[feature] Add `avif` file support (#4331)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

This pull request implements support for reading avif images properly.

closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4330

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4331
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/internal/media/ffmpeg.go b/internal/media/ffmpeg.go
index 676eba9be..05e8c69a6 100644
--- a/internal/media/ffmpeg.go
+++ b/internal/media/ffmpeg.go
@@ -342,16 +342,21 @@ func (res *result) GetFileType() (gtsmodel.FileType, string, string) {
 	case "mov,mp4,m4a,3gp,3g2,mj2":
 		switch {
 		case len(res.video) > 0:
-			if len(res.audio) == 0 &&
-				res.duration <= 30 {
+			switch {
+			case res.video[0].framerate == 0 && res.video[0].stream.codec == "av1":
+				// Looks like an avif image.
+				return gtsmodel.FileTypeImage,
+					"image/avif", "avif"
+			case len(res.audio) == 0 && res.duration <= 30:
 				// Short, soundless
 				// video file aka gifv.
 				return gtsmodel.FileTypeGifv,
 					"video/mp4", "mp4"
+			default:
+				// Video file (with or without audio).
+				return gtsmodel.FileTypeVideo,
+					"video/mp4", "mp4"
 			}
-			// Video file (with or without audio).
-			return gtsmodel.FileTypeVideo,
-				"video/mp4", "mp4"
 		case len(res.audio) > 0 &&
 			res.audio[0].codec == "aac":
 			// m4a only supports [aac] audio.