Top or Bottom field first ?

[FranckV]

I am trying to find out wether I should select Top Field First or Bottom Field First when encoding an avi file to mpeg.

When looking at the extra 2 frames coming from the 3:2 pulldown of an interlaced video avi file in Virtual Dub, when there is movement, which field is suppose to move first A (top) or B (bottom) ?


Thanks for any tips.

[ktnwin]

If you are encoding to VCD (MPEG1), it does not matter.

However, for SVCD (MPEG-2) it's very important to get it right.

I have followed many advises and only one works for me.

Just encode a 5 min video clip (with enough motion) using each setting, burn both MPEGs files on the CD-RW as SVCD and see which one works best.

Then remember that settings.

The bad news is the setting varies based on the source video (captured from digital camcorder, from capture cards, from DVD rips).

Even for DVD rip, each DVD title could use one or the other !!! I got fooled many times.

Heard that the new TMPGenc automatically detects the field order, it did not work for me.

[FranckV]

Here is what I found out so far:

Open the AVI file into VirtualDub
Select the deinterlace filter w/unfold side by side option

Move to one first 3:2 pulldown frame, then if the first field that shows motion is the right one (bottom), then you need to encode with bottom field first, if it is the left field (top), it is the opposite.

[VidGuy]

Even easier - open the video with TMPGEnc - go top Advanced tab, Set top field first, check Deinterlace, then double-click it - choose Method: Even-Odd field (field).
Then preview the video right there in the same screen. If it looks good - you're right. If it is jumpy, you're wrong. THen choose Bottom field first, and verify the decision. One way will look obviously wrong (it will move forward, then jump back, then move forward again). The other way will look smooth.

If you're encoding in CCE - TMPGEnc Top Field first = uncheck the field box (I forget what it's labeled). Bottom Field first = check the field box.

[tat2jr]

Thanks VidGuy for that EZ way to find out!

[iant]

Just in case you're having trouble determining whether you have the right value set, I have a simple solution.

Encode a section that has vertically scrolling credits. Play it back. If you have the correct field set, everything looks fine. If not, it jerks like all get out. If that's the case, switch fields.

Hope this is useful.
Ian

[FranckV]

Thanks for the tip.

As far as CCE encoding is concerned, checking or unchecking the Upper Field First has no effect, CCE always encodes with Top Field First (at least version 2.5 & 2.64).

The trick is you can use one of the MPEGFixer tool of the DVMPEG package to change which field you want first without having to re-encode.

[iant]

Sorry FranckV but I beg to differ.

Using the technique I described earlier in this post, I realised that mine required bottom field first. So I unchecked 'Top Field First' in CCE 2.5 and encoded. Credits were fine.

Now, if that's not doing changing field order, it's doing something else darn peculiar.

Ian

[homerpez]

I think we were discussing just what the "Upper Field First" check does in another thread here... my suspicions are (again) that it's not a toggle between "top" and "bottom", but it only forces "top" first.

So, if FranckV has "top field first" source video, I'm thinking that, for whatever reason, CCE can't fix it.

If I'm totally wrong on this (Truman? Other CCE Experts? HELP) let me know... but for me, unchecking that box in CCE has the effect of letting me specify the correct field to go first in the frameserving program (in my case, TMPGEnc).

[FranckV]

Like I said in an other post, here is what I found out:

CCE always creates MPG file with the Top Field First flag set (easy to check with Bitrate Viewer) no matter what the source is.

So, if source (AVI) is upper field first, then do not check the Upper Field First box in CCE. CCE will leave the field order alone and movie will play fine.

If source is bottom field first, then check the Upper Field First box in CCE and this will invert the field order.

The above can be checked by using DVD2AVI to convert the mpg back to avi and verify that the field order in new avi is opposite of the original.


Like I said, using MpgFixer from the DVMPEG package allows you to change the Top Field First flag in the MPG file without having to re-encode.