Visemes

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Visemes (pormanteau for visual phonemes) are an avatar feature that mimics lip and mouth movement, when synchronized with human speech.

Within Unity, visemes are a type of, or set of shapekey(s) that can be programmed onto an avatar. In the Oculus LipSync Library, there are 15 mouth‑shape targets that can be used while you speak.

VRChat converts your live microphone audio through that library, converts the sound into a single integer (0‑14) every video frame, and writes it into the built‑in Animator parameter Viseme (often shown in the docs as "VisemeOculus"). Your avatar's FX layer (or the VRChat SDK's default layer) turns that number into blend‑shape or bone animation so the mouth appears to pronounce your words in real time.

Viseme Slots

Index	Name	Phonemes	Examples	Mouth description
0	sil	(silence)		Neutral, lips relaxed
1	pp	p, b, m	put, bat, mat	Lips fully closed, slight pout
2	ff	f, v	fat, vat	Lower lip touches upper teeth
3	th	th	that	Tongue between teeth
4	dd	t, d	tip, dip	Tip of tongue touches ridge
5	kk	k, g	call, gas	Back of tongue touches palate
6	ch	ch, sh, ts, dz, j	chair, she, its, join	Lips rounded, jaw slightly down
7	ss	s, z	sit, zoom	Teeth almost together, lips wide
8	nn	n, l	lot, not	Tongue presses ridge, lips apart
9	rr	r	red	Lips slightly rounded, cheeks firm
10	aa	ah, aw	fast, father	Jaw open, oval mouth
11	e	eh	men	Mouth wider, mid‑open
12	i	ih, ee	tip, tea	Lips stretched, jaw higher
13	o	oh	toe	Lips rounded, jaw mid‑open
14	u	ou	boot	Lips rounded, slightly forward

Oculus Docs use the longer spellings ih/oh/ou; VRChat's parameter list trims them to i/o/u.

Wiring Avatar

1. Add blend‑shapes (shape keys) or a jaw bone. Each shapekey should be named exactly like the codes above (case‑sensitive in Unity). Keep the sil key—even if it only moves one vertex—to stop Unity deleting it on import.
2. Set the Avatar Descriptor’s › Lip‑Sync mode to “Viseme Blend Shape”. Hit Auto Detect! first; if the SDK guesses wrong, pick the correct shapekey for every slot in the dropdown.
3. Test in‑editor: play the scene, enable the Lip Sync preview on the descriptor, or simply talk into your mic while the Game view is active.
4. Fine‑tune in your FX Animator (optional). The int parameter Viseme updates every frame; you can:
   • Drive a 15‑way BlendTree that weights each shapekey.
   • Branch to custom mouth animations (e.g., a “big scream” version of aa) when volume is high by also reading the Voice float (0‑1).
5. Performance tip: keep viseme blend‑shapes on a separate head mesh; the GPU only has to update the vertices it actually changes.

Troubleshooting quick‑hits

Symptom	Likely cause	Fix
Mouth never moves	Lip‑Sync mode still on Jaw Flap or Default	Switch to Viseme Blend Shape
Wrong shapes (e.g., “th” looks like “ff”)	Mis‑matched dropdown slots	Re‑assign each viseme in the Descriptor
Shapes snap instead of blend	Using an Int blend‑tree with thresholds too close	Use a 1D float tree driven by 0‑14 or add smoothing
Shapes missing on Quest	Head mesh not included in the Android build	In Build tab, mark head mesh for both PC & Android

Take‑away

Visemes are simply numbered mouth cues. Name 15 blend‑shapes (or equivalent bone poses) to match the Oculus set, point your Avatar Descriptor at them, and VRChat’s built‑in Viseme parameter will make your character lip‑sync automatically—no extra scripts required.

Resources

• Animation Parameters on VRChat's Creator Documentation
• Viseme Reference on Meta Developers' Documentation

See also

• Avatars
• Blendshapes
• VRChat Creator Companion
• VRChat SDK