Field alignment vs. Vegas

Cheesehole wrote on 3/27/2004, 8:34 PM
This one is for the experts. I'm trying to find the trick to get Vegas to offset a track of video by 1 field. It isn't as easy as I thought it would be. Here's the deal:

I have two ttracks of video that were taken by two cameras pointing at the same subject. This was a 3D shoot of a karate tournament so there is lots of fast motion - hence the importance of getting the tightest alignment possible - at the field level. Unfortunately, field 1 of camera one sometimes lines up best with field 2 of camera two. They aren't genlocked or anything... I'm using tiny Canon Optura 300s so that isn't an option.

Field 1 of track 1 syncs to field 2 of track 2. See the vertical alignment

======TRACK 1====
1-----1-----1-----1----
---2-----2-----2-----2-
1-----1-----1-----1----
---2-----2-----2-----2-
=================
======TRACK 2====
---1-----1-----1-----1-
2-----2-----2-----2----
---1-----1-----1-----1-
2-----2-----2-----2----
=================

INTERPOLATE = YES
RESAMPLE = NO


I tried turning on resampling but it seems to use a "blend fields" technique to construct the in-between frames. I don't want any temporal overlap.

I want Track 1 Field 1 to mix with Track 2 Field 2 to create Field 1 of my output video - and I want Track 1 Field 2 to mix with T4rck 2 Field 1 (of the following frame) to become Field 2 of my output video. And so on.

I can just flip the field order by changing my source media properties to Upper Field First, but that makes every other field go backwards in time so that's no good! :D I just want to OFFSET the media by one field.

The only way I've come up with involves re-rendering the video source at half-speed which would force each field of the source video to become a whole frame. Then I can easily sync the two tracks at the frame level. But that invovles a lot of extra time and disk space. There must be a way to do this in Vegas right? I mean people must do this kind of thing all the time, no? :D

THANKS FOR ANY HELP!!!

- Ben

Comments

TVCmike wrote on 3/27/2004, 8:47 PM
Just a thought here, but...

Have you tried reversing field order in an app like Avisynth or VirtualDub? If you need to offset by more than one frame, then I think you could actually nudge the video track one frame ahead of the audio track and back-fill it with blank media or a copy of the previous frame right at the beginning of the video.

Or maybe I don't understand the problem late on a Saturday night... :)
Cheesehole wrote on 3/27/2004, 10:25 PM
>>>Have you tried reversing field order in an app like Avisynth or VirtualDub?

This sounds like the right track... but no I haven't tried that. But just to be clear, I don't want to reverse the order of the fields... I want to push the entire video forward by one field. So yes, lower fields will become upper fields, but they can't be reversed time-wise.

Frame 1 Field 1 would become Frame 1 Field 2
Frame 1 Field 2 would become Frame 2 Field 1
etc...

Guess I'll have to check out those apps and see if they can do that. Thanks for the lead.
ZippyGaloo wrote on 3/27/2004, 11:00 PM
DELETED
Cheesehole wrote on 3/27/2004, 11:28 PM
What I've been doing is editing at double the frame rate. 59.94 fps. What is the proper frame rate to use anyway? It can't be exactly 59.94...

I looked at VDub and AVISynth and couldn't find an obvious way to shift the fiellds. I tried swap fields, but that made things move in reverse every other field.

What I need is to be able to move the frame boundary forward by one field, or half a frame - and then set the field order to upper field first.
taliesin wrote on 3/28/2004, 12:30 AM
It can easily be done in Vegas by deselecting the "Quantize to Frames" option. Set the Ruler Format to "Time" to get precise control displayed in milliseconds and then simply shift one event for the time shift value of one field - 40 milliseconds for PAL video or 33 milliseconds for NTSC video.

Marco
Cheesehole wrote on 3/28/2004, 1:53 PM
Yes this worked! Thanks for the assistance and the hard numbers.

What makes it difficult is Vegas doesn't have an option to view the preview window as "Fields". So I have to do my alignment looking at a mix of two different time slices.

I hope Vegas 5 has this ability. We should be able to right click on the preview window and hit Field A, or Field B - if our project is set for interlaced output. Better hit the feature suggestion page quick! :D
Cheesehole wrote on 3/28/2004, 9:29 PM
59.940060

That's the number I was looking for to get Vegas to double the 29.970 preset. I hope they include the preset in Vegas 5.