# What input requirements, failure modes and options does a hosted lip-sync API (sync.so) document for angle, occlusion, resolution, duration mismatch and multiple faces?

- id: art_01M5NP61RXHSA9XW32A8YYM46V
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T06, T10, T13 · tags: none
- updated: 2026-10-24T00:50:14.423Z
- url: https://veyrul.com/articles/art_01M5NP61RXHSA9XW32A8YYM46V

Problem. Preparing footage so a hosted lip-sync service does not distort the face or sync the wrong person. Conditions. sync.so (Sync Labs) models lipsync-2, lipsync-2-pro, sync-3, react-1 as named in its docs. Method. (1) Angle: frontal or near-frontal faces give best results on lipsync-2/-pro; extreme profile makes detection unreliable and can distort; sync-3 is documented to support extreme angles and over-the-shoulder shots. (2) Occlusion: hands, microphones, hair, sunglasses over the mouth degrade lipsync-2/-pro; enable the occlusion_detection_enabled option for those models; sync-3 handles obstructions automatically. (3) Resolution: at least 480p for face detection; up to 4096x2160; 1080p recommended; MP4/H.264; if compositing back, export SDR BT.709 with explicit colour tags, H.264 yuv444p when colour consistency matters. (4) Faces: keep one speaker visible, or use Speaker Selection (active_speaker_detection, auto_detect, or bounding box/frame reference) - otherwise the most ...

Problem. Preparing footage so a hosted lip-sync service does not distort the face or sync the wrong person. Conditions. sync.so (Sync Labs) models lipsync-2, lipsync-2-pro, sync-3, react-1 as named in its docs. Method. (1) Angle: frontal or near-frontal faces give best results on lipsync-2/-pro; extreme profile makes detection unreliable and can distort; sync-3 is documented to support extreme angles and over-the-shoulder shots. (2) Occlusion: hands, microphones, hair, sunglasses over the mouth degrade lipsync-2/-pro; enable the occlusion_detection_enabled option for those models; sync-3 handles obstructions automatically. (3) Resolution: at least 480p for face detection; up to 4096x2160; 1080p recommended; MP4/H.264; if compositing back, export SDR BT.709 with explicit colour tags, H.264 yuv444p when colour consistency matters. (4) Faces: keep one speaker visible, or use Speaker Selection (active_speaker_detection, auto_detect, or bounding box/frame reference) - otherwise the most prominent face is chosen. (5) Audio: clean single-speaker speech; isolate vocals for songs; use the Segments API for multi-speaker. (6) Duration mismatch: sync_mode cut_off, bounce, loop, silence, remap. (7) Long videos are processed internally in 30-40 s chunks; chunk boundaries at moving or absent faces can degrade quality - split under 2 minutes with the Segments API. Failure modes. Distorted face on bad angle, wrong-face sync, degraded output at chunk boundaries. Limitations. Vendor documentation, not an independent test; model names and options may change; pricing deliberately not recorded. Version/date. Page fetched 2026-10-23 (no date shown).

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: All vendor claims; no independent verification.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://sync.so/docs/compatibility-and-tips/improving-lip-sync-quality",
      "note": "Use a front-facing camera angle; Use a front-facing camera angle; Minimize face obstructions; Meet resolution requirements; Preserve color metadata; Match audio and video duration; Quality degrades in long videos; Keep one face in frame; Audio Input Best Practices"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. Preparing footage so a hosted lip-sync service does not distort the face or sync the wrong person. Conditions. sync.so (Sync Labs) models lipsync-2, lipsync-2-pro, sync-3, react-1 as named in its docs. Method. (1) Angle: frontal or near-frontal faces give best results on lipsync-2/-pro; extreme profile makes detection unreliable and can distort; sync-3 is documented to support extreme angles and over-the-shoulder shots. (2) Occlusion: hands, microphones, hair, sunglasses over the mouth degrade lipsync-2/-pro; enable the occlusion_detection_enabled option for those models; sync-3 handles obstructions automatically. (3) Resolution: at least 480p for face detection; up to 4096x2160; 1080p recommended; MP4/H.264; if compositing back, export SDR BT.709 with explicit colour tags, H.264 yuv444p when colour consistency matters. (4) Faces: keep one speaker visible, or use Speaker Selection (active_speaker_detection, auto_detect, or bounding box/frame reference) - otherwise the most prominent face is chosen. (5) Audio: clean single-speaker speech; isolate vocals for songs; use the Segments API for multi-speaker. (6) Duration mismatch: sync_mode cut_off, bounce, loop, silence, remap. (7) Long videos are processed internally in 30-40 s chunks; chunk boundaries at moving or absent faces can degrade quality - split under 2 minutes with the Segments API. Failure modes. Distorted face on bad angle, wrong-face sync, degraded output at chunk boundaries. Limitations. Vendor documentation, not an independent test; model names and options may change; pricing deliberately not recorded. Version/date. Page fetched 2026-10-23 (no date shown). · locator: Use a front-facing camera angle; Use a front-facing camera angle; Minimize face obstructions; Meet resolution requirements; Preserve color metadata; Match audio and video duration; Quality degrades in long videos; Keep one face in frame; Audio Input Best Practices · source: https://sync.so/docs/compatibility-and-tips/improving-lip-sync-quality

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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