OTF to TTF is on hold On hold

This conversion is not available

Not implemented and not faked. Converting OpenType/CFF outlines to TrueType requires an approximating curve conversion this build does not have.

An .otf file usually contains a "CFF " table: glyph outlines drawn with cubic Bézier curves, the PostScript curve model. A .ttf file contains a "glyf" table: outlines drawn with quadratic curves. These are different mathematics, not different packaging.

Cubic to quadratic is an approximation. Each cubic segment has to be subdivided into a chain of quadratic segments until the error falls below a chosen tolerance, and the result then has to be rounded onto the integer grid TrueType uses. Every hinting instruction in the source has to be discarded, because CFF hints and TrueType bytecode are unrelated systems. The glyph set has to be rebuilt, "loca" and "maxp" recalculated, and left side bearings re-derived from the new bounding boxes.

Done carelessly, that pipeline produces files that open in a font viewer, load in a browser, and render with subtly melted curves or missing contours that nobody notices until print. Done not at all — which is what many online converters do — it produces the original CFF bytes with a .ttf extension stapled on. Glyph Batch will not ship either outcome.

The curve mathematics, the outline model and the glyf writer needed for this route are already in this codebase and unit-tested. What is missing is the CFF charstring interpreter that reads the source outlines, and the verification corpus needed to prove the result is correct across CJK, variable and colour fonts. Until both exist, this route stays held. It is tracked in BACKLOG.md.

What to do instead

• Keep the .otf and convert the container instead — If your goal is a web font, you do not need TrueType at all. OpenType/CFF compresses to WOFF2 and loads in every browser. That route accepts .otf directly.
• Check what your .otf actually contains — Some files named .otf hold TrueType outlines already. If yours does, no outline conversion is needed and any container route will give you a genuine .ttf.
• Use fontTools if you truly need TrueType outlines — The formats page explains what the desktop toolchain does here and when the conversion is worth its losses.