Inject Spatial Audio Metadata into MP4 with FFmpeg

This guide provides a straightforward tutorial on how to use FFmpeg to inject spatial audio metadata into an MP4 container. You will learn the exact command-line syntax required to combine your video and multi-channel audio tracks, apply the correct spatial layout, and generate a file ready for platforms like YouTube that support immersive 360-degree and spatial audio playback.

To inject spatial audio (specifically First-Order Ambisonics, or FOA) into an MP4 container, your audio source must be a 4-channel audio file formatted in the AmbiX (ACN/SN3D) standard. FFmpeg can mux this audio with your video and tag the audio stream with the correct spatial metadata.

Run the following FFmpeg command in your terminal:

ffmpeg -i input_video.mp4 -i spatial_audio.wav -map 0:v -map 1:a -c:v copy -c:a aac -channel_layout ambisonic output_spatial.mp4

Command Breakdown

• -i input_video.mp4: Specifies your input video source file.
• -i spatial_audio.wav: Specifies your 4-channel spatial audio file (AmbiX format).
• -map 0:v: Selects the video stream from the first input file.
• -map 1:a: Selects the audio stream from the second input file.
• -c:v copy: Copies the video stream directly without re-encoding, saving time and preserving original video quality.
• -c:a aac: Encodes the spatial audio to AAC format, which is widely compatible with MP4 containers and web players.
• -channel_layout ambisonic: This is the crucial flag that tells FFmpeg to tag the audio channel layout as ambisonic, injecting the necessary spatial metadata into the MP4 container structure.
• output_spatial.mp4: The final output file containing the merged video and spatial audio.

Verification

Once the command completes, you can verify that the metadata was successfully applied by running ffprobe on the output file:

ffprobe -v error -show_entries stream=channel_layout -of default=noprint_wrappers=1 output_spatial.mp4

The output should display channel_layout=ambisonic, confirming that your MP4 file is properly configured for spatial audio playback.