Python GUI Video Volume Changer App | MoviePy + CustomTkinter Les

1. What We Are Building

We are building a Python desktop application that works like a small video editing utility. The user selects a video file, chooses the volume level, selects the output location, and exports a new video.

Input A video file such as MP4, MOV, AVI, MKV, or WEBM.

Processing MoviePy reads the video, scales the audio volume, and attaches the modified audio.

Output A new MP4 video file with changed volume.

Full forms: GUI means Graphical User Interface. MP4 means MPEG-4 Part 14. AAC means Advanced Audio Coding.

2. GUI Look and Layout

The application has a modern dark interface. The left side contains navigation, the middle area shows video information, and the right side contains the volume controls and export options.

Home

Open Video

Change Volume

Export

About

Video Volume Changer

Preview

Change Volume

150%

Mute | 50% | 100% | 150% | 200%

Checkpoint: At this stage, the student should understand what the app is supposed to do before touching the code.

3. Tools and Libraries Used

Tool	Full Form / Meaning	Use in This Project
Python	Programming language	Main language for the app
CustomTkinter	Modern styled Tkinter framework	Creates the desktop GUI
MoviePy	Python video editing library	Reads video and changes audio volume
Threading	Running work in a separate thread	Keeps GUI responsive while exporting
OS module	Operating System utilities	Handles file paths and file names

4. Project Setup

First, create a project folder. Then install the required Python libraries.

Terminal command

mkdir video-volume-changer
cd video-volume-changer
pip install customtkinter moviepy pillow

Recommended Folder Structure

Folder structure

video-volume-changer/
│
├── video_volume_changer_gui.py
│
├── input/
│   └── sample-video.mp4
│
└── output/
    └── final-video.mp4

Checkpoint: Type python --version. You should see your installed Python version. Then type pip show moviepy. You should see MoviePy details.

5. The Core Logic

The most important part of the app is simple. We open the video file, get the audio track, scale the volume, attach the new audio to the video, and export the result.

Core MoviePy logic

from moviepy import VideoFileClip

video = VideoFileClip("input.mp4")

volume_factor = 1.5
new_audio = video.audio.with_volume_scaled(volume_factor)

final_video = video.with_audio(new_audio)

final_video.write_videofile(
    "output.mp4",
    codec="libx264",
    audio_codec="aac"
)

video.close()
final_video.close()

Important idea: 100% volume means factor 1.0. 50% means factor 0.5. 150% means factor 1.5. 200% means factor 2.0.

6. Full Python GUI App Code

Create a file named video_volume_changer_gui.py and paste the following complete code.

video_volume_changer_gui.py

import os
import threading
import tkinter as tk
from tkinter import filedialog, messagebox

import customtkinter as ctk
from moviepy import VideoFileClip


ctk.set_appearance_mode("dark")
ctk.set_default_color_theme("blue")


class VideoVolumeChangerApp(ctk.CTk):
    def __init__(self):
        super().__init__()

        self.title("Video Volume Changer")
        self.geometry("1200x720")
        self.minsize(1050, 650)

        self.video_path = None
        self.output_folder = None
        self.volume_percent = tk.IntVar(value=100)

        self.build_ui()

    def build_ui(self):
        self.configure(fg_color="#07111f")

        self.grid_columnconfigure(0, weight=0)
        self.grid_columnconfigure(1, weight=1)
        self.grid_rowconfigure(1, weight=1)

        self.create_title_bar()
        self.create_sidebar()
        self.create_main_area()
        self.create_status_bar()

    def create_title_bar(self):
        self.title_bar = ctk.CTkFrame(
            self,
            height=58,
            fg_color="#1d2366",
            corner_radius=0
        )
        self.title_bar.grid(row=0, column=0, columnspan=2, sticky="ew")
        self.title_bar.grid_columnconfigure(0, weight=1)

        title = ctk.CTkLabel(
            self.title_bar,
            text="🔊  Video Volume Changer",
            font=("Segoe UI", 24, "bold"),
            text_color="white"
        )
        title.grid(row=0, column=0, padx=24, pady=12, sticky="w")

