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Supported file formats on the forums

Gwyneth Llewelyn


Hi! I've been experimenting with a few file formats that can be attached to the SL Community forums. We all know about JPEG and GIF. However, these days, there are a gazillion more (and better!) formats. For instance, this is a file uploaded in Animated PNG (APNG) format, which is allegedly supported on almost every browser except IE (if you just see a static image, it means your browser doesn't support APNG):


Naturally enough, there is no documentation about the support of APNG. This is not very surprising: after all, APNG files use the very same .png extension (and graciously fall back to the first frame...). Thus, APNG should work on any website that doesn't resize the image or convert it to an 'internal' format. There are some exceptions, depending on the kind of backend is used. For instance, if phpBB is installed with ImageMagick as the resizing engine, ImageMagick will have no issue with dealing with APNG correctly. Other graphical backends may simply not support anything beyond the first frame (while happily accepting GIFs — others will not even allow that, of course).

The trend, however, is not only to resize images (sometimes on the fly, for the benefit of mobile users), but to convert it to a completely different format, thus destroying the original image in the process, and whatever 'special features' it might have included at some point.

The reasoning behind this is the fear of hackers surreptitiously exploring some bugs (usually memory buffer allocation) in order to trick the webserver to run some sort of malicious software. While this is harder to accomplish than one might think, the truth is that image resizing and/or format conversion will get rid of any malicious code (possibly trashing the image in the process, but hey, that's what you deserve if you're attempting to crack a system...). Thus, restricting image file formats to just a few, or allowing a few more but ultimately converting everything to a single format (such as plain, old, boring, inefficient JPEG...), is a simple (but reasonably effective) method for virus & malware destruction.

Sadly, it also means that the options given to users is limited.

JPEG, GIF and even PNG are ancient, obsolete formats. They just have the advantage of being widespread. Nowadays, however, we have far better encoding systems. Just try to convert a WebP or HEIF image to PNG, and watch how much the file size will grow. Reversely, convert an image (even a PNG already minified by TinyPNG) to WebP or HEIF (or even to the venerable JPEG2000 — used internally by Second Life itself!), and you see how much you can save that way — which is a reason why those formats were designed in the first place, namely, to address ever-growing image resolution sizes.

And what about vector images? SVG, a standard for over twenty years, is supported by all browsers — but almost no applications. Why? Very early implementations of SVG — which has the ability to run JavaScript or other embedded code) — were deemed 'dangerous' (because, indeed, some people have managed to take over systems by merely uploading a SVG), and so, it's rare to find a software that supports it from scratch (even WordPress doesn't support SVG by default, although there are tricks to allow it to do so). Again, the 'danger' comes from an excess of caution. Because SVG is a text format (more precisely, it's a XML file, conforming to its standards), it can very easily be parsed for any embedded code, which can be stripped out, at absolutely no loss in functionality or quality. SVG is also an animation format: you can do pretty complex animations inside SVG, without the need for anything else, and let the browser render it pixel-perfectly at whatever resolution the user wants — that's the beauty of vector images!

But... well, because it was felt to be 'dangerous', this simple, compact, efficient and extremely powerful file format is usually 'banned' from being uploaded to most software out there :-(

And what about video?

Well, I can imagine that the major problem with video is its size. That's especially true with the most universal of all formats, MPEG4. On sites supporting it — not the case of the SL Community forums! — videos tend to get re-dimensioned during upload, and automatically converted to MPEG4 (this is how YouTube used to work, for example). That's all very nice, but there are far better formats, both in terms of what they can support (e.g. Matroska containers can have several audio and subtitle channels, automatically selected to match the browser's language settings), and in how well they can compress video (such as Theora or WebM), even with lossy quality, but giving much better results than Plain Old MPEG4. LL's limitation on 4.88 MBytes for the file size is not really much for MPEG4, but it goes a long way with the more contemporary formats — you can both get better quality and longer videos on Theora/WebM/H.265, etc.)

It's incredibly rare to find video support to anything else besides MPEG4 — if at all — and when it is supported, it just goes into a queue, scheduled for internal conversion to... MPEG4, thus losing all the savings made in the first place!

I couldn't figure out how to upload any video file format to the SL Community Forums. I wonder if there is an (undocumented) 'trick' to make it work? AFAICS, the answer is 'no'. An alternative, of course, is to embed a link to YouTube (that works at the cost of not having autoplay...):

The same approach apparently also works for Vimeo:

... and possibly a few more popular sites.

However, if you wish to embed your own video... there seems to be no simple way to accomplish that, unless you use one of the 'supported' providers.

Anyway, this was just a rant... a friend asked me what kids of file formats the SL Community Forums supported. 'Not many', it seems. That's why I seriously suspect that she'll just stick to the plain old (animated) GIF format to upload small-ish 'videos'...

Unless anyone could point me to an up-to-date list of supported image and video formats?...

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Nice to see you posting. You have been quite lately... or am I just missing your posts?

I suspect you are right about video file size being the reason for non-support of video files. We do have an image file size restriction. So it figures.

I suspect the Lindens don't pay much attention to supported file formats in the SL Forum. They likely let the author of the forum software deal with those issues. So, one could dig through Invision's documentation to see what all they support. I'll go with trial and error.

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Do other Forum-type sites let you upload videos and other large files - besides the actual social Media sites such as Facebook, Mastodon, Twitter, Instagram, and obviously YouTube and Vimeo, all of which people usually embed videos "from"?

If not, it would seem "embedding" is the standard.


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