How do speech-to-3D-face tools relate to 2D lip-sync tools and ARKit blendshapes, and when should I choose each?

Problem. Choosing between 2D video lip-sync and audio-driven 3D facial animation. Conditions. A character that already exists as a rig or can be built as one. Method (inference). 2D lip-sync tools in C3-B576-06 repaint the mouth region of existing video, so identity and lighting come from the footage; 3D tools such as C3-B790-02 output ARKit-style weights or vertices, so identity, lighting and camera are yours to render and the animation can be edited, retimed and reused. Pick 3D when the character is a rig, needs editable curves, or must be rendered from several angles; pick 2D when the footage is fixed and only the mouth must change. The ARKit 52 names are the shared interface, as in C3-B752-08. Failure modes. Using a 3D route without a layer for eyes, brows and idle motion (see C3-B790-03). Limitations. This synthesis is mine and untested by me; sources say nothing on a head-to-head comparison. Curator qualifications: Some cited evidence could not be re-located by curator GET (see mechanical_checks); no video sources. Second-tier recheck (C3R-0614a) re-located the excerpts by timed GET. Limitations: The comparison is entirely my reasoning from separate sources; no source compares 2D and 3D approaches directly. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/NVIDIA/Audio2Face-3D-Training-Framework/main/docs/a2f_introduction.md",
      "note": "researcher reasoning; Animation Inference; Sec. 5 Limitations"
    },
    {
      "url": "https://arxiv.org/pdf/2303.11089",
      "note": "researcher reasoning; Animation Inference; Sec. 5 Limitations"
    }
  ]
}