    def create_sidebar(self):
        self.sidebar = ctk.CTkFrame(
            self,
            width=170,
            fg_color="#0d1b31",
            corner_radius=0
        )
        self.sidebar.grid(row=1, column=0, sticky="ns")
        self.sidebar.grid_propagate(False)

        buttons = [
            ("🏠  Home", self.show_home),
            ("📁  Open Video", self.select_video),
            ("🔊  Change Volume", self.focus_volume),
            ("📄  Export", self.export_video_start),
            ("ℹ️  About", self.show_about),
        ]

        for i, (text, command) in enumerate(buttons):
            btn = ctk.CTkButton(
                self.sidebar,
                text=text,
                command=command,
                height=48,
                corner_radius=10,
                fg_color="#7c3aed" if i == 0 else "transparent",
                hover_color="#6d28d9",
                text_color="white",
                font=("Segoe UI", 15),
                anchor="w"
            )
            btn.pack(fill="x", padx=12, pady=(42 if i == 0 else 12, 0))

    def create_main_area(self):
        self.main = ctk.CTkFrame(
            self,
            fg_color="#07111f",
            corner_radius=0
        )
        self.main.grid(row=1, column=1, sticky="nsew", padx=20, pady=20)

        self.main.grid_columnconfigure(0, weight=1)
        self.main.grid_columnconfigure(1, weight=1)
        self.main.grid_rowconfigure(0, weight=1)

        self.left_panel = ctk.CTkFrame(self.main, fg_color="#07111f")
        self.left_panel.grid(row=0, column=0, sticky="nsew", padx=(0, 10))

        self.right_panel = ctk.CTkFrame(self.main, fg_color="#07111f")
        self.right_panel.grid(row=0, column=1, sticky="nsew", padx=(10, 0))

        self.create_preview_section()
        self.create_file_info_section()
        self.create_volume_section()
        self.create_output_section()

    def section_title(self, parent, text):
        label = ctk.CTkLabel(
            parent,
            text=f"▌ {text}",
            font=("Segoe UI", 20, "bold"),
            text_color="white"
        )
        label.pack(anchor="w", pady=(0, 12))

    def create_preview_section(self):
        preview_container = ctk.CTkFrame(self.left_panel, fg_color="transparent")
        preview_container.pack(fill="x", pady=(0, 18))

        self.section_title(preview_container, "Preview")

        self.preview_box = ctk.CTkFrame(
            preview_container,
            height=340,
            fg_color="#101c31",
            border_width=1,
            border_color="#263855",
            corner_radius=12
        )
        self.preview_box.pack(fill="x")
        self.preview_box.pack_propagate(False)

        self.preview_label = ctk.CTkLabel(
            self.preview_box,
            text="No video selected\n\nClick Open Video to choose a file",
            font=("Segoe UI", 18),
            text_color="#b8c4d9"
        )
        self.preview_label.pack(expand=True)

        controls = ctk.CTkFrame(self.preview_box, fg_color="transparent")
        controls.pack(fill="x", padx=16, pady=14)

        play_btn = ctk.CTkButton(
            controls,
            text="▶",
            width=48,
            height=40,
            corner_radius=8,
            fg_color="#1b2a44",
            hover_color="#263855"
        )
        play_btn.pack(side="left", padx=(0, 10))

        stop_btn = ctk.CTkButton(
            controls,
            text="■",
            width=48,
            height=40,
            corner_radius=8,
            fg_color="#1b2a44",
            hover_color="#263855"
        )
        stop_btn.pack(side="left", padx=(0, 14))

        self.fake_progress = ctk.CTkSlider(
            controls,
            from_=0,
            to=100,
            number_of_steps=100,
            progress_color="#8b5cf6",
            button_color="#a78bfa",
            button_hover_color="#c4b5fd"
        )
        self.fake_progress.set(20)
        self.fake_progress.pack(side="left", fill="x", expand=True, padx=(0, 14))

