Video Interlacing

I got into this newsletter subject in a Support Space session a week ago with Mark, about how Movie Maker handles interlaced files... TFF versus BFF. He was seeing it converting TFF files to BFF, something I had only read about but not tested.

What happens when you have the wrong field first during playback. From what I read, the official word is visual 'jittering'.

Each frame of an interlaced file is made of two 'half-frames', half the lines on the first part and the other half on the second. The 30 frames per second of an NTSC video are made of 60 half frames. Similarly the 25 fps of PAL video are 50 half frames per second.

When it comes to Movie Maker and interlacing, my notes boil down to this short paragraph...

That may be so, but what it doesn't tell you is that if your source file is an MPEG-2 file with TFF, and you save it to a DV-AVI file, it'll come out BFF, not preserving the interlacing. When it switches the fields without your involvement... you'll end up with some jittering.

One of the filters in VirtualDub is named 'field bob'... which compensates for field jumping in field-split video by applying bob-deinterlacing techniques . How it does it is on page 148 of 'Learning VirtualDub' by Georgios Diamantopoulos, Sohail Salehi, and PapaJohn.

Here's a screen grab of part of a clip in VirtualDub, magnified 4x. At the left is how it looks in the interlaced DV-AVI file captured from my mini-DV camcorder. The adjusted one at the right is after applying VirtualDub's field bob filter (with Smoothing). It gets rid of the 'jaggies' but leaves the 'ghosting'.

If you work with DV-AVI or other interlaced files, the 'jaggies' will stay until you save the movie to a wmv which de-de-interlaces it, or view it on a TV where the hardware does the same. Saving to a WMV file will be similar to using the field bob filter of VirtualDub.

Enough background. What does it all mean and what options do you have if you see a video clip that you think could be handled better when it comes to?

As I mostly work with and distribute wmv files that are not interlaced, I'm not ready yet to see and show you what happens when you input a TFF file and get a BFF one back. This week's newsletter is more about interlaced or not, and takes a look at how the different files effect bluescreening in XP and Vista. I'm really doing a jump-shift from the TFF/BFF subject.

Support Space entered the next phase of starting up... charging a standard $25 fee for a session... with the first one free to new customers. The expert gets $20 and the house gets $5.

Customers I know have been extremely pleased with the service when it was a free ride though the early beta phase. We'll see how many keep going when they have to ante up a modest fee.

Over at my other startup, my 11 software reviews are now online at BrightHub and I'll be attending the first writers' conference call next week with Bill Phelan, the CEO.

It's a Tivo file, an MPEG-2 one that GSpot says is a SVCD (Super VCD). I marked it to show where GSpot says it's an interlaced TFF file... which seems to be the 'normal' for MPEG files.

I used MM2.1 to convert it to DV-AVI and saw the same thing Mark had. It goes in as TFF and comes out BFF. As Mark suspected when he contacted me, Movie Maker and the Microsoft DV codec are changing the field order.

We haven't found a DV-AVI file that is TFF, so it seems the standard for the file type is BFF. So it wouldn't be Movie Maker doing the changing as much as it would be the codec applying the standard, something we need to be aware of and live with.

Anything with a mix of TFF and BFF?... yes, the VOB files on a DVD made by Vista's DVD Maker from recorded TV files.

When going online to check the DV standard, I got as far as finding a website that sells you a copy of the DV-AVI spec for 50,000 yen... a bit too steep for my needs, whatever the exchange rate.

Some video apps let you select the field order, and others take care of it for you.

TMPGEnc lets you set the field order of saved MPEG files as TFF or BFF... if you bring in a BFF DV-AVI file made by Movie Maker, you can make the MPEG-2 files needed for a disc as either BFF or TFF.

A bit more checking indicates that MPEG files are TFF by default, unless changed by the user... while DV-AVI files are always BFF.

As anything I shot with my camcorder or ran through Movie Maker to DV-AVI files was automatically made BFF to align with the DV spec, I had to satisfy my quest to do some testing by checking interlaced versus non-interlaced clips.

