I have trouble to figure out what frequencies mean for a video
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The DCT process converts values from the spatial and temporal domain into the frequency domain. Here is a comprehensive article about it:
http://www.cs.cf.ac.uk/Dave/Multimed..._Transform.pdf
After the conversion into the frequency domain the next step is the data reduction by quantization. First of all you specify an average quantizer value like 2, but the quantizer which is actually used is not the same for each frequency, it is calculated by using the matrix coefficients. If you use a matrix where all coefficients have the same value (like 8 or 16) then your given quantizer value of 2 would indeed influence all frequencies the same.
Quote from Dark Shikari from the old thread I linked to above:
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If you halve all the values in a quantization matrix, it is mathematically EXACTLY THE SAME as if you halved the average quantizer.
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Have fun studying all that stuff...
manolito