        self.time_label = ctk.CTkLabel(
            controls,
            text="00:00:00 / 00:00:00",
            font=("Segoe UI", 13),
            text_color="white"
        )
        self.time_label.pack(side="right")

    def create_file_info_section(self):
        info_container = ctk.CTkFrame(self.left_panel, fg_color="transparent")
        info_container.pack(fill="x")

        self.section_title(info_container, "File Information")

        self.info_box = ctk.CTkFrame(
            info_container,
            fg_color="#101c31",
            border_width=1,
            border_color="#263855",
            corner_radius=12
        )
        self.info_box.pack(fill="x", ipady=18)

        self.file_name_label = self.info_row(self.info_box, "📄 File Name:", "-")
        self.duration_label = self.info_row(self.info_box, "⏱ Duration:", "-")
        self.format_label = self.info_row(self.info_box, "🧾 Format:", "-")
        self.resolution_label = self.info_row(self.info_box, "▣ Resolution:", "-")
        self.size_label = self.info_row(self.info_box, "💾 Size:", "-")
        self.audio_label = self.info_row(self.info_box, "🔊 Audio:", "-")

    def info_row(self, parent, label_text, value_text):
        row = ctk.CTkFrame(parent, fg_color="transparent")
        row.pack(fill="x", padx=22, pady=7)

        label = ctk.CTkLabel(
            row,
            text=label_text,
            width=120,
            anchor="w",
            font=("Segoe UI", 14),
            text_color="#dbe5f5"
        )
        label.pack(side="left")

        value = ctk.CTkLabel(
            row,
            text=value_text,
            anchor="w",
            font=("Segoe UI", 14),
            text_color="white"
        )
        value.pack(side="left", fill="x", expand=True)

        return value

    def create_volume_section(self):
        volume_container = ctk.CTkFrame(self.right_panel, fg_color="transparent")
        volume_container.pack(fill="x", pady=(0, 22))

        self.section_title(volume_container, "Change Volume")

        self.volume_box = ctk.CTkFrame(
            volume_container,
            fg_color="#101c31",
            border_width=1,
            border_color="#263855",
            corner_radius=12
        )
        self.volume_box.pack(fill="x", ipady=18)

        label = ctk.CTkLabel(
            self.volume_box,
            text="Volume:",
            font=("Segoe UI", 18),
            text_color="#e5ecf8"
        )
        label.pack(anchor="w", padx=22, pady=(10, 5))

        self.big_volume_label = ctk.CTkLabel(
            self.volume_box,
            text="100%",
            font=("Segoe UI", 56, "bold"),
            text_color="white"
        )
        self.big_volume_label.pack(pady=(10, 0))

        sub = ctk.CTkLabel(
            self.volume_box,
            text="Volume",
            font=("Segoe UI", 22, "bold"),
            text_color="#a855f7"
        )
        sub.pack()

        self.volume_slider = ctk.CTkSlider(
            self.volume_box,
            from_=0,
            to=300,
            number_of_steps=300,
            progress_color="#8b5cf6",
            button_color="#a78bfa",
            button_hover_color="#c4b5fd",
            command=self.on_volume_change
        )
        self.volume_slider.set(100)
        self.volume_slider.pack(fill="x", padx=28, pady=(30, 8))

        scale_row = ctk.CTkFrame(self.volume_box, fg_color="transparent")
        scale_row.pack(fill="x", padx=28)

        ctk.CTkLabel(scale_row, text="0%", text_color="white").pack(side="left")
        ctk.CTkLabel(scale_row, text="100%\nOriginal", text_color="white").pack(
            side="left",
            expand=True
        )
        ctk.CTkLabel(scale_row, text="300%", text_color="white").pack(side="right")

        preset_row = ctk.CTkFrame(self.volume_box, fg_color="transparent")
        preset_row.pack(fill="x", padx=22, pady=(22, 4))

        presets = [
            ("🔇 Mute", 0),
            ("50%", 50),
            ("100%", 100),
            ("150%", 150),
            ("200%", 200),
        ]

