[Python] Failed to add audio to mp4 with moviepy

I generated an audio sound.wav and a video temp.mp4 that makes use of the audio. Both with the same duration.

I got the following warning when generating the temp.mp4. The animation is out of sync, it means that it freezes before the audio finishes.

.venv\Lib\site-packages\moviepy\video\io\ffmpeg_reader.py:178: UserWarning: In file temp.mp4, 1080000 bytes wanted but 0 bytes read at frame index 299 (out of a total 300 frames), at time 4.98/5.00 sec. Using the last valid frame instead. warnings.warn(
​

Complete code:

# to generate sound.wav
import numpy as np
import soundfile as sf
from tqdm import tqdm
from os import startfile

# Parameters
filename = "sound.wav"
duration = 5 # seconds
num_voices = 1000
sample_rate = 44100 # Hz
chunk_size = sample_rate # write in 1-second chunks


t = np.linspace(0, duration, int(sample_rate * duration), endpoint=False)

# Create many detuned sine waves (Deep Note style)
start_freqs = np.random.uniform(100, 400, num_voices)
end_freqs = np.linspace(400, 800, num_voices) # target harmony

# Each voice sweeps from start to end frequency
signal = np.zeros_like(t)
for i in range(num_voices):
freqs = np.linspace(start_freqs, end_freqs, t.size)
voice = np.sin(2 * np.pi * freqs * t)
voice *= np.sin(np.pi * i / num_voices) # slight variance
signal += voice

# Volume envelope
envelope = np.linspace(0.01, 1.0, t.size)
signal *= envelope

# Normalize
signal /= np.max(np.abs(signal))

# Save with progress bar using soundfile
with sf.SoundFile(
filename, "w", samplerate=sample_rate, channels=1, subtype="PCM_16"
) as f:
for i in tqdm(range(0, len(signal), chunk_size), desc=f"Saving {filename}"):
f.write(signal[i : i + chunk_size])


startfile(filename)


# to generate temp.mp4
from numpy import pi, sin, cos
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
from os import startfile
from tqdm import tqdm
from moviepy import VideoFileClip, AudioFileClip, CompositeAudioClip

# Output settings
filename = "temp.mp4"
duration = 5 # seconds of animation
maxdim = 4 # canvas size in plot units (scaled)
fps = 60

# Real-world parameters
r = 40 # km (radius)
endtime = 2 # hours (duration of real motion)
rph = 0.5 # rotations per hour
omega = 2 * pi * rph # rad/hour
speed = omega * r # km/hour

# Animation setup
frames = duration * fps
scale = maxdim / r # scale from km to plot units
dt = endtime / frames # time per frame in hours

# Prepare figure and axes
fig, ax = plt.subplots(figsize=(6, 6))
ax.set_xlim(-maxdim - 1, maxdim + 1)
ax.set_ylim(-maxdim - 1, maxdim + 1)
ax.set_aspect("equal")
ax.grid()



# Plot circle path
circle = plt.Circle((0, 0), r * scale, color="lightgray", fill=False, linestyle="--")
ax.add_patch(circle)

# Moving point
(point,) = ax.plot([], [], "ro")

# Info text at center of the circle
info_text = ax.text(
0, 0, "", fontsize=10,
ha="center", va="center",
bbox=dict(boxstyle="round,pad=0.4", facecolor="white", alpha=0.8)
)


def init():
point.set_data([], [])
info_text.set_text("")
return point, info_text


def update(frame):
t = frame * dt # time in hours
theta = omega * t # angle in radians

x = r * cos(theta) * scale
y = r * sin(theta) * scale

point.set_data([x], [y])
info_text.set_text(
f"Time: {t:.2f} hr\nRadius: {r:.1f} km\nSpeed: {speed:.2f} km/h"
)
return point, info_text



# Create animation
anim = FuncAnimation(
fig, update, frames=frames, init_func=init, blit=True, interval=1000 / fps
)


with tqdm(total=frames, desc="Saving", unit="frame") as pbar:
anim.save(filename, fps=fps, progress_callback=lambda i, n: pbar.update(1))

# Add sound using MoviePy
video = VideoFileClip(filename)
video.audio = CompositeAudioClip([AudioFileClip("sound.wav")])
video.write_videofile(filename)

startfile(filename)


Could you figure out what the culprit is and how to fix it?



Edit


Based on the given comment, I did the following but the problem still exists.

# Add sound using MoviePy
video = VideoFileClip(filename)
audio = AudioFileClip("sound.wav")
audio.duration = video.duration
video.audio = CompositeAudioClip([audio])
video.write_videofile(filename)

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