Can you share code to reproduce the effect? If I only run a basic example like this one (clip.mp4 is the 30-second big buck bunny clip from medias/):

%%snakeviz
import moviepy as mp
clip = mp.VideoFileClip("clip.webm")
clip.write_videofile("output.mp4")

I get the following profile, where ~90% of the time is spent waiting for ffmpeg to encode the video. Yes 20 seconds to encode a 30-second clip is slow, but only a very small part of that is decorator inspection:

For audio-only I also get ~90% spent in IO with ffmpeg:

%%snakeviz
import moviepy as mp
clip = mp.VideoFileClip("clip.webm")
clip.audio.with_speed_scaled(0.2).write_audiofile("output.mp3")

Upon testing with the latest moviepy from pypi I too can't reproduce the performance problems, with either Python 3.10 or 3.12.

That example would have been good enough to reproduce, a plain reencode with no effects was making enough audio-related get_frame() calls to get bogged down with function inspection.

However I'm running on OS X now and don't have easy access to a Windows box. Maybe it's still a problem on Windows, or maybe something peculiar to my setup on that machine was making function inspection very expensive