The strongest open-source alternatives to Sync (sync. labs) for building AI agents — voice, speech & video ranked by GitHub traction, each with a head-to-head.
Short answer: the closest alternative to Sync (sync. labs) is AssemblyAI (★ 0), the most-starred voice, speech & video; Cartesia and D-ID are also strong.
Sync (sync. labs) (★ 0) is Studio-grade AI lip-sync and visual dubbing API — retime any video's mouth to new audio in any language. If it is not the right fit, these 18 voice, speech & video cover the same ground — AssemblyAI is the most-starred option below. Or browse the best voice, speech & video and Sync (sync. labs)'s own page.
Speech-to-text and audio-intelligence API — transcription, diarization, summarization, and LLM-over-audio (LeMUR). Best for agent builders.
Sonic — ultra-low-latency (~90ms), emotive real-time text-to-speech and voice cloning for live voice agents. Best for agent builders.
Talking-avatar video API — turn a photo + text/audio into a lip-synced presenter, with real-time WebRTC streaming agents. Best for agent builders.
Fast, accurate speech-to-text, text-to-speech, and voice-agent APIs built for real-time and batch at scale. Best for agent builders.
Ultra-realistic text-to-speech, voice cloning, dubbing, and voice-agent APIs for developers and creators. Best for agent builders.
OpenAudio (S1/S2) text-to-speech and voice cloning — open models plus a hosted pay-as-you-go API. Best for agent builders.
Audio-infrastructure API for voice products — async and real-time speech-to-text with diarization and translation. Best for agent builders.
Programmatic AI avatar video generation and video translation/dubbing with lip-sync, via a REST API. Best for agent builders.
Empathic Voice Interface (EVI) and Octave TTS — emotionally intelligent, context-aware expressive speech. Best for agent builders.
Low-latency (150–200ms) multilingual text-to-speech with studio-quality voices and instant cloning. Best for agent builders.
Generative text-to-speech API with 900+ voices, instant voice cloning, and low-latency streaming for conversational AI. Best for agent builders.
Voice cloning and generative speech API, plus deepfake detection and audio watermarking, billed per second. Best for agent builders.
Voice-agent API for AI phone calls — build, test, and deploy production call agents with usage-based per-minute pricing. Best for agent builders.
Enterprise TTS with 200+ realistic voices, sub-200ms latency, and linguistically-aware markup for voice agents. Best for agent builders.
High-accuracy speech-to-text across 55+ languages, plus real-time transcription and the Flow voice-agent API. Best for agent builders.
Studio-grade AI avatar video generation API — script-to-video with 200+ avatars, translation, and templates. Best for agent builders.
Conversational Video Interface (CVI) and Phoenix replica API — real-time, face-to-face AI video agents ('digital twins'). Best for agent builders.
Developer-first platform to build, test, and deploy real-time voice AI agents with pluggable STT/LLM/TTS and telephony. Best for agent builders.
AssemblyAI (★ 0) is the most-starred voice, speech & video alternative to Sync (sync. labs). Speech-to-text and audio-intelligence API — transcription, diarization, summarization, and LLM-over-audio (LeMUR).
The strongest voice, speech & video alternatives to Sync (sync. labs) are AssemblyAI, Cartesia, D-ID, Deepgram and more — each with a head-to-head comparison.
Yes — the alternatives listed are open source and free to self-host; you bring your own model keys.
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