The ._ files your Mac leaves on USB drives, and how to stop them showing up on the TV

You copied twenty photos to a USB stick for the TV. The TV shows forty, and half of them are named ._IMG_1234.jpg and will not open. Your Mac put them there. They are tiny and harmless, and you can remove them in one command.

What they are

Mac files can carry extra information that other formats cannot store, like Finder tags, labels, which app opens the file, and a note that the file was downloaded from the internet. On a drive formatted as ExFAT or FAT32, there is nowhere to put that, so macOS writes it into a separate hidden file with the same name and ._ in front. The system is called AppleDouble. A Mac hides these files; Windows, TVs and cameras show them.

.Trashes is the only one that can be large, and it empties when you empty the Trash with the drive plugged in. External drive taking up space covers it.

Removing them

macOS includes a tool made for exactly this. It merges the ._ files back or deletes them:

# Replace USBSTICK with your drive's name
dot_clean -m /Volumes/USBSTICK

To see how many there are first:

find /Volumes/USBSTICK -name '._*' | wc -l

Eject the drive afterwards and do not open it in Finder again before plugging it into the TV, since browsing can create new .DS_Store files.

Stopping .DS_Store files on network and USB drives

defaults write com.apple.desktopservices DSDontWriteNetworkStores -bool true
defaults write com.apple.desktopservices DSDontWriteUSBStores -bool true

Log out and back in for it to take effect. It stops .DS_Store files, not ._ files, which dot_clean handles. More on .DS_Store in DS_Store files taking up space.