title: linphone_call_take_video_snapshot saved empty file
body: <p>I am working on a project based on <strong>Linphone-iPhone</strong>, the project requires taking a snapshot of current video stream (both in and out). </p>
  
  <p>I've found this '<em>linphone_call_take_video_snapshot</em>' in liblinphone and gave it a try. 
  The code was simple and running without any error, but the size of the saved file is always <strong>0 kb</strong>! </p>
  
  <p>Here's the code:</p>
  
  <pre><code>- (void)capture {
      NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
      NSString *documentsDirectory = [paths objectAtIndex:0];
      NSString *file_path = [documentsDirectory stringByAppendingPathComponent:@"snapshot.jpeg"];
      LinphoneCall *call = linphone_core_get_current_call([LinphoneManager getLc]);
      const char *c_file_path = [file_path cStringUsingEncoding:NSUTF8StringEncoding];
      int ret = linphone_call_take_video_snapshot(call, c_file_path);
  
      if (ret &gt;= 0 &amp;&amp; [[NSFileManager defaultManager] fileExistsAtPath:file_path]) {
          UIImageWriteToSavedPhotosAlbum([UIImage imageWithContentsOfFile:file_path], nil,nil,nil);
      }
  }
  </code></pre>
  
  <p>Does <em>linphone_call_take_video_snapshot</em> really work? If so, what have I been doing wrong? </p>