[Python] Minimizing video export time in Moviepy

I'm trying to export videos programmatically using Moviepy. The code below generates a video from input in the form of audio and image, and adds a zoom-out effect.

I'm using this program to generate very long (2.5+ h) videos and I'm looking to speed up the export. What are some ideas for achieving this? Thanks!

Moviepy version is 2.1.2 Pillow version is 9.5.0

# import
import math
import numpy

from PIL import Image

from moviepy import AudioFileClip, ImageClip, CompositeVideoClip
from moviepy.audio.fx import MultiplyVolume
from moviepy.video.fx import FadeOut


def generate_video(video_folder_path, audio_file_path, image_file_path, temp_path):

# define zoom effect function
def zoom_effect(clip, zoom_ratio=1.2):
def effect(get_frame, t):
img = Image.fromarray(get_frame(t))
base_size = img.size

new_size = [
math.ceil(img.size[0] * zoom_ratio * 1 / (1 - (t / clip.duration) * (1 - zoom_ratio))),
math.ceil(img.size[1] * zoom_ratio * 1 / (1 - (t / clip.duration) * (1 - zoom_ratio)))
]

img = img.resize(new_size, Image.LANCZOS)

x = math.ceil((new_size[0] - base_size[0]) / 2)
y = math.ceil((new_size[1] - base_size[1]) / 2)

img = img.crop([
x, y, new_size[0] - x, new_size[1] - y
]).resize(base_size, Image.LANCZOS)

result = numpy.array(img)
img.close()

return result

return clip.transform(effect)

# define export settings
audio_volume = 1
aspect_ratio = 16 / 9
z_ratio = 1.18
fade_out_duration = 1.15
export_fps = 24

# create clips
audio_clip = AudioFileClip(audio_file_path).with_effects([MultiplyVolume(audio_volume)])
image_clip = ImageClip(image_file_path, duration=audio_clip.duration).with_position(('center', 'center'))

# set dimensions
height = image_clip.size[1]
width = int(height * aspect_ratio)

# apply zoom effect
image_clip = zoom_effect(image_clip, z_ratio)

# compose
video_clip = CompositeVideoClip([image_clip], size=(width, height)).with_effects([FadeOut(fade_out_duration)])

# set audio
video_clip.audio = audio_clip

# write
video_clip.write_videofile(
video_folder_path + '/main_video.mp4', fps=export_fps,
temp_audiofile_path=temp_path, preset='ultrafast', threads=18)



Then, the function runs inside a for loop for every subdirectory in a directory:

for video_folder in sorted([f for f in os.scandir('path/to/directory')
if os.path.isdir(f)], key=lambda x: id_to_num(x.name)):
generate_video(video_folder.path)



I have tried different options for the parameters "preset" and "threads" in write_videofile. I'm guessing there is room for improvement with the zoom effect. Disabling the zoom effect results in circa 23 it/s increase. The rate is about 24 it/s with the zoom enabled.

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