@Morgan_Hardwood while using your script with 422 material ffmpeg issued the advice
No pixel format specified, yuv422p for H.264 encoding chosen.
Use -pix_fmt yuv420p for compatibility with outdated media players.
Not saying that’s something wrong with the script 
, but as I wanted a 420 x264, added the before mentioned -pix_fmt yuv420p. Not problem with 10bit streams ( AFAIK x264 also supports 10 bit) which gets the 8bit frog-mask 
On a side note, while the extra info _libx264_23_slow might be useful say if one encodes with different parameters and wants to remember or compare different versions, on a practical scenario becomes “noise”; again this is just my personal view, but if I’m delivering a light copy to someone the extra long tail is confusing. I guess that changing ${cv}_${crf}_${preset} to just _copy or _x264 would do the trick. Nevertheless I felt like giving user feedback and thank you for sharing it =)
ffmpeg version 3.3
OSX 10.11.6
PS
Also had an error with libfdk_aac, but that was a missing library from ffmpeg’s compilation. brew install ffmpeg --with-fdk-aac solved it