gRPC API Reference

Basic Transcription

These requests are used to transcribe audio. The Transcribe request is suitable for transcription of shorter audio segments, while the TranscribeStream request is suitable for transcription of possibly long audio as well as real-time audio.

rpc Transcribe

rpc Transcribe(TranscribeRequest) returns (TranscribeResponse) {}

message TranscribeRequest {
  string api_key = 1;
  TranscribeConfig config = 2;
  bytes audio = 3;
}

message TranscribeConfig {
  string audio_format = 1;
  int32 sample_rate_hertz = 2;
  int32 num_audio_channels = 3;
  SpeechContext speech_context = 4;
}

message TranscribeResponse {
  Result result = 1;
}

The Transcribe request transcribes an audio of limited duration and returns the complete transcription at once.

The audio is provided in the audio field of the request message. By default, the audio is assumed to use a container format which is automatically inferred. The maximum audio size is 5 * 1024² bytes and the maximum audio duration is 60 seconds (exceeding these limits will result in an error and no transcription). The result of the transcription is available in the result field in the response, which is a Result message. Words returned in a Transcribe are always final (is_final=true).

The following container formats are supported: aac, aiff, amr, asf, flac, mp3, ogg, wav. If config.audio_format is set to one of these formats, that format will be used without auto-detection.

PCM audio can be provided if config.audio_format is set to one of the supported PCM formats, which are: pcm_f32le, pcm_f32be, pcm_s32le, pcm_s32be, pcm_s16le, pcm_s16be. For example, pcm_f32le means float-32 little endian. When using a PCM format, config.sample_rate_hertz and config.num_audio_channels must be set. Supported sample rates are 2000 to 96000 Hz and supported numbers of channels are 1 and 2.

If desired, a speech context can be specified using config.speech_context. There are two methods of specifying a speech context. First, the speech context entries can be provided directly in config.speech_context.entries. Second, a speech context stored in the context of the user's Soniox account can be referenced using config.speech_context.name. It is in error if both entries and name are non-empty. For information about speech context, refer to Speech Adaptation.

rpc TranscribeStream

rpc TranscribeStream(stream TranscribeStreamRequest) returns (stream TranscribeStreamResponse) {}

message TranscribeStreamRequest {
  string api_key = 1;
  TranscribeStreamConfig config = 2;
  bytes audio = 3;
}

message TranscribeStreamConfig {
  string audio_format = 1;
  int32 sample_rate_hertz = 2;
  int32 num_audio_channels = 3;
  SpeechContext speech_context = 4;
  bool include_nonfinal = 5;
}

message TranscribeStreamResponse {
  Result result = 1;
}

The TranscribeStream request transcribes audio in streaming mode, either optimized for throughput or low-latency.

The client sends a stream of TranscribeStreamRequest requests to the service. The api_key and config are provided in the first request and must not be included in later request. The audio is provided in chunks using the audio field, which may be empty in any request.

TranscribeStream supports the same audio formats as Transcribe. If a container format is used, the audio chunks together must form a single container (audio file) and the boundaries between them have no significance. If a PCM format is used, then each audio chunk must contain a whole number of samples. The maximum audio size in a single request is 5 * 1024² bytes.

TranscribeStream can use a speech context the same as Transcribe.

The service returns a stream of TranscribeStreamResponse messages, with transcription results available in the result field. The result field may be missing, it is important that the client checks for its presence before interpreting it (e.g. has_result() in C++, HasField("result") in Python). The client should not make any assumption about the corresponsence of requests to responses.

If include_nonfinal is false, TranscribeStream returns only final words and does not offer any latency guarantees. This mode is optimized for throughput and is essentially a streaming version of Transcribe, enabling transcription of audio of longer duration. The complete sequence of words is obtained by joining the words from all results.

If include_nonfinal is true, TranscribeStream returns both final and non-final words while minimizing the recognition latency. This mode is suitable for transcription of real-time audio streams where transcribed words need to be received as soon possible after the audio where they are pronounced has been sent to the service. The current available transcription from the start of the audio is obtained by joining final words in responses before the last one followed by all words in the last response (equivalently, by joining final words from all responses followed by non-final words in the last response).

