Quote:
Originally posted by Tommy Carrot
I don't know, but every mpeg4 codec has this issue, so it's the standard's fault. Even halfpel does this, just to a lesser extent. So the integer transforms definetaly help here.
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The main qpel issue with different codecs is primarily related to the definition of the qpel interpolation specified in the ISO/IEC standard. The first specification was very confusing and was completely updated lately (in a draft corrigendum from wg11, not publicly published yet). The result is that different codecs have their own implementation that follows more or less the standard and aren't not 100% interoperable.
Concerning the DCT mismatch issue, it is more visible in mpeg4 compared to mpeg1/2 because the usual GOP is much larger (~300 frames is common) and because most encoders don't intra-code macroblocks after 132 consecutive preditive coding to reduce the accumulation of DCT mismatch errors as required by the standard.
This mismatch problem is probably one of the motivations that leads to the choice of an integer transform.
-- bobololo.