Is converting a font licensed for use as a web font to WOFF2 generally considered to be modification?
My primary concern is with fonts licensed under the SIL OFL. There is a caution in the guidance for the licence that an irreversible conversion to WOFF constitutes a modification, so if I need to create a WOFF for somebody else's font, I first check that back conversion to TTF/OTF yields the same font. (On a very small sample set, I haven't had the problem yet.) However, there seems to be a far greater likelihood of a conversion to WOFF2 not being reversible. If one creates a modified font under the SIL OFL, one has to give it a new name, and propagate the licence.
To quote my own EULA (which has pretty standard language on this score) "You are prohibited from decompiling or disassembling the Font Software for the purpose of converting, porting, adapting or modifying it in any manner." The next sentence explains you need us for "modifications" (by which we mean changes to the design components).
Reformatting usually isn't permitted as a baseline. For no fee, many of us will let a licensee who asks do it – so long as we think they know what they are doing. We just don't want to have to clean up someone's mess after the fact.
WOFF is completely reversible — it’s really a transport wrapper that supports some additional metadata, but whatever font that goes in comes out exactly the same. (You can think of it as a ZIP archive in that sense.)
WOFF2, as I understand it, will change font data to gain further compression, but will always preserve functional equivalence. I believe tables can be reordered and superfluous data removed, but I’ll bet someone here will correct me if needed!
My point is that WOFF (not WOFF2) will never modify a font.
WOFF (1.0) is explicitly lossless, so I don’t follow this. I mean, OFL-licensed fonts are regularly distributed inside container files like ZIP, and nobody seems concerned about that.
Yes, a WOFF converter could modify the font, but that’s really something outside the WOFF spec, which is designed to allow a font to be WOFF-wrapped with no modification. The OFL FAQ even addresses this.
This is why I permit pdf embedding in my basic license, even though we want to have a hard line that embedding isn't covered at the basic level. That is, most end users have no clue that "printing to pdf" involves font embedding (unless you actively disable it). So, even though it's not technically correct we permit it because it doesn't feel like embedding.
I'd argue that turning an otf into a woff is the opposite example
This is fully a license issue and not a technical one.
Really, my original point was that the original WOFF format does not modify a font. That’s it.
I think it’s interesting to debate, as we have here, whether a font that has been “converted” to WOFF becomes some other kind of font. I obviously think it’s the same font in a wrapper, but I understand the opposing argument. The point of the OP was to ask whether WOFF conversion is considered modification. My intention was to clarify a subtle difference between WOFF and WOFF2 in that regard.
I agree it’s perfectly reasonable for one to specify a EULA prohibition against WOFF conversion if one doesn’t want their EULA to allow web use. That’s one way to accomplish that. Another would be to say, “You do not have permission to use this font on the web.” Again, that was not my point at all.
And since the OP and a lot of this thread is focused on the OFL, I think it’s a distraction to talk about what commercial EULAs “intend.” It’s not controversial to say that the OFL intends to permit web use, is it? We only get tripped up there because of reserved font names and modification.
Stuart, you’re making good points and I agree with some of what you say, but I want to be clear that it has very little to do with the point I’m trying to make and the OP’s question, which was primarily about open source licensing.
Getting back to WOFF and modification: Yes, apparently some WOFF converters are not lossless. The FAQ’s answer to the question, “Can I make and use WOFF (Web Open Font Format) versions of OFL fonts?” is “Yes, but you need to be careful. ...” Of course one should be mindful of what a WOFF converter is doing, but I’m only saying exactly what the FAQ says: “Because of the design of the WOFF format, however, it is possible to create a WOFF version that is not considered modification, and so would not require a name change.”
Personally, from what I know about WOFF2 (I left the working group not long after work on WOFF2 got started), it sounds like its potential modifications are minor enough to preserve Functional Equivalence under the OFL, and Victor’s 7-year-old Web Fonts and Reserved Font Names also says that is likely. I’d love to see that part updated now that WOFF2 is more settled.
So the question whether a WOFF file is the same font or a different font from its contents depends whether one considers the functional distinction to be part of what defines a distinct font.
I believe the FAQ has been updated a few times in the last decade to attempt to add clarity to common web font redistribution situations.
WOFF 1 doesn't modify the font it compresses at all; it's easy to confirm that with a checksum. And similarly WOFF 2 does modify the font data during compression, but the output should be functionally equivalent to the input.
There's a document by SIL (https://scripts.sil.org/OFL_web_fonts_and_RFNs) that introduces the idea of "functional equivalence" as a kind of modification which might be interpreted as non modification under the OFL terms, that I would summarize as "while the checksum might be different on the binary, if no user can tell a difference, what does it matter?"
But still, to answer the original question, since the copyright notices is a boilerplate, there's no RFN in play, and so this doesn't matter for that particular case.