Quote:
Originally Posted by foxyshadis
Doesn't seem to have ever been discussed in public. I bet it was a test an engineer inserted and it was just never removed; I wonder if it's ever been used in real life.
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Rationales of many AV1 features seem me vague. Woo-Jin Han in LinkedIn forum "AV1 Learning" commented 1/8-pel precision:
" It was proven that high precision mc is only effective for low resolution. Beyond 1080p, even 1/4 pel seems not very effective to justify its complexity. I remember that 1/4 pel shows 30% coding gain for famous Mobile CIF sequence (low res, complex texture, slow motion, aliasing from inadequate down sampler) but average 5-8% over various test sequences. Very high frame rate with non hierarchical structure may change the situation but it seems clear that it is highly sequence dependent tool"
I remember a paper "Motion-Compensating Prediction with Fractional-Pel Accuracy", by B. Girod, 1993 . If we omit a mathematical part of the article and go to the conclusion part, it's written (in my wording): for blocks 16x16 of TV video resolution 1/4-pel motion accuracy appears to be sufficient.