So I'm using Premiere CC on my Mac laptop and I imported some GoPro 4 footage that was 1920 x 1080. My sequence settings were 1280 x 720. For all the clips, I selected "set to frame size" because I'm a fool and didn't realize what I was doing. (clearly I'm still learning)
After I realized what I did after editing the whole video, I went to change the sequence settings to 1920 x 1080 and a black box appeared around the footage. "set to frame size" doesn't change it.
So I guess what happened is I set it to the smaller frame size, change the sequence settings, and tried to set it back to the size of the source clips, but it had already changed to the smaller size like I told it to.
This is a meticulously edited video with most clips being trimmed in the timeline rather than in the source monitor, and then with a change of speed/duration, so it's not a simple clip replacement solution. I clearly have a lot of bad habits to break. Is there anything to be done??
Change one clips SCALE to 100% in the Effects Controls and under the Motion settings. Highlight that clip in the timeline and COPY it. Then highlight all the other clips you want to scale up, right click, and select Paste Attributes. Only check the MOTION box in the pop up window. This should bring all your clips back to 1920x1080.
Note - if you have done any scaling or key framing on the clips it will override them. Select wisely.