Re[2]: [XviD-devel] xvid + bframes and mplayer/ffmpeg decoding

[Christoph Lampert]

On Sat, 17 Aug 2002, Michael Militzer wrote:
> The MPEG-4 VM 18 requires the coeffs to be clipped into the range [-128,
> 127] (8 Bit) but the VM 18 seems outdated and the reference codecs (momusys
> and f-dam) use 12 Bits to code coeff data in fixed length mode. Therefore
> clipping is not necessarily needed at all. Latest XviD versions don't clip
> the coeffs anymore, so all clamping artifacts should be gone...

If I'm not mistaken, it should be clipped to   [-2^(bpp+3), 2^(bpp+3)-1] 

So for 8bit material (like XviD) that's [-2048,2047], which I guess means,
no clipping is needed at all. 

Still that doesn't solve any of the iDCT "problems". Would it be much work
to either adapt iDCT  that nonzero->zero is not possible anymore or 
to detect if the output is all zero?
 
Christoph

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