A few days ago, I was tweaking a video clip in Photoshop CS4. I remember converting the video to a smart object, selecting the green channel, hitting the "load channel as selection button," then using the selection as a mask (Layer > Layer Mask > Reveal Selection) on the smart object layer.
The result was a mask that followed the action of the video. Great, exactly what I wanted.
Trying to repeat that same technique today with a different piece of video results in a mask that has only the selection that was visible when I loaded the channel as a selection - a still frame mask, not a motion mask.
I reopened the previous work and there was my layer with a moving mask on it, so I didn't imagine my previous success. I must be forgetting a step here somewhere. Photoshop, of course, doesn't save the history with the file, so no luck there.
I'm trying to create a moving mask (in Photoshop) for a video clip from the green channel. Any help would be appreciated.