I'm using the smart object stack mode (mean) in the typical way that you would for noise reduction in an image.
However, I'm using videos.
Everything goes smoothly (File>Scripts>Import as Stack, Select all layers, Convert to smart object), at that step, the video still plays.
As soon as I click Stack Mode>Mean, it averages the frames I am on in the timeline, but no longer plays as video. Anywhere I am in the timeline still just shows that one frame I was on when I applied the effect.