QuickTime Player converts legacy media files before playing them

You might see a progress bar showing that your file is converting.

In OS X Mavericks and later, QuickTime Player (version 10.0 and later) converts legacy media files that use certain older or third-party compression formats.

When you open such a file, a window with a progress bar shows that the file is converting. To stop converting, just close the window.

Converting window

Media files that use many of these older formats will not be compatible with future macOS releases, so you should save the converted file before closing it. Conversion doesn't modify or replace the original file.

To preserve the quality of the original file, the converted file might be larger than the original.

Learn more

  • QuickTime Player uses Apple ProRes to convert legacy formats used in video workflows, such as those encoded with the Animation codec. It uses H.264 to convert other older or third-party media formats.
  • Learn what to do if QuickTime Player can't open a file.
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