FLV video thumbnails in Windows Explorer

Windows ships no decoder for VP6 or Sorenson Spark, the video codecs of older Flash videos. SageThumbs 2K decodes both itself, so old .flv files show a real frame as their thumbnail.

What you see

FLV files in H.264 are handed to Windows' own decoder; VP6 and Sorenson Spark are decoded by SageThumbs in pure Rust, in a separate short-lived process.
F4V files are drawn through Windows' Media Foundation codecs.

Limits

In OneDrive and other synced folders, files stored on the PC get thumbnails as anywhere else. Online-only files are left to the cloud app, since nothing is downloaded just to draw a thumbnail.

Extensions this covers

.flv .f4v

See every format SageThumbs 2K supports or browse all format guides.

Get SageThumbs 2K

Install it with winget:

winget install LunarWerxs.SageThumbs2K

Or download the installer from GitHub and run it.

Download the installer

Windows 11 and 10, 64-bit, on x64 and Arm. The same page has a portable zip that needs no installing.

Free for personal use

Home, hobby and other non-commercial use is free: every format and every tool. A company, a shop or anyone doing paid work needs a business licence for each PC.

A business licence is US$49 per PC once, with 12 months of updates, or US$2.99 per PC a month. See business licence pricing

Thumbnails not showing?

Windows caches thumbnails, and a file it failed on once stays failed. In SageThumbs, Settings ▸ Advanced ▸ Rebuild thumbnail cache clears the cache and restarts Explorer.
Make sure File Explorer's "Always show icons, never thumbnails" option is off, and that the format is ticked in SageThumbs Settings ▸ File types.
Run st2k doctor in a terminal. It only reads, checks the whole chain, and prints a fix under anything that is wrong.