1,000 videos measured: YouTube WebP thumbnails halve bytes only at large sizes

A measurement of 1,000 videos found YouTube WebP thumbnails are about half the bytes of JPEG at 1280x720 and 640x480, but at 480x360 WebP is larger for 56% of recent uploads and 72% of 2026 videos. A missing WebP returns a 404 with a 120x90 placeholder image, so onerror never fires.

• At 1280x720 median WebP is 50.8 KB vs 96.7 KB JPEG (0.53)
• At 480x360 WebP is larger than JPEG for 72% of 2026 uploads
• 30 of 1,000 videos had no WebP at any size
• A missing WebP is a 404 with a 552-byte image body