Additionally, if include_nonfinal is true:

Audio should not be sent at a rate faster than real-time. If it is, the service may throttle processing or return an error. There are margins such that this should not occur for real-time streams under normal circumstances.
Minimum latency is achieved when using the PCM format pcm_s16le with sample rate 16 kHz and one audio channel. Alternatively any supported PCM format can be used with only a small increase of latency. Using a container format in this mode is not recommended due to possibly large latency resulting from audio decoding.

message Result

message Result {
  repeated Word words = 1;
  int32 final_proc_time_ms = 2;
  int32 total_proc_time_ms = 3;
}

The Result message represents a speech recognition result received in a response from Transcribe or TranscribeStream, containing transcribed words and other data.

The words field contains a sequence of Word messages representing transcribed words.

The final_proc_time_ms and total_proc_time_ms fields determine the duration of processed audio in milliseconds, resulting in final and all words respectively. In a Transcribe request, both values are equal. In a TranscribeStream request, these behave as described in Processed Audio Duration.

message Word

message Word {
  string text = 1;
  int32 start_ms = 2;
  int32 duration_ms = 3;
  bool is_final = 4;
}

The Word message represents an individual recognized word, which is given in the text field.

start_ms and duration_ms represent the time interval of the word in the audio. Understood as half-open interval [start_ms, start_ms+duration_ms), it is guaranteed that there is no overlap between transcribed words from the start.

is_final specifies if the word is final. This disinction relevant only when using TranscribeStream with include_nonfinal=true; in other cases is_final is always true, Refer to Final vs Non-final Words.

Asynchronous Transcription

These requests allow a client to upload files to be transcribed asynchronously and to retrieve the transcription results later. This feature supports a variety of media file formats including video files.

A file is uploaded for transcription using TranscribeAsync. The status of the transcription can be queried using GetTranscribeAsyncStatus. The result of the transcription is retrieved using GetTranscribeAsyncResult.

A file that has been uploaded (and not yet deleted) is in one of the following states:

QUEUED: The file is queued to be transcribed.
TRANSCRIBING: The file is being transcribed.
COMPLETED: The file has been transcribed successfully, the result is available.
FAILED: Transcription has failed, the result is not and will not be available.

A file that is not in the TRANSCRIBING state can be deleted using DeleteTranscribeAsyncFile. It is the responsibility of the user to delete files, they are not deleted automatically.

There is a limit on the numbers of files in the QUEUED and TRANSCRIBING states (by default 20) and also a limit on the total number of files (by default 200). If any of these limits is reached, further TranscribeAsync requests will be rejected with gRPC status code RESOURCE_EXHAUSTED and details message starting with <too_many_pending_files> or <too_many_files> respectively. It is the responsibility of the user to prevent or handle these errors.

rpc TranscribeAsync

rpc TranscribeAsync(stream TranscribeAsyncRequest) returns (TranscribeAsyncResponse) {}

message TranscribeAsyncRequest {
  string api_key = 1;
  string reference_name = 3;
  bytes audio = 4;
}

message TranscribeAsyncResponse {
  string file_id = 1;
}

The TranscribeAsync request is used to upload a file for asyncronous transcription. The client sends a stream of TranscribeAsyncRequest messages, where the first message specifies the api_key and reference_name and may contain an audio chunk, and any further messages contain only an audio chunk. The audio chunks are concatenated to form the complete audio file. The maximum size of an audio chunk is 5 * 1024². The maximum total size is 100 * 1024² bytes. The maximum total duration of audio is 2 hours.

Audio is extracted from the file as a part of TranscribeAsync. For larger files, it may take a few seconds to decode the audio after all the audio data has been received by the service. If there is an error during decoding, the TranscribeAsync request will fail with gRPC status code UNKNOWN and details message starting with <invalid_media_file>.

The reference_name specified in the first request is intended to enable the user to identify the file after it has been uploaded. It can be any string not longer than 256 characters, including the empty string, and duplicates are allowed. The service does not use this field, it is only for reference.

If TranscribeAsync succeeds, the automatically assigned file_id is returned. The current state of the file can be queried by calling GetTranscribeAsyncStatus with the file_id.

