Mac: Batch rename (and renumber) files every n number of files

(macOS / Terminal question)

I am rendering frames of an animation sequence and need to slow down the whole thing to get sub-frame blur and composite each each final frame from four composited frames. This means extending the number of frames by 400%. However the software outputting the images can only output filenames sequentially and can't be instructed to group them.

The output for what will ultimately become 2 frames will look like this (8 frames):

Frame 1: 0001.png 0002.png 0003.png 0004.png

Frame 2: 0005.png 0006.png 0007.png 0008.png

To "stack" these in compositing, I need to remap them into "layers", let's call them A, B, C, D:

Frame 1: a0001.png b0001.png c0001.png d0001.png

Frame 2: a0002.png b0002.png c0002.png d0002.png

Then they could optionally be moved into folders quite easily, and composited from there:

<img src="https://i.stack.imgur.com/vM1JB.png" width="135"/>

The compositor will "step" according to the number in the file names. So as long as ABCD are aligned with the correct corresponding frame numbers, the problem is solved.

I have also installed a batch file renaming app called Transnomino, so if it's easier to do this using that app, I am open to doing it that way too. Or by using AppleScript in Automator, come to think of it. Thanks.

This should do both parts of what you need. The script makes some basic assumptions, e.g. that input files are names as in the question, e.g. "0001.png", but this is straightforward enough to change as required.

First, it creates output sorting folders on the desktop, inside a 'frames' folder. It looks in a folder named 'inputs' on the desktop for your source files. It asks for a count of how many to process but it could be set to just grab every file in the folder.

Next, it creates some lists: of frames (e.g. 0001, 0002), of frame file names (0001.png, 0002.png) and of prefixes (a, b, c, d).

It then cycles through each frame and determines which letter should be prepended to its file name, builds the new file name and renames the file (using System Events). Finally, it cycles through the prefixes and moves all matching files to the appropriate sorting folder (based on the first letter).

-- create frames destination folders
do shell script "cd ~/Desktop ; /bin/mkdir -p frames/{a,b,c,d}"
-- specify input and destination folders
set inputDir to (path to desktop) & "inputs:" as text
set frameDir to (path to desktop) & "frames:" as text

set padX to {"000", "00", "0"} -- pads out to 3 zeroes, e.g. 0001
set frameList to {}
set nameList to {}
set inputFrameCt to 4
set inpFr to display dialog "Enter number of input frames" default answer 4
set inputFrameCt to text returned of inpFr as integer

repeat with x from 1 to inputFrameCt
	set y to x as string -- 1 to frame count
	set zx to item (length of y) of padX & y --  4 characters, e.g. 0005
	set end of frameList to zx
	set end of nameList to zx & ".png"
end repeat
frameList -- list of frame numbers, does not include extension
nameList -- list of frame file names, includes extension

set preList to {"d", "a", "b", "c"} -- letter to prepend to file name
set fNameList to {} -- list of resulting file names

tell application "System Events"
	repeat with f in frameList -- cycle through frame numbers
		
		set inFile to inputDir & item f of nameList -- frame's path and name
		set pre to item (f mod 4 + 1) of preList -- get appropriate prefix
		set preName to pre & item f of nameList -- frame's resulting file name
		set end of fNameList to (pre & item f of nameList)
		
		set name of file inFile to preName -- rename file, e.g. 0001.png > a0001.png
	end repeat
	
	set letterList to {"a", "b", "c", "d"}
	repeat with l in letterList
		set lFiles to (disk items of folder inputDir whose name begins with l)
		move lFiles to folder l of folder frameDir -- move files based on prefix
	end repeat
end tell

NB The script uses x mod 4 to determine which of the letters to use as the prefix. Since every fourth number will result in 0, it adds 1 and moves 'd' to the beginning of the list.

Should you want to change the script in the future to account for a different ratio of frames, you could simply alter the various letter lists and change the mod value to match. It's easy enough to automate this so that you could just enter a single number and everything else would follow.

It is possible with Transnomino using "Reset every 4" in the numbering renaming action. You can set it to hexadecimal and start at 10 to let it create A, B, C, D for every 4 files.

• Location: At Beginning
• Format: Hexadecimal
• Start: 10
• Reset every: 4

This will rename:

00001.png
00002.png
00003.png
00004.png
00005.png
00006.png
00007.png
00008.png

to:

A00001.png
B00002.png
C00003.png
D00004.png
A00005.png
B00006.png
C00007.png
D00008.png

If it is important that you get for example:
A00001.png, A00002.png, A00003.png, A00004.png
instead of
A00001.png, A00005.png, A00009.png, A00013.png
you could trim the last digits of and add an additional numbering step using "Repeat 4":

• Location: At End
• Format: Decimal
• Digits: 4
• Repeat: 4

This would end up in something like this:

A00001.png
B00001.png
C00001.png
D00001.png
A00002.png
B00002.png
C00002.png
D00002.png

I have found one solution. There are probably better ways to do this, so I'm still open to other answers. But here's what has worked for me:

The following works because I have the option to skip frames when rendering. So I can set the frame step to 4 before rendering, set the output to /a/Image

It will give me Image0001.png, Image0005.png, etc within folder a

Increment the start frame by 1, and change the output path to /b/Image

It will produce Image0002.png, Image0006.png, etc within folder b

After that, I was able to use an app called NameChanger to rename the files in sequence. (This app allows control over the file order, unlike Automator.)

The file extensions get stripped in that step, but can easily be appended in a subsequent step:

Edit: I have since discovered that there is a setting in NameChanger's Preferences to hide extensions. With this enabled, extensions are left untouched by any renaming operations.

<img src="https://i.stack.imgur.com/IfDd6.png" width="300"/>