facial-and-lipsync

name	facial-and-lipsync
description	Use when the user has a voice-over (or wants one) and needs the character's mouth to actually move with the words — phoneme extraction from audio, mapping to viseme blendshapes, plus emotional facial expressions (smile, frown, surprise). Trigger on "lipsync", "lip sync", "talking head", "phonemes", "viseme", "facial animation", "blendshapes", "make him talk", "dialogue animation".
license	MIT
compatibility	["Cursor","Claude Code","Windsurf","Codex"]
category	animation
user-invocable	false
allowed-tools	Read Grep Edit Write summer_search_assets summer_inspect_resource summer_inspect_node summer_generate_audio summer_generate_motion summer_add_node summer_set_prop summer_set_resource_property summer_save_scene summer_get_script_errors
paths	["**/*.gd","**/*.tscn","**/*.tres"]

Facial Animation & Lipsync

Half generative, half authored. The generative half: an audio file (TTS via summer_generate_audio with capability: "text_to_speech") goes through a phoneme-extraction tool (Summer does NOT wrap one — you run it externally), out comes a viseme timeline — a list of { phoneme, start_time, duration } triples. The authored half: the character's face mesh must have BlendShapes named for the standard viseme set, or the timeline has nothing to drive. Without both halves, you get a talking robot.

The 2026 production stack:

1. Audio in — .wav/.mp3 from summer_generate_audio({capability: "text_to_speech", ...}) or imported VO.
2. Phoneme extraction — done OUTSIDE Summer. Recommended: Rhubarb Lip Sync (open source, the industry standard for game-dev lipsync; outputs JSON with mouth-shape cues over time). Alternatives: gentle, allosaurus, or a Whisper-phoneme model on Replicate / Hugging Face. There is no summer_* MCP for this in the current engine.
3. Viseme mapping — phonemes / Rhubarb cues → Oculus / Apple ARKit viseme set (15 standard shapes covers English).
4. BlendShape driver — at runtime, lerp the mesh's BlendShape weights along the timeline, synced to audio playback.
5. Optional emotional layer — separate BlendShape track for smile, brow_raise, eye_squint etc., authored in code or at clip-edit time.

When to use this skill

• NPC has voice lines and the mouth doesn't move.
• Cinematic with VO that needs lipsync.
• "Make him sing the lyrics."
• Animating expressions on a face that has BlendShapes (Meshy character heads ship with the ARKit-52 set by default).
• Reactive face: smile when player gives gold, scowl when attacked.

When NOT to use this skill

• Character has no face / no BlendShapes (helmeted soldier, robot, mascot). Hard-skip to body language via summer:animation/generate-motion.
• The dialogue is written but not yet voiced — generate audio first via summer_generate_audio({capability: "text_to_speech", ...}). Lipsync without audio has nothing to sync to.
• Pre-rendered cinematic from external DCC. Lipsync is in the rendered video, not the engine.

Steps

1. Confirm the head has BlendShapes

summer_inspect_node "./World/NPC/Head"     # or wherever the head MeshInstance3D lives

Look for mesh.blend_shape_count > 0 and a list of names. The Meshy ARKit-52 set (default for Meshy character heads) has names like jawOpen, mouthClose, mouthFunnel, mouthPucker, mouthLeft, mouthRight, mouthSmile_L, mouthSmile_R, mouthFrown_L, mouthFrown_R, browInnerUp, browOuterUp_L, browDown_L, eyeBlink_L, eyeWide_L, eyeSquint_L (mirrored on R).

If the head has zero BlendShapes, stop. Tell the user: "This head mesh has no BlendShapes — facial animation is impossible without re-meshing. Options: regenerate the character with the face_blendshapes: arkit option (summer_generate_3d({ kind: \"image-to-3d\", options: { rig: true, face_blendshapes: \"arkit\" } })), use an emotional body-language overlay instead, or hand off the character to a 3D artist for shape-key authoring." Don't proceed.

Note: the face_blendshapes option is a Meshy passthrough; if your target backend doesn't support it, the rig will use the default skeleton — adjust manually in the Meshy dashboard.

2. Get the audio

If the user has VO already, use it. If not, generate via TTS. The voiceId is an ElevenLabs voice ID — the user has to pick one from the ElevenLabs voice library (https://elevenlabs.io/app/voice-library) or upload/clone their own. There is no "voice name" string; it's always an ID like 21m00Tcm4TlvDq8ikWAM (Rachel) or a custom-cloned ID.

summer_generate_audio({
  capability: "text_to_speech",
  text: "Welcome to the village, traveler.",
  voiceId: "<elevenlabs_voice_id>"
})
// returns { jobId, ... } — poll with summer_check_job for the audio asset

If the user hasn't picked a voice yet, stop and ask: "Which ElevenLabs voice ID should I use? You can browse the library at elevenlabs.io/app/voice-library and copy the ID, or paste a custom-clone ID from your account."