        for text, value in presets:
            btn = ctk.CTkButton(
                preset_row,
                text=text,
                command=lambda v=value: self.set_volume(v),
                height=42,
                fg_color="#15233a" if value != 150 else "#7c3aed",
                hover_color="#6d28d9",
                border_width=1,
                border_color="#334663",
                corner_radius=8,
                font=("Segoe UI", 14, "bold")
            )
            btn.pack(side="left", expand=True, fill="x", padx=5)

    def create_output_section(self):
        output_container = ctk.CTkFrame(
            self.right_panel,
            fg_color="#101c31",
            border_width=1,
            border_color="#263855",
            corner_radius=12
        )
        output_container.pack(fill="x", ipady=18)

        title = ctk.CTkLabel(
            output_container,
            text="Output",
            font=("Segoe UI", 20, "bold"),
            text_color="white"
        )
        title.pack(anchor="w", padx=22, pady=(12, 14))

        file_row = ctk.CTkFrame(output_container, fg_color="transparent")
        file_row.pack(fill="x", padx=22, pady=6)

        ctk.CTkLabel(
            file_row,
            text="Output File:",
            width=110,
            anchor="w",
            font=("Segoe UI", 14),
            text_color="#dbe5f5"
        ).pack(side="left")

        self.output_file_entry = ctk.CTkEntry(
            file_row,
            height=38,
            fg_color="#15233a",
            border_color="#334663",
            text_color="white"
        )
        self.output_file_entry.pack(side="left", fill="x", expand=True, padx=(10, 10))

        browse_file_btn = ctk.CTkButton(
            file_row,
            text="Browse",
            width=90,
            height=38,
            fg_color="#15233a",
            hover_color="#263855",
            border_width=1,
            border_color="#7c3aed",
            command=self.choose_output_file
        )
        browse_file_btn.pack(side="right")

        folder_row = ctk.CTkFrame(output_container, fg_color="transparent")
        folder_row.pack(fill="x", padx=22, pady=12)

        ctk.CTkLabel(
            folder_row,
            text="Save To:",
            width=110,
            anchor="w",
            font=("Segoe UI", 14),
            text_color="#dbe5f5"
        ).pack(side="left")

        self.output_folder_entry = ctk.CTkEntry(
            folder_row,
            height=38,
            fg_color="#15233a",
            border_color="#334663",
            text_color="white"
        )
        self.output_folder_entry.pack(side="left", fill="x", expand=True, padx=(10, 10))

        browse_folder_btn = ctk.CTkButton(
            folder_row,
            text="Browse",
            width=90,
            height=38,
            fg_color="#15233a",
            hover_color="#263855",
            border_width=1,
            border_color="#7c3aed",
            command=self.choose_output_folder
        )
        browse_folder_btn.pack(side="right")

        self.export_btn = ctk.CTkButton(
            output_container,
            text="⬆  Export Video",
            height=54,
            corner_radius=10,
            fg_color="#7c3aed",
            hover_color="#6d28d9",
            font=("Segoe UI", 18, "bold"),
            command=self.export_video_start
        )
        self.export_btn.pack(fill="x", padx=22, pady=(18, 4))

    def create_status_bar(self):
        self.status_bar = ctk.CTkFrame(
            self,
            height=48,
            fg_color="#07111f",
            corner_radius=0
        )
        self.status_bar.grid(row=2, column=0, columnspan=2, sticky="ew")
        self.status_bar.grid_columnconfigure(0, weight=1)

        self.status_label = ctk.CTkLabel(
            self.status_bar,
            text="✅ Ready",
            font=("Segoe UI", 15),
            text_color="#6ee787"
        )
        self.status_label.grid(row=0, column=0, sticky="w", padx=190, pady=10)

        self.progress = ctk.CTkProgressBar(
            self.status_bar,
            width=260,
            progress_color="#8b5cf6"
        )
        self.progress.grid(row=0, column=1, padx=25)
        self.progress.set(0)

    def show_home(self):
        self.set_status("✅ Ready", "#6ee787")

    def focus_volume(self):
        self.volume_slider.focus()

