Converting progressive (60 fps) to standard MPEG2 (30fps)

[natebetween]

Question....I have a divx .avi file that has been de-interlaced and converted to a progressive (60 fps, correct?) file. I have no idea of the process involved but I'm sitting here thinking.....if I encode this file in TMPGEnc down to a 30fps mpeg2 for burning as an SVCD wouldn't there necessarily be either:

A: Substantial Quality loss or

B: A change in frequency in sound or picture so that either the sound sounds funny or the picture jumps.

This is my first dealing with a progressive file and any help would be appreciated. I looked at other similar questions but they were'nt exactly what I was asking.

THANKS!!

-Nate

[keithsebastian]

... and converted to a progressive (60 fps, correct?) file.... -Nate

WRONG !

Most probably it's already 30fps (or 25fps PAL).

Just go ahead with your conversion.

PS : Most deinterlacing techiniques work by either disposing off
one of the fields or by blending/blurring or intelligently
averaging between the 2 fields. And, generally you end up
with the full framerate (1/2 no. of fields).

[natebetween]

Thanks....I'm going to go ahead with my conversion....but here is what I found.

The person I got this from seperated the fields, and then put them together again using a filter in vdub that gives you the 60 Half interlaced frames as 60 full progressive frames. (Does that make sense) He pointed me to www.100fps.com and I've read a little about the process. It seems using this filter in VitrualDub, with AVISynth allows you to de-interlace the images and then place them one after another in full resolution.


.......OF COURSE I could be misinterpreting the whole thing and I don't know what I'm talking about.....that's always the most obvious choice!!

-Nate

[keithsebastian]

WOW! That's news to me. Gonna check out the website.

[Gazorgan]

I have several clips in that format. The theory is you won't have any interlacing artifacts from motion between fields. (there shouldn't be any motion between fields, but converting films cheats, as does pure digital sources).

Changing the framerate in VDUB didn't work for me, since I essentially lose 1/2 my fields. (it looked like a 15 fps porn trailer). I haven't gotten back to the project, because I really didn't have a need to make an MPEG out of it. What you need to do is convert frames to fields, then de-interlace (if that's possible after the conversion, not so sure of that).

[keithsebastian]

nate - Why don't you just open the avi in Virtualdub and check the file info.
This way, you'll be sure of the framerate. I'd like to know if it's
actually 60 fps.

[energy80s]

It's probably 60 FIELDS per second which is 30 FRAMES per second.

[natebetween]

Okay......I was working on this ALL night and here's what I found out.

First off ....this DID change my 29.970 (I believe that was the exact number) FRAME per second movie into a 59.940 (I believe that was the exact number) FRAME per second movie.

I've only had chances to experiment with tiny clips, but here's what I did.

I ripped the .vob files from some ol' DVD I had lying around and frameserved them to vdub to save the .avi using the divx codec.

I slept.

When I got up this morning I followed the directions at www.100fps.com. I created a quick script using avisynth that would split the fields. Then I picked up the vdub filter it said to get "Deinterlace = Smooth", I messed around with some of the values in there...I had to click "Alternate field order." Again I saved as .AVI using divx and it seems to me success. Now, I've only been able to do a 1 minute piece as of yet, but it shows up in VDUB as a 60 frames per second .avi clip........and no interlace lines as far as I can see.

I know I probably could have frameserved to vdub using avisynth and the filter FIRST.....but I wanted to compare the 2 clips!!

SO....I'm left with 2 questions/problems.

If I'm taking a field and dividing it into it's 2 seperate frames.......since I'm saving it as the same resolution as the original....wouldn't my resulting picture be half the quality of the original?!

Second.......My original question. If I encode this 60fps movie down to the 29.970 required for (S)VCD............won't I be losing even more info?!?!

Hmm............perplexing..........I can't wait to try it!

-Nate

P.S. This method is SLOW!! I only did a 1 minute clip and it took 15 minutes. I can't imagine what a whole movie would cost in terms of time. As far as I understand it.........AVISynth is very limited in speed.

[natebetween]

Ahh Screw it..............I'm just going to frameserve it directly to TMPGENC and de-interlace it using the included filters........The "Double (Field)" filter seems, at least to me, to do the close to the same thing as the 100fps methond anyways. Seems to be better quality than discarding fields anyways.

Why make the 30fps movie into a 60fps .AVI and THEN convert to a 30fps MPEG?? Too many steps!! Anyways...doesn't too much processing degrade a video?

-Nate

[keithsebastian]

Hey, I use the Smart Deinterlace filter for VirtualDub. Works like a charm and is quite fast too. Get it from here :

http://shelob.mordor.net/dgraft/smart27b2.zip

Deinterlacing is performed only on moving areas (with interlace artefacts). So the full vertical resolution is preserved. Moreover you can use the "Show motion areas only" option to analyse the strength of motion detection before you apply it. Play with various options untill you get a satisfactory result. And, don't forget to read the included help file.
-Keith

[natebetween]

Thanks for the advice...I'll try it. Still things.....

It seems I get better results when I capture my vob's straight to mpeg rather than AVI, as evidenced during times when there's just a blank black screen. When captured to DIVX AVI at I think 12MBPS I see pixelated boxes during black screens......Captured at 2520 MPEG2 I have NO pixelated boxes.

Any thoughts??

Thanks.

-Nate