Another nasty, latent Vegas rendering bug

johnmeyer wrote on 3/28/2015, 9:36 PM

I was going to post some results in another thread about PAL to NTSC conversions. Kelly mentioned that he preferred turning off resampling when rendering PAL to NTSC. I was expecting to not like the results, but they looked far worse than I would have expected. Why?

Well, I found that I had stumbled across a really nasty field reversal bug.

To create this bug, I imported a PAL Upper Field First SD video clip into Vegas, matched project properties to that clip, right-clicked on the event and disabled resample. I then rendered to MPEG-2 using the NTSC DVD Architect template, which I changed to upper field first to match the source. The initial point of the exercise was to convert a PAL SD video into an NTSC SD video.

Here is a link to a short DV AVI PAL clip, along with the Vegas 10 VEG project file I initially used. I have verified this problem also exists on the latest version of Vegas 13. I also included the results of that render, in case you don't want to take the time to do the test yourself.

Resample Disabled Bug

To really see the field reversal, you need to look at the video field-by-field. What you'll see is that the gymnast takes several steps forward and then one step backwards. Really nasty, and totally unsuable video. You can view interlaced video within Vegas by using this trick:

1. Set the preview quality to Best Full.
2. In Project Properties, set the frame rate to double the normal frame rate which is 59.940 (Double NTSC) for 29.97 video.
3. In Project Properties, set field order to "None (progressive scan)."
4. Set Deinterlace Method to None.

The video will now be displayed field by field instead of frame by frame.

I hope that someone can test this and confirm my bug. I don't know whether I'll bother submitting it to Sony, since they don't seem interested in fundamental bugs like this.)

I have confirmed this to be a problem on Vegas 7, 8, 10, and 13 (latest build).

Finally, it is possible that this has something to do with an industry convention where uncompressed PAL video reverses fields (I had to deal with this in the Deshaker scripts I wrote half a dozen years ago). However, I am just some poor user trying to render video, and Vegas isn't doing what I told it to do.

Comments

johnmeyer wrote on 3/28/2015, 9:48 PM

I can "fix" the problem if I set deinterlace method to blend rather than interpolate. However, interpolate works just fine if I set resample to Force or Smart.

TheHappyFriar wrote on 3/28/2015, 11:09 PM

Currently what bothers me more (since I never go PAL to NTSC) is that I can't see the individual frames of your original PAL clip by changing the project to 50fps, progressive, no deinterlace. :( In YOUR project only. I can import your original source in to a new project, same settings, and it works. Go figure.

ANYWAY....

testing, please hold...

Ok, I'm back.

Did you disable resampling on the clip you rendered out & imported in to check the fields? To view it @ 60fps.

johnmeyer wrote on 3/28/2015, 11:18 PM

I take back what I said in my second post: I am unable to get any MPEG-2 NTSC render to create correctly, not matter what combination of upper & lower I choose in project settings and render templates, and not matter whether I choose blend or interpolate (none is not an option because of the resizing).

Conclusion: with this project, if you want to render with resample disabled, you cannot avoid getting totally screwed up video.

TheHappyFriar wrote on 3/28/2015, 11:34 PM

Try this (I think it works, I may just be tired... it's 12:30 here).

Change the original footage to lower, project to lower, render properties to lower.

Then render that and and see if it's good.

Looks soooooooo much better to me.

NickHope wrote on 3/29/2015, 12:42 AM

Same result as you John in V10, 12 and 13. Backwards steps mixed amongst the forwards steps.

I also get the same type of "backwards steps" when I convert my own BFF PAL DV AVI clips to NTSC in this way (i.e. Interpolate deinterlace method and disable resample). This appears to be a really bad combo!

TheHappyFriar wrote on 3/29/2015, 6:54 AM

I lowered the project properties to 1/2 vert res (288), progressive, 50fps, no deinterlacing & used pan/crop to show the fields (move up/down one unit) and the original video has the same "backwards" in it.

Not all the time, but they're there.

Former user wrote on 3/29/2015, 9:04 AM

I used your files, (not your VEG) in V11. with deinterlace NONE, I got an NTSC file, upper field first at 29.97 with no stepping backwards. Try with deinterlace NONE, smart resample.

my result

https://www.dropbox.com/s/5beam8pz4mks7mg/Untitled.mpg?dl=0

Message last edited on 3/29/2015 9:05:53 AM, by DonaldT.

johnmeyer wrote on 3/29/2015, 10:16 AM

As I said in my earlier post, you can't set deinterlace to none because the video is being scaled (from PAL to NTSC resolution) and a clip must be deinterlaced prior to resizing or else you get horrendous scaling artifacts. That is definitely true for this clip (I tried it!).

Former user wrote on 3/29/2015, 10:56 AM

Did you download my version? Did you see the artifacts that you are concerned about?

Former user wrote on 3/29/2015, 11:18 AM

https://www.dropbox.com/s/5beam8pz4mks7mg/Untitled.mpg?dl=0

This is a video I scaled from 1080i to SD interlaced.

