How do you save an animation/upload it to the web?

I tried rendering it in gif but a red x appears when I try to load it…

red x? well that quite unusual, what Operative System are you using and what version of Synfig do you have?

red X might be because of your gif viewer loading an image that is either empty or in a another format and thus not recognised as gif. You could try to open the gif with another software (firefox?) to see if it displays correctly.

B.

a failed rendered file will often be 0 bytes size. check that

Silly question… but does the “red x” look something like this?

If so, it’s more likely a 404 error in your HTML and the browser’s not finding the gif in the first place! How are you trying to open the image?