idct=7 is not applied

[djan]

Hi,

I checked the option idct=7 but it is not applied in the avs files. Is it a bug or am I missing something ?

Thx.

[Alex_Rowe]

I think the idct=7 option is applied to the .d2v files and not the avs files.

But my question is how does the idct=7 affects the movie? and if it´s best than idct=2, then why it´s not the DEFAULT? :confused:

[wmansir]

Originally posted by Alex_Rowe
I think the idct=7 option is applied to the .d2v files and not the avs files.

But my question is how does the idct=7 affects the movie? and if it´s best than idct=2, then why it´s not the DEFAULT? :confused:

The iDCT can be set in either the .d2v or the MPEG2Source(...) line in the .avs file. But I think the OP is right, I don't see it being changed in either place.

The various iDCT are just different methods of doing (really approximating) the complex math needed to decode MPEG2. IEEE-1180 Reference is the standard, this is what the output 'should look like', but it is very slow (in part because it uses 64-bit precision). The other methods give you approximately the same output mathematically, but not exactly, and are a heck of a lot faster. Visually, difference is very small. You can try them out yourself and see if you can tell the difference, but you probably won't. But since idct=7 is about the same speed as the default, but more accurate, you might as well use it.

idct=7 is not the default because it didn't exist in earlier versions of MPEG2Dec.

[jdobbs]

It should be setting it in the .AVS file. I'll take a look at it when I get a chance.

[djan]

DVD-RB 0.48
- Fixed an error in which "IDCT7" was not being properly applied when selected. Thx to djan to have discovered the bug. ;)

[jdobbs]

Originally posted by djan
Thx to djan to have discovered the bug. ;) Let me say it: "My thanks to djan for discovering this bug."

I'll put that in the README on the next version.

[djan]

Originally posted by jdobbs
Let me say it: "My thanks to djan for discovering this bug."

I'll put that in the README on the next version. Very thx jdobbs, it's an honor for me. :) Don't forget it... No, I'm kidding. :)

[jdobbs]

It's already there.

[djan]

You are the best jdobbs. :)

[onesoul]

I see what is happening, jdobbs is giving credit to anyone who catch bugs to get them all squashed in no time. Way to go :D

[redfive19]

I am prolly gonna get flamed for this, but what is idct?

[wmansir]

Originally posted by redfive19
I am prolly gonna get flamed for this, but what is idct?

Inverse discrete cosine transform. It's a function used in a lot of multimedia programs. MPEG, jpeg, mp3, ect. It' really just complex math.

IEEE-1180 defines the standard function, and also some guidelines as to what output is acceptable. Because decoders can be written on different platforms, or hardcoded into different hardware, it would be difficult to require an exact match of the function. So instead the 1180 guidelines give a high precision reference function and the decoder's designer can implement their method of iDTC however they want, as long as it is within a defined tolerance. All the versions included with Mpeg2dec are within that tolerance, but some may not match the reference as closely as others.

[redfive19]

okay! so should i be enabling this by default?

[Sir Didymus]

The point has been already discussed in this forum. If I remind, one of the gentlemen who specifically asked to have this option enabled in DVD-RB is Unplugged.

See for reference the post:

http://forum.doom9.org/showthread.php?s=&threadid=73051&perpage=20&pagenumber=50

and the relative replies...

The choice of using it or not is left to the end user...
Somebody (myself included) is quite happy about it...

Cheers,
SD

[djan]

Does idct=7 give better luminance/contrast or does it have nothing to do about ?

[Sir Didymus]

We risk to go a bit OT, and in this forum it would be better asking specifically to more expert people; anyway... as I know...

...and as Wmansir have already explained...

the choice is related to the numerical software (and hw) adopted to approximate the reference 64 bit IEEE-1180 IDC Transform, so it is more a matter related to the numerical compliance with the reference IDCT of different computational schemes (to be balanced with the time you accept to pay for them), than to the luma/chroma characteristics of the encoded stream...

[The_Flash]

Jeez. Is that English? Some of us didn't go to college for computers. Nor do we have 'forums' where we can wow those not in tune with our specific study.

[Sir Didymus]

Originally posted by The_Flash
Jeez. Is that English? ...
Something wrong with being specific and technical in the answers ?
Would you prefer just a simple answer like "no, it has nothing to do with luminance and chrominance - stop" ?

Or would you prefere an answer like: "ok, the reason for having all the options enabled is that for you to test them and to choose the ones that most fits with your feelings" ?

Maybe people who asked was happier than you of getting some more...

In any case you are right English is not my mother tongue...
:rolleyes:

And I am afraid if my mispelled technicalities disturbed your quiet...
:sly:

[djan]

Originally posted by Sir Didymus
We risk to go a bit OT, and in this forum it would be better asking specifically to more expert people; anyway... as I know...

...and as Wmansir have already explained...

the choice is related to the numerical software (and hw) adopted to approximate the reference 64 bit IEEE-1180 IDC Transform, so it is more a matter related to the numerical compliance with the reference IDCT of different computational schemes (to be balanced with the time you accept to pay for them), than to the luma/chroma characteristics of the encoded stream... Thx for your explanation, I well understood what you told even if English is not my mother language.