Why do some YouTube videos show a thumbnail when you hover the mouse cursor over the time bar, while others don't?


This shows thumbnails. This doesn't show.

This is an older video and has thumbnails. This was published yesterday and doesn't have thumbnails.

  • I've always wondered this too - though it used to always show, it must be a new thing
    – Ethan
    Commented Oct 30, 2017 at 12:00
  • @Booligoosh At least a few years, if my memory is right.
    – Rodrigo
    Commented Oct 30, 2017 at 12:14

2 Answers 2


Had you said previews on the progress bar (or even had uploaded images) I might not have misunderstood first time around. IF that is what you mean:

The progress bar preview works on some videos and doesn't work on others. There is no explanation for it, nor can you fix it.

from YouTube Help Forum might be of interest (though I'm not convinced correct).

  • It seems that your link refers to the 1 thumbnail that represents the video. Look at the text in bold font, I'm asking something else. (Why most people won't read this carefully enough?)
    – Rodrigo
    Commented Aug 30, 2017 at 21:12

It might probably be the format in which the video was uploaded. For instance where the script used in handling the thumbnail function can only read certain formats of videos like mp4

  • Nice guess. It would be great to be sure if that's the case, or at least cite a trustworthy source.
    – Rodrigo
    Commented Oct 30, 2017 at 12:13
  • I don't think that's it. I've had cases where I'll play a video and it has the preview then I'll pause the video for later. Come back the next day and usually what happens then is it'll auto reload the video (recache, whatever) and now the preview is gone. No amount of reloading it will get it back. Not even on another browser. I'm starting to wonder if what happened is I switched to a different bank of machines that's feed it to me. Now that new machine bank isn't configured the same and YT just isn't getting their "stuff" together. Commented Oct 8, 2018 at 23:28

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