Question about Decoder iDCT

[gobama05]

Ok, this is the question I have. I could not find anything referring to this using the search function. I have an AMD 64 3500+ cpu and in Rebuilder within the AVS options there is a "set decoder idct" option. Should I use the default for this or would another option be best for my processor? Thanks :cool:

[jdobbs]

I think testing is the only way to be sure. Do a small segment and compare the time involved with each iDCT -- then use the one that's fastest.

[gobama05]

I found the fastest method for me was to use the 32 bit SSE2/MMX option for the decoder iDCT. It cut my encode times about an hour and a half. Which is simply amazing to me. :D

[Carpo]

i use idct=3 - and leave it going over night while i sleep :) (woot 400th post :D)

[NaN]

It's not so simple. The idcts use different rounding and not all are therefore equally precise. I recommend idct=7 (xvid simple MMX), it's fast and precise.

Cheers, NaN

PS: I mean 'precise' in the sense of not perfectly reconstructing the given frame.

[gobama05]

Cool, I'll give iDCT=7 a try. Thanks for the advice. :cool:

[mod]

idct 7 too, works fine :)

[apfraats]

Interesting.......

I never gave this much thought.


Most important question: Does it differ in picture quality or reproduction quality/precision or is it only a speed consideration ???

I use '64 Bit Floating Point' because it left me with feeling it should be the most precise, but hey, what do I know ???

So just regarding QUALITY any differences ????

If yes, what's the best ? (may be the slowest, I don't care)

I consider the best: The one option that is reproducing a frame as most accurate to what it should be.

And a second one:

Does AVISYNTH and DECODING take advandtage of DUAL CORE ATHLONS ??

Or is only 2.70.x.x having pleasure on a dual core system using 100% of 2 cores in stead of one ????

[Boulder]

Avisynth doesn't support multithreading (yet). However, you can use tsp's MT plugin or his special avisynth.dll build to make use of the two cores.

[jdobbs]

If you want to see how accurate the iDCT algorithms are, you can always use AVISYNTH to do a comparison of pictures for differences using the IEEE 1180 as the baseline. I think you'll find the differences negligible. Most of them do the the same things, only they use different CPU instructions (taking advantage of SSE/SSE2 or using integer math).

[gobama05]

I did some tests, and found that idct 5 works best for my system. Thanks for all the advice. I am learning :)

[J-Wo]

idct=6 is faster than idct=7 on my system by a little bit. The two 64 bit ones were the slowest. I have an AMD dual core Opteron 165 overclocked to 2.6Ghz with 2x512mb ram running on WinXP Pro. Never did any benchies until now so I'll stick with idct 6! Gonna try that MT plugin and see if I can figure it out... Anyone here have experience with it pls PM me I may have questions!