Identify hexadecimal video not syncing to iPhone

If, for example, you get an uninformative alert like [because that iPad Pro 9,7" A9X 1st generation A1674 did not support 4K HEVC movies]:

“F0928C00-633E-42A4-BB3D-2001E36F017C.mov” was not copied to the iPad “matti’s iPad Pro” because it cannot be played on this iPad.

Some videos were not copied to the iPad “matti’s iPad Pro” because they cannot be played on this iPad.

Warning: Do not in any way modify contents of the Photos library package because might corrupt it! So work on a copy or at least make a backup.

Notice that this does not work on older macOS like AFAIR High Sierra:

First cd (change directory) to the Photos library's enclosing folder so the search is targeted there. Then in the Terminal you can search the offending file from Photos Library.photoslibrary recursively with a command like (paste the offending name to the command example):

find . -name F0928C00-633E-42A4-BB3D-2001E36F017C.mov

To find all files related to that movie you can use the following command with a wildcard:

find . -name 'F0928C00-633E-42A4-BB3D-2001E36F017C*'

which outputs something like:

/resources/derivatives/F/F0928C00-633E-42A4-BB3D-2001E36F017C_1_105_c.jpeg
/resources/derivatives/F/F0928C00-633E-42A4-BB3D-2001E36F017C_1_102_o.jpeg
/resources/derivatives/masters/F/F0928C00-633E-42A4-BB3D-2001E36F017C_4_5005_c.jpeg
/originals/F/F0928C00-633E-42A4-BB3D-2001E36F017C.mov

In this example *102_o* is the largest thumbnail, *105_c* smaller and *4_5005_c* the smallest thumbnail, and .mov the movie itself.

Then copy the any interesting file out from the library package elsewhere to further check it (with MediaInfo, Invisor, exiftool etc).

I used that a few years ago to spot movies with incompatible old codecs which I then re-encoded to be compatible.

Movie files usually have names like IMG_0012, so there can be lots of files in Photos that have the same name. Instead, Photos uses a GUID, a 128 bit global unique identifier. With 128 bits, there are 10³⁸ different possible names, so a random number generator is very very very (38 verys) unlikely to produce a duplicate name. Pretty cool.

Spotlight doesn't look for those names, since you're unlikely to remember them. But you can use the app Find Any File ($6) to hunt for a GUID. It's a handy app to have, in any case.

Once you find it, you can double click on it to see what movie it is. But here is a BIG WARNING: anything you do to change this file or to move it may corrupt the Photos database! This may not be fixable! So do this at your own risk! Just looking will be OK, but you might want to make a copy of your Library before messing with it!

Again, don't mess the the file itself. But once you know which one it is, you can avoid transferring it.