How to Store the Output of FFmpeg in a Python Variable

What will you learn?

Explore how to efficiently capture the output of an FFmpeg command and store it in a Python variable for further processing and logging.

Introduction to the Problem and Solution

When executing external commands like FFmpeg within Python, it’s crucial to capture their outputs for various purposes such as monitoring progress or handling errors. The subprocess module in Python empowers us to interact with external processes seamlessly. In this scenario, we’ll focus on capturing the output of an FFmpeg command.

To save the desired output of an FFmpeg command into a Python variable, we’ll utilize subprocess.Popen() to run the command and then extract its stdout using .communicate(). This technique allows us to retain the output within a variable for subsequent usage in our Python script.


import subprocess

# Run the FFmpeg command using subprocess.Popen()
process = subprocess.Popen(['ffmpeg', '-i', 'input.mp4', 'output.mp4'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)

# Capture and decode both stdout and stderr
output, error = process.communicate() 
output_str = output.decode('utf-8')

# Store the desired output in a Python variable (e.g., result)
result = output_str

# Utilize or print 'result' based on your requirements

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# Copyright PHD


In this code snippet: – We import subprocess module for managing external processes. – Employing subprocess.Popen(), we execute an FFmpeg command converting ‘input.mp4’ file into ‘output.mp4’. – By specifying stdout=subprocess.PIPE, we redirect standard output stream from FFmpeg. – The .communicate() method reads data from both stdout and stderr streams. – We decode the byte string retrieved from stdout (output) into UTF-8 format. – Finally, we store this decoded string in a variable named result.

This methodology enables effective capture and storage of FFmpeg command outputs within a Python script.

  1. How can I handle errors that occur during execution?

  2. Inspect the contents of error to check if any errors occurred during execution. If it’s not empty, there may have been issues during processing.

  3. Can I pass arguments dynamically to my FFmpeg command?

  4. Construct your argument list dynamically based on varying values before passing it to the subprocess.Popen() function.

  5. Is it possible to run multiple concurrent commands with subprocess?

  6. Manage multiple concurrent commands by utilizing different instances of Popen or other methods like call() or run() provided by subprocess module.

  7. What if I only need specific lines from the output instead of storing everything?

  8. Process individual lines as they are generated while reading stdout instead of storing all output at once.

  9. How do I handle large outputs efficiently without consuming excessive memory?

  10. For large outputs, consider processing them line-by-line rather than loading everything into memory simultaneously. Implement file operations or streaming techniques for such scenarios.


Efficiently capturing and storing outputs from external tools like FFmpeg is pivotal for automation tasks involving multimedia processing. By mastering Python’s subprocess module as demonstrated above, you gain a robust skill set to seamlessly navigate diverse domains requiring integration between system-level operations and high-level scripting functionalities.

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