Hi Greg,
To add to Jon’s comments – in Premiere, right-click the 4K clip in the 1080p timeline and select Set to Frame Size (not SCALE to frame size). This will make it so you can see the entire 4K clip inside the HD frame, but you can still use Adobe Motion effect to scale and pan in the image as Jon said – maybe you want to zoom in closer to highlight something in the image. Premiere will use the extra pixels available in the 4K source to provide a clean zoom in HD. As long as you don’t zoom (scale) past 100%, no quality loss. In fact, you can go above 100% and still look good, up to you how far to push it.
Sometimes easier to cut source clip into pieces and apply different scaling to each piece than to struggle with keyframes. Meaning, when you want to go from original “wide” view to a closer blow-up, use the Razor tool to apply a CUT in the clip. Now each “piece” of footage can have different scaling applied without keyframes being needed.
I shoot stage events on a wide angle using 4K, then edit as 720p and can cut or dissolve from a wide shot to a medium or close-up and it looks like multiple cameras were used. The quality is excellent since no pixels are being blow-up/duplicated using the higher-resolution source video.
When done editing the 1080p Sequence, export as 1080p.
Thanks
Jeff Pulera
Safe Harbor Computers