Adding logos to mp4 with Avisynth

[Bencuri]

I would like to know if this one is still the recommended script for adding logos to videos?

a1=avisource("movie.avi")
a2=ImageReader("logo1.png")
a3=ImageReader("logo1.png",pixel_type="RGB32").ShowAlpha(pixel_type="RGB32")
Overlay(a1,a2,mask=a3)

I am not sure though if this will work because my color codes are these:

LWLibavVideoSource("video.mpg") 
ColorMatrix(mode="rec.601->rec.709")

I am converting to mp4. I want to know as well how to merge this adding logo command with my conversion code? This a1 a2... method is quite new to me.

This is my full code so far, the logo procedure should be added to this:

LWLibavVideoSource("video.mpg") 
ColorMatrix(mode="rec.601->rec.709")
Crop(0,8,-0,-0)
QTGMC()
SMDegrain(thsad=1000, tr=3, prefilter=4)
nnedi3_rpow2(2, cshift="Spline36Resize", fwidth=960, fheight=720)
aWarpSharp2(depth=5)
CAS(0.5)
nnedi3_rpow2(2, cshift="Spline36Resize")
CropResize(1920,1080,  CropDAR=4.0/3.0, Resizer="Resize8", Borders=true)
aWarpSharp2(depth=5)
CAS(0.5)
Prefetch(4)

I would like to add the logo to the top right corner in the black area of the letterbox.

[jagabo]

Something like:

LWLibavVideoSource("video.mpg") 
ColorMatrix(mode="rec.601->rec.709")
Crop(0,8,-0,-0)
QTGMC()
SMDegrain(thsad=1000, tr=3, prefilter=4)
nnedi3_rpow2(2, cshift="Spline36Resize", fwidth=960, fheight=720)
aWarpSharp2(depth=5)
CAS(0.5)
nnedi3_rpow2(2, cshift="Spline36Resize")
CropResize(1920,1080,  CropDAR=4.0/3.0, Resizer="Resize8", Borders=true)
aWarpSharp2(depth=5)
CAS(0.5)
a2=ImageReader("logo1.png")
a3=ImageReader("logo1.png",pixel_type="RGB32").ShowAlpha(pixel_type="RGB32")
Overlay(last,a2,mask=a3)

Prefetch(4)