New rule that converts images to WebP and AVIF and checks the gain

lib/metadata/policies.js

@@ -729,7 +729,7 @@ var policies = {
     "totalWeight": {
         "tool": "redownload",
         "label": "Total weight",
-        "message": "<p>The weight is of course very important if you want the page to load fast. Try to stay under 1MB, which is already very long to download over a slow connection.</p>",
+        "message": "<p>The weight is of course very important if you want the page to load fast. Try to stay under 1.5MB.</p>",
         "isOkThreshold": 1572864,
         "isBadThreshold": 3145728,
         "isAbnormalThreshold": 5242880,
@@ -746,6 +746,16 @@ var policies = {
         "hasOffenders": true,
         "unit": 'bytes'
     },
+    "oldImageFormats": {
+        "tool": "redownload",
+        "label": "Old image formats",
+        "message": "<p>Measures the number of bytes that could be saved by converting images to newer and more efficient formats. The current best image format for the web is AVIF and the second best is WebP.</p><p>Be careful, you need to provide a fallback for old browsers that don't support them (for example, Microsoft Edge doesn't support AVIF on Windows 10 or earlier) and search engine bots.</p>",
+        "isOkThreshold": 30720,
+        "isBadThreshold": 307200,
+        "isAbnormalThreshold": 512000,
+        "hasOffenders": true,
+        "unit": 'bytes'
+    },
     "imagesTooLarge": {
         "tool": "redownload",
         "label": "Oversized images",

lib/metadata/scoreProfileGeneric.json

@@ -5,6 +5,7 @@
             "policies": {
                 "totalWeight": 5,
                 "imageOptimization": 2,
+                "oldImageFormats": 2,
                 "imagesTooLarge": 1,
                 "compression": 2,
                 "fileMinification": 2