    def show_about(self):
        messagebox.showinfo(
            "About",
            "Video Volume Changer\n\n"
            "A simple Python GUI app made with CustomTkinter and MoviePy.\n\n"
            "Use it to mute, reduce, or increase video volume."
        )

    def select_video(self):
        path = filedialog.askopenfilename(
            title="Select Video",
            filetypes=[
                ("Video Files", "*.mp4 *.mov *.avi *.mkv *.webm"),
                ("All Files", "*.*")
            ]
        )

        if not path:
            return

        self.video_path = path
        self.output_folder = os.path.dirname(path)

        name = os.path.basename(path)
        base, _ = os.path.splitext(name)
        output_name = f"{base}_volume_{self.volume_percent.get()}.mp4"

        self.output_file_entry.delete(0, "end")
        self.output_file_entry.insert(0, output_name)

        self.output_folder_entry.delete(0, "end")
        self.output_folder_entry.insert(0, self.output_folder)

        self.load_video_info(path)
        self.set_status("✅ Video loaded", "#6ee787")

    def load_video_info(self, path):
        try:
            clip = VideoFileClip(path)

            duration_seconds = int(clip.duration or 0)
            video_duration = self.format_time(duration_seconds)

            width, height = clip.size
            video_resolution = f"{width} x {height}"

            file_size_mb = os.path.getsize(path) / (1024 * 1024)
            video_size = f"{file_size_mb:.1f} MB"

            ext = os.path.splitext(path)[1].replace(".", "").upper()

            if clip.audio is None:
                video_audio = "No audio track"
            else:
                video_audio = "Audio detected"

            clip.close()

            self.file_name_label.configure(text=os.path.basename(path))
            self.duration_label.configure(text=video_duration)
            self.format_label.configure(text=ext)
            self.resolution_label.configure(text=video_resolution)
            self.size_label.configure(text=video_size)
            self.audio_label.configure(text=video_audio)

            self.time_label.configure(text=f"00:00:00 / {video_duration}")

            self.preview_label.configure(
                text=f"Video Selected\n\n{os.path.basename(path)}\n\nPreview area"
            )

        except Exception as e:
            messagebox.showerror("Error", f"Could not read video:\n{e}")

    def on_volume_change(self, value):
        value = int(float(value))
        self.volume_percent.set(value)
        self.big_volume_label.configure(text=f"{value}%")
        self.update_output_name()

    def set_volume(self, value):
        self.volume_slider.set(value)
        self.volume_percent.set(value)
        self.big_volume_label.configure(text=f"{value}%")
        self.update_output_name()

    def update_output_name(self):
        if not self.video_path:
            return

        base = os.path.splitext(os.path.basename(self.video_path))[0]
        output_name = f"{base}_volume_{self.volume_percent.get()}.mp4"

        self.output_file_entry.delete(0, "end")
        self.output_file_entry.insert(0, output_name)

    def choose_output_folder(self):
        folder = filedialog.askdirectory(title="Choose Output Folder")

        if folder:
            self.output_folder = folder
            self.output_folder_entry.delete(0, "end")
            self.output_folder_entry.insert(0, folder)

    def choose_output_file(self):
        path = filedialog.asksaveasfilename(
            title="Choose Output File",
            defaultextension=".mp4",
            filetypes=[
                ("MP4 Video", "*.mp4"),
                ("All Files", "*.*")
            ]
        )

        if path:
            folder = os.path.dirname(path)
            filename = os.path.basename(path)

            self.output_folder = folder

            self.output_folder_entry.delete(0, "end")
            self.output_folder_entry.insert(0, folder)

            self.output_file_entry.delete(0, "end")
            self.output_file_entry.insert(0, filename)

    def export_video_start(self):
        if not self.video_path:
            messagebox.showerror("Error", "Please select a video first.")
            return

        output_file = self.output_file_entry.get().strip()
        output_folder = self.output_folder_entry.get().strip()

        if not output_file:
            messagebox.showerror("Error", "Please enter output file name.")
            return

        if not output_folder:
            messagebox.showerror("Error", "Please select output folder.")
            return

        if not output_file.lower().endswith(".mp4"):
            output_file += ".mp4"

