How to Use FFmpeg sendcmd for Multiple Filter Adjustments

The sendcmd (and asendcmd for audio) filter in FFmpeg allows you to dynamically change filter parameters at specific timestamps during playback or rendering. This article provides a straightforward guide on how to configure and run sendcmd to apply multiple filter adjustments simultaneously, using both external command files and inline commands.

Step 1: Assign Unique IDs to Your Filters

To control multiple filters at the same time, FFmpeg needs to know exactly which filter instance you are targeting. You do this by assigning a unique ID to each filter in your filtergraph using the id parameter.

For example, to control both the eq (brightness/contrast) and hue (saturation) filters, define them like this: * eq=id=my_eq * hue=id=my_hue

Step 2: Define the Simultaneous Commands

You can trigger multiple adjustments at the exact same timestamp. Each command must follow this syntax:

[timestamp] [target_filter] [parameter] [value];

To execute multiple adjustments simultaneously, list them sequentially using the same timestamp.

For complex adjustments, create a text file named commands.txt and define your timeline:

# At 3 seconds, increase brightness and double the saturation
3.0 eq@my_eq brightness 0.3;
3.0 hue@my_hue saturation 2.0;

# At 7.5 seconds, return both parameters back to normal
7.5 eq@my_eq brightness 0.0;
7.5 hue@my_hue saturation 1.0;

Method B: Using Inline Commands

If you prefer not to use an external file, you can pass the commands directly inside the FFmpeg command line using the c parameter. Note that you must escape semicolons and spaces properly.

sendcmd=c='3.0 eq@my_eq brightness 0.3; 3.0 hue@my_hue saturation 2.0; 7.5 eq@my_eq brightness 0.0; 7.5 hue@my_hue saturation 1.0'

Step 3: Run the FFmpeg Command

Combine the sendcmd filter with your target filters in a filter chain. The sendcmd filter must be placed before the filters it is meant to control.

Example using an external file:

ffmpeg -i input.mp4 -vf "sendcmd=f=commands.txt,eq=id=my_eq,hue=id=my_hue" -c:a copy output.mp4

Example using inline commands:

ffmpeg -i input.mp4 -vf "sendcmd=c='3.0 eq@my_eq brightness 0.3; 3.0 hue@my_hue saturation 2.0',eq=id=my_eq,hue=id=my_hue" -c:a copy output.mp4

Key Considerations