How it's counted

YouTube doesn't publish a live global upload count, and its API has no endpoint for one. So the big number is an estimate:

• Hours uploaded today = minutes since midnight UTC × hours uploaded per minute (default 500).
• Videos today = those hours ÷ the average video length you choose.

Sources

• YouTube said "more than 500 hours of content are uploaded every minute" (YouTube Official Blog / press statements, 2019). See Wikipedia: YouTube for the citation history.
• Channel uploads come from YouTube's public per-channel feeds: youtube.com/feeds/videos.xml?channel_id=… (no key, latest ~15 videos per channel).