Premiere Pro 2026: Why is my 4K timeline stuttering even with a powerful PC?

Hey! Proxy workflow is definitely your friend here. The issue is that your A7S III shoots 10-bit 4:2:2, which is a heavy codec (likely XAVC S or S-I). Even with a 4090, Premiere's software decoding for that codec isn't optimized as well as something like ProRes. Creating proxies in ProRes 422 Proxy (if you're on Mac) or CineForm (on Windows) will make playback buttery smooth. In Premiere, just right-click your footage in the Project panel, go to Proxy > Create Proxies, and choose the format. I'd recommend using 'ProRes 422 Proxy' or 'CineForm 1080p' with QuickTime wrapper. Make sure to enable 'Use Proxies' in the Program Monitor toolbar (the icon that looks like a small rectangle with a line through it). Once you're done editing, you can switch back to full-res for export—Premiere handles that automatically. Also, check your media cache settings—move the cache to a fast SSD if you haven't already. That can help with scrubbing.

I'll second the proxy advice, but also want to point out something else: you mentioned you're using 4K 10-bit 4:2:2 from a Sony A7S III. That's likely XAVC S-I, which is an intraframe codec but still hogs bandwidth. Even with a 4090, the decoding is done by the CPU and GPU, but Premiere's implementation is not as efficient as it could be. One trick is to use the 'Mercury Playback Engine' with 'Mercury Transmit' off (unless you need it) and set the 'Playback Resolution' to 1/4 during editing. But honestly, proxies are the way to go.

For proxy format, if you're on Windows, I'd suggest CineForm 1080p (in QuickTime or AVI wrapper) because it's natively supported and fast. If you're on Mac, ProRes 422 Proxy is perfect. Also, make sure your proxies are stored on a different drive than your source footage to avoid I/O bottlenecks. And don't forget to generate proxies in the background—you can keep editing with the originals while they're created, then switch over. Once you're done, just export and Premiere will use the full-res media automatically. That should solve your stuttering completely!

Just wanted to follow up and thank both of you for the tips! I created proxies in CineForm 1080p and enabled 'Use Proxies' in the Program Monitor, and the difference is night and day. Playback is now smooth as butter, even with multiple layers of 4K footage. I also moved my media cache to a fast NVMe drive as suggested, and scrubbing is instant. I'm a bit annoyed I didn't try this earlier, but now I'll always use proxies for any 4K project. Thanks again for the help—problem solved!