Can you tell me if you see the scaling artifacts here?

thanks

johnmeyer wrote on 3/29/2015, 11:38 AM

I used your files, (not your VEG) in V11. with deinterlace NONE, I got an NTSC file, upper field first at 29.97 with no stepping backwards. Try with deinterlace NONE, You missed a key step in my description of the problem: the problem only happens with resample disabled. If you use Smart Resample, everything works OK.

OldSmoke wrote on 3/29/2015, 11:47 AM

DonaldT

I assume you left resample ON, that is why you don't get the artifacts John is talking about.
I have plenty of D8 PAL tapes from the days I lived in PAL land and I don't have any issue with those. I drop it on the timeline, match properties and render them out to NTSC, no issue at all. However, the D8 files are all BFF and not TFF as John's original file.

Former user wrote on 3/29/2015, 11:55 AM

Okay, thanks I did miss that John.

Former user wrote on 3/29/2015, 11:56 AM

Oldsmoke, I used John's provided file which was TFF and a 1080i file which was TFF. Rendered to TFF.

John mentioned that you always deinterlace when scaling, and I did not, so I was curious if artifacts were there that I did not see.

If smart sample eliminates the artifacts, then I guess I miss the point of the problem.

OldSmoke wrote on 3/29/2015, 12:08 PM

DonaldT
[I]If smart sample eliminates the artifacts, then I guess I miss the point of the problem.[/I]

I agree. I thought that is what smart resample was for? When I change my PAL videos, D8 and HDV, from 50i to 50p I leave smart resample ON and set deinterlace to "Interpolate".

johnmeyer wrote on 3/29/2015, 12:20 PM

Yes, leaving resample in the default "smart" option avoids the field reversal bug, and is the way many people would create PAL to NTSC conversions. However, as Kelly ("chienworks") pointed out in the recent thread about doing these conversions, he prefers to have Vegas do the conversion using "pulldown," the word often used to describe doing frame rate conversions by duplicating fields. This is, of course, how 24p sound film has been converted to NTSC interlaced video since the the dawn of the television era.

I do frame rate conversions, using pulldown, within Vegas, all the time, but I do it from NTSC progressive sources. This problem seems to exist for, at least, PAL interlaced sources.

OldSmoke wrote on 3/29/2015, 12:46 PM

But is it really a bug or just a problem that is actually not their for all those users that don't care changing the default smart resample from on to off?

johnmeyer wrote on 3/29/2015, 12:49 PM

John mentioned that you always deinterlace when scaling, and I did not, so I was curious if artifacts were there that I did not see. Yes, you MUST have a deinterlace method specified in the Project Properties when both of the following are true:

1. The source video is interlaced.
2. You are re-sizing the video

You can re-size progressive video without deinterlacing. Also, you can change frame rate without deinterlacing, as long as you do not re-size. However, if you re-size interlaced video without deinterlacing, you will end up with a massive mess.

Put another way, if you make the mistake of doing this, you won't miss the problem, and you won't be able to use the video. However, that problem is simply a matter of the "physics" of video and is not in any way a Vegas bug. By contrast, the problem that I reported as the topic of this thread is a Vegas bug, although I suspect it only affects PAL video, and only when you render to a different frame rate with resample disabled.

Former user wrote on 3/29/2015, 2:24 PM

John,

That makes me curious. On viewing the videos I resized without deinterlacing, I do not see anything that makes the video not able to be used. I will admit they are a bit softer, but I don't see unusable.

Can you point to in the videos I posted, what makes them bad?

Thanks again

OldSmoke wrote on 3/29/2015, 3:44 PM

DonaldT

As long as you left smart resample on, it will work. But switch it off and you will see problem. I believe the issue is mainly caused by John's original clip having different field order.

johnmeyer wrote on 3/29/2015, 4:46 PM

I used your files, (not your VEG) in V11. with deinterlace NONE, I got an NTSC file, upper field first at 29.97 with no stepping backwards. Try with deinterlace NONE, smart resample.

[later ...]Did you download my version? Did you see the artifacts that you are concerned about?

Yes I did.

Here is the very first frame from the video you posted, showing the classic, massive jigsaw "tooth" pattern. The later frames don't show this because resample is masking the issue.

johnmeyer wrote on 3/29/2015, 4:48 PM

https://www.dropbox.com/s/5beam8pz4mks7mg/Untitled.mpg?dl=0That appears to be the same video you posted before, which is your NTSC rendering from my SD PAL video.

johnmeyer wrote on 3/29/2015, 4:51 PM

But is it really a bug or just a problem that is actually not their for all those users that don't care changing the default smart resample from on to off?Well, I guess what you are saying is that it isn't a bug for those who don't do the thing which exposes the bug. So for them, it is true that the bug doesn't seem to exist.

However it is there, and it most definitely is a bug.

My big concern is that whatever causes this to happen may also cause other bad things to happen.

Former user wrote on 3/29/2015, 5:30 PM

Sorry about the link. Thanks for your explanation aboaut the sawtooth look.