Set resolution for the picamera, I use it to select the field of view, see https://picamera.readthedocs.io/en/release-1.12/fov.html

picam.swift

//
//  picam.swift
//  picam
//
//  Created by Marcello Seri on 31/05/2021.
//

import Foundation
import AVFoundation

let usage = """
picam
Set capture format for pi camera

USAGE:
    picam [FLAGS] <index>

FLAGS:
    -h --help   Prints help information
    -s --show   Prints available options and their indices

ARGS:
    <index>     Index of the option to select. Will enter into an interactive prompt if not present.

"""

func show_formats(_ formats: [AVCaptureDevice.Format]) {
    print("Compatible formats: ")
    for (idx, format) in formats.enumerated() {
        let desc = format.formatDescription
        let dimensions = CMVideoFormatDescriptionGetDimensions(desc)
        print("  \(idx). \(dimensions)")
    }
}

func apply_setting(_ picam: AVCaptureDevice, _ sel: Int) throws -> Bool {
    if sel >= 0 && sel < picam.formats.count {
        let format = picam.formats[sel]
        try picam.lockForConfiguration()
        picam.activeFormat = format
        picam.unlockForConfiguration()
        print("Setup completed\n")
        return true
    } else {
        print("Incorrect value\n")
        return false
    }
}

let arguments = CommandLine.arguments

if arguments.count > 2 {
    print(usage)
    exit(EXIT_FAILURE)
}

if arguments.count == 2 {
    switch arguments[1] {
    case "-h", "--help":
        print(usage)
        exit(EXIT_SUCCESS)
    default:
        // In all the other cases we need to have picam available
        break
    }
}

let ds = AVCaptureDevice.DiscoverySession.init(deviceTypes: [AVCaptureDevice.DeviceType.externalUnknown], mediaType: AVMediaType.video, position: AVCaptureDevice.Position.unspecified)
let picam = ds.devices.first(where: {device in return device.localizedName.hasPrefix("UVC")})

if let picam = picam {
    
    if arguments.count == 2 {
        switch arguments[1] {
        // Done above!
        // case "-h", "--help":
        //    print(usage)
        //    exit(EXIT_SUCCESS)
        case "-s", "--show":
            show_formats(picam.formats)
            exit(EXIT_SUCCESS)
        default:
            let sel = Int(arguments[1]) ?? -1
            if sel == -1 {
                print("Unparsable argument\n")
                print(usage)
                exit(EXIT_FAILURE)
            }
            if try apply_setting(picam, sel) {
                exit(EXIT_SUCCESS)
            } else {
                print("An error has occurred\n")
                exit(EXIT_FAILURE)
            }
        }
    }
    
    show_formats(picam.formats)
    print("Type 'q' or 'quit' to exit")
    
    while let input = readLine() {
        guard !["quit", "q"].contains(input) else {
            break
        }
        
        if let sel = Int(input.trimmingCharacters(in: .whitespacesAndNewlines)) {
            if !(try apply_setting(picam, sel)) {
                show_formats(picam.formats)
                print("Type 'q' or 'quit' to exit")
            }
        } else { print("Unparsable value\n") }
    }
    
} else {
    print("Unable to initialize pi camera\n")
    exit(EXIT_FAILURE)
}