获取保存在摄像头滚动iOS上的视频音频部分

我想把一段视频的音频文件保存到iPhone的照相/摄像机上。我有播放视频的代码，但我不知道如何获得实际的视频文件并从那里转换成mp3

这就是我目前所拥有的

 - (IBAction)PlayVideo:(id)sender {
[self startMediaBrowserFromViewController: self usingDelegate: self];
}

- (BOOL) startMediaBrowserFromViewController: (UIViewController*) controller
                           usingDelegate: (id <UIImagePickerControllerDelegate,
                                           UINavigationControllerDelegate>) delegate{

if (([UIImagePickerController isSourceTypeAvailable:
      UIImagePickerControllerSourceTypeSavedPhotosAlbum] == NO)
    || (delegate == nil)
    || (controller == nil))
    return NO;

UIImagePickerController *mediaUI = [[UIImagePickerController alloc] init];
mediaUI.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;

mediaUI.mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeMovie, nil];

mediaUI.allowsEditing = YES;

mediaUI.delegate = delegate;

[controller presentModalViewController: mediaUI animated: YES];
return YES;

}

 - (void) imagePickerControllerDidCancel: (UIImagePickerController *) picker {

[self dismissModalViewControllerAnimated: YES];
}

 - (void) imagePickerController: (UIImagePickerController *) picker
 didFinishPickingMediaWithInfo: (NSDictionary *) info {

NSString *mediaType = [info objectForKey: UIImagePickerControllerMediaType];

[self dismissModalViewControllerAnimated:NO];

if (CFStringCompare ((__bridge_retained CFStringRef)mediaType, kUTTypeMovie, 0)
    == kCFCompareEqualTo) {

    NSString *moviePath = [[info objectForKey:
                            UIImagePickerControllerMediaURL] path];
    MPMoviePlayerViewController* theMovie =
    [[MPMoviePlayerViewController alloc] initWithContentURL: [info objectForKey:
                                                              UIImagePickerControllerMediaURL]];
    [self presentMoviePlayerViewControllerAnimated:theMovie];

    [[NSNotificationCenter defaultCenter]
     addObserver: self
     selector: @selector(myMovieFinishedCallback:)
     name: MPMoviePlayerPlaybackDidFinishNotification
     object: theMovie];


}
}

-(void) myMovieFinishedCallback: (NSNotification*) aNotification
{
[self dismissMoviePlayerViewControllerAnimated];

MPMoviePlayerController* theMovie = [aNotification object];

[[NSNotificationCenter defaultCenter]
 removeObserver: self
 name: MPMoviePlayerPlaybackDidFinishNotification
 object: theMovie];
 }

-（iAction）播放视频：（id）发送方{
[自启动MediaBrowserFromViewController:self-usingDelegate:self]；
}
-（BOOL）startMediaBrowserFromViewController:（UIViewController*）控制器
usingDelegate:（id）delegate{
如果（（[UIImagePickerController]资源类型可用：
UIImagePickerControllerSourceTypeSavedPhotosAlbum]==否）
||（委托==零）
||（控制器==零）
返回否；
UIImagePickerController*mediaUI=[[UIImagePickerController alloc]init]；
mediaUI.sourceType=UIImagePickerControllerSourceTypeSavedPhotosAlbum；
mediaUI.mediaTypes=[[NSArray alloc]initWithObjects:（NSString*）KuttypeMoine，nil]；
mediaUI.allowsEditing=是；
mediaUI.delegate=委托；
[控制器显示ModalViewController:mediaUI动画：是]；
返回YES；
}
-（无效）ImagePickerController IDCancel:（UIImagePickerController*）选择器{
[自我解散Modalviewcontrolleranimated:是]；
}
-（无效）imagePickerController:（UIImagePickerController*）选择器
didFinishPickingMediaWithInfo:（NSDictionary*）信息{
NSString*mediaType=[info objectForKey:UIImagePickerControllerMediaType]；
[自我解散Modalviewcontrolleranimated:否]；
if（CFStringCompare（（uu桥u保留的CFStringRef）媒体类型，kUTTypeMovie，0）
==KCFComparequalto）{
NSString*moviePath=[[info objectForKey:
UIImagePickerControllerMediaURL]路径]；
MPMoviePlayerViewController*theMovie=
[[MPMoviePlayerViewController alloc]initWithContentURL:[info objectForKey:
UIImagePickerControllerMediaURL]]；
[自我呈现的电影播放服务控制器：theMovie]；
[[NSNotificationCenter defaultCenter]
addObserver:self
选择器：@selector（myMovieFinishedCallback:）
名称：MPMoviePlayerPlaybackDidFinishNotification
对象：theMovie]；
}
}
-（作废）myMovieFinishedCallback：（NSNotification*）通知
{
[self DismissionMoviePlayerServiceController]；
MPMoviePlayerController*theMovie=[aNotification object]；
[[NSNotificationCenter defaultCenter]
移除观察者：自我
名称：MPMoviePlayerPlaybackDidFinishNotification
对象：theMovie]；
}