How to Load SOFA Files into FFmpeg

This guide provides a straightforward tutorial on how to load and use Spatially Oriented Format for Acoustics (SOFA) files within FFmpeg. You will learn the exact command-line syntax required to apply Head-Related Transfer Function (HRTF) spatial audio to your multi-channel audio tracks using the sofalizer and headphone filters.

Prerequisites

To load SOFA files, your FFmpeg build must be compiled with the libmysofa library. You can verify if your installation supports it by running the following command in your terminal:

ffmpeg -filters | grep sofa

If you see sofalizer or references to mysofa in the output, your FFmpeg build is ready.

Method 1: Using the Sofalizer Filter

The sofalizer filter is the most direct way to apply spatial audio using a SOFA file. It takes a multi-channel audio input and renders it as binaural 3D audio for headphones.

Use the following basic command structure:

ffmpeg -i input_surround.wav -af "sofalizer=sofa='/path/to/your/file.sofa'" output_binaural.wav

Key Parameters for Sofalizer:

  • sofa: Specifies the absolute or relative path to your .sofa file.
  • gain: Adjusts the gain in dB (default is 0). Useful if the spatialization process lowers the overall volume.
  • type: Sets the processing type. You can choose between time (time domain, default) or freq (frequency domain, which can be faster for long impulse responses).

Example with custom parameters:

ffmpeg -i input_51.wav -af "sofalizer=sofa='spatial_profile.sofa':gain=9:type=freq" output_spatial.wav

Method 2: Using the Headphone Filter

FFmpeg also features a headphone filter, which can map specific input channels to virtual speaker positions defined by a SOFA file.

The command below maps a 5.1 surround sound input to virtual positions using a SOFA file:

ffmpeg -i input_51.wav -af "headphone=map=FL|FR|FC|LFE|BL|BR:sofa='/path/to/your/file.sofa'" output_binaural.wav

Key Parameters for Headphone:

  • map: Specifies the order of the input channels to be mapped (e.g., Front Left FL, Front Right FR, etc.).
  • sofa: Points to the path of your SOFA configuration file.
  • type: Choose between time or freq processing domains.