A THM file is a thumbnail image that Windows creates automatically to show a preview of a video or photo

When you record a video on a digital camera, camcorder, or phone, Windows generates a small preview image called a THM file alongside the video file itself. The THM stands for "thumbnail." You will usually find it in the same folder as the video, with the same filename but a .thm extension instead of .avi, .mov, or .mp4.

The thumbnail file is not the video itself — it is a still image extracted from the first frame or an early moment of the video. Its only purpose is to let you see what the video contains without opening the full file. On older cameras and some phones, these files appear automatically. On newer devices, Windows often handles thumbnails differently, so you may not see separate THM files as often as you used to.

THM files are most common with videos recorded on Canon cameras, Sony camcorders, and some older digital devices. They are small — usually just a few kilobytes — and safe to delete if you want to clean up storage space, since they can be regenerated.

Key Takeaways

  • A THM file is a thumbnail preview image that appears alongside a video file, created automatically by cameras and some recording devices.
  • THM files use the same base filename as the video but with a .thm extension, and they appear in the same folder.
  • You can open a THM file with any image viewer, including Windows Photos, Preview on Mac, or standard image editing software.
  • Deleting a THM file will not affect the video itself, and Windows can recreate the thumbnail if needed.

How to open a THM file on Windows

Right-click the THM file and select Open with. Choose Photos (the built-in Windows image viewer) or any other image program you have installed, such as Paint, Photoshop, or GIMP. The thumbnail will open as a still image.

If Open with does not appear, click Open with another app at the bottom of the menu. Scroll down and select Photos or Paint. You can also drag the THM file directly onto an open image viewer window to display it.

On Windows 11, you can also double-click the THM file directly. Windows will attempt to open it with your default image viewer. If nothing happens, the file type may not be registered, and you will need to use the right-click method above.

How to open a THM file on Mac

Double-click the THM file. Mac's Preview application will open it automatically. If Preview does not launch, right-click the file, select Open With, and choose Preview from the list.

You can also drag the THM file onto the Preview icon in your Dock. Other Mac image viewers, such as Pixelmator or Adobe Photoshop, will also open THM files without any conversion needed.

Why cameras create THM files

Cameras generate THM files so that the device itself — and your computer — can display a quick preview without loading the entire video into memory. A video file can be hundreds of megabytes or larger, while a thumbnail is usually under 50 kilobytes. This makes browsing your video library much faster on the camera's small screen or in a file manager window.

When you connect a camera to a computer, the THM file lets Windows show you a preview in File Explorer or a photo management program before you decide whether to transfer or delete the video. This was especially useful on older devices with limited processing power, though modern phones and cameras often handle thumbnails differently.

Can you delete THM files safely

Yes. Deleting a THM file will not affect the video file at all. The video will play normally, and you will lose only the thumbnail preview. If you later want a thumbnail back, most image viewers and video players can regenerate one automatically.

If you are trying to free up storage space, deleting THM files will recover only a small amount — usually a few kilobytes per file. If your camera or phone created many videos, the combined THM files might add up to a few megabytes, but this is rarely worth the effort unless you are working with extremely limited storage.

Converting or editing a THM file

A THM file is already a standard image format — usually JPEG — so you do not need to convert it. You can edit it like any other image using Paint, Photoshop, GIMP, or any image editor. Simply open it and make your changes.

If you want to rename the file or change its extension, you can do so safely. Renaming a THM file to .jpg will not change what it is — it is already a JPEG image. However, there is usually no reason to rename it, since most programs recognize the .thm extension without trouble.

THM files from different devices

Canon cameras are the most common source of THM files, but Sony, Panasonic, and some older Nikon models also create them. The format is the same across all devices — a small JPEG preview image stored alongside the video.

Some phones and modern cameras no longer create separate THM files. Instead, they store thumbnail data inside the video file itself or rely on the operating system to generate previews on demand. If you are working with older camera footage and see THM files, they are safe to work with and can be opened in any image viewer.

Frequently Asked Questions

Can I recover a video if I delete the THM file?

Yes. The THM file is only a preview image. Deleting it does not affect the video file at all. The video will play normally, and you can regenerate a thumbnail if needed.

Why does my camera create a THM file for every video?

The THM file lets your camera display a quick preview on its screen and helps your computer show thumbnails in file managers without loading the entire video. It is a convenience feature that saves processing power and storage bandwidth.

What program should I use to open a THM file?

Any image viewer will work: Windows Photos, Preview on Mac, Paint, Photoshop, or GIMP. You can also open it by right-clicking and selecting Open with, then choosing any image program you have installed.

Is a THM file the same as a JPG?

A THM file is usually a JPEG image with a different file extension. You can rename it to .jpg and it will work identically. The .thm extension simply tells your system it is a thumbnail associated with a video.

Do I need to keep THM files if I transfer videos to my computer?

No. Once you have the video file on your computer, the THM file is optional. Your computer can generate its own thumbnails. You can delete THM files to save space, though they take up very little room.