Creating Cross-Platform Caption Displays

The examples on this page are screenshot images from QuickTime movies with captions. However, the same cross-platform compatibility issues that QuickTime developers experience impact SMIL developers also.

When captions are incorporated into a QuickTime movie or are referenced in a SMIL file, specific height and width values need to be set to define the captions area during playback. The height and width, typically defined by a number of pixels, is set by the developer incorporating the captions, but the size of the font displayed within the caption area is dependant on the viewer's computer.

Developers of QuickTime movies are given the option of selecting 'Best Fit' for the caption height and width. In this case, QuickTime will set the width of the captions area to equal the width of the rest of the movie and it will set the height to the smallest number of pixels that will fit the captions. Whether values are chosen by a developer or by QuickTime, it is important to understand how the captions will look on other machines.

Below are a series of links which connect to pages of screenshots of the captions area of movies. Each link represents a different development environment, and the page the link leads to will display the results of various combinations of caption area height and viewer platform. In these examples, the width remains constant because the convention is to create and include captions at a width equal to that of the captioned media.

How captions were added to the media, with results

The three links below each lead to a page with images showing how captions display differently depending on the decisions made during development and on the viewing environment.

Developer used a Mac.

Developer used a Windows machine with small fonts.

Developer used a Windows machine with large fonts.

Brief analysis of differences, and recommendations

Looking at the images that are shown in the rollovers above, you can tell that fonts do not display the same in Windows as they do on the Mac. In general, fonts in Windows display larger than fonts on the Mac. This difference is exaggerated if the Windows user has their font size set to 'Large fonts'.

Based on the differences in font displays, we recommend:

Avoid using 'Best Fit' for height sizing in QuickTime. Unless you can be certain that all of the viewers of the captioned media will use the same operating system and/or windows font size, you should specify the caption area height.
If your captions are 3 lines, use a caption area height of 75. If your captions are 2 lines, use a caption area height of 60.
After you create a captioned movie, view it from each of the configurations discussed on this page.