Why does AutoGK resize and convert to 23.976 fps?

[LarryEvilsizer]

Hi,

We are investigating VOB size-reduction methods and are testing AutoGK. Each time I run a VOB through AutoGK, the resulting AVI has been resized from 720x480 to 720x500-something (the lastest try was 720x540). It also converts the frame rate from 29.970 down to 23.975.
I'm using the 75% target quality. In advanced settings we are using fixed width set to 720 and in the Hidden Settings dialog have disabled auto-cropping (threshold set to 0).

We want to have the output AVI framesize and fps the same as the original, and are wondering how we can do this in AutoGK or if we have to use the Gordian Knot program directly, or try something else.

Thanks for your time,
Larry

[AlanHK]

The fps would be because that's what the real number of frames per second in the file is. In the VOB the pulldown flag tells the player to duplicate some frames on playing the file to make it up to 29.997.

Avis play perfectly well at 23.976, and there should be no sync or other problems.

The height change may be something to do with compensating for square/rectangular pixels (TV pixels are different from monitor pixels). There's probably a setting (under aspect?) that lets you control that.

[guns1inger]

720 x 540 is a 1:1 representation of NTSC 4:3 full-D1. Next step down would be 640 x 480.

[manono]

We want to have the output AVI framesize and fps the same as the original...

The framerate is the same as the original, with pulldown removed. You don't really want 720x480, unless you plan on having your player do the resizing. If you do want that (although I don't think you do), then the Hidden Options can take care of that for you.

And if you don't know what you're doing (and from what I can see, you don't), I'd leave the Hidden Options alone, if I were you. Do you really want to waste bits and make amateurish looking AVIs by leaving in any black around the active video (which is what disabling the autocrop does)?

[jagabo]

The framerate is the same as the original, with pulldown removed.

I'd go so far as to say it's the same frame rate as the original without adding pulldown. You don't want to add pulldown or you'll create interlaced video from your progressive source. That's generally a bad thing for Divx/Xvid.

[manono]

Yeah, I purposely didn't get into that. This is AutoGK we're talking about, so it won't give you back an interlaced AVI. It's not really possible for him to force a 29.97fps framerate unless it's been detected as a hybrid. Film on DVD, whether hard or soft telecined, will always wind up back at 23.976fps. AutoGK will do it right, no matter how much the user tries to screw up.

If he goes with GKnot, and makes his D2V using Honor Pulldown Flags, then he could wind up with that nasty looking 3 progressive/2 interlaced in every cycle of 5. If he does that once, I think he'll quickly learn the error of his ways.

[AlanHK]

We want to have the output AVI framesize and fps the same as the original

You've seen several posts on why this isn't working as you expected.

If it really is important to have the same specs, and not just look the same, you could just convert the VOB to MPEG (use VOB2MPG, for instance). The VOB is essentially an MPEG anyway. MPEGS are generally about twice as large as an equivalent quality AVI, but it may be what you want, and most media players can handle them.

[jagabo]

If you really want to keep the frame size, open your file directly in VirtualDubMod. Set Video -> Fast Recompress. Use Video -> Compression to select Xvid. Press the Config button, press the More button in the top right corner, select the Aspect Ratio tab, then set the proper Display Aspect Ratio. Set up the other compression particulars, then File -> Save As.