enhance: convert video thumbnail to webp

packages/backend/src/core/VideoProcessingService.ts

@@ -36,7 +36,7 @@ export class VideoProcessingService {
 					});
 			});
 
-			return await this.imageProcessingService.convertToJpeg(`${dir}/out.png`, 498, 280);
+			return await this.imageProcessingService.convertToWebp(`${dir}/out.png`, 498, 280);
 		} finally {
 			cleanup();
 		}