无法将.mp4视频文件保存到iphone相机卷？

我收到了NSData格式的视频文件内容，并使用以下代码在MPMoviePlayerController中成功播放该文件

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];

NSString *FileExtension=[[NSString alloc]init];

if([contentType hasPrefix:@"video"] || [contentType isEqualToString:@"application/video"]) {
    FileExtension=@"mov";
   //FileExtension=@"mp4";
}
else
{
  FileExtension=[contentType lastPathComponent];
}

 //appFile is type of NSString.
 appFile = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"MyFile.%@",FileExtension]];

//videoData is type of NSData
[videoData writeToFile:appFile atomically:YES]; 

NSURL *fileURL = [NSURL fileURLWithPath:appFile isDirectory:NO];

moviePlayerController = [[MPMoviePlayerController alloc] initWithContentURL:fileURL];
moviePlayerController.view.frame = self.view.bounds;
moviePlayerController.movieSourceType = MPMovieSourceTypeFile;
moviePlayerController.fullscreen = YES;
moviePlayerController.shouldAutoplay=NO;

[self.view addSubview:moviePlayerController.view];
[moviePlayerController prepareToPlay];

但我无法将此视频文件写入/保存到相机卷，这是我将代码写入相机卷的代码

  ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
  NSURL *filePathURL = [NSURL fileURLWithPath:appFile isDirectory:NO];
  if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:filePathURL]) {
    [library writeVideoAtPathToSavedPhotosAlbum:filePathURL completionBlock:^(NSURL *assetURL, NSError *error){
        if (error) {
            NSLog(@"Not success");
        } else {
            NSLog(@"success");
        }
    }];

} 

---

当我将mimeType/file_格式设置为.mov和.3Gp时，这段代码可以正常工作，但当mimeType/file_格式设置为.mp4文件时，我遇到了将视频保存到相机卷的问题

如果通过以下方式更改应用文件，则可以将.mp4转换为.mov：

您的代码：

 appFile = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"MyFile.%@",FileExtension]];

新代码：

 appFile = [documentsDirectory stringByAppendingPathComponent:@"MyFile.mov"];

SO会自动将.mp4转换为.mov