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| Pricing | Free | Free |
| Capabilities | 10 decomposed | 11 decomposed |
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Generates natural-sounding speech from text using a lightweight 82-million parameter transformer-based neural model (KModel class) that operates on phoneme sequences rather than raw text, with parallel Python and JavaScript implementations enabling deployment from CLI to web browsers. The KPipeline orchestrates text processing through language-specific G2P conversion (misaki or espeak-ng backends) followed by neural synthesis and ONNX-based audio waveform generation via istftnet modules.
Unique: Combines 82M parameter efficiency (vs 1B+ parameter competitors) with dual Python/JavaScript architecture enabling both server and browser deployment; uses misaki + espeak-ng hybrid G2P pipeline for language-agnostic phoneme conversion rather than language-specific models
vs alternatives: Smaller model size and Apache 2.0 licensing enable unrestricted commercial deployment where cloud-dependent TTS (Google Cloud, Azure) or GPL-licensed alternatives (Coqui) are impractical; JavaScript support gives browser-native synthesis unavailable in most open-source TTS
Converts text characters to phoneme sequences using a dual-backend architecture: misaki library as primary G2P engine for most languages, with espeak-ng fallback for Hindi and other languages requiring rule-based phonetic conversion. The text processing pipeline (in kokoro/pipeline.py) selects the appropriate G2P backend based on language code, handles text chunking for long inputs, and produces phoneme sequences that feed into neural synthesis.
Unique: Hybrid G2P architecture using misaki as primary engine with espeak-ng fallback provides better phonetic accuracy than single-backend approaches; language-specific backend selection (misaki for most, espeak-ng for Hindi) optimizes for each language's phonetic complexity rather than one-size-fits-all approach
vs alternatives: More flexible than single-backend G2P (e.g., pure espeak-ng) by combining neural-trained misaki with rule-based espeak-ng; avoids dependency on large language models for phoneme conversion, reducing latency vs LLM-based G2P approaches
Generates raw audio waveforms from phoneme token sequences using ONNX-optimized istftnet modules that perform inverse short-time Fourier transform (ISTFT) synthesis. The KModel class produces mel-spectrogram embeddings from phoneme tokens, which are then converted to linear spectrograms and finally to waveforms via the ONNX-compiled istftnet vocoder, enabling efficient CPU/GPU inference without PyTorch overhead.
Unique: Uses ONNX-compiled istftnet vocoder for inference optimization rather than PyTorch-based vocoding, reducing memory footprint and enabling deployment on ONNX Runtime across heterogeneous hardware (CPU, GPU, mobile); istftnet provides direct spectrogram-to-waveform synthesis without intermediate neural vocoder layers
vs alternatives: ONNX vocoding is faster than PyTorch-based vocoders (HiFi-GAN, Glow-TTS) on CPU inference; smaller model size than end-to-end neural vocoders enables edge deployment where alternatives require significant computational overhead
Enables selection from multiple pre-trained voice styles (e.g., 'af_heart' for American female, various British voices) by conditioning the neural model with voice-specific embeddings. The KModel class accepts a voice identifier parameter that retrieves corresponding embeddings from HuggingFace Hub, which are concatenated with phoneme embeddings during synthesis to produce voice-specific speech characteristics without retraining the base model.
Unique: Implements speaker conditioning via pre-trained voice embeddings rather than speaker ID tokens or speaker-specific model variants, enabling voice selection without model duplication; embeddings are downloaded on-demand from HuggingFace Hub rather than bundled, reducing package size
vs alternatives: More efficient than maintaining separate model checkpoints per voice (as some TTS systems do); embedding-based conditioning is lighter-weight than speaker encoder networks used in some alternatives, reducing inference latency
Provides parallel Python (KPipeline, KModel classes) and JavaScript (KokoroTTS class) implementations with identical functional semantics, enabling code portability and consistent behavior across environments. Both implementations share the same text processing pipeline, model inference logic, and audio synthesis approach, with language-specific optimizations (PyTorch for Python, ONNX.js for JavaScript) while maintaining API compatibility.
Unique: Maintains semantic equivalence between Python and JavaScript implementations through shared pipeline design (KPipeline abstraction) rather than transpilation or wrapper layers; both implementations use identical text processing and model inference logic with language-specific runtime optimization
vs alternatives: More maintainable than separate Python/JavaScript implementations because core logic is unified; avoids transpilation overhead and complexity of maintaining two codebases with different semantics, unlike some TTS projects with separate Python and JS versions
Provides CLI tools for text-to-speech synthesis without programmatic API usage, supporting both interactive input and batch file processing. The CLI wraps the KPipeline class, accepting text input via stdin or file arguments, language/voice parameters, and output file specifications, enabling integration into shell scripts and data processing pipelines.
