Skip to main content

​
Overview

The BlurDissolve transition creates a distinctive effect where the first clip progressively blurs and fades out, while the second clip fades in sharply (without blur). This creates a dreamy, cinematic transition effect.
Unique feature: Unlike CrossFade and Dissolve, BlurDissolve does NOT require overlapping clips. It can work with consecutive clips or clips with gaps.

​
Constructor

from movielite import vtx

transition = vtx.BlurDissolve(duration, max_blur=21)

​
Parameters

​
duration
float
required
Duration of the blur dissolve effect in seconds. This controls how long the blur and fade transitions take.
​
max_blur
int
default:"21"
Maximum blur intensity (Gaussian kernel size). Must be an odd number. The blur progressively increases from 1 to this value during the transition.
  • Default: 21 (strong blur)
  • Range: Any odd integer ≥ 3
  • Auto-correction: Even values are automatically incremented to the next odd number
Blur intensity guide:
  • 3-7: Subtle blur
  • 9-15: Moderate blur
  • 17-25: Strong blur (default)
  • 27+: Very strong blur

​
Methods

​
apply()

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

​
Parameters

​
clip1
GraphicClip
required
The outgoing clip that will blur and fade out at the end. The blur+fade occurs during the last duration seconds of this clip.
​
clip2
GraphicClip
required
The incoming clip that will fade in sharply (no blur) at the beginning. The fade-in occurs during the first duration seconds of this clip.

​
Raises

  • ValueError: If clips are not in proper sequence (clip2 must start at or after clip1)

​
How It Works

​
Clip1 (Outgoing)

During the last duration seconds:
  1. Progressive blur: Gaussian blur kernel size increases from 1 to max_blur
  2. Fade out: Opacity decreases from 1.0 to 0.0
  3. Both effects happen simultaneously

​
Clip2 (Incoming)

During the first duration seconds:
  1. Fade in: Opacity increases from 0.0 to 1.0
  2. No blur: Remains sharp throughout

​
Visual Effect

The outgoing clip becomes progressively blurrier and transparent, creating a dreamy “out of focus” effect, while the incoming clip appears sharply.

​
Usage Examples

​
Basic Blur Dissolve (No Overlap Required)

from movielite import VideoClip, VideoWriter, vtx

# Clips can be consecutive (no overlap needed!)
clip1 = VideoClip("scene1.mp4", start=0, duration=5)
clip2 = VideoClip("scene2.mp4", start=5.0, duration=5)  # No overlap

# Apply blur dissolve with default blur intensity
transition = vtx.BlurDissolve(duration=1.0)
clip1.add_transition(clip2, transition)

total_duration = 10.0  # Full 5 + 5 seconds (no overlap to subtract)

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

clip1.close()
clip2.close()

​
Custom Blur Intensity

# Subtle blur (max_blur=9)
clip1 = VideoClip("scene1.mp4", start=0, duration=5)
clip2 = VideoClip("scene2.mp4", start=4.0, duration=5)  # 1s overlap (optional)

transition = vtx.BlurDissolve(duration=1.0, max_blur=9)
clip1.add_transition(clip2, transition)

# Very strong blur (max_blur=31)
transition = vtx.BlurDissolve(duration=1.5, max_blur=31)
clip1.add_transition(clip2, transition)

​
Slow, Dreamy Transition

# Longer duration with strong blur creates cinematic effect
clip1 = VideoClip("scene1.mp4", start=0, duration=8)
clip2 = VideoClip("scene2.mp4", start=8.0, duration=8)

# 2.5 second slow blur dissolve
transition = vtx.BlurDissolve(duration=2.5, max_blur=25)
clip1.add_transition(clip2, transition)

total_duration = 16.0

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

​
Multiple Blur Dissolves

# Create sequence with varying blur intensities
clip1 = VideoClip("scene1.mp4", start=0, duration=4)
clip2 = VideoClip("scene2.mp4", start=4.0, duration=4)
clip3 = VideoClip("scene3.mp4", start=8.0, duration=4)

# Vary the blur intensity for different effects
clip1.add_transition(clip2, vtx.BlurDissolve(duration=0.8, max_blur=15))
clip2.add_transition(clip3, vtx.BlurDissolve(duration=1.2, max_blur=25))

total_duration = 12.0

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

​
With Overlapping Clips

# BlurDissolve also works with overlapping clips
clip1 = VideoClip("scene1.mp4", start=0, duration=5)
clip2 = VideoClip("scene2.mp4", start=4.0, duration=5)  # 1s overlap

transition = vtx.BlurDissolve(duration=1.0, max_blur=21)
clip1.add_transition(clip2, transition)

