利用AVFoundation框架实现视频格式转码，下面以mov转mp4为例：

/**mov转mp4格式*/
-(void)convertMovSourceURL:(NSURL \*)sourceUrl
{
    AVURLAsset \*avAsset = [AVURLAsset URLAssetWithURL:sourceUrl options:nil];
    NSArray \*compatiblePresets=[AVAssetExportSession exportPresetsCompatibleWithAsset:avAsset];
    //NSLog(@"%@",compatiblePresets);
    if ([compatiblePresets containsObject:AVAssetExportPresetHighestQuality]) {
        AVAssetExportSession \*exportSession=[[AVAssetExportSession alloc] initWithAsset:avAsset presetName:AVAssetExportPresetHighestQuality];
        NSDateFormatter \*formater=[[NSDateFormatter alloc] init];//用时间给文件全名
        [formater setDateFormat:@"yyyyMMddHHmmss"];
        NSString \*mp4Path=[[NSUserDefaults standardUserDefaults] objectForKey:@"kMP4FilePath"];
        NSString \*resultPath=[NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES)[0] stringByAppendingFormat:@"/output-%@.mp4", [formater stringFromDate:[NSDate date]]];
        
        exportSession.outputURL=[NSURL fileURLWithPath:resultPath];
        exportSession.outputFileType = AVFileTypeMPEG4;
        exportSession.shouldOptimizeForNetworkUse = YES;
        [exportSession exportAsynchronouslyWithCompletionHandler:^(void){
             switch (exportSession.status) {
                case AVAssetExportSessionStatusCancelled:
                     NSLog(@"AVAssetExportSessionStatusCancelled");
                     break;
                 case AVAssetExportSessionStatusUnknown:
                     NSLog(@"AVAssetExportSessionStatusUnknown");
                     break;
                 case AVAssetExportSessionStatusWaiting:
                     NSLog(@"AVAssetExportSessionStatusWaiting");
                     break;
                 case AVAssetExportSessionStatusExporting:
                     NSLog(@"AVAssetExportSessionStatusExporting");
                     break;
                 case AVAssetExportSessionStatusCompleted:
                 {
                     //NSLog(@"resultPath = %@",resultPath);
                     UIAlertController \*alert=[UIAlertController alertControllerWithTitle:@"提示" message:@"转换完成" preferredStyle:UIAlertControllerStyleAlert];
                     UIAlertAction \*confirm=[UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:nil];
                     [alert addAction:confirm];
                     [[UIApplication sharedApplication].keyWindow.rootViewController presentViewController:alert animated:YES completion:nil];
                     BOOL success=[[NSFileManager defaultManager]moveItemAtPath:resultPath toPath:[mp4Path stringByAppendingPathComponent:@"1.mp4"] error:nil];
                     if(success)
                     {
                         NSArray \*files=[[NSFileManager defaultManager] contentsOfDirectoryAtPath:mp4Path error:nil];
                         NSLog(@"%@",files);
                         NSLog(@"success");
                     }
                     
                     break;
                 }
                 case AVAssetExportSessionStatusFailed:
                     NSLog(@"AVAssetExportSessionStatusFailed");
                     break;
             }
         }];
    }
}

用法如下：

@interface ViewController ()<UIImagePickerControllerDelegate,UINavigationControllerDelegate>

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor=[UIColor whiteColor];
    self.navigationController.navigationBar.barStyle=UIBarStyleBlack;
    self.title=@"视屏格式转换";
    
    UIButton \*btn=[[UIButton alloc]initWithFrame:CGRectMake(0, 0, 100, 50)];
    [btn setTitle:@"转换" forState:UIControlStateNormal];
    btn.backgroundColor=[UIColor orangeColor];
    [self.view addSubview:btn];
    [btn addTarget:self action:@selector(convert:) forControlEvents:UIControlEventTouchUpInside];
    btn.center=self.view.center;
}
#pragma mark - UIImagePicker
-(void)imagePickerController:(UIImagePickerController \*)picker didFinishPickingMediaWithInfo:(NSDictionary \*)info
{
    NSURL \*videoURL=[info objectForKey:@"UIImagePickerControllerMediaURL"];
    //[ProgressHUD show:@"转换中..."];
    [self convertMovSourceURL:videoURL];
    [picker dismissViewControllerAnimated:YES completion:nil];
}
-(void)imagePickerControllerDidCancel:(UIImagePickerController \*)picker
{
    [picker dismissViewControllerAnimated:YES completion:nil];
}