Determining true field order of a video

MikeLV wrote on 8/12/2016, 5:37 PM

I just had a long off-forum discussion with john meyer about this topic. He was helping me with an issue when going from HD to SD for DVD. I sent him a video clip of my source footage which I believed (based on my video camera manual) to be 60i. But he told me it was in fact 30fps progressive.

He said:

"The field order reported by the video header, which is what you see in Vegas, means absolutely nothing. You can check field order within Vegas this way:

1. Match project properties.
2. In project properties, double the frame rate (in this case to 59.940 (Double NTSC))
3. In project properties, change field order to None (progressive).
4. In project properties, set full-resolution rendering quality to "best," and change "deinterlace method" to "none."
5. Make sure you have the video preview quality set to "Best-Full"
6. Make sure that resample for the event you want to check is set to "smart" or "forced."

Now, use the cursor keys to go forward one "frame" at a time. You will actually now be looking at individual fields that have been bobbed. If the clip is interlaced, you will see horizontal movement between each and every frame/field. If the clip is progressive (as your clip is), you will see no horizontal movement between each pair of fields, only a slight up/down "bob".

The point is to make individual frames out of each video field. When you do this, you can move through the video one "frame" (which is actually a field) at a time. With progressive video, each field is taken at the same moment in time. Therefore when you do this operation on progressive video, you will see no movement whatsoever between each "frame," although you will see a slight up/down motion between fields from the same frame because, of course, they are located in different points in space.

When you do this with interlaced video, you will see obvious motion between each "frame." This is not subtle in any way, and the results are totally different than you get from progressive video."

So I went through this procedure with a video clip he sent me that was true 60i and my clip that is supposedly progressive. I looked for this movement that he described and didn't see it at all (I don't know exactly what I'm looking for) The only thing I did see was what you see during fast motion on interlaced video, the horizontal lines. When I told him this, he said,

"you did something wrong. There should be absolutely no herring bone pattern in the interlaced video (i.e., my clip)."

So now I'm really thrown for a loop. He's saying I shouldn't see the lines, but instead should see horizontal movement. Can anyone shed more light on this issue? I really want to understand it, especially since my camcorder doesn't shoot what it says it does (which is the reason I had so much trouble with crappy quality encodes) I was setting my projects up as interlaced when they weren't.

Comments

OldSmoke wrote on 8/12/2016, 5:59 PM

What is the make and model of your camcorder and what is the setting you used? I doubt a manufacturer would list a setting and then record something different.
Can you upload a sample clip so that others can help too?

MikeLV wrote on 8/12/2016, 6:11 PM

It's a Canon XA10, using the 60i setting, described in the manual as:
" 60 fields per second, interlaced. Standard frame rate of NTSC analog TV signals"

However, after John enlightened me about the footage, and digging deeper, we came across this:
See the first two paragraphs.

http://www.sierradescents.com/reviews/canon/xa10.html

I'll have to record something short to upload for a sample clip, probably tomorrow...

wwaag wrote on 8/12/2016, 6:29 PM

If you have Vegasaur, there is a Field Order Analyzer under Tools that you might try. From what I remember, the procedure sounds very similar to what John suggested.

wwaag

riredale wrote on 8/12/2016, 7:25 PM

Field order questions can get confusing.

The one time I got field order wrong in authoring a DVD it was extremely obvious on a conventional interlaced TV set. So I'd suggest doing a very short test and look at it on an old TV set. If the image is nearly unwatchable, change the field order in the encoder.

MikeLV wrote on 8/12/2016, 7:35 PM

Not so much field order, but more about whether it's interlaced or progressive (field order of none)

I actually called Canon today and the support guy said he's never heard that 60i isn't interlaced on the XA10, but John was pretty darn sure of it. The part that I don't understand is his test. I couldn't see what he was talking about. All I saw was the interlace resolution lines during a camera pan. Which oddly enough, he said I shouldn't see (in this particular test)

MikeLV wrote on 8/12/2016, 7:44 PM

Here's the two samples, files named accordingly:

https://www.dropbox.com/s/702sxl1316snz3v/john-interlaced.MTS?dl=0

https://www.dropbox.com/s/uming83igpj9nff/XA10-60i.MTS?dl=0

OldSmoke wrote on 8/12/2016, 8:01 PM

@Mike

What was the shutter speed on your sample?

I downloaded the manual for the XA10 and it does record 60i. It also records 30p and 24p as 60i. Make sure you selected the Standard 60i recording mode. I am surprised it doesn't record 60p.

Here is what MediaInfo reports on both files:



Scan type                                : Interlaced

Scan type, store method                  : Separated fields

Scan order                               : Top Field First

wwaag wrote on 8/12/2016, 8:08 PM

Just downloaded the two files and tested in Vegasaur and it agrees with John's analysis. The file john-interlaced is indeed interlaced. Each time you click the right arrow key in the test, the video moves. OTOH, the file XA10 is progressive. For that file, it takes two clicks of the right arrow key to make the video move. In other words, the upper and lower fields are the same. Hence, the file is progressive.

wwaag

BTW. The field analyzer in Vegasaur is exactly the same as what John suggested in the OP. It just does the proper settings automatically.

MikeLV wrote on 8/12/2016, 8:33 PM

It's definitely set to 60i, M shooting mode, not using cinema or face detection. Not sure on shutter speed ATM, away from computer..

How can Canon say 60i if it's not? If it weren't for John, I'd still be cursing Vegas' lousy quality. Turns out it wasn't Vegas at all.

OldSmoke wrote on 8/12/2016, 8:37 PM

@Mike

When I look at your sample video I would rather say it's PF30 stored as 60i. When you pan and the chair appears on the left the pan is no longer smooth. Considering the rather low light conditions it was recorded at, I would assume that the shutter is 60 or lower. In any case, the pan should be smooth which it isn't.

EricLNZ wrote on 8/12/2016, 9:35 PM

It probably is 30p stored as 60i. The Manual of my Canon HFG10 states that "25fps progressive is recorded as 50i". Probably this irritating habit of Canon's is carried through to their bigger pro cameras.

farss wrote on 8/13/2016, 6:58 AM

Yes, just because video is recorded as interlaced does not mean it is shooting 50/60 fields per second. The correct designation here would be 30psf60.

http://wolfcrow.com/blog/understanding-terminology-progressive-segmented-frames-psf/

Bob.

MikeLV wrote on 8/13/2016, 9:47 AM

Thanks for the input. So knowing that this video is in fact not interlaced, to get the best quality MPEG-2 files out of Vegas for DVD, am I correct that I should:

1. Change project properties to progressive (field order to none, deinterlace method to none) full res rendering quality to Best

2. Disable resampling for all clips on the timeline.

3. Customize the MPEG-2 render template by changing the field order to none, video rendering quality to Best

OldSmoke wrote on 8/13/2016, 10:45 AM

Yes, correct on all three. This will create a progressive file that most layers will play without a problem. But you can also render to 60i and it won't look much different.