A QTPXCOMPOSITION file is an archive created by QuickTime, a video playback program bundled with macOS. It contains files that make up an unsaved recording created in QuickTime, which may include .MOV files for video recordings or .M4A files for audio recordings.

The QTPXCOMPOSITION file is only used for unsaved compositions created in QuickTime. As you are making a recording, whether it be video or just audio, the information is autosaved by QuickTime in the QTPXCOMPOSITION file. The file is meant to be temporary until you save the recording in a specific format. If you lose a recording that has not yet been saved, you can use the QTPXCOMPOSITION file to retrieve the lost recording from the point at which it was last autosaved. This proves especially helpful in instances where QuickTime crashes before a recording can be saved. QTPXCOMPOSITION files are located in the following location: /Users/[username]/Library/Containers/com.apple.QuickTimePlayerX/Data/Library/Autosave Information/