ydobemos:

Hmm, output resolution may make the preview generation faster, but it will still happen every single time you mildly change something. From my experience so far making reasonably low resolution temporary files allows to turn previews off completely and enjoy some smooth sailing from there.

It may not be the most efficient way, but it does provide results.

What you are effectively doing is creating proxy files. When AVCHD first came on the scene, and computers couldn't handle it, that is what everyone did. Create lower resolution files for editing. The Multicam Editor does the same thing to be able to switch quickly between up to 6 cameras (with the Ultimate version) smoothly. 

@Candive. It's easy to test. Take a 4k clip and put it on the timeline. Change the timeline settings to something low. Then when you Export, change the export settings to reflect the original file format and then look at the the exported clip.

acsscott:

A different timeline aspect ratio than export ratio will make changes to titles and effects.

 I have no issues between 4k and 1080p. 

Hi acsscott,

Unfortunately I'm still confused with your workflow. Is it as follows?:

1. Set timeline to 1920x1080.
2. Load timeline with 4k clips (3840x2160)
   
3. Edit the clips on the timeline.
4. Don't change the aspect ratio to 3840x2160 before Export
5. Export at 1920x1080 

Tony P:

@Candive. It's easy to test. Take a 4k clip and put it on the timeline. Change the timeline settings to something low. Then when you Export, change the export settings to reflect the original file format and then look at the the exported clip.

Tony, so you don't think its necessary to change the timeline back to 4K prior to export? acsscott indicated that a different aspect ratio on the timeline vs the Export would/may distort titles and effects. I guess I'll have to play with the system and find out for myself.  

The aspect ratio of 3840x2160 is the same as 1920x1080?  Timeline resolution has nothing to do with the export resolution.

acsscott:

The aspect ratio of 3840x2160 is the same as 1920x1080?  Timeline resolution has nothing to do with the export resolution.

My mistake  I re-read your comments and realised I confused aspect ratio to resolution. So what you are saying is that editing on the timeline is "easier," if you reduced the resolution but maintain the aspect ratio. Upon export, you specify the increased resolution. So as an example, you could set the timeline at 1280x720 (16/9) and Export at 3840x2160 (16/9). Editing is easier while export resolution is not lost. 

1080p on my computer is no delay.  I set my render threshold to 10, so only a few transitions have to bg render.  No complaints with timeline speed. 

I've conducted some testing. My rig is slower than Tony's and Acsscott so their results will differ. In PS24, using a 4k clip 50 fps, 1 minute long, I timed the preview rendering (brown bar turn to green) with the following results;

Timeline = 3840x2180 50fps; 3 min 20 seconds

Timeline = 1280x720 25fps; 3 min 14 seconds

Note; on my computer, anything more than zero  for Playback Optimization would render the clip. I had it set at 5%

Now I conducted the same test using PS23:

Timeline = 3840x2180 50fps; 1 minute

Timeline = 1280x720 25fps; 40 seconds

Reducing the resolution while keeping the aspect ratio the same did improve the render marginally on my computer, the big difference is between the two systems themselves; PS24 vs PS23. PS24 is 3 times slower on my machine.