> Why do movies keep getting backed up?
My Mac’s backups are growing huge, mainly because whenever I browse movie files using VLC, Time Machine makes another copy of the whole movie. How do I control that?
Like other backup systems, Time Machine only backs up files which have changed. Normally when an app opens a document, especially something potentially large like a movie, it doesn’t change the file or its contents, so it shouldn’t get backed up. What’s happening here is that VLC is probably updating the metadata in the movie files, which results in their modification date being changed. Time Machine then has to make a fresh backup copy of the whole movie.
One workaround is to make the movies read–only, or to lock them, which will prevent any app from writing to them, although some apps might then complain. Another solution is to change the way your backups are created and maintained. When you upgrade to Big Sur or later and Time Machine backs up to an APFS volume, it tries to copy as little as necessary in backups, so will only copy a small section of each movie file. This is both quicker and more economical in space on your backup storage.