Application or Script to Batch Trim Video Clips - FFmpeg, QuickTime, etc

I need a simple application or script that will batch trim a specified number of frames off the beginning and/or end of a folder of video clips (.mov). This might need to use FFmpeg, QuickTime, Automator or other. Here's how this should work: 1. ask the user to select the source folder 2. ask how many frames to trim from the beginning of each video clip (default "4") 3. ask how many frames to trim from the end of each video clip (default "7") 4. and then select the destination folder. It would be good if the last numbers entered could be automatically saved as the default for next time. I also need this to automatically insert the letter "G" after the 6th character in each new filename. This needs to run natively on a Mac and all completed files need to be exactly the same as the source files except for the shorter length. The quality, format, codecs, data rate and compression cannot change from the source clips and it needs to work on files saved in the Apple ProRes 422 HQ codec. I work with thousands of very short video clips, which are each only about 5-30 seconds long. Each batch would usually be about 50 to 200 clips, but this needs to work on any quantity in a folder.