PapaJohn Productions
Newsletter #97 - April 1, 2006

Tags in DVD Files



Movie files can be of most any video size, as measured in pixels. There are some standard sizes, and then there's the ability to make and use a custom profile for others.
A DVD needs to be made of standard formatted and sized movies. MPEG-2 is the format, and one of the standard sizes for NTSC TV systems is 720x480 pixels. For this newsletter I made 4 discs, 2 in the new Vista Windows DVD Maker and 2 in MyDVD8 on my Windows XP laptop. Each disc has 9 movies.
All 36 of the movies are of the standard size of 720x480 pixels....
... but 12 of them were made from files of lower visual quality than standard DVDs. Another 12 are from files on a par with DVD quality. And the remaining 12 were made from the High Definition movie options in Vista's Movie Maker.
... and somehow each with 720x480 pixels can look different when played... why? It has to do with some tags in the files that tell the players how to display the movie, and how the players interpret those tags. 
The tags are things that I'm still trying to understand. You don't add them directly, and you don't know what they say, and there isn't a utility that will let you read them.
This issue won't have a definitive conclusion.  All I hope to share is an awareness of the tags and how important they are to what you see when watching your DVDs.

DV-AVI PropertiesHere's an example of tags in action. One DV-AVI file saved from a widescreen Movie Maker project, and another DV-AVI file from a standard aspect ratio project. 
Looking at the properties of each in WMP10, see what the player is getting from the tags. It's saying the widescreen movie has an actual aspect ratio of 4:3 but it'll display it at a widescreen 16:9.
And the standard one has an aspect ratio of 4:3.
720x480 isn't 4:3 or 16:9... it's someplace in the middle. if you check the math, it takes 640x480 to be 4:3 and 852x480 to be 16:9. The tags are telling the player to squeeze the pixels in a bit to show the standard file at 4:3, and stretch them out as needed to show the widescreen one appropriately. If the player does it right, the movies will look as you want.
... before getting into it further, here's a couple notes...

The Vista Corner... I've been busy this week with Vista's Movie Maker and Windows DVD Maker. In addition to this newsletter, the Setup Movie Maker > Vista Preview > DVD Maker page of my website is pretty well fleshed out with new screen shots and more info.
I added 1/2 GB of RAM to my Vista system, doubling the RAM to 1 GB... the max for the system. It runs peppier, as expected.
A project file in Vista has the same .MSWMM extension that we're familiar with... but if you try to open it in MM2, you'll get
Error Message
... but all the movies and discs made in Vista work in XP... that's more important.
.... back to the main topic...

Making and Viewing DVDs
I imported some standard and widescreen camcorder footage into my Vista system, and made two sets of 1 minute test movies... one set at the standard 4:3 aspect ratio, and another at widescreen 16:9.
Publishing OptionsEach set has 9 files, the same project file rendered to each of Movie Maker's built-in publishing choices.
The standard set was used as the input files for a standard DVD, and the widescreen set for a widescreen disc.
That gave me some files to play with... to compare file sizes, quality, playback in various players, etc. What were the tags saying and how were the players interpreting them? 

The 9 publishing choices in Vista's Movie Maker are a good mix... with standard DVD quality right in the middle.
  • 3 less than DVD quality (Portable Device, Low Bandwidth, and VHS
  • 3 standard or aligned with DVD quality (DV-AVI, DVD Quality, and DVD Widescreen)
  • 3 higher than standard DVD quality (HD 720p, HD 1080, and HD 1080 VC-1)
Positive Side Note: as low-end a system that I'm using for Vista, and as much as it's pre-beta, the captures never drop frames, and I've yet to make a coaster instead of a DVD that plays well.
Standard Set
All of the MPEG-2 files on the discs have video sizes of 720x480, but they play differently. Rather than using words to explain the similarities and differences, I did a lot of picture-taking so you could see for yourself.
Here are 1/4 size snapshots of the DVDs playing on my Windows XP laptop in InterVideo's WinDVD, which has a neat frame snapshot feature. The pictures at the left are from the standard disc, and those on the right from the widescreen.
9 have black borders at the top/bottom, left/right, or all around... and 9 don't. Some are appropriately shaped to align with 4:3 or 16:9 aspect ratios, and some are not.
Here are typical frames from each movie, and some comments. The pixel dimensions that I note are the movies as saved by Movie Maker and used as inputs to Windows DVD Maker... not the transcoded MPEG-2 files on the discs, which are all the same size.

