Duplicate your sequence that has the 720×480 settings to keep as a backup in case you screw something up.
Next, right-click your sequence in the browser and select “Settings”
In the bottom left corner of the window that opens, you will see “Load Sequence preset”. Click it and choose the correct preset. You will probably be warned your editing timebase will not be changed.
Now you have the proper sequence settings (except for timebase) and your video surrounded by black. Select all of your clips and choose “Remove Attribute”. Choose Basic motion and distort. Click OK.
You should now have full frame HD video.
Finally, select all of the media in your timeline. Hit “cmd+x” to cut ALL media from your timeline. Right click on your sequence in the browser again and change the frame rate to the frame rate you need it to be (probably 59.94 for 720p). Click OK. Paste all of you media back in to the timeline bu hitting “cmd+v”
I know some of that may seem redundant, but it’s important to make sure you use a sequence preset so you don’t introduce other problems.
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