Widescreen VCD

How to encode a VCD optimized for widescreen TVs

Author Miles

The following guide assumes some prior knowledge of using TMPGEnc to convert an AVI file to MPEG-1. If you have not already done so, I suggest you read the following guide first:
KingJohns Guide, My First VCD V2

Introduction

First, let?s take a look at the original AVI file that we will use as the source for our VCD. It is shown here slighly reduced from it's actual size:

This particular video was shot during a holiday in the French Alps, and was captured and encoded to an AVI file with following properties:

Resolution of 560 ?270 pixels
Framerate of 25 frames per second (fps)

When the video is played on a computer monitor displaying a standard VGA resolution, each pixel is practically square (1:1); therefore, the aspect ratio (AR) = 560 / 270 = 2.07:1

You should find that aspect ratios of DVD backups are usually between 1.8:1 and 2.4:1 - you can find more information on aspect ratios at Doom9.net and The Letterbox and Widescreen Advocacy Page.

Creating a VCD ?the usual way?

Encoding

Since our source is 25 fps, we will be making a PAL VCD ? resolution 352 ?288. If it was 23.976 fps, we would select the ?NTSC ? film? template (352 ?240).

The usual procedure under the Other Settings -> Advanced tab in TMPGEnc is to select source aspect ratio ?1:1 (VGA)? and output ?Full screen (keep aspect ratio)?.

This is what the resulting MPEG file looks like - the image below is the actual picture that will be stored on the VCD:

Compare it carefully with the original source above. Can you tell it looks ever so slightly ?squashed? in the horizontal direction? (You will have to look very closely.) When a PAL VCD is displayed on a standard TV, the picture is stretched very slightly; the stretch is actually about 9%. NTSC VCDs are the opposite ? when played back, the picture is slightly squashed by 9%, i.e. the horizontal aspect is reduced to 91% of its original size.

Notice also the black bars top and bottom. Although the VCD stores a video resolution 352 ?288, only 352 ?185 is used for the actual picture. Carrying out a quick check on the aspect ratio, remembering to apply the 9% horizontal correction:

AR = (352 ?1.09) / 185 = 2.07:1

So TMPGEnc has correctly retained the aspect ratio.

Playback

Playing on a standard 4:3 TV poses no problems, the 9% horizontal stretch occurs automatically and everything looks fine:

But what happens when you want to play this disc on a widescreen 16:9 TV?

Widescreen TV setups have selectable ?picture modes?. All widescreen TVs will have a 4:3 mode and a 16:9 mode, but neither of these will do for watching our VCD. Why?

Well, if the TV is set to 4:3 mode, then the picture is stretched by 9% as for our standard TV. The picture does not reach the edges of the screen, resulting in black bars to the left and right:

If the TV is set to 16:9 mode, the 4:3 picture is stretched horizontally by another 33%! There are no side black bars, but the aspect ratio of the picture ends up as (352 ?1.09 ?1.33) / 185 = 2.77:1.

Watching the video in this mode makes everyone look short and fat!

Fortunately, in addition to the two standard modes, the vast majority of widescreen TVs have extra custom modes. What we want is a mode that stretches the picture shown above vertically by 33%. Depending on the make of your TV, this is known as ?zoom? or ?cinema? mode. Selecting this mode, the picture is now displayed thus:

The aspect ratio is now corrected :- (352 ?1.09 ?1.33) / (185 ?1.33) = 2.07:1

Creating a VCD for widescreen TVs

In the last section, we saw that a VCD encoded using normal settings can be correctly displayed on a widescreen TV with a ?zoom? picture mode. So why bother using different settings?

Well, remember our encoded video had a vertical resolution of 288 lines, but only 185 were actually used for the picture - the other 103 lines just made up the black bars top and bottom. Doesn't that seem like a bit of a waste? If we were to use more of the available vertical resolution, we would get a higher resolution picture, and in theory higher resolution means a better quality image when displayed on the TV.

Encoding

Here?s how we do it then. In TMPGEnc, the source is still 1:1 (VGA), but this time we select Video arrange Method: Center (custom size). Enter the full 352 pixels for the horizontal width, and use one of these formulas to work out the vertical height:

PAL: 512/(aspect ratio of source)
NTSC: 426.67/(aspect ratio of source)

In our case, we get 512/2.07 = 247

This time we end up with a file that looks like this (again, this is the actual image stored on VCD):

Note that the size of the black bars is reduced; however, on your monitor everyone in the video looks tall and thin! (Video like this is known as anamorphic - the data on most widescreen DVDs is stored in this form.)

Playback

Now here?s the really clever part. To watch this VCD, the TV is set to 16:9 mode:

Now the video aspect ratio looks fine! Examining the AR calculation now, and remembering that the picture (352 ?247) is stretched horizontally by 9% and 33%, we can see why it works:

(352 ?1.09 ?1.33) / 247 = 2.07:1

2.07:1 is of course the same as the original video source, so our widescreen TV is playing the video in its correct AR.

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