Stop bullying me @TeamYouTube & give me my thumbnails back!pic.twitter.com/4em3d1kpLE
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Then maybe they won't have stats to compare and based things on. As in, if a video doesn't have custom thumbnail then how can you know it will perform worse or better with their experiment. While the ones with custom, they will be able to compare the before and after.
They are testing auto-generated thumbnails nothing to do with custom thumbnails or anything to do with performing against custom thumbnails. Clickbait thumbnails will always perform better against auto generated thumbnails.
Good thumbnails increase click rate. They might be trying to improve auto generated thumbnails on videos so that is selects the best possible thumbnail from the video instead of 3 crappy ones they give you. But then again they dont need to hide custom thumbnails from certain user
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