The auto-resume feature is located in a Theme. Inside your Theme navigate to to Player Settings:

Then you'll see the option:

This option is disabled by default. When enabled, your viewers will automatically go back to the same place in the video where they left off.

For example, if a viewer watches the video until the :25 second mark and then closes the tab/browser and then comes back to the video later, when they click play the video will start at the :25 second mark.

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