Quantcast Bitrates: How Long Should the Prediction Take? - digitalFAQ.com Forums [Archives]
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08-02-2003, 01:48 PM
ak47 ak47 is offline
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I tried Cqmatic 1.02 a while ago on Rush Hour 2 which is 90mins, and I think the results were about 10 minutes. Then later I tried a Spirited away an anime that is 124min. But when I did Spirited away the movie took almost as long as to predict to encode. I was wondering how long should it take compared to a full encode (%). By the way I am using mpeg-2 and gop of 12 and 3000max and 64min bitrate and 544x480 resolution everything else is the same as the templates.

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08-02-2003, 02:59 PM
kwag kwag is offline
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Hi ak47,

The prediction should take no more that ~15% of the total time of the movie. However, if the final CQ will fall in the unlinear range (varies if CQ or CQ_VBR), then it can take WAY longer, because there's just no way to calculate
So the best thing that CQMatic be do, is start bracketing down (or up) on CQ values, until the target is reached. In another way, say I want a target sample of 10MB. I encode with a CQ of 50 and I get a 20MB sample. If TMPEG's CQ was linear, then simply dividing by 2 (50/2) would give me a 10MB sample, but this is not the case, and I can wind up with 14MB. So you see, it's a real pain to calculate the correct target, and every CQ value creates a different file size completely out of proportion.
So the best you can do is ~2 passes, to a max of "I don't know", depending on your material.

-kwag
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