Re: Re: [mpeg2-dev] A funny stream

[Arpi <ar...@th...>]

Hi,

> Well I still dont understand, because you said you use the same IDCT
> in the encoder and the decoder, and in that case errors should not
> accumulate... basically the prediction frames should be bitwise
> identical in the encoder and the decoder and so there is no reason to
> get error accumulation... is there ? Also given our statistics in the
> IEEE tests, I dont see that the errors should be visible after 100
> frames. In my maths the errors should still be a deviation of about 1
> level of gray after 100 frames - not anything noticeable really.

you should try to dump idct blocks from that broken files, and do some
testing with them. what about some code to do idct with both algo (your and
Michael's) and compare results, and save block if differs, so you can
do further tests with them?

btw, idct artifacts usually come at constant, bright, flat parts of the
image. like white walls, light-blue sky.
maybe it's from handling boundaries (0/255 limits).

> (basically one stream that has very little I pictures, I think one I
> every 100 or 132 pictures) they get bad error accumulation, in the
usually 500-1000. (every 10-20 secs)


A'rpi / Astral & ESP-team

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