Unique: CLI implementation wraps KPipeline class directly without separate CLI-specific code, maintaining consistency with programmatic API; supports both interactive and batch modes through unified interface
vs alternatives: Simpler than cloud-based TTS CLIs (Google Cloud, Azure) because no authentication or API key management required; more accessible than programmatic APIs for non-developers and shell script integration
Provides utilities (examples/export.py) to export the KModel neural network and istftnet vocoder to ONNX format for optimized inference across different hardware and runtime environments. The export process converts PyTorch models to ONNX intermediate representation, enabling deployment on ONNX Runtime (CPU, GPU, mobile) without PyTorch dependency, reducing model size and inference latency.
Unique: Provides explicit export utilities rather than automatic ONNX export, giving developers control over export parameters and optimization settings; separates export from inference, enabling offline optimization workflows
vs alternatives: More flexible than automatic export because developers can customize export parameters; avoids runtime overhead of on-demand export compared to systems that export during first inference
Implements generator-based processing pipeline that yields audio segments incrementally as they are synthesized, rather than buffering entire output. The KPipeline class returns Python generators that yield tuples of (graphemes, phonemes, audio_segment) for each text chunk, enabling memory-efficient processing of long texts and streaming output to audio devices or files.
Unique: Uses Python generators to yield audio segments incrementally rather than buffering entire output, enabling memory-efficient processing of arbitrarily long texts; generator pattern provides both phoneme and audio output for each segment, enabling downstream analysis or processing
vs alternatives: More memory-efficient than batch processing entire texts; enables real-time streaming output unavailable in systems that require complete synthesis before output; generator pattern is more Pythonic than callback-based streaming
+2 more capabilities
Transcribes audio in 98 languages to text in the original language using a unified Transformer sequence-to-sequence architecture with a shared AudioEncoder that processes mel spectrograms into language-agnostic embeddings, then a TextDecoder that generates tokens autoregressively. The system handles variable-length audio by padding or trimming to 30-second segments and uses task-specific tokens to signal transcription mode, enabling a single model to handle multiple languages without language-specific branches.
Unique: Uses a single shared AudioEncoder across all 98 languages rather than language-specific encoders, trained on 680,000 hours of diverse internet audio enabling zero-shot cross-lingual transfer. The mel-spectrogram preprocessing pipeline (via log_mel_spectrogram) standardizes variable audio into fixed 30-second segments, allowing the same model weights to handle any language without retraining.
vs alternatives: Outperforms language-specific ASR models on low-resource languages and handles 98 languages in a single model, whereas Google Cloud Speech-to-Text and Azure Speech Services require separate API calls per language and have higher latency due to cloud round-trips.
Translates non-English speech directly to English text by using a task-specific token in the TextDecoder that signals translation mode, bypassing the need for intermediate transcription-then-translation pipelines. The AudioEncoder processes mel spectrograms identically to transcription, but the decoder generates English tokens directly from audio embeddings, reducing latency and error propagation compared to cascaded systems.
Unique: Implements end-to-end speech translation via task-specific decoder tokens rather than cascaded transcription-then-translation, eliminating intermediate text generation and reducing error propagation. The decoder uses a special token prefix to signal translation mode, allowing the same AudioEncoder and TextDecoder weights to handle both transcription and translation without separate model branches.
Kokoro TTS scores higher at 59/100 vs Whisper CLI at 58/100.
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vs alternatives: Faster and more accurate than cascaded pipelines (Google Translate + Speech-to-Text) because it avoids intermediate transcription errors and reduces round-trip latency; however, less flexible than specialized translation models for domain-specific or style-controlled output.
Exposes two levels of API abstraction: a high-level transcribe() function that handles end-to-end transcription with automatic audio loading, preprocessing, and result formatting, and a low-level decode() function that provides fine-grained control over decoding options (beam width, temperature, language constraints). The high-level API is suitable for simple use cases, while the low-level API enables advanced customization for researchers and developers building complex pipelines.
Unique: Provides dual-level API abstraction with transcribe() for simplicity and decode() for control, allowing users to start with simple code and gradually adopt lower-level APIs as needs become more complex. The high-level API automatically handles audio loading, preprocessing, and result formatting, while the low-level API exposes DecodingOptions for fine-grained control.
vs alternatives: More flexible than single-level APIs (like some cloud services that only expose high-level endpoints) because it supports both simple and advanced use cases; however, requires more learning and boilerplate than opinionated frameworks that make decisions for users.
