Thumbnail webp images as webp to avoid losing transparency

synapse/config/repository.py

@@ -47,10 +47,8 @@ THUMBNAIL_SIZE_YAML = """\
 THUMBNAIL_SUPPORTED_MEDIA_FORMAT_MAP = {
     "image/jpeg": "jpeg",
     "image/jpg": "jpeg",
-    "image/webp": "jpeg",
-    # Thumbnails can only be jpeg or png. We choose png thumbnails for gif
-    # because it can have transparency.
-    "image/gif": "png",
+    "image/webp": "webp",
+    "image/gif": "webp",
     "image/png": "png",
 }
 
@@ -102,6 +100,10 @@ def parse_thumbnail_requirements(
                 requirement.append(
                     ThumbnailRequirement(width, height, method, "image/png")
                 )
+            elif thumbnail_format == "webp":
+                requirement.append(
+                    ThumbnailRequirement(width, height, method, "image/webp")
+                )
             else:
                 raise Exception(
                     "Unknown thumbnail mapping from %s to %s. This is a Synapse problem, please report!"

synapse/media/thumbnailer.py

@@ -38,7 +38,7 @@ class ThumbnailError(Exception):
 
 
 class Thumbnailer:
-    FORMATS = {"image/jpeg": "JPEG", "image/png": "PNG"}
+    FORMATS = {"image/jpeg": "JPEG", "image/png": "PNG", "image/webp": "WEBP"}
 
     @staticmethod
     def set_limits(max_image_pixels: int) -> None: