How to add audio only to a video

I am using Vision.VideoFileWriter to write a video I need to add video frame from a file and add audio frame from another file But I always get this error Reported by vision.VideoFileWriter: Not enough input arguments; expected 2 (in addition to the object handle), got 1.

My code is the following:

while ~isDone(videofile)  

      [videoFrame] = step(videofile);      
      step(noisevideofile,videoFrame)                 
  end

release(noisevideofile);

noisevideofile.AudioInputPort=true;

while ~isDone(noiseaudiofile)

      [audio] = step(noiseaudiofile);      
      step(noisevideofile,audio);

end

release(videofile);
release(noiseaudiofile);

[Kaustubha Govind]

Could you also paste the code that instantiates videofile, noisevideofile and noiseaudiofile. It is not clear what System objects you are using for each.