The file will initially be in the QUEUED state and will transition to the TRANSCRIBING state when the transcription starts. The time that this takes depends on the current service load. When transcription has completed, the file will transition to the COMPLETED state and the results can be retrieved using GetTranscribeAsyncResult. If transcription fails, the file will instead transition to the FAILED state. The file will then remain in the COMPLETED or FAILED state until it is deleted using DeleteTranscribeAsyncFile

rpc GetTranscribeAsyncStatus

rpc GetTranscribeAsyncStatus(GetTranscribeAsyncStatusRequest) returns (GetTranscribeAsyncStatusResponse) {}

message GetTranscribeAsyncStatusRequest {
  string api_key = 1;
  string file_id = 2;
}

message GetTranscribeAsyncStatusResponse {
  repeated TranscribeAsyncFileStatus files = 1;
}

message TranscribeAsyncFileStatus {
  string file_id = 1;
  string reference_name = 2;
  // One of: QUEUED, TRANSCRIBING, COMPLETED, FAILED
  string status = 3;
  // UTC timestamp
  google.protobuf.Timestamp created_time = 4;
}

The GetTranscribeAsyncStatus request returns the state and other information for a specific file or for all existing files.

If file_id in the request is non-empty, information for a file with that ID is returned. In this case, if there is no file with that ID, the request fails with gRPC status code NOT_FOUND and details message starting with <file_id_not_found>. If file_id is empty, information about all existing files is returned.

The files field in the response is a sequence of TranscribeAsyncFileStatus messages. If file_id in the request was non-empty, there will be exactly one element, otherwise there will be one element for each existing file ordered by increasing created_time.

The following information is returned for each file in the response file_id, reference_name, status (state) and created_time (UTC timestamp when TranscribeAsync has completed).

rpc GetTranscribeAsyncResult

rpc GetTranscribeAsyncResult(GetTranscribeAsyncResultRequest) returns (stream GetTranscribeAsyncResultResponse) {}

message GetTranscribeAsyncResultRequest {
  string api_key = 1;
  string file_id = 2;
}

message GetTranscribeAsyncResultResponse {
  Result result = 1;
}

The GetTranscribeAsyncResult request retrieves the the transcription results for a file in the COMPLETED state.

The file for which to retrieve results is specified by file_id. If there is no file with that ID, the request fails with gRPC status code NOT_FOUND and details message starting with <file_id_not_found>.

If the file is still in the QUEUED or TRANSCRIBING state, the request fails with gRPC status code FAILED_PRECONDITION and details message starting with <file_not_transcribed_yet>. If the file is in the FAILED state, it fails with gRPC status code FAILED_PRECONDITION and details message starting with <file_transcription_failed>.

The transcription results are returned as a sequence of Result messages embedded in a stream of GetTranscribeAsyncResultResponse responses, similar to TranscribeStream. The user can assemble the complete result by concatenating the words from all responses, which are guaranteed to be final, and taking final_proc_time_ms and total_proc_time_ms from the last response, which are equal and represent the audio duration.

rpc DeleteTranscribeAsyncFile

rpc DeleteTranscribeAsyncFile(DeleteTranscribeAsyncFileRequest) returns (DeleteTranscribeAsyncFileResponse) {}

message DeleteTranscribeAsyncFileRequest {
  string api_key = 1;
  string file_id = 2;
}

message DeleteTranscribeAsyncFileResponse {
}

The DeleteTranscribeAsyncFile request deletes a specific file.

The file to delete is specified by file_id. If there is no file with that ID, the request fails with gRPC status code NOT_FOUND and details message starting with <file_id_not_found>.

A file can be deleted as long as it is not in the TRANSCRIBING state. If it is, the request fails with gRPC status code FAILED_PRECONDITION and details message starting with <file_being_transcribed>.

Speech Context

These requests are used to manage the user's speech contexts stored in the Soniox Cloud. Storing a speech context enables using it in a Transcribe or TranscribeStream request as an alternative to directly specifying it. For general information about speech contexts, refer to Speech Adaptation.

