aPNG is the only lossless animated medium I know how to use. Probably not the best format for animations that require more color information than GIF can handle, but I found that SWF conversions added more compression artifacts (even at "100% Quality").

Pixiv Animations are just archives of JPGs played in Javascript. Run a bookmark containing "javascript:window.location = pixiv.context.ugokuIllustFullscreenData.src;" (without quotation marks) while viewing a Pixiv Animation to download the archive.

Problem is that only Firefox seems to be showing aPNG files correctly right now and other browsers won't even bother supporting it, IE and Chrome being biggest ones. Many image manipulation/animation programs also refuse to recognize the format, including photoshop, GIMP and paint.NET.
That's actually quite shame as aPNG would have it's uses being almost lossless and supporting partial transparency.

Other problem is that if source files are in JPG you will get artifacts which PNG doesn't handle that well making filesize much bigger. You can use selective blurring to get rid of minor artifacts but it still won't be perfect.

WebM is actually best one thus far as animations usually don't need transparency and being supported by almost every browser means they work everywhere without need for plugins - including mobile devices. Filesize is almost ridiculously low meaning animation will start almost instantly instead of lagging one loop.
Only problem with those are that to make them loop without controls it has to be set with HTML flag instead of inside the file meaning you can't just post them everywhere...

You are right about SWF as that's the WORST! If you convert from video instead of directly from flash there will be massive amount of artifacts and biggest filesize there can be, lose/lose situation.

With this file GIF is almost identical to aPNG because of so little information and so few frames: http://gfycat.com/ScarySpotlessKawala

e621 give this when trying to upload WebM:
Error: File is an invalid content type: webm

It would be nice if admins added support for them. Danbooru seems to already have it with thumbnails.

Ok, who is Midori, what was she in, and who is her original artist? I've seen her in a few mayoineko works (I think every time by Nakagami Takashi), here is a pic by Shiron (possibly. dunno if that just means they did the colors or what), and I've seen a few obvious fan works besides, but what she's from has been bugging me (if she's even "from" anything)

chdgs said:
aPNG is the only lossless animated medium I know how to use. Probably not the best format for animations that require more color information than GIF can handle, but I found that SWF conversions added more compression artifacts (even at "100% Quality").

Pixiv Animations are just archives of JPGs played in Javascript. Run a bookmark containing "javascript:window.location = pixiv.context.ugokuIllustFullscreenData.src;" (without quotation marks) while viewing a Pixiv Animation to download the archive.

Holy shit. Even though it has been one year since your comment, it sure is nifty. Thank you so much, now i don't have to capture animated stuff on Pixiv anymore.

Hmm, this brings back memories from finding this green feline character on Pixiv. https://i.pximg.net/img-zip-ugoira/img/2014/07/22/22/41/42/44870657_ugoira1920x1080.zip To download this, you'd need to both be logged in, and have referrers for Pixiv.net. I have not seen a non-Pixiv source and likely won't. The artist uploading to other sites would have likely lead to non-Ugoira formats being used, though.