When changing the number of output channels from source material, the following settings control how source audio amplitude and positioning will be mixed into the requested output.

Parameter	Description	Allowed Values	Default Value
dmix_center_level	Sets Lt/Rt and Lo/Ro downmix(5.1-to-stereo) levels for the central channel.	+3.0, +1.5, 0.0, –1.5, –3.0, –4.5, –6.0, and –inf.	–3.0
dmix_center_level_ltrt	Overrides the Lt/Rt downmix level setting for the central channel when <dmix_center_level> is used.	+3.0, +1.5, 0.0, –1.5, –3.0, –4.5, –6.0, and –inf.	–3.0
dmix_center_level_loro	Overrides the Lo/Ro downmix level setting for the central channel when <dmix_center_level> is used.	+3.0, +1.5, 0.0, –1.5, –3.0, –4.5, –6.0, and –inf.	–3.0
dmix_surround_level	Sets Lt/Rt and Lo/Ro downmix(5.1-to-stereo) levels for Ls and Rs channels.	–1.5, –3.0, –4.5, –6.0, and –inf.	–3.0
dmix_surround_level_ltrt	Overrides the Lt/Rt downmix level setting for Ls and Rs channels when <dmix_surround_level> is used.	–1.5, –3.0, –4.5, –6.0, and –inf.	–3.0
dmix_surround_level_loro	Overrides the Lo/Ro downmix level setting for Ls and Rs channels when <dmix_surround_level> is used.	–1.5, –3.0, –4.5, –6.0, and –inf.	–3.0
dmix_preference	DMG audio-dmix-preference option	loro, ltrt, pl2, unknown	none
downmix_mode	Dolby Encoding Engine downmix mode	pl2, loro, ltrt	pl2
hybrid_downmix	Hybrid downmix	yes, no	none

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Note
The metadata does not contain downmix coefficients when the encoded audio is stereo.