3. Extract phonemes (the generative step — runs OUTSIDE Summer)

Summer does not wrap a phoneme-extraction MCP tool. Run it externally, then import the result. Recommended: Rhubarb Lip Sync — an open-source CLI built for game-dev lipsync. Mouth shapes A–H map cleanly to viseme shapes.

Install once:

# macOS
brew install rhubarb-lip-sync
# Windows / Linux: download release from https://github.com/DanielSWolf/rhubarb-lip-sync

Run per VO line:

rhubarb -f json -o welcome_traveler.json welcome_traveler.wav

Output JSON shape:

{
  "metadata": { "duration": 2.34 },
  "mouthCues": [
    { "start": 0.00, "end": 0.08, "value": "B" },
    { "start": 0.08, "end": 0.18, "value": "C" },
    { "start": 0.18, "end": 0.25, "value": "D" },
    { "start": 0.25, "end": 0.30, "value": "B" },
    { "start": 0.30, "end": 0.42, "value": "A" },
    { "start": 0.42, "end": 0.50, "value": "B" },
    { "start": 2.30, "end": 2.34, "value": "X" }
  ]
}

Rhubarb mouth-shape → ARKit viseme cheat sheet (apply during the bake step):

Rhubarb	ARKit viseme	Notes
A	viseme_PP	closed (P, B, M)
B	viseme_kk	slightly open, neutral
C	viseme_E	open, lips spread (EH, IH)
D	viseme_aa	wide open (AA, AH)
E	viseme_O	rounded (OW, ER)
F	viseme_U	small rounded (UW, OO)
G	viseme_FF	F, V (lower lip + teeth)
H	viseme_RR	L, R (tongue raised)
X	viseme_sil	silence / closed neutral

Manual fallback (no Rhubarb available): for short lines you can hand-type a mouthCues array by listening to the clip and tagging vowel/consonant boundaries. Painful past ~3s of audio; use Rhubarb for anything longer.

Cloud fallback: a Whisper-phoneme model on Replicate or a Hugging Face inference endpoint will emit ARPAbet phonemes with timestamps. Then map ARPAbet → ARKit visemes via the table in the Reference card section. More accurate than Rhubarb on noisy audio; slower and costs cents per minute.

Cost: Rhubarb is free + ~5s CPU per 30s clip locally. Cloud fallback ~$0.02 / minute, ~5s wall-clock for a 30s clip.

4. Persist the viseme track as an AnimationLibrary entry

Convert Rhubarb's mouthCues into a Godot Animation resource — one track per BlendShape, keyframes at each viseme transition. This makes lipsync replayable via the same AnimationPlayer/AnimationTree as body motion.

# scripts/lipsync_baker.gd — run once per VO line at edit time
const RHUBARB_TO_VISEME := {
    "A": "viseme_PP",  "B": "viseme_kk", "C": "viseme_E",
    "D": "viseme_aa",  "E": "viseme_O",  "F": "viseme_U",
    "G": "viseme_FF",  "H": "viseme_RR", "X": "viseme_sil",
}

static func bake_from_rhubarb(rhubarb_json_path: String, head_path: NodePath) -> Animation:
    var f := FileAccess.open(rhubarb_json_path, FileAccess.READ)
    var data: Dictionary = JSON.parse_string(f.get_as_text())
    var cues: Array = data["mouthCues"]
    var anim := Animation.new()
    anim.length = float(data["metadata"]["duration"])
    var visemes := ["viseme_aa", "viseme_E", "viseme_I", "viseme_O", "viseme_U",
                    "viseme_PP", "viseme_FF", "viseme_TH", "viseme_DD", "viseme_kk",
                    "viseme_CH", "viseme_SS", "viseme_nn", "viseme_RR", "viseme_sil"]
    var tracks := {}
    for v in visemes:
        var idx := anim.add_track(Animation.TYPE_BLEND_SHAPE)
        anim.track_set_path(idx, NodePath(str(head_path) + ":" + v))
        tracks[v] = idx
    # For each cue, set the active viseme to 1.0 and others to 0.0 at cue.start
    for cue in cues:
        var active_viseme: String = RHUBARB_TO_VISEME.get(cue["value"], "viseme_sil")
        for v in visemes:
            var weight: float = 1.0 if v == active_viseme else 0.0
            anim.track_insert_key(tracks[v], float(cue["start"]), weight)
    return anim

Bake once, save into the character's AnimationLibrary as dialogue_<line_id>, and play via the AnimationTree.

