How to make a movie constituted of image loops and audio?

I've wrote a procedure according to the Igor example FM Modulation Movie to make a movie constituted of image loops and audio. The experiment, procedure and pictures for the movie are in the attachment.

Macro MakeMovie(nframes,fRate,wAudio)
	Variable nframes=NumVarOrDefault("gnframes",10)
	Variable fRate=NumVarOrDefault("gwFPS",30)
	Variable wAudio=NumVarOrDefault("gwAudio",2)
	Prompt nframes,"Number of movie frames"
	Prompt fRate,"Frame rate"
	Prompt wAudio,"Sound:",popup "Off;On"
	
	Variable/G gnframes= nframes
	Variable/G gwFPS= fRate
	Variable/G gwAudio= wAudio
	
	DoMakeMovie(nframes,gwFPS,wAudio-1)
end

// returns error flag
Function ValidatePath()
	PathInfo moviesPath
	if( V_Flag==0 )
		NewPath/o/Q moviesPath,  SpecialDirPath("Igor Pro User Files", 0, 0, 0 )
		if( V_Flag != 0 )
			return 1		// abort or failure
		endif
	endif
	return 0
End
	

Function DoMakeMovie(nframes,fRate,wAudio)
	Variable nframes,fRate,wAudio
	wave scar
	Execute/Q "SetIgorOption VerboseMode=2"
	
	newpath/o IgorSpace, "F:"
	
	ValidatePath()
 
	String fName= "sampleMovie"
	String fExtension= ".mp4"
	
	Variable isMac= CmpStr(IgorInfo(2),"Macintosh") == 0

	Make/O/W/N=( 963332/fRate,2) yuanAudio
	SetScale/P x,0,20/ 963332,"s" yuanAudio
   
	variable i=0
	do 
	   int a=mod(i,4)
	   string nextImage = "pict"+num2str(a+1)+".bmp"
	   imageload /O/P=IgorSpace /T=bmp  nextimage
       duplicate/o $nextimage,w
	   redimension/n=(259,183,-1) w
       newimage /n=season/s=0 w
   
      if(i==0)  
	       if( wAudio)
		        fName += "Audio"
		        NewMovie/cf=1/O/F=(fRate)/P=moviesPath/S=yuanAudio as fName+fExtension
	       else
		        NewMovie/cf=1/O/F=(fRate)/P=moviesPath as fName+fExtension
	       endif
	       if( V_Flag!=0 )
		        Print "OpenMovie failed, err= ",V_Flag
		        return 0			// probably canceled
	       endif
	   endif
	   
	   doupdate
		AddMovieFrame
		killwindow season
		killwaves $nextimage
		if( V_Flag!=0 )
			Print "Add movie frame failed, err= ",V_Flag,", frame ",i
			if( isMac && wAudio )
				Print "Specifing sound may not work on Mac"
			endif
			break 
		endif
		
		i += 1
	while(i<nframes)
	if( wAudio )
			yuanAudio= scar[100000+p]
			AddMovieAudio/Z yuanAudio
			if( V_Flag!=0 )
				Print "Add movie audio failed, err= ",V_Flag 
			endif
	endif
	CloseMovie/Z
	if( V_Flag!=0 )
		Print "Close movie failed, err= ",V_Flag
	endif
	Sleep/S 1		// without this, Mac sometimes gives a file not a movie error; DoUpdate did not help
	PlayMovie/P=moviesPath as fName+fExtension
end

When I run this procedure it always turns out :

  Add movie frame failed, err=   1  , frame   1

I don't know where the error is.

And when I delete these lines in the procedure 

	if( V_Flag!=0 )

			Print "Add movie frame failed, err= ",V_Flag,", frame ",i

			if( isMac && wAudio )

				Print "Specifing sound may not work on Mac"

			endif

			break 	
       endif

the procedure can run as I expect but the image quality in the movie becomes worse with the loop number increasing.

Can someone help me?  My Igor version is Igor Pro 8.  The operating system version is win10 64 bit. I think the best value for nframes and fRate in the procedure are 20 and 1, respectively.

Thanks a lot!