iOS：如果视频太大，如何将视频压缩到预期的大小？

Question

如果太大，我想将视频压缩到预期的大小。例如，如果我的视频大于2mb，我想将它压缩到2mb旁边。我的目标不是拥有超过2mb的视频。

- (void)convertVideoToLowQualityWithInputURL:(NSURL*)inputURL 
                                   outputURL:(NSURL*)outputURL 
                                     handler:(void (^)(AVAssetExportSession*))handler
{
    [[NSFileManager defaultManager] removeItemAtURL:outputURL error:nil];
    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:inputURL options:nil];
    AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetLowQuality];
    exportSession.outputURL = outputURL;
    exportSession.outputFileType = AVFileTypeQuickTimeMovie;
    [exportSession exportAsynchronouslyWithCompletionHandler:^(void) 
    {
        handler(exportSession);
        [exportSession release];
    }];
}
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{   
    NSURL *videoURL = [info objectForKey:UIImagePickerControllerMediaURL];
    NSURL *outputURL = [NSURL fileURLWithPath:@"/Users/josh/Desktop/output.mov"];
    [self convertVideoToLowQualityWithInputURL:videoURL outputURL:outputURL handler:^(AVAssetExportSession *exportSession)
     {
         if (exportSession.status == AVAssetExportSessionStatusCompleted)
         {
             printf("completed\n");
         }
         else
         {
             printf("error\n");
         }
     }];
}

提前致谢。