If you used the Whisper/ARPAbet cloud fallback instead of Rhubarb, swap bake_from_rhubarb for a variant that consumes { phoneme, start, duration } triples and applies the ARPAbet → viseme table from the Reference card.

5. Wire into the AnimationTree

Add a OneShot node Lipsync that overlays the viseme animation as an additive layer over the base face. Fire from the dialogue system:

@onready var tree: AnimationTree = $AnimationTree
@onready var audio: AudioStreamPlayer3D = $VoicePlayer

func say(line_id: String) -> void:
    var clip_id := "dialogue_" + line_id
    tree.set("parameters/Lipsync/animation", clip_id)
    audio.stream = load("res://audio/" + line_id + ".ogg")
    audio.play()
    tree.set("parameters/Lipsync/request", AnimationNodeOneShot.ONE_SHOT_REQUEST_FIRE)

Sync is preserved as long as both fire on the same frame. ~16ms drift is the threshold of perception; AnimationTree + AudioStreamPlayer3D are both sample-accurate, so drift only happens if the engine hitches mid-line.

6. Add the emotional layer (authored, not generative)

A second OneShot or persistent additive track for expressions. Key the relevant BlendShapes (mouthSmile_L, mouthSmile_R, browInnerUp, etc.) at design time:

func smile(intensity: float) -> void:
    var head: MeshInstance3D = $Head
    head.set_blend_shape_value(head.find_blend_shape_by_name("mouthSmile_L"), intensity)
    head.set_blend_shape_value(head.find_blend_shape_by_name("mouthSmile_R"), intensity)

func surprise(intensity: float) -> void:
    var head: MeshInstance3D = $Head
    head.set_blend_shape_value(head.find_blend_shape_by_name("browInnerUp"), intensity)
    head.set_blend_shape_value(head.find_blend_shape_by_name("browOuterUp_L"), intensity * 0.7)
    head.set_blend_shape_value(head.find_blend_shape_by_name("browOuterUp_R"), intensity * 0.7)
    head.set_blend_shape_value(head.find_blend_shape_by_name("eyeWide_L"), intensity)
    head.set_blend_shape_value(head.find_blend_shape_by_name("eyeWide_R"), intensity)
    head.set_blend_shape_value(head.find_blend_shape_by_name("jawOpen"), intensity * 0.3)

Driven from gameplay events; orthogonal to the lipsync layer.

Confirmation gates

• Before extracting: show audio length, est. cost, est. wait. Wait for OK.
• Before baking the Animation resource: confirm the head's BlendShape names match the standard set. If they're custom-named, ask for the mapping.
• Before saving the scene: confirm the AnimationTree changes (added Lipsync OneShot, library entry).

Reference card

ARKit-52 viseme subset (the 15 that matter for English lipsync)

Viseme	Triggered by phonemes (ARPAbet)	Mouth shape
viseme_sil	silence	closed neutral
viseme_PP	P, B, M	lips pressed
viseme_FF	F, V	lower lip + upper teeth
viseme_TH	TH, DH	tongue tip + teeth
viseme_DD	T, D, N, S, Z	tongue + alveolar
viseme_kk	K, G, NG	back-tongue, mouth slightly open
viseme_CH	CH, JH, SH, ZH	lips rounded forward
viseme_SS	S, Z (sometimes split from DD)	teeth nearly closed
viseme_nn	N, L	tongue-tip + open mouth
viseme_RR	R, ER	mouth slightly rounded
viseme_aa	AA, AH, AE	wide open
viseme_E	EH, EY, IH	mid open + lips spread
viseme_I	IY, IH	narrow + spread
viseme_O	OW, AO	rounded
viseme_U	UW, UH	rounded + small

Phoneme → viseme mapping (for hand-rolled extraction)

If the user has a CMUDict-style phoneme list and wants to map manually, this is the table to apply.