Standard << DV-AVI >> Widescreen
The only one of the 9 choices that looks right in both standard or widescreen mode... they display in the appropriate aspect ratio and have no black borders.
On a TV, one would have black borders... InterVideo WinDV on my computer has more than enough room on the screen to play the movies in a changeable window size. Snapshots of them on a TV would be different.
Pixel dimensions of 720x480.
Standard << DVD Quality >> Widescreen
The aspect ratios are correct... but the widescreen mode uses a 4:3 overall size with a letter-boxed widescreen video within it.
Pixel dimensions of 720x480.
Standard << DVD-Widescreen >> Widescreen
A DVD widescreen movie doesn't belong in a standard aspect ratio DVD... where it displays as 1:1. And it's just a bit better in a widescreen DVD, showing as 4:3. In neither case is it showing the desired widescreen 16:9. 
Pixel dimensions of 720x480.
Standard << HD 1080 VC-1 >> Widescreen
Displays the same as DVD-Widescreen... 1:1 within a 4:4 overall window, with black borders... and 4:3 aspect ratio in a widescreen DVD.
Pixel dimensions of 1440x1080, a 4:3 ratio.
Standard << HD 1080 >> Widescreen
Displays the same as HD 1080 VC-1... and both files have the same pixel dimensions of 1440x1080.                                                         
Standard << HD 720p >> Widescreen
This one stands out in the crowd... appropriately shaped at 16:9 when in a standard DVD, but with black borders all around. And wider than widescreen when viewed in a widescreen DVD.... measuring 21+:9 instead of 16:9...
Pixel dimensions of 1280x720, a ratio of 16:9.
Standard << Low Bandwidth >> Widescreen
Normal looking at both regular aspect ratio and widescreen, but letterboxed in widescreen.
320x240 pixel dimensions, a ratio of 4:3.
Standard << Portable Device >> Widescreen
Appropriate for portable players that have a standard 4:3 aspect ratio screen, with the widescreen mode letterboxed to be viewed right.
640x480 pixel dimensions, a ratio of 4:3.
Standard << VHS Quality >> Widescreen
The 3rd of 3 lower quality options also views in appropriate aspect ratios, using the letterbox approach for the widescreen DVD option.
640x480 pixel dimensions, a ratio of 4:3.
Let's finish this section with a look at the set of thumbnails for the widescreen DVD. They look the same as the regular aspect ratio set... at 4:3.
Viewing the DVDs with Windows Media Player 10 in Windows XP shows the same results... so it's not the viewer, but the tags in the disc files that account for the differences.

MyDVD Premier 8
For a cross-check... I used the same movie sets of input files to make DVDs with MyDVD Premier 8, running on Windows XP... a standard DVD and a widescreen one.
Here's the results, using the same InterVideo WinDVD app to view the discs and take frame snapshots. The snapshots of the standard disc are at the left, and the widescreen one at the right.
Most noticeable are how much better the High Definition widescreen files are displayed than those on the disc made by Vista's DVD Maker.

Conclusions and Closing
Widescreen and standard mode video starts with your camcorder, flows through the editing phase, then into the saved movies, the transcoding for discs, and then the display by the players. Most of the alignment needed is handled by the software behind the scenes. You'll accept things that look right and perk up when it doesn't, and then wonder why not.
This newsletter is about an increased awareness about the role of the tags in the files, and about how various files can play back differently than you expect.
For me, the standard versus widescreen footage sometimes starts with the camcorder... my Sony TRV-80 mini-DV uses a letterbox approach when recording in widescreen. It's the camcorder I used for the footage in this newsletter. That sets the stage for how the video stream is processed during editing.
My older Hi8 model TRV-615 gives me the option of letterboxing when recording as widescreen, or of using the full recording area of the chip.
DVD making options vary with the software
There's more to learn about tags and the effects they have... it's best to test your process with a little pilot file and learn how your systems work... burn a test disc and look at it before doing your big projects... adapt as needed. 

Have a great week...