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Fade effects create smooth transitions by animating the opacity of a clip over time. MovieLite provides two fade effects: FadeIn and FadeOut.

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FadeIn

Gradually increases opacity from 0 to the clip’s original opacity over the specified duration.

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Constructor

FadeIn(duration: float)
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duration
float
required
Duration of the fade in seconds, measured from the start of the clip.

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Example

from movielite import VideoClip, VideoWriter, vfx

clip = VideoClip("input.mp4")
clip.add_effect(vfx.FadeIn(duration=2.0))

writer = VideoWriter("output.mp4", fps=clip.fps, size=clip.size)
writer.add_clip(clip)
writer.write()
clip.close()

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How It Works

The FadeIn effect modifies the clip’s opacity function to create a gradual transition:
  • t < duration: Opacity = original_opacity × (t / duration)
  • t ≥ duration: Opacity = original_opacity (no change)
Source: src/movielite/vfx/fade.py:4-30

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FadeOut

Gradually decreases opacity from the clip’s original opacity to 0 over the specified duration.

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Constructor

FadeOut(duration: float)
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duration
float
required
Duration of the fade in seconds, measured from the end of the clip.

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Example

from movielite import VideoClip, VideoWriter, vfx

clip = VideoClip("input.mp4")
clip.add_effect(vfx.FadeOut(duration=1.5))

writer = VideoWriter("output.mp4", fps=clip.fps, size=clip.size)
writer.add_clip(clip)
writer.write()
clip.close()

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How It Works

The FadeOut effect modifies the clip’s opacity function:
  • t ≤ (clip_duration - duration): Opacity = original_opacity (no change)
  • t > (clip_duration - duration): Opacity = original_opacity × (1 - fade_progress)
Where fade_progress = (t - (clip_duration - duration)) / duration Source: src/movielite/vfx/fade.py:32-59

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Combining Fade Effects

You can apply both fade-in and fade-out to the same clip: 
clip = VideoClip("input.mp4")
clip.add_effect(vfx.FadeIn(duration=2.0))
clip.add_effect(vfx.FadeOut(duration=1.5))
Make sure the combined duration of fade-in and fade-out doesn’t exceed the clip duration, or they will overlap.

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With Other Effects

Fade effects work well with other visual effects: 
clip = VideoClip("input.mp4")

# Fade in with blur
clip.add_effect(vfx.FadeIn(1.0))
clip.add_effect(vfx.BlurIn(duration=1.0, max_intensity=15.0))

# Color adjustments
clip.add_effect(vfx.Saturation(1.3))
clip.add_effect(vfx.Vignette(intensity=0.5))

# Fade out
clip.add_effect(vfx.FadeOut(1.5))

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Technical Details

Fade effects modify the clip’s opacity function rather than manipulating pixel values directly. This makes them very efficient and allows them to work seamlessly with other effects.

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Implementation Notes

  • Fade effects wrap the existing opacity function with a time-based multiplier
  • The original opacity is preserved and multiplied by the fade factor
  • Linear interpolation is used for smooth transitions
  • No pixel-level operations are performed, making fades very fast

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See Also

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