Pitfalls

• Mouth never closes between words. No viseme_sil keyframes at silence intervals. The bake step must scan the audio for silence (RMS below threshold for 100ms+) and insert sil keys, OR the phoneme extractor must emit silence markers. Rhubarb emits X cues for silence (mapped above to viseme_sil); cloud Whisper-phoneme models often don't — add a silence-detection pass if you go that route.
• Lipsync drifts behind audio. Audio playback latency on some platforms is 30–60ms. Either delay the audio start by 1 frame, or pre-shift the animation by the platform's known latency. On desktop Linux audio output can be 60ms behind; on Steam Deck ~20ms.
• Visemes pop on/off. Crossfade between viseme keyframes — set Animation.TRACK_INTERPOLATION_LINEAR (default) and ensure each viseme's weight ramps from previous to current. Default bake does this; if you wrote custom keyframes with NEAREST interp, switch.
• Smile fights lipsync. Both write to mouth BlendShapes. Solve by additive layering: lipsync layer outputs deltas from neutral, smile layer outputs deltas from neutral, sum them, clamp 0..1. ARKit shapes are sum-safe up to ~1.5; clamp prevents over-rotation.
• Eyes look dead. Lipsync is mouth-only; without blinks and saccades the face is uncanny. Add an idle blink track (every 4–8s, jittered) and a small saccade track (random eye movement up to 5°). Both can be one-shots fired by a Timer.
• Phoneme extraction returns gibberish. Audio is too noisy, mismatched language code, or compressed too aggressively. Re-export the source as 22kHz mono WAV before sending. Don't lipsync from a 64kbps MP3.
• Custom rig has different BlendShape names. The bake assumes ARKit-52. If the rig uses Preston Blair or a custom set, write a name-mapping Dictionary and apply it during bake. Only do this once per character.

Quality bar

• ~12 phonemes/sec is normal English speech; the bake produces ~25 keyframes/sec across all tracks. Below 60fps playback on weak hardware: enable BlendShape track interpolation = NEAREST (loses smoothness, gains 30% perf). Reserve for mobile / very crowded crowd scenes.
• Lipsync alone is ~70% of "alive". Add idle blink + idle micro-head-bob (summer:animation/procedural-animation) and you're at ~95%. The remaining 5% is brow articulation tied to dialogue sentiment, which is bespoke per scene.

Anti-patterns

• Driving BlendShape weights from _process with hand-coded curves. The Animation track is sample-accurate and re-uses the AnimationTree's interpolation; manual code drifts and stutters.
• Using a single "talking" loop instead of phoneme-driven lipsync. The 1990s look. Always extract phonemes; the cost is trivial.
• Forgetting to gate audio + animation on the same frame. If you play() audio in _ready and fire the OneShot in _process, you'll see ~16ms drift at line start. Both calls in the same function, same frame.
• Using lipsync for non-talking sounds (groans, screams). Lipsync needs phonemes; non-verbal vocals confuse the extractor. For grunts, drive jawOpen from the audio's RMS envelope instead — much simpler.

Edge cases

• Multilingual VO. Rhubarb supports English best; for other languages, pass --recognizer phonetic (language-agnostic, less accurate) or use a multilingual Whisper-phoneme model on Replicate / HF. Cross-language lipsync (extract as English on Spanish audio) gives ~70% accuracy — bad enough that subtitles are needed regardless.
• Singing. Phoneme extractor handles sustained vowels well, but consonant timing is loose. For sung dialogue, manually keyframe consonants and let extracted vowels fill in.
• Aside / muttering at low volume. Phoneme extractor needs > -40 dB. Boost the source clip before extracting if the line is intentionally quiet, then play it at the original volume in-engine.
• Stylized character with no jaw bone (e.g., a cartoon ball). No bone, but BlendShapes can still drive a "morph open" shape. Same pipeline; skip the jaw-bone-track and only animate BlendShapes.

Fallback (no Rhubarb)

If Rhubarb won't install on the user's platform, run a Whisper-phoneme model on Replicate (e.g., cjwbw/whisper-phoneme) or aeneas-align for forced alignment. Download the JSON, swap the bake function for one that consumes ARPAbet phonemes (table in Reference card). Same end result — replayable BlendShape Animation resource.

For projects that can't use any cloud or third-party tool, Godot 4.5's AudioStreamGenerator with hand-rolled vowel/consonant detection from RMS + zero-crossings gives ~50% accuracy — enough for a stylized character but not photoreal.

Handoff

• For voice generation upstream, summer:audio/generate-voice (which wraps summer_generate_audio({capability: "text_to_speech", ...})).
• For dialogue scripts and conversation flow, summer:ai-and-npcs/design-npc.
• For the AnimationTree this layer composes into, summer:animation/animation-tree.
• For idle blinks, saccades, and head-tracking that complement lipsync, summer:animation/procedural-animation.
• For full performance capture (face + body together), out of scope — see Meshy's mocap docs or external pipelines.

See also

• summer:audio/generate-voice — TTS upstream of this skill.
• summer:animation/animation-tree — wire the lipsync OneShot into the character's tree.
• summer:animation/procedural-animation — eye blinks, saccades, head idle.
• references/mcp-tools-reference.md — summer_generate_audio schema (TTS).
• Rhubarb Lip Sync — https://github.com/DanielSWolf/rhubarb-lip-sync (external tool; phoneme extraction).