How to Use the FFmpeg Entropy Filter

This article provides a practical guide on how to use the entropy filter in FFmpeg to measure the complexity and information density of your video files. You will learn the basic command syntax, how the filter analyzes video frames, and how to extract the resulting metadata for quality control, scene-change detection, or analysis.

What is the Entropy Filter?

The entropy filter in FFmpeg measures the information density (or randomness) of a video’s color channels. A frame with flat colors and low detail has low entropy, while a highly detailed, noisy, or complex frame has high entropy.

By default, the filter measures spatial entropy, but it can also measure temporal entropy (the difference between consecutive frames) when switched to “difference” mode.

Basic Syntax and Parameters

The basic syntax for applying the entropy filter is:

-vf entropy=mode=normal

The filter accepts one primary option: * mode: Can be set to normal (default) to measure spatial entropy within each frame, or diff to measure temporal entropy between consecutive frames.

How to View Entropy Metadata

Because the entropy filter only calculates values and attaches them as metadata to each frame, running it on its own will not modify the visual output. To see the results, you must either print the metadata to a log file or use ffprobe to extract the values.

Method 1: Saving Entropy Data to a Text File

You can use the metadata filter alongside the entropy filter to print the calculated values directly to a text file:

ffmpeg -i input.mp4 -vf entropy,metadata=mode=print:file=entropy_log.txt -f null -

This command runs the analysis without rendering a new video file (-f null -) and saves the frame-by-frame entropy values to entropy_log.txt.

Method 2: Exporting Specific Values with FFprobe

If you want to extract specific entropy metrics (such as the luminance channel, Y) to a CSV format for spreadsheet analysis, use ffprobe:

ffprobe -f lavfi -i "movie=input.mp4,entropy" -show_entries frame=pkt_pts_time:frame_tags=lavfi.entropy.normalized_entropy.Y -of csv=p=0 > entropy_values.csv

Understanding the Output Metadata

The filter generates several keys that you can access in your metadata reports:

• lavfi.entropy.entropy.Y: The raw entropy value of the luminance channel (typically between 0 and 8).
• lavfi.entropy.normalized_entropy.Y: The normalized entropy value of the luminance channel (scaled between 0.0 and 1.0).
• lavfi.entropy.entropy.U and lavfi.entropy.entropy.V: The raw entropy of the blue-difference and red-difference chroma channels.

Measuring Temporal Changes (Difference Mode)

To analyze motion or changes between frames rather than static detail, change the mode to diff. This is highly useful for identifying sudden cuts or high-motion sequences:

ffmpeg -i input.mp4 -vf entropy=mode=diff,metadata=mode=print:file=diff_log.txt -f null -