SubFontManager

Sub Font Manager is a tool for editing font settings in .ASS or .SSA subtitle files. It allows you to integrate fonts and subtitles with virtually no cost.

Specifically, Sub Font Manager collects all fonts used in the subtitles and allows you to subset those fonts based on the characters occurred in the subtitles, then embed them directly into the subtitle file.

Why do you need this? SubStation Alpha (.SSA) and Advanced SubStation Alpha (.ASS) are among the most popular subtitle formats for video effects, offering rich styling and animation capabilities that greatly enhance the visual expressiveness of subtitles.

SSA/ASS subtitles often require multiple fonts to render properly. These fonts need to be pre-installed in the operating system in order for the player to read and display them correctly. For most users, this process is too complicated.

Isn't there a simpler solution for stylized subtitle fonts?

In fact, subtitles and fonts can be combined into a single file. Not only is it possible — it's actually a supported approach by both subtitle formats and media players.

The SSA/ASS format natively supports embedded files, with its most common use being font embedding. However, it uses UUEncoding to encode binary files into text form. For non-Western languages, font files are typically large to begin with, so embedding them as text is not only inefficient but also significantly increases the size of the subtitle file.

Fortunately, Font Subsetting technology solves this problem. Font subsetting means extracting only the subset of characters needed from a font, removing the rest to reduce file size.

In many subtitle files, special-effect fonts are used for very few characters, while the majority of the font’s character set goes unused. This leads to wasted space. Font subsetting removes unused characters, dramatically reducing file size.

But, there are still problems. Font subsetting isn't a simple task. Tools are limited, most GUI-based ones are difficult to use, and while command-line tools like fonttools exist, they come with a steep learning curve. You need to not only learn the command syntax, but also manually collect the characters to include.

If you're not familiar with the tools, font subsetting may also remove the name table, which can cause font references to fail.

The name table stores font names used across various languages and systems. For example, the Chinese name “????” corresponds to the English “Microsoft Yahei.” Both names can reference the same font — but if either one is removed, the font can no longer be recognized under that name.

Additionally, a subsetted font file contains only a limited set of characters. If new characters are added to the subtitles later, the subsetted font won't be able to display them. This creates obstacles for further subtitle editing.

These complications have effectively discouraged most users from ever attempting font subsetting and embedding.