How to Speed Up a Video in MoviePy Without Errors: Apply MultiplySpeed via apply() or with_effects()

Learn to speed up video in MoviePy the right way: apply MultiplySpeed to a VideoFileClip and avoid the write_videofile AttributeError. With code examples.

Speeding up a video in MoviePy can be surprisingly tricky if you treat effects as if they were clips. A common trap is assigning MultiplySpeed directly to a variable and then calling write_videofile on it, which leads to an AttributeError. If you faced the message that a MultiplySpeed object has no write_videofile attribute, you’re in the right place.

Problem demonstration

The following snippet tries to accelerate a video but fails because the effect is not applied to the clip:

from moviepy import *
import moviepy.video.fx as vfx
from moviepy.video.fx import MultiplySpeed

# load and then mistakenly replace the clip with an effect object
media_in = VideoFileClip(r"xxx.mp4")
media_in = MultiplySpeed(2)
media_in.write_videofile("fast_export.mp4", codec="libx264")

This throws an AttributeError because the variable that previously held the clip now holds the effect instance.

What’s actually happening

MultiplySpeed is an effect. It doesn’t become a video; it must be applied to an existing clip. When you overwrite the clip variable with MultiplySpeed(2), you lose access to clip methods like write_videofile. The correct flow is to keep a real clip in the variable and apply the effect either via apply() or via with_effects() on the clip. The documentation describes applying the effect object with apply(), and the source code reveals that with_effects() on the clip is also available.

Working solution and corrected code

First approach: apply the effect object to the clip.

from moviepy import *
import moviepy.video.fx as vfx
from moviepy.video.fx import MultiplySpeed

source_clip = VideoFileClip(r"xxx.mp4")
faster_clip = MultiplySpeed(2).apply(source_clip)
faster_clip.write_videofile("output_fast.mp4", codec="libx264")

Alternative approach: attach the effect via with_effects() on the clip.

from moviepy import *
import moviepy.video.fx as vfx
from moviepy.video.fx import MultiplySpeed

src = VideoFileClip(r"xxx.mp4")
accelerated = src.with_effects([MultiplySpeed(2)])
accelerated.write_videofile("output_fast.mp4", codec="libx264")

Here is a practical variant that multiplies the speed by four and writes to a nested output path:

from moviepy import *
import moviepy.video.fx as vfx
from moviepy.video.fx import MultiplySpeed

video_pathname = r"xxxxxx.mp4"
base = VideoFileClip(video_pathname)
boosted = base.with_effects([MultiplySpeed(4)])
boosted.write_videofile("Random/output_fast.mp4", codec="libx264")

Why this matters

Understanding the boundary between “clip” and “effect” saves time and prevents confusing errors. You keep the clip’s API intact only if you maintain a proper VideoFileClip (or derived clip) and apply effects to it, not the other way around. Whether you prefer the explicit apply() on the effect or the concise with_effects() on the clip, both routes keep your pipeline predictable and your code readable.

Conclusion

When you need to speed up a video in MoviePy, don’t reassign your clip variable to an effect object. Load the clip, apply MultiplySpeed with apply() or with_effects(), and then render with write_videofile. This small distinction eliminates the AttributeError and keeps your processing chain clean and maintainable.