# Account for overlap in total duration
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()

​
Image Slideshow with Blur Effect

from movielite import ImageClip, VideoWriter, vtx

# Create dreamy photo slideshow
images = [
    ImageClip("photo1.jpg", start=0, duration=3),
    ImageClip("photo2.jpg", start=3.0, duration=3),     # No overlap needed
    ImageClip("photo3.jpg", start=6.0, duration=3),
]

# Apply blur dissolve between images
for i in range(len(images) - 1):
    images[i].add_transition(images[i + 1], vtx.BlurDissolve(duration=0.8, max_blur=17))

total_duration = 9.0

writer = VideoWriter("slideshow.mp4", fps=30, size=images[0].size, duration=total_duration)
writer.add_clips(images)
writer.write()

​
Comparison with CrossFade/Dissolve

FeatureBlurDissolveCrossFade/Dissolve
Overlap requiredNo (works with consecutive clips)Yes (must overlap by at least duration)
Outgoing clip effectProgressive blur + fade outFade out only
Incoming clip effectFade in (sharp)Fade in only
Visual styleDreamy, cinematicClean, professional
Audio crossfadeNoYes

​
Blur Intensity Examples

Choosing the right max_blur value: 
# Subtle blur - good for professional/corporate videos
vtx.BlurDissolve(duration=1.0, max_blur=7)

# Moderate blur - balanced effect
vtx.BlurDissolve(duration=1.0, max_blur=15)

# Strong blur - default, good for most cases
vtx.BlurDissolve(duration=1.0, max_blur=21)

# Very strong blur - dramatic/artistic effect
vtx.BlurDissolve(duration=1.0, max_blur=31)
Higher max_blur values increase processing time as they require larger Gaussian kernel operations on each frame.

​
Common Use Cases

​
Dream Sequences

# Transition to dream/flashback with strong blur
real_scene = VideoClip("reality.mp4", start=0, duration=5)
dream_scene = VideoClip("dream.mp4", start=5.0, duration=8)

# Heavy blur for surreal effect
transition = vtx.BlurDissolve(duration=2.0, max_blur=35)
real_scene.add_transition(dream_scene, transition)

​
Time Passing Effect

# Show passage of time with blur
morning = VideoClip("morning.mp4", start=0, duration=4)
evening = VideoClip("evening.mp4", start=4.0, duration=4)

transition = vtx.BlurDissolve(duration=1.5, max_blur=21)
morning.add_transition(evening, transition)

​
Soft Photo Montage

# Gentle blur for photo montages
from movielite import ImageClip

photo1 = ImageClip("memory1.jpg", start=0, duration=4)
photo2 = ImageClip("memory2.jpg", start=4.0, duration=4)

# Soft blur for nostalgic feel
transition = vtx.BlurDissolve(duration=1.0, max_blur=13)
photo1.add_transition(photo2, transition)

​
Implementation Details

The blur dissolve is implemented using:
  1. Gaussian Blur: Applied using OpenCV’s cv2.GaussianBlur() with progressively increasing kernel size
  2. Kernel size calculation: Linearly interpolated from 1 to max_blur based on transition progress
  3. Opacity modification: Same fade-out/fade-in technique as CrossFade
  4. Transform function: Applied as a frame transform to clip1 during the last duration seconds
Source code reference: /home/daytona/workspace/source/src/movielite/vtx/blur_dissolve.py:15

​
Kernel Size Auto-Correction

Gaussian blur requires odd kernel sizes. The constructor automatically adjusts: 
# Even values are incremented
vtx.BlurDissolve(duration=1.0, max_blur=20)  # Becomes max_blur=21
vtx.BlurDissolve(duration=1.0, max_blur=14)  # Becomes max_blur=15

# Minimum value enforced
vtx.BlurDissolve(duration=1.0, max_blur=1)   # Becomes max_blur=3

​
Performance Considerations

Processing intensive: Blur operations are computationally expensive. Higher max_blur values and longer duration increase render time.
Optimization tips:
  • Use lower max_blur values (7-15) for faster rendering
  • Keep duration reasonable (0.5-2.0 seconds)
  • Consider reducing video resolution if render time is too long

​
See Also

Build docs developers (and LLMs) love

Get started for freeTalk to us