How to Change Video Brightness Over Time with FFmpeg sendcmd

Adjusting video brightness dynamically during playback is a powerful technique for creating transitions, correcting exposure issues, or adding creative visual effects. This guide demonstrates how to use the FFmpeg sendcmd filter to pass commands to the eq (equalizer) filter, allowing you to precisely control and alter a video’s brightness at specific timestamps.

Understanding the Components

To change brightness over time, you must chain two FFmpeg filters together: 1. sendcmd: This filter reads commands (either from a text file or an inline string) and dispatches them to other filters at designated timestamps. 2. eq: This filter adjusts video properties like brightness, contrast, and saturation. It accepts real-time commands to change these parameters during processing.

The brightness parameter in the eq filter accepts values from -1.0 (completely black) to 1.0 (completely white), with 0.0 being the default utility value.

Method 1: Using an Inline Command (For Simple Changes)

For quick adjustments, you can write the commands directly inside your terminal command.

Here is the basic syntax:

ffmpeg -i input.mp4 -vf "sendcmd=c='[time] eq brightness [value]',eq" -c:a copy output.mp4

Example:

To start a video dark, increase the brightness at 2 seconds, and return it to normal at 5 seconds, use the following command:

ffmpeg -i input.mp4 -vf "sendcmd=c='0.0 eq brightness -0.5, 2.0 eq brightness 0.3, 5.0 eq brightness 0.0',eq" -c:a copy output.mp4

How it works: * 0.0 eq brightness -0.5: At 0 seconds, brightness is set to -0.5 (darker). * 2.0 eq brightness 0.3: At 2 seconds, brightness changes to 0.3 (brighter). * 5.0 eq brightness 0.0: At 5 seconds, brightness resets to its default state. * ,eq: This instantiates the eq filter immediately after sendcmd so it can receive the instructions.

Method 2: Using a Command File (For Complex Timelines)

If you have many brightness changes to make, writing them inline can become messy. Instead, you can save your commands in a external text file.

Step 1: Create the command file

Create a text file named brightness_commands.txt and define your timeline:

0.0 eq brightness -0.4;
2.5 eq brightness 0.2;
4.0 eq brightness -0.1;
6.0 eq brightness 0.0;

Note: Each command line must end with a semicolon (;).

Step 2: Run the FFmpeg command

Point the sendcmd filter to your text file using the f (file) parameter:

ffmpeg -i input.mp4 -vf "sendcmd=f=brightness_commands.txt,eq" -c:a copy output.mp4

Key Considerations