How to effectibly use AVAsset and AVAssetExportSession to convert files between .mov and .m4v on Mac OS X using the "User Selected File Read/Write Access" entitlement

README.md

• Don't forget to link the (IBAction)doSelect: to some kind of button otherwise nothing will happen.

UNRAppDelegate.h

//
//  UNRAppDelegate.h
//

#import <Cocoa/Cocoa.h>
#import <AVFoundation/AVFoundation.h>

@interface UNRAppDelegate : NSObject <NSApplicationDelegate>

@property (assign)  IBOutlet NSWindow *window;
@property (weak)    IBOutlet NSButton *select;

-(IBAction)doSelect:(id)sender;
-(AVAsset*)getAsset:(NSString*)folder;

@end

UNRAppDelegate.m

//
//  UNRAppDelegate.m
//

#import "UNRAppDelegate.h"

@implementation UNRAppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
}

-(IBAction)doSelect:(id)sender
{
    // Create a File Open Dialog class.
    NSOpenPanel* dialog = [NSOpenPanel openPanel];
    
    // Setup options in the dialog.
    [dialog setCanChooseFiles:NO];
    [dialog setCanChooseDirectories:YES];
    [dialog setAllowsMultipleSelection:NO];
    
    if ([dialog runModal] == NSOKButton) {
        // Gets list of all files selected
        NSArray *files = [dialog URLs];
        
        // Get the asset
        NSString* aFolder = [files objectAtIndex:0];
        AVAsset* asset = [self getAsset:aFolder];
        
        // List compatible presets for the asset
        NSArray* compatiblePresets = [AVAssetExportSession exportPresetsCompatibleWithAsset:asset];
        NSLog(@"%@", compatiblePresets);
        
        // Is the asset readable?
        if ([asset isReadable]) {
            NSLog(@"The asset is readable, ok.");
        }
        else {
            NSLog(@"Bad news. You should probably perform a different action");
        }
        
        // Is the m4v SD compatible with the current asset?
        if ([compatiblePresets containsObject:AVAssetExportPresetAppleM4V480pSD]) {
            
            // Then, start the export session
            NSLog(@"Starting export session");
            AVAssetExportSession* session = [AVAssetExportSession exportSessionWithAsset:asset
                                                                      presetName:AVAssetExportPresetAppleM4V480pSD];
            NSString *outputFile = [NSString stringWithFormat:@"%@FILENAME.m4v", aFolder];
            NSURL *outputURL = [NSURL URLWithString:outputFile];
            session.outputURL = outputURL;
            session.outputFileType = AVFileTypeAppleM4V;
            
            NSLog(@"%@", session);
            [session exportAsynchronouslyWithCompletionHandler:^{
                
                switch ([session status]) {
                    case AVAssetExportSessionStatusFailed:
                        
                        NSLog(@"Export failed: %@", [[session error] localizedDescription]);
                        NSLog(@"%@", [[session error] localizedFailureReason]);
                        NSLog(@"%@", [[session error] localizedRecoveryOptions]);
                        NSLog(@"%@", [[session error] localizedRecoverySuggestion]);
                        break;
                    case AVAssetExportSessionStatusCancelled:
                        NSLog(@"Export canceled");
                        break;
                    default:
                        NSLog(@"Export succeded");
                        break;
                }
            }];

        }
        
        // If it is not compatible!
        else {
            // TODO should raise exception and send exception mail
        }
    }
}

-(AVAsset*)getAsset:(NSString*)folder
{
    // filePath
    NSString *filePath = [NSString stringWithFormat:@"%@FILENAME.mov", folder];
    NSURL *url = [NSURL URLWithString:filePath];
    
    // Build asset
    return [AVURLAsset URLAssetWithURL:url options:nil];
}

@end

Not pictured: how to read the folder in search for files. I leave that to you.