In OS X Mavericks through macOS Mojave, 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.
Save the converted file
macOS Mojave is the final version of macOS to convert many of these older formats, so you should save the converted file in its compatible format 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.
- 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.
- About Pro Video Formats and MXF