MP4s lose thumbnails, but gain icons; AVIs still have thumbnails.

Sebastian42 · 02 Jan 2021

Something happened to my HDD today causing MP4s to lose their thumbnails, but a clone that was made a few days ago, first shows generic icons for the default Player, then after a moment, they turn into thumbnails. I'd like to understand what is going on, and above all, how to make the non-clone show thumbnails again for MP4s.

Much discussion 'on the web' suggests the icon cache may be corrupt so I made the main HDD a slave to the clone which shows the thumbnails satisfactorily, and cleaned out the icon cache, and refilled it with a copy of the clone's cache. NO improvement !

Alkl · 03 Jan 2021

Not sure if it helps, but my video thumbnail related issues were always missing / corrupted codecs.
My issue were mainly that explorer could not load any thumbnail anymore, as the subprocess for generating the thumbnails was stuck on certain videos.

I solved my video thumbnail issues by installing K-Lite Video Codec Pack (it's free).

I noticed these issues mainly appearing with Windows 20H2, but I can't prove it.

You may also try following: Clear and Reset Thumbnail Cache in Windows 10

Another possibility is a corrupted windows system or filesystem: Run SFC Command in Windows 10 |

f14tomcat · 03 Jan 2021

May want to check and verify your setting here. Unchecked for Thumbnails, Checked for Icons.

Sebastian42 · 03 Jan 2021

Clear and Reset Thumbnail Cache in Windows 10 - I wrote that I made the HDD a slave to the clone where the problem does NOT exist, and cleared out the cache and refilled it with the contents of the clone (that does not have the problem).

K-Lite Video Codec Pack - I update that every month.

I COULD (and have) run SFC, but I notice it is an all-purpose remedy recommended for the widest varieties of problems.

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f14tomcat - I do have the box for 'Always show icons, never thumbnails' unticked' moreover, thumbnails are missing ONLY for MP4s. There are another two locations for a setting like that - in Group Policy and Visual Effects - also OK.

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I have just installed the latest K-Lite; I do not remember the vast series of options previously; one of them, THUMBNAILS, caught my eye, and I noticed that MP4 and FLV were the only video formats NOT ticked, so I reversed that, and now have thumbnails again for MP4s ! Thank you so much.

f14tomcat · 03 Jan 2021

Sebastian42 said:

Clear and Reset Thumbnail Cache in Windows 10 - I wrote that I made the HDD a slave to the clone where the problem does NOT exist, and cleared out the cache and refilled it with the contents of the clone (that does not have the problem).

K-Lite Video Codec Pack - I update that every month.

I COULD (and have) run SFC, but I notice it is an all-purpose remedy recommended for the widest varieties of problems.

- - - Updated - - -

f14tomcat - I do have the box for 'Always show icons, never thumbnails' unticked' moreover, thumbnails are missing ONLY for MP4s. There are another two locations for a setting like that - in Group Policy and Visual Effects - also OK.

- - - Updated - - -

I have just installed the latest K-Lite; I do not remember the vast series of options previously; one of them, THUMBNAILS, caught my eye, and I noticed that MP4 and FLV were the only video formats NOT ticked, so I reversed that, and now have thumbnails again for MP4s ! Thank you so much.

Glad you've got it now!