Merging Large Photo Libraries w. Limited Mac Storage

I would discard iCloud entirely. iCloud will only sync with system libraries. Are both set to being system libraries?

Given you have 1TB external drives which is more than enough, I would say the easiest way to do this, is to move the libraries to the external drive. You have more than enough space in just one of them for both libraries.

Make sure the external drive is formatted as APFS or HFS+.

Anyway once both libraries are copied successfully to the external drive, with the Photos app shutdown, double click the Photos App icon in the Applications folder in Finder while holding down the option key on your keyboard.

This should provide a dialog box asking you to create a new library or load a different one. Click on Create a new Library and navigate to the other external drive if you want to save it, though you can do it on the same external one to create it.

With the empty library created, you can then go to the File menu, and select Import and then Import Library, navigate to the location of the libraries on the external drive and import them. Repeat for the second library.

This should bring in both libraries in their entirety. You can then give it enough time to index and it should provide a Duplicates folder with any duplicates from the import you can then delete.

The benefit of this, is neither original library is affected or modified so you have backups in case the results are not what you want.

Load the library you want to get the photos from in the Photos app as above, and then export the photos you want to transfer to the other library into a folder. Once you've exported the photos, shutdown the Photos app, open it gain with the option key held down and load the other library. Use the Import option in the File menu and import the files you just exported. The export should contain all the meta data and info for the photos, so the Photos library can re-import them without losing any data hopefully.

Phil0124 wrote: …With the empty library created, you can then go to the File menu, and select Import and then Import Library, navigate to the location of the libraries on the external drive and import them. Repeat for the second library.

Phil0124's method will import only pictures, not albums or folders. If albums and folders are important (how could they not be for such large libraries?) then using the trusted 3rd party app PowerPhotos ($40) is the only way to go that doesn't use iCloud. PowerPhotos is also useful lots of other things, especially multiple Libraries.

However, PipesSurf doesn't say if the Libraries are from the same version of Photos. If not, then either Photos or PowerPhotos would require that the older Library be upgraded to the newer version. Again, backups are important.

But iCloud Photos is the only way to work with different version Libraries. It takes longer than using PowerPhotos, though. Again, we can provide details if you need.

There are two ways to go:

1. Use PowerPhotos, which means you have to have space for both Libraries and, perhaps the merged one.
2. Use iCloud, which means you need lots of iCloud storage space.

You also need room for backups if you're at all prudent.

I haven no idea about your video.

To use iCloud, you connect one Library to iCloud, fill iCloud Photos with its contents, and then connect the other. The second Library would end up with the combined results, and there should be no exact duplicates. The two Libraries would be on external SSDs, so it seems like you have enough storage for that.

Do you need details?