Avisynth subtitle() + zoom + overlay, is there any simpler way to do this?

[gzaloprgm]

Hi, I am trying to do this in AviSynth: static background + title zooming in.

I tried using "animate()" (as the wiki says) but the result of this is a really choppy zoom (I guess it is because of font sizes getting "snapped" to some values).

BlankClip(width=320, height=240)
return Animate(0,48,"Subtitle", "Hello, World!",160,120,0,99999,"Arial",0,
  \  "Hello, World!",25,130,0,99999,"Arial",48)

So then I searched and found a script called "KenBurnsEffect", which works nice. The problem is that I need to render the subtitle into a temporary surface (otherwise I get the effect in the background too), and subtitle() doesn't modify the alpha value of the pixels, so to blend it into the background, I need to create a mask.

bg = ImageSource("test.png", end=100, fps=30).convertToRGB32()

blank = BlankClip(length=100, width=640, height=360, pixel_type="RGB32", color=$000000, fps=30)
white = blank.Subtitle("Test Subtitle", x=320, y=180, size=40, text_color=$00FF00, halo_color=$000000, align=5)
alpha = blank.Subtitle("Test Subtitle", x=320, y=180, size=40, text_color=$FFFFFF, halo_color=$000000, align=5)
return Overlay(bg, white, mask=alpha)

The problem is that Overlay does "non pre-multiplied alpha" (aka Flat matte) blending, so the subtitles appear with a black outline (undesired):



My solution is to manually do the premultiplied alpha blending (using a multiply of the background with the inverse of the alpha and then an addition to the foreground):

bg = ImageSource("test.png", end=100, fps=30).convertToRGB32()

blank = BlankClip(length=100, width=640, height=360, pixel_type="RGB32", color=$000000, fps=30)
white = blank.Subtitle("Test Subtitle", x=320, y=180, size=40, text_color=$00FF00, halo_color=$000000, align=5)
alpha = blank.Subtitle("Test Subtitle", x=320, y=180, size=40, text_color=$FFFFFF, halo_color=$000000, align=5).invert("RGB")
return Overlay(Overlay(bg,alpha,mode="multiply"), white, mode="add")

This works perfectly, but I'm guessing there has to be a simpler way to perform that...

Thanks,
Gzaloprgm

[Cornucopia]

A workaround for jerkiness/positioning might be to uprez+uprateconvert the footage prior to adding the text/subs being animated, then downrezzing+downrateconverting after. Yes it is a quality compromise, but it will get you smooth sub-pixel positioning.

There are probably other workarounds as well...Gavino? jagabo?...

Scott

[Gavino]

This works perfectly, but I'm guessing there has to be a simpler way to perform that...

The problem is actually due to the way the halo_color interacts with the anti-aliasing performed by Subtitle().
The solution is to set the halo_color to the same as the text_color in the first Subtitle call.

bg = ImageSource("test.png", end=100, fps=30).convertToRGB32()
blank = BlankClip(length=100, width=640, height=360, pixel_type="RGB32", color=$000000, fps=30)
white = blank.Subtitle("Test Subtitle", x=320, y=180, size=40, text_color=$00FF00, halo_color=$00FF00, align=5)
alpha = blank.Subtitle("Test Subtitle", x=320, y=180, size=40, text_color=$FFFFFF, halo_color=$000000, align=5)
return Overlay(bg, white, mask=alpha)

Since you are using RGB, you could also replace the last line by (faster and better quality):
return Layer(bg, white.Mask(alpha))

Regarding the jerky zooming, use floating point instead of integer for the positions to allow the animation to perform a smooth interpolation and allow Subtitle to use sub-pixel positioning.

BlankClip(width=320, height=240)
return Animate(0,48,"Subtitle", "Hello, World!",160.0,120.0,0,99999,"Arial",0,
 \  "Hello, World!",25.0,130.0,0,99999,"Arial",48)

although there may still be jerkiness (in size) if fonts are not available for all point sizes.