NSString+MIMEType.h

#import <Foundation/Foundation.h>

@interface NSString (MIMEType)
- (NSString *)MIMEType;
- (NSString *)MIMEType2;
@end

NSString+MIMEType.m

#import "NSString+MIMEType.h"

#import <MobileCoreServices/MobileCoreServices.h>

@implementation NSString (MIMEType)

- (NSString *)MIMEType{
    if (![[NSFileManager defaultManager] fileExistsAtPath:self]) {
        return nil;
    }
    
    CFStringRef UTI = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (__bridge  CFStringRef)[self pathExtension], NULL);
    CFStringRef MIMEType = UTTypeCopyPreferredTagWithClass (UTI, kUTTagClassMIMEType);
    CFRelease(UTI);
    
    if (!MIMEType) {
        return @"application/octet-stream";
    }
    
    return (__bridge NSString *)MIMEType;
}

- (NSString *)MIMEType2{
    NSURLResponse *response = nil;
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL fileURLWithPath:self]];
    [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
    return response.MIMEType;
}

@end

NSLog(@"%@", [@"/Users/zhaoyingxin/Desktop/mimetype/test.mp4" MIMEType]);
NSLog(@"%@", [@"/Users/zhaoyingxin/Desktop/mimetype/test.png" MIMEType2]);

//2016-08-07 15:59:21.326 文件的MIMEType[56270:855419] video/mp4
//2016-08-07 15:59:21.358 文件的MIMEType[56270:855419] image/png

+ (NSString *)mimeTypeForFileAtPath:(NSString *)path{
    if (![[NSFileManager defaultManager] fileExistsAtPath:path]) {
        return nil;
    }
    
    CFStringRef UTI = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (__bridge  CFStringRef)[path pathExtension], NULL);
    CFStringRef MIMEType = UTTypeCopyPreferredTagWithClass (UTI, kUTTagClassMIMEType);
    CFRelease(UTI);
    
    if (!MIMEType) {
        return @"application/octet-stream";
    }
    
    return (__bridge NSString *)MIMEType;
}


- (void)MIMEType{
    //NSString *urlString = @"file:///Users/zhaoyingxin/Desktop/mimetype/test.mp4";
    //NSURL *url = [NSURL URLWithString:urlString];
    
    NSURL *url = [NSURL fileURLWithPath:@"/Users/zhaoyingxin/Desktop/mimetype/test.png"];
    
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    [NSURLConnection sendAsynchronousRequest:request
                                       queue:[NSOperationQueue mainQueue]
                           completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
                               NSLog(@"%@", response.MIMEType);
    }];
    
    NSURLResponse *response = nil;
    [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
    NSLog(@"%@", response.MIMEType);
}


NSLog(@"%@", [ViewController mimeTypeForFileAtPath:@"/Users/zhaoyingxin/Desktop/mimetype/test.png"]);
[self MIMEType];