I just lost an hour of my life trying to figure out how to set my MacBook Pro to 1280×720 on the main display, so to save anyone else from banging their head against the desk, here's the steps that finally worked for me:
1 – Download and install SwitchResX
2 – Go to System Preferences and click on the SwitchResX icon
3 – Click on Color LCD on the left side
4 – Choose the Custom Resolutions tab
5 – Click on the plus icon to create a new resolution
6 – Choose Scaled Resolution from the top drop-down menu
7 – Enter the resolution you want in the two boxes below
8 – Click OK
9 – Check to make sure the resolution that now shows up in the list is correct. I've found it will sometimes forget one of the values and set it to zero! If it does that, go back in and re-edit and save it until it does appear correctly.
10 – The Type column should read Scaled, and the Status should be Uninstalled. Now press Command-S to save your changes.
11 -You should now see Needs to Reboot in the Status column. As you may have guessed, this means you need to reboot your machine so choose Restart from the main system menu.
12 – Once the system has restarted, go to the normal display preferences and you should see your new resolution listed there.
If this does fix your problem, please buy a copy of SwitchResX for 14 Euros to support its development.
Wondering why I needed a custom resolution of 1280×720? I'm working on building some more professional screencasts that are going to be run through a 720p video production pipeline, so I need to capture my whole screen at that resolution. I expected it to be fairly simple to set up, but everywhere I turned I hit baffling UI. It makes no sense that you can't set a custom resolution within Apple's preferences in the first place, and then I spent a lot of time and $20 on DisplayConfigX with no luck, before I figured out how to get SwitchResX working.