APNG avatar loses animation information on upload

[silverwind]

Gitea Version

fd273b0

Can you reproduce the bug on the Gitea demo site?

Yes

Description

APNG files lose animation information on upload. For example when uploading this APNG as an avatar, postprocessing squares it and the resulting file no longer animates.

[Gusted]

image/png doesn't support APNG, we would need to detect this kind of PNG and use a appropriate encoder like: https://github.com/kettek/apng

[silverwind]

Possibly way of detection: https://stackoverflow.com/a/4525194

[stale]

This issue has been automatically marked as stale because it has not had recent activity. I am here to help clear issues left open even if solved or waiting for more insight. This issue will be closed if no further activity occurs during the next 2 weeks. If the issue is still valid just add a comment to keep it alive. Thank you for your contributions.

[silverwind]

Related: #24248 (comment)

WEBP is currently converted to PNG which is not ideal. Avatar convertion module should output WEBP for WEBP input, maybe even convert all avatars to WEBP instead of PNG.

[silverwind]

Let's continue in #24263.