I turned to my camcorder and digicam, and had Aeromouse walk around in front of a blue screen (RGB of 0,0,255 in Paint)... I did green and red ones too, but the blue ones give the best results, so the rest of this newsletter is about bluescreening.

I put the cameras on a tripod and shot my laptop's LCD screen. That puts some sort of analog encoding processes between the pure blueness of the Paint screen and the digital file on the tape or card... actually I kind of like the added complexity of the analog steps.

Here's what the pure blueness of the screen in Paint looks like... to compare to the different background patterns you'll see below. The differences didn't effect things as much as I expected.

The custom XML code for bluescreening in MM2.1 is on my website (the Persian Gal's code) and in the forum library of custom transitions (Blaine's code). Both of them use the same settings.

The code for bluescreen transitions in Vista isn't in the forum library yet, but Rehan's Shader TFX package includes 10 different bluescreen transitions. I used two of the five Chroma blue B ones for these samples.

I packaged the results in a couple 2-1/2 minute clips. Each is of the same series of clips, the only real differences being the making of one in MM2.1 and the other in MM6, so the bluescreening technology is different.

These images show you a bit of what's happening in the videos. There are pairs of clips, the first of which shows the bluescreen clip before it's used as an overlay... with Aeromouse over the blue background. The next clip shows what you see when you put the video clip over a black still picture. The blackness could be any picture or video clip, still or moving. I usually use pictures or video clips as backgrounds, but it's easier to see what you get of Aeromouse when it's over a solid colored background.

The Motion JPEG clips easily win over the mini-DV interlaced or progressive ones. In XP you can hardly see anything from the progressive clip. Vista is considerably better but falls short of the MJPEG files.

Thinking that Vista was doing a better job of bluescreeing than XP, and Movie Maker automatically de-interlaces when making WMV files, I decided to make a test file in Vista, letting it do the de-interlacing. I used Vista's profile of 3 Mbps, and then used it in XP and Vista to get some more to ponder when watching the bluescreening clips.

My quest of the week started with Mark's email asking about Movie Maker converting TFF source files into BFF, and ended with more of a study of bluescreening using various interlaced and non-interlaced files.

There's the technology of compression, and interlacing TFF and BFF fit into it. I've always wanted a copy of the book Digital Video Compression by Peter Symes. I ordered it in the middle of writing this newsletter... it's in the mail.

Then there's the application of the technology. If you're putting low quality on YouTube, I'm sure you won't care about which field is first in a video. But if you're looking at your new Hi-Def 60 inch screen and playing a DVD, you might get better results by aligning the fields all the way through the process. If you start with BFF files from your mini-DV camcorder, and don't take steps to change it, you might have TFF files on your discs and wondering what's causing the flickering. Maybe your flickering is 'jittering' and you can fix it.

I look forward to comments and discussion about this and other newsletters on the forums at:

I'm involved in anything and everything that supports the users of Movie Maker and Photo Story, and adding more regularly. Some are free and others reasonably priced.

About John 'PapaJohn' Buechler from Microsoft.com

John "PapaJohn" Buechler, of Kalamazoo, Mich., goes by PapaJohn online. An avid user of Movie Maker since its first release, and a regular supporter of the community of Movie Maker users, John received a 2003 MVP award from Microsoft for that support. In March 2003, he started a comprehensive website about Movie Maker 2 at www.PapaJohn.org. He maintains the website, writes books and articles, teaches, and provides support services - all for the community of Movie Maker 2 users. An engineer by formal education, John is a computer database and multimedia expert by business and personal experience. He co-authored the first book about Movie Maker 2 and is actively working on a second one. You can find his advice in the Windows XP Movie Maker newsgroup and in the Windows Movie Makers Forums.

This newsletter is republished with permission of John "PapaJohn" Buechler.
Please note that this is an archive of newsletters and some information may become outdated. PapaJohn, and the webmaster of this site, provides this information "AS IS" with no warranties.

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Interlacing