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Overview

Dissolve is an alias for CrossFade with identical behavior. It smoothly blends from one clip to another by fading out the first clip while simultaneously fading in the second clip. This applies to both video (opacity) and audio (volume).
Dissolve and CrossFade are the same transition effect. Use whichever name you prefer - both produce identical results.
Requires overlapping clips: The clips must have overlapping time ranges with at least duration seconds of overlap.

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Constructor

from movielite import vtx

transition = vtx.Dissolve(duration)

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Parameters

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duration
float
required
Duration of the dissolve effect in seconds. The clips must overlap by at least this amount.

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Methods

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apply()

Apply the dissolve transition between two clips. 
transition.apply(clip1, clip2)

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Parameters

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clip1
GraphicClip
required
The outgoing clip that will fade out at the end. The fade-out occurs during the last duration seconds of this clip.
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clip2
GraphicClip
required
The incoming clip that will fade in at the beginning. The fade-in occurs during the first duration seconds of this clip.

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Raises

  • ValueError: If clips don’t have sufficient overlap for the transition duration
  • ValueError: If clips are not in proper sequence (clip2 must start after clip1)

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Usage Examples

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Basic Dissolve

from movielite import VideoClip, VideoWriter, vtx

# Create clips with 1 second overlap
clip1 = VideoClip("scene1.mp4", start=0, duration=5)
clip2 = VideoClip("scene2.mp4", start=4.0, duration=5)  # Starts 1s before clip1 ends

# Apply 1 second dissolve
transition = vtx.Dissolve(duration=1.0)
clip1.add_transition(clip2, transition)

# Calculate total duration accounting for overlap
total_duration = clip1.duration + clip2.duration - 1.0  # 9 seconds

writer = VideoWriter("output.mp4", fps=30, size=clip1.size, duration=total_duration)
writer.add_clips([clip1, clip2])
writer.write()

clip1.close()
clip2.close()

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Dissolve vs CrossFade (Identical)

These two examples produce exactly the same result: 
# Using Dissolve
clip1.add_transition(clip2, vtx.Dissolve(duration=0.5))

# Using CrossFade - produces identical output
clip1.add_transition(clip2, vtx.CrossFade(duration=0.5))

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Multiple Dissolves in Sequence

# Create three clips with overlaps
clip1 = VideoClip("scene1.mp4", start=0, duration=4)
clip2 = VideoClip("scene2.mp4", start=3.5, duration=4)  # 0.5s overlap
clip3 = VideoClip("scene3.mp4", start=7.0, duration=4)  # 0.5s overlap with clip2

# Apply dissolves between each pair
clip1.add_transition(clip2, vtx.Dissolve(duration=0.5))
clip2.add_transition(clip3, vtx.Dissolve(duration=0.5))

total_duration = 11.0  # 4 + 4 + 4 - 0.5 - 0.5

writer = VideoWriter("output.mp4", fps=30, size=clip1.size, duration=total_duration)
writer.add_clips([clip1, clip2, clip3])
writer.write()

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Dissolve with Image Clips

from movielite import ImageClip, VideoWriter, vtx

# Create image slideshow
img1 = ImageClip("photo1.jpg", start=0, duration=3)
img2 = ImageClip("photo2.jpg", start=2.5, duration=3)  # 0.5s overlap
img3 = ImageClip("photo3.jpg", start=5.0, duration=3)  # 0.5s overlap

# Apply dissolve transitions
img1.add_transition(img2, vtx.Dissolve(duration=0.5))
img2.add_transition(img3, vtx.Dissolve(duration=0.5))

total_duration = 7.5  # 3 + 3 + 3 - 0.5 - 0.5

writer = VideoWriter("slideshow.mp4", fps=30, size=img1.size, duration=total_duration)
writer.add_clips([img1, img2, img3])
writer.write()

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How It Works

The dissolve transition works identically to CrossFade:

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Video Dissolve

  1. Clip1 fade-out: During the last duration seconds, opacity gradually decreases from 1.0 to 0.0
  2. Clip2 fade-in: During the first duration seconds, opacity gradually increases from 0.0 to 1.0
  3. The overlapping region shows both clips blended together

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Audio Dissolve

If both clips are VideoClip instances with audio:
  1. Clip1 audio fade-out: Volume decreases at the end
  2. Clip2 audio fade-in: Volume increases at the beginning
  3. Creates smooth audio transition without abrupt cuts

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Common Errors

Insufficient overlap error
ValueError: Insufficient overlap for transition. 
Required overlap: 1.0s, actual overlap: 0.5s.
Solution: Adjust clip start times to ensure sufficient overlap. If the transition duration is 1.0s, clip2 must start at least 1.0s before clip1 ends.
No overlap error
ValueError: Clips do not overlap. 
Clip1 ends at 5.0s, but Clip2 starts at 5.0s.
Solution: Move clip2’s start time earlier. For example, if clip1 ends at 5.0s and you want a 1.0s dissolve, set clip2 to start at 4.0s.

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When to Use Dissolve vs CrossFade

Both names are valid and produce identical results:
  • Use CrossFade if you think of the effect as “cross-fading” between clips
  • Use Dissolve if you prefer traditional video editing terminology
  • Use either - they are functionally identical
In traditional video editing, “dissolve” and “crossfade” are often used interchangeably. MovieLite provides both names for convenience.

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Implementation Details

Dissolve is implemented as a direct subclass of CrossFade with no additional modifications: 
class Dissolve(CrossFade):
    """Dissolve transition (alias for CrossFade)."""
    pass
Source code reference: /home/daytona/workspace/source/src/movielite/vtx/dissolve.py:4

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See Also

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