Matplotlib Movie Frame Extraction

Introduction

This tutorial will guide you through the process of using Matplotlib to grab individual frames from a movie and write them to a file. This method is useful for generating animations and can be done without event loop integration.

VM Tips

After the VM startup is done, click the top left corner to switch to the Notebook tab to access Jupyter Notebook for practice.

Sometimes, you may need to wait a few seconds for Jupyter Notebook to finish loading. The validation of operations cannot be automated because of limitations in Jupyter Notebook.

If you face issues during learning, feel free to ask Labby. Provide feedback after the session, and we will promptly resolve the problem for you.

Import necessary libraries

We first need to import the necessary libraries for generating the animation. We will be using numpy for generating random numbers, matplotlib for plotting, and FFMpegWriter for writing the frames to a file.

import numpy as np
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
from matplotlib.animation import FFMpegWriter

Set up the writer

We need to set up the writer that will be used to write the frames to a file. We set the frames per second (fps) and add metadata such as the title, artist, and comment.

metadata = dict(title='Movie Test', artist='Matplotlib',
                comment='Movie support!')
writer = FFMpegWriter(fps=15, metadata=metadata)

Set up the figure

We create a figure and set the x and y limits for the plot.

fig = plt.figure()
plt.xlim(-5, 5)
plt.ylim(-5, 5)

Set up the plot

We create a line plot and set the initial data to be an empty array.

l, = plt.plot([], [], 'k-o')

Grab frames and write to file

We loop through 100 iterations and generate random numbers for the x and y coordinates. We update the data for the line plot and grab the frame using the writer. Finally, we save the frames to a file.

x0, y0 = 0, 0

with writer.saving(fig, "writer_test.mp4", 100):
    for i in range(100):
        x0 += 0.1 * np.random.randn()
        y0 += 0.1 * np.random.randn()
        l.set_data(x0, y0)
        writer.grab_frame()

Summary

This tutorial showed you how to use Matplotlib to grab frames from a movie and write them to a file. We covered the necessary steps from setting up the writer to looping through iterations and generating random numbers for the plot. This method is useful for generating animations without event loop integration.