Detects the spoken language in audio by generating a language token from the AudioEncoder embeddings before decoding text, using the model's multilingual training to recognize acoustic patterns distinctive to each language. The system identifies language during the initial decoding step and can be queried directly via the language identification task token, enabling language detection without full transcription.
Unique: Leverages the shared AudioEncoder's learned acoustic representations across 680,000 hours of multilingual training data to identify language without explicit language classification head — the language token emerges naturally from the decoder's first output token, making detection a byproduct of the transcription architecture rather than a separate classifier.
vs alternatives: Supports 98 languages in a single model with zero-shot capability on low-resource languages, whereas language identification libraries like langdetect or textcat require separate training or pre-built models for each language and cannot handle audio directly.
Converts raw audio files in multiple formats (MP3, WAV, M4A, FLAC, OGG) to mel-spectrogram features via FFmpeg decoding and log-scale mel-frequency filtering, then normalizes variable-length audio to fixed 30-second segments via padding or trimming. The pipeline uses whisper.load_audio() for format-agnostic decoding, whisper.pad_or_trim() for segment normalization, and whisper.log_mel_spectrogram() for feature extraction, enabling the model to process diverse audio sources with consistent preprocessing.
Unique: Integrates FFmpeg as a subprocess for format-agnostic audio decoding rather than using Python-only libraries, enabling support for any FFmpeg-compatible format without maintaining codec-specific parsers. The fixed 30-second segment design allows the model to use a single AudioEncoder without variable-length handling, simplifying the architecture at the cost of preprocessing inflexibility.
vs alternatives: Handles more audio formats than librosa-based pipelines (which require separate codec installations) and avoids the latency of cloud-based audio conversion services; however, less flexible than custom preprocessing pipelines that can adjust segment length or mel-spectrogram parameters.
Generates transcription or translation tokens autoregressively using a TextDecoder that processes AudioEncoder embeddings and previously generated tokens, with support for multiple decoding strategies including greedy decoding, beam search, and temperature-based sampling. The system uses a sliding-window context approach to handle audio longer than 30 seconds by processing overlapping segments and merging results, and supports DecodingOptions for fine-grained control over decoding behavior (beam width, temperature, language constraints).
Unique: Implements sliding-window decoding for long audio by processing overlapping 30-second segments and merging results via token-level overlap detection, avoiding the need to retrain the model for variable-length inputs. The DecodingOptions abstraction allows fine-grained control over beam width, temperature, language constraints, and other decoding parameters without modifying model weights.
vs alternatives: More flexible than fixed-greedy-decoding-only systems (like some edge-deployed models) because it supports beam search and temperature sampling; however, slower than specialized streaming decoders (like Kaldi or Vosk) that use HMM-based decoding optimized for low-latency online processing.
Generates precise word-level timestamps by aligning decoded tokens to audio segments using the model's internal attention weights and token probabilities, enabling subtitle generation and fine-grained audio-text synchronization. The system decodes text at the segment level (30 seconds), then uses token timing information to map each word back to its position in the original audio, producing timestamps accurate to ~100ms granularity.
Unique: Derives word-level timestamps from the model's token-to-audio alignment without a separate alignment model, using the decoder's implicit timing information from mel-spectrogram frame positions. The approach avoids the need for external forced-alignment tools (like Montreal Forced Aligner) by leveraging the model's learned audio-text correspondence.
vs alternatives: Simpler than forced-alignment pipelines (Montreal Forced Aligner + Whisper) because it uses a single model; however, less accurate than specialized alignment models trained specifically on timing prediction, and requires custom implementation to extract timing metadata from the model.
Provides six model sizes (tiny, base, small, medium, large, turbo) with parameter counts ranging from 39M to 1550M, enabling users to select optimal speed-accuracy tradeoffs based on hardware constraints and latency requirements. Each model has English-only variants (tiny.en, base.en, small.en) that sacrifice multilingual capability for 10-40% speed improvement, and the turbo model (809M) optimizes large-v3 for 8x faster inference with minimal accuracy degradation but no translation support.
Unique: Provides both multilingual and English-only variants for smaller models (tiny, base, small) to enable language-specific optimization, whereas most speech recognition systems offer only a single model per size. The turbo model represents a specialized optimization of large-v3 for inference speed using knowledge distillation or quantization techniques, not just parameter reduction.
vs alternatives: More granular model selection than Google Cloud Speech-to-Text (which offers only one model per language) and more transparent about speed-accuracy tradeoffs than commercial APIs that hide model details; however, requires manual model selection and management, whereas cloud services handle this automatically.
+3 more capabilities