Interlace Checking

[poisondeathray]

This will give you an idea of what scalloping looks like. Note the wavy pattern. Picture scalloping was a common malady in quad videotape machines when the guide height was set incorrectly.

https://upload.wikimedia.org/wikipedia/commons/0/09/Argopecten_irradians.jpg

I know what a scallop is

"Wavy"- ahhh - you're probably not viewing it at 1:1 at normal dimensions . I'm thinking you have it scaled to fit a frame, and it's scaling it progressively

Take a screenshot with VLC . Shift+S is the default hotkey

Also try the ffplay suggestion above , and/or take a screenshot with ffmpeg

[chris319]

How about checking interlace (picture content) using VLC's "Phosphor" deinterlacer?

[poisondeathray]

How about checking interlace (picture content) using VLC's "Phosphor" deinterlacer?

Not for interlace checking
https://wiki.videolan.org/File:Example-Phospor_Doubler.png/


You have to examine videos at 100% , 1:1 unscaled in order to diagnose interlace and patterns (in any program). If using a smaller display, you can examine a portion of the frame at a time, pan around

But it does not work well for this purpose either in VLC. I just downloaded the newest 3.0.8 , same problems with bob and yadif 2x too. If you can get bob and yadif2x working properly on your setup where you can advance frame by frame ("e" key) to diagnose, then it should be usable. Does not work for me.

[chris319]

If bob and yadif don't work for you then why would they work for me?

I'm confused. With the deinterlacer turned off I get different visual artifacts depending on whether or not the video was encoded with interlace (or tinterlace). You say this is not reliable. Why? If I advance frame by frame or field by field then I see motion in every frame/field, interlaced or not.

Let's keep telecine out of the discussion for now, please.

I also use idet to check interlace. Here is the output:

[Parsed_idet_0 @ 00000245a7add040] Repeated Fields: Neither:    61 Top:     0 Bottom:     0
[Parsed_idet_0 @ 00000245a7add040] Single frame detection: TFF:     2 BFF:     0 Progressive:     0 Undetermined:    59
[Parsed_idet_0 @ 00000245a7add040] Multi frame detection: TFF:    51 BFF:     0 Progressive:     0 Undetermined:    10

[poisondeathray]

If bob and yadif don't work for you then why would they work for me?

Sometimes players work differently for whatever reason, different HW, different drivers, etc... . eg if your GPU was decoding it might be different, SW decoding might be different etc...

I'm confused. With the deinterlacer turned off I get different visual artifacts depending on whether or not the video was encoded with interlace (or tinterlace). You say this is not reliable. Why? If I advance frame by frame or field by field then I see motion in every frame/field, interlaced or not.

If you can advance by fields reliably , then it can be used

You cannot examine interlace reliably looking frame by frame, or you will misdiagnose some streams. If a deinterlacer is turned "off" it you should be looking at weaved fields as a single frame. This is not reliable because you are looking at 2 moments in time at once.

If a 2x or bob deinterlacer is turned "on" you should be looking at fields separated out (de-weaved) , and resized to full sized frames . But it doesn't work in VLC.

[Parsed_idet_0 @ 00000245a7add040] Repeated Fields: Neither:    61 Top:     0 Bottom:     0
[Parsed_idet_0 @ 00000245a7add040] Single frame detection: TFF:     2 BFF:     0 Progressive:     0 Undetermined:    59
[Parsed_idet_0 @ 00000245a7add040] Multi frame detection: TFF:    51 BFF:     0 Progressive:     0 Undetermined:    10

Probably not reliable

[chris319]

If a deinterlacer is turned "off" it you should be looking at weaved fields as a single frame. This is not reliable because you are looking at 2 moments in time at once.

I believe the interleaved fields are the basis of the artifacts I'm seeing.

With a moving object, I'm going to see a different image every 1/60 second. If interlaced, the image will be every other scan line (odd or even lines) or one field. If progressive, it will be every scan line or one frame. I think this is what the "phosphor" deinterlacer does but I could be wrong.

The basis of my confusion is that I'm going to see a slightly different image every 1/60 second whether an interlaced field or progressive frame.

If you can advance by fields reliably , then it can be used

If I can view one field at a time of interlaced video, then I should see only every other scan line, and this would tell me if it's properly interlaced, right? So what I need is a player that displays fields, right?

[manono]

So what I need is a player that displays fields, right?

What you need is a simple AviSynth script opened in VDub. One of the problems with what might appear to be interlaced is that it might be phase-shifted, a particular problem in PAL land. And field-blended crap can also fool someone into thinking it might be truly interlaced when viewing frames.

But a simple Yadif(Mode=1) will bob the video and then you can look for the blending of the bobbed fields to decide if the source is field-blended, if it's phase-shifted and really progressive, telecined or really interlaced. And what you see will point you to how to handle it. That might be to use an unblender, realign the fields with TFM, apply an IVTC or bob it with the better QTGMC.

This isn't rocket science. How the original source looks by itself combined with how it looks when bobbed will almost always tell you what you have and how to treat it. Trying to figure it out with a player is a waste of time, in my opinion. Especially when the 'fix' might need an AviSynth script anyway.

[poisondeathray]

Or one that can apply double rate deinterlace, and allows you to advance frame by frame. So essentially each field is separated and resized to a frame. So you're looking at all individual 60 pictures per second

vdub2 (not vdub) was suggested earlier ; if you don't want to get your feet wet with avisynth just yet

You can apply yadif 2x in vdub2 . This works and many people still use it

[chris319]

But a simple Yadif(Mode=1) will bob the video and then you can look for the blending of the bobbed fields to decide if the source is field-blended, if it's phase-shifted and really progressive, telecined or really interlaced.

You're not explaining what I'm going to see. I can't look for "blending of the bobbed fields" if I don't know what it looks like.

vdub2 (not vdub) was suggested earlier

Can't use vdub owing to the simple fact that it can't open a common .mp4 file. Gotta use vdub2.


In vdub2:

video=>filters => add=> deinterlace . Select yadif , double frame rate, top field first

. (Or you could use bob instead of yadif)

[manono]

You're not explaining what I'm going to see. I can't look for "blending of the bobbed fields" if I don't know what it looks like.

You don't know what 'blending' means? How about 'double exposure'? How about 'double image'? How about 'ghosting' or 'ghost image'? I can show you a picture, if you prefer, as unblending field-blended films is a big part of my life, unfortunately. I don't know what your source is like as you haven't provided a sample, have you?

And even if using Yadif2X in VDub2 as pdr suggests to help examine the video, fixing it is something else again. Sure, you can use Yadif2X on it if you decide to keep the bobbed image. But AviSynth has much better bobbers. Is there a robust IVTC in VDub2, if that's what's called for? Can it realign the fields in cases where the video is phase-shifted? I don't know as I don't use VDub2 for those things. But I'm pretty sure you can't unblend a field-blended video.

There are programs that use AviSynth in case you don't want to have to learn it. Both StaxRip and Hybrid can do all the things I mentioned, I believe.

[chris319]

I finally got a chance to look at some videos with vdub2.

On interlaced videos I can see distinct line pairing with no filtering at all (no deinterlacing). The line pairing is visible if the recommended deinterlacing filters are engaged.

When playing progressive-scan videos, there is no line pairing to see.

Quite a different experience from VLC.

The interlacing is added to progressive video with ffmpeg.