Audio Channels

Sets the channel layout of the audio-only output.

video-audio-channels applies to audio-only output (fm=m4a, fm=mp3, fm=wav) and accepts one of three string values:

• stereo (default) — downmixes to 2 channels
• mono — downmixes to 1 channel
• source — preserves the source’s native channel layout (e.g. 5.1 surround)

https://assets.imgix.net/videos/girl-reading-book-in-library.mp4?fm=m4a&video-audio-channels=stereo

By default, audio-only output is downmixed to stereo — the right choice for <audio> elements, iOS playback, and podcast delivery. Use mono to reduce file size for speech content where stereo separation adds no value.

The source value preserves multichannel layouts such as 5.1 and is supported by fm=m4a and fm=wav only. fm=mp3 always outputs stereo regardless of this parameter, because libmp3lame has no multichannel mode.

This parameter does not apply to muxed video output (fm=mp4, fm=hls, fm=dash) — those paths always produce stereo audio.

See Audio-Only Output for more on the audio-only output modes.