How to assess mp4 video quality in code with macOS - cocoa

Question

Q1) How can I get video file details with macOS APIs?
Q2) How do I assess video quality of an mp4 file?
I need a program to separate a large archive of mp4 files based on the video quality - i.e., clarity, sharpness - roughly, where they'd appear along the TV spectrum of analog -> 720 -> 1080 -> 2/4k. In this case, audio, color levels, file size, CPU/GPU load, etc., are not considerations per se.
Q1) It is easy to find "natural" dimensions with AVPlayer. A bit more poking around (https://developer.apple.com/documentation/avfoundation/avpartialasyncproperty/3816116-formatdescriptions ), my files have "avc1" as the media subtype; I gather that means h264. Can't locate ways to get more details with Apple APIs, like bit rate, that even Quicktime Player provides.
Lots of info is available with ffprobe, so I added it to my program. You too can embed a CLI program that runs inside a macOS application in background - see code at bottom.
Q2) To a video noob, dimensions are the obvious first approximation for video quality ... and codec, but mine have previously been converted to h264. Then I consider bit rates from ffprobe.
For testing, I located two h264 files with same dimensions (1280, 720), bit depth (8), and similar file size, frame rate, duration, amount of motion, color content. To my eye, one of the two looks better, distinctly sharper; that file is smaller and has a lower video bit rate (20-40%), even when normalized for its slightly lower frame rate and duration.
From an info theory perspective, doesn't seem possible. I've learned codecs can provide "quality" optimizations during compression - way past my understanding - but I can't find, looking at the video stream data, indicators of any that would impact quality/sharpness. Nothing in per-frame and per-packet data from ffprobe stands out.
Are there any tell-tale signs I should look for? Is this a fool's errand?
Here's my swift hack to run ffprobe inside a macOS application (written with XC 13 on 11.6). If you know how to run a Process() that lives in /usr/bin/..., please post - I don't get the entitlements thing. (Aliases/links to home directory don't work.)
// takes a local fileURL and determines video properties using ffprobe
func runFFProbe(targetURL:URL){
func buildArguments(url:URL) -> [String] {
// for ffprobe introduction,see: https://ottverse.com/ffprobe-comprehensive-tutorial-with-examples/
// and for complete info: https://ffmpeg.org/ffprobe.html
var arguments:[String] = []
// note: don't interpolate URL paths - may have spaces in them
let argString = "-v error -hide_banner -of default=noprint_wrappers=0 -print_format flat -select_streams v:0 -show_entries stream=width,height,bit_rate,codec_name,codec_long_name,profile,codec_tag_string,time_base,avg_frame_rate,r_frame_rate,duration_ts,bits_per_raw_sample,nb_frames "
let _ = argString.split(separator: " ").map{arguments.append(String($0))}
// let _ suppresses compiler warning about unused result of map call
arguments.append(url.path) // spaces in URL path seem to be okay here
return arguments
}
let task = Process()
// task.executableURL = URL(fileURLWithPath: "/usr/local/bin/ffprobe")
// reports "doesn't exist", but really access is blocked by macOS :(
// statically-linked ffprobe is added to the app bundle
// downloadable here - https://evermeet.cx/ffmpeg/#sExtLib-ffprobe
task.executableURL = Bundle.main.url(forResource: "ffprobe", withExtension: nil)
task.arguments = buildArguments(url: targetURL)
let pipe = Pipe()
task.standardOutput = pipe // ffprobe writes console thru standardOutput
// (ffmpeg uses standardError)
let fh = pipe.fileHandleForReading
var cumulativeResults = "" // adds the result from each buffer dump
fh.waitForDataInBackgroundAndNotify() // setup handle for listening
// object must be specified when running multiple simultaneous calls
// otherwise every instance receives messages from all other filehandles too
NotificationCenter.default.addObserver(forName: .NSFileHandleDataAvailable, object: fh, queue: nil) {notif in
let closureFileHandle:FileHandle = notif.object as! FileHandle
// Get the data from the FileHandle
let data:Data = closureFileHandle.availableData
// print("received bytes: \(data.count)\n") // debugging
if data.count > 0 {
// re-arm fh for any addition data
fh.waitForDataInBackgroundAndNotify()
// append new data to the accumulator
let str = String(decoding: data, as: UTF8.self)
cumulativeResults += str
// optionally insert code here for intermediate reporting/parsing
// self.printToTextView(string: str)
}
}
task.terminationHandler = {task -> Void in
DispatchQueue.main.async(execute: {
// run the whole termination on the main queue
if task.terminationReason==Process.TerminationReason.exit {
// roll your own reporting method
self.printToTextView(string: targetURL.lastPathComponent)
self.printToTextView(string: targetURL.fileSizeString) //custom URL extension
self.printToTextView(string: cumulativeResults)
let str = "\nSuccess!\n"
self.printToTextView(string: str)
} else {
print("Task did not terminate properly")
// post an error in UI too
return
}
// successful conversion if this point is reached
}) // end dispatchqueue
} // end termination handler
do { try
task.run()
} catch let error as NSError {
print(error.localizedDescription)
// post in UI too
return
}
} // end runFFProbe()