        output_path = os.path.join(output_folder, output_file)

        self.export_btn.configure(state="disabled", text="Processing...")
        self.progress.set(0.2)
        self.set_status("🔄 Processing video...", "#93c5fd")

        thread = threading.Thread(
            target=self.export_video,
            args=(self.video_path, output_path, self.volume_percent.get()),
            daemon=True
        )
        thread.start()

    def export_video(self, input_path, output_path, volume_percent):
        try:
            video = VideoFileClip(input_path)

            if video.audio is None:
                self.after(0, self.export_failed, "This video has no audio track.")
                return

            volume_factor = volume_percent / 100

            new_audio = video.audio.with_volume_scaled(volume_factor)
            final_video = video.with_audio(new_audio)

            self.after(0, lambda: self.progress.set(0.5))

            final_video.write_videofile(
                output_path,
                codec="libx264",
                audio_codec="aac",
                fps=video.fps,
                logger=None
            )

            video.close()
            final_video.close()

            self.after(0, self.export_success, output_path)

        except Exception as e:
            self.after(0, self.export_failed, str(e))

    def export_success(self, output_path):
        self.progress.set(1)
        self.export_btn.configure(state="normal", text="⬆  Export Video")
        self.set_status("✅ Export complete", "#6ee787")

        messagebox.showinfo(
            "Success",
            f"New video saved successfully:\n\n{output_path}"
        )

    def export_failed(self, error_message):
        self.progress.set(0)
        self.export_btn.configure(state="normal", text="⬆  Export Video")
        self.set_status("❌ Export failed", "#f87171")

        messagebox.showerror(
            "Export Failed",
            error_message
        )

    def set_status(self, text, color):
        self.status_label.configure(text=text, text_color=color)

    @staticmethod
    def format_time(seconds):
        hours = seconds // 3600
        minutes = (seconds % 3600) // 60
        secs = seconds % 60
        return f"{hours:02d}:{minutes:02d}:{secs:02d}"


if __name__ == "__main__":
    app = VideoVolumeChangerApp()
    app.mainloop()

Run the App

Run command

python video_volume_changer_gui.py

7. Checkpoints

Check Python

Type this command:

python --version

You should see a Python version like Python 3.11 or newer.

Check Libraries

Type this command:

pip show customtkinter

You should see package information for CustomTkinter.

Run the App

Type:

python video_volume_changer_gui.py

You should see a dark modern window titled Video Volume Changer.

Select a Video

Click Open Video. Select an MP4 file.

You should see file name, duration, format, resolution, size, and audio status.

Change Volume

Move the slider to 150% or click the 150% button.

The big volume number should change immediately.

Export

Click Export Video.

A new file should be created in the selected output folder.

8. Common Errors and Fixes

Error: No module named customtkinter
Fix: Run pip install customtkinter.

Error: No module named moviepy
Fix: Run pip install moviepy.

Error: The video has no audio track.
Fix: Choose another video that already has sound.

Error: Export is slow.
Fix: Use a smaller video for practice. Large videos take time to re-encode.

9. Practice Tasks

Very Simple Change the app title to your own brand name.

Simple Add a 25% volume preset button.

Medium Add a checkbox for mute and unmute.

Advanced Add a feature to extract only audio from the video.

Project Add intro video + main video + outro video merging.

Infinity Build a full lesson video editor with watermark, background music, subtitles, and export profiles.

10. Quick Quiz

Q1. What is the use of MoviePy in this project?

MoviePy is used to read the video, change the audio volume, and export the final video.

Q2. What does 150% volume mean as a volume factor?

150% volume means a volume factor of 1.5.

Q3. Why do we use threading during export?

Threading keeps the GUI responsive while the video export process runs in the background thread.

11. Final Summary

In this lesson, we learned how to build a real Python desktop application. We created a graphical interface with CustomTkinter, selected a video file, changed the audio volume with MoviePy, and exported a new MP4 video.

Final Checkpoint: The project is complete when the app opens, loads a video, shows video information, changes the volume percentage, and successfully exports a new video.