C API

See also the list of error codes including descriptions for each error in Error codes.

int STT_CreateModel(const char *aModelPath, ModelState **retval)

An object providing an interface to a trained Coqui STT model.

Return

Zero on success, non-zero on failure.

Parameters
  • aModelPath: The path to the frozen model graph.

  • [out] retval: a ModelState pointer

void STT_FreeModel(ModelState *ctx)

Frees associated resources and destroys model object.

int STT_EnableExternalScorer(ModelState *aCtx, const char *aScorerPath)

Enable decoding using an external scorer.

Return

Zero on success, non-zero on failure (invalid arguments).

Parameters
  • aCtx: The ModelState pointer for the model being changed.

  • aScorerPath: The path to the external scorer file.

int STT_DisableExternalScorer(ModelState *aCtx)

Disable decoding using an external scorer.

Return

Zero on success, non-zero on failure.

Parameters
  • aCtx: The ModelState pointer for the model being changed.

int STT_AddHotWord(ModelState *aCtx, const char *word, float boost)

Add a hot-word and its boost.

Words that don’t occur in the scorer (e.g. proper nouns) or strings that contain spaces won’t be taken into account.

Return

Zero on success, non-zero on failure (invalid arguments).

Parameters
  • aCtx: The ModelState pointer for the model being changed.

  • word: The hot-word.

  • boost: The boost. Positive value increases and negative reduces chance of a word occuring in a transcription. Excessive positive boost might lead to splitting up of letters of the word following the hot-word.

int STT_EraseHotWord(ModelState *aCtx, const char *word)

Remove entry for a hot-word from the hot-words map.

Return

Zero on success, non-zero on failure (invalid arguments).

Parameters
  • aCtx: The ModelState pointer for the model being changed.

  • word: The hot-word.

int STT_ClearHotWords(ModelState *aCtx)

Removes all elements from the hot-words map.

Return

Zero on success, non-zero on failure (invalid arguments).

Parameters
  • aCtx: The ModelState pointer for the model being changed.

int STT_SetScorerAlphaBeta(ModelState *aCtx, float aAlpha, float aBeta)

Set hyperparameters alpha and beta of the external scorer.

Return

Zero on success, non-zero on failure.

Parameters
  • aCtx: The ModelState pointer for the model being changed.

  • aAlpha: The alpha hyperparameter of the decoder. Language model weight.

  • aLMBeta: The beta hyperparameter of the decoder. Word insertion weight.

int STT_GetModelSampleRate(const ModelState *aCtx)

Return the sample rate expected by a model.

Return

Sample rate expected by the model for its input.

Parameters

char *STT_SpeechToText(ModelState *aCtx, const short *aBuffer, unsigned int aBufferSize)

Use the Coqui STT model to convert speech to text.

Return

The STT result. The user is responsible for freeing the string using STT_FreeString(). Returns NULL on error.

Parameters
  • aCtx: The ModelState pointer for the model to use.

  • aBuffer: A 16-bit, mono raw audio signal at the appropriate sample rate (matching what the model was trained on).

  • aBufferSize: The number of samples in the audio signal.

Metadata *STT_SpeechToTextWithMetadata(ModelState *aCtx, const short *aBuffer, unsigned int aBufferSize, unsigned int aNumResults)

Use the Coqui STT model to convert speech to text and output results including metadata.

Return

Metadata struct containing multiple CandidateTranscript structs. Each transcript has per-token metadata including timing information. The user is responsible for freeing Metadata by calling STT_FreeMetadata(). Returns NULL on error.

Parameters
  • aCtx: The ModelState pointer for the model to use.

  • aBuffer: A 16-bit, mono raw audio signal at the appropriate sample rate (matching what the model was trained on).

  • aBufferSize: The number of samples in the audio signal.

  • aNumResults: The maximum number of CandidateTranscript structs to return. Returned value might be smaller than this.

int STT_CreateStream(ModelState *aCtx, StreamingState **retval)

Create a new streaming inference state. The streaming state returned by this function can then be passed to STT_FeedAudioContent() and STT_FinishStream().

Return

Zero for success, non-zero on failure.

Parameters
  • aCtx: The ModelState pointer for the model to use.

  • [out] retval: an opaque pointer that represents the streaming state. Can be NULL if an error occurs.

void STT_FeedAudioContent(StreamingState *aSctx, const short *aBuffer, unsigned int aBufferSize)

Feed audio samples to an ongoing streaming inference.

Parameters
  • aSctx: A streaming state pointer returned by STT_CreateStream().

  • aBuffer: An array of 16-bit, mono raw audio samples at the appropriate sample rate (matching what the model was trained on).

  • aBufferSize: The number of samples in aBuffer.

char *STT_IntermediateDecode(const StreamingState *aSctx)

Compute the intermediate decoding of an ongoing streaming inference.

Return

The STT intermediate result. The user is responsible for freeing the string using STT_FreeString().

Parameters

Metadata *STT_IntermediateDecodeWithMetadata(const StreamingState *aSctx, unsigned int aNumResults)

Compute the intermediate decoding of an ongoing streaming inference, return results including metadata.

Return

Metadata struct containing multiple candidate transcripts. Each transcript has per-token metadata including timing information. The user is responsible for freeing Metadata by calling STT_FreeMetadata(). Returns NULL on error.

Parameters
  • aSctx: A streaming state pointer returned by STT_CreateStream().

  • aNumResults: The number of candidate transcripts to return.

char *STT_FinishStream(StreamingState *aSctx)

Compute the final decoding of an ongoing streaming inference and return the result. Signals the end of an ongoing streaming inference.

Return

The STT result. The user is responsible for freeing the string using STT_FreeString().

Note

This method will free the state pointer (aSctx).

Parameters

Metadata *STT_FinishStreamWithMetadata(StreamingState *aSctx, unsigned int aNumResults)

Compute the final decoding of an ongoing streaming inference and return results including metadata. Signals the end of an ongoing streaming inference.

Return

Metadata struct containing multiple candidate transcripts. Each transcript has per-token metadata including timing information. The user is responsible for freeing Metadata by calling STT_FreeMetadata(). Returns NULL on error.

Note

This method will free the state pointer (aSctx).

Parameters
  • aSctx: A streaming state pointer returned by STT_CreateStream().

  • aNumResults: The number of candidate transcripts to return.

void STT_FreeStream(StreamingState *aSctx)

Destroy a streaming state without decoding the computed logits. This can be used if you no longer need the result of an ongoing streaming inference and don’t want to perform a costly decode operation.

Note

This method will free the state pointer (aSctx).

Parameters

void STT_FreeMetadata(Metadata *m)

Free memory allocated for metadata information.

void STT_FreeString(char *str)

Free a char* string returned by the Coqui STT API.

char *STT_Version()

Returns the version of this library. The returned version is a semantic version (SemVer 2.0.0). The string returned must be freed with STT_FreeString().

Return

The version string.