Stored speech contexts exist in the context of a user account, where they are uniquely identified by a user-specified name. The user account is inferred from the API key used in the request.

rpc CreateSpeechContext

rpc CreateSpeechContext(CreateSpeechContextRequest) returns (CreateSpeechContextResponse) {}

message CreateSpeechContextRequest {
  string api_key = 1;
  SpeechContext speech_context = 2;
}

message CreateSpeechContextResponse {
}

The CreateSpeechContext request creates a stored speech context.

The name of the speech context to create is specified as a part of the speech context in speech_context.name, which must be non-empty.

If a speech context with that name already exists, an error with status code ALREADY_EXISTS is returned. If the speech_context does not satisfy the SpeechContext requirements, an error with status code INVALID_ARGUMENT and a message describing the problem is returned.

rpc UpdateSpeechContext

rpc UpdateSpeechContext(UpdateSpeechContextRequest) returns (UpdateSpeechContextResponse) {}

message UpdateSpeechContextRequest {
  string api_key = 1;
  SpeechContext speech_context = 2;
}

message UpdateSpeechContextResponse {
}

The UpdateSpeechContext request updates an existing stored speech context.

The name of the speech context to update is specified as a part of the speech context in speech_context.name.

If there is no speech context with that name, an error with status code NOT_FOUND is returned. If the speech_context does not satisfy the SpeechContext requirements, an error with status code INVALID_ARGUMENT and a message describing the problem is returned.

rpc DeleteSpeechContext

rpc DeleteSpeechContext(DeleteSpeechContextRequest) returns (DeleteSpeechContextResponse) {}

message DeleteSpeechContextRequest {
  string api_key = 1;
  string name = 2;
}

message DeleteSpeechContextResponse {
}

The DeleteSpeechContext deletes a stored speech context.

The name of the speech context to delete is specified in name. If there is no speech context with that name, an error with status code NOT_FOUND is returned.

rpc ListSpeechContextNames

rpc ListSpeechContextNames(ListSpeechContextNamesRequest) returns (ListSpeechContextNamesResponse) {}

message ListSpeechContextNamesRequest {
  string api_key = 1;
}

message ListSpeechContextNamesResponse {
  repeated string names = 1;
}

The ListSpeechContextNames request returns the names of all stored speech contexts.

The names are returned in the names field in no specific order.

rpc GetSpeechContext

rpc GetSpeechContext(GetSpeechContextRequest) returns (GetSpeechContextResponse) {}

message GetSpeechContextRequest {
  string api_key = 1;
  string name = 2;
}

message GetSpeechContextResponse {
  SpeechContext speech_context = 1;
}

The GetSpeechContext request retrieves a stored speech context.

The name of the speech context to retrieve is sepecified in the name field. If there is no speech context with that name, an error with status code NOT_FOUND is returned.

message SpeechContext

message SpeechContext {
  repeated SpeechContextEntry entries = 1;
  string name = 2;
}

The SpeechContext message represents a speech context.

The entries field contains the entries defining the speech context, represented by SpeechContextEntry messages. The name field represents the name of the speech context.

The presence of entries and name depends on the context:

When a speech context is sent in CreateSpeechContext or UpdateSpeechContext, or returned in GetSpeechContext, both are required or guaranteed to be non-empty respectively.
In a Transcribe or TranscribeStream request, either both or exactly one must be non-empty. If both are empty, no speech context is used; if entries is non-empty, these entries are used; if name is non-empty, a stored speech context with that name is used.

Requirements:

The size of the name must not exceed 50 characters.
For each entry: SpeechContextEntry requirements.
The number of phrases in the entire speech context must not exceed 100.
There must be no duplicate phrases in the entire speech context, after removing leading, trailing and repeated spaces.

message SpeechContextEntry

message SpeechContextEntry {
  repeated string phrases = 1;
  double boost = 2;
}

The SpeechContextEntry message represents an entry in a speech context, defined by a list of phrases and a single boost value that applies to these phrases. Words in each phrase are separated by spaces.

Requirements:

There must be at least phrase.
The size of a phrase must not exceed 100 characters.
The number of words in a phrase must be between 1 and 5
The size of a word must not exceed 25 characters.
A phrase may contain only the following characters: a-z (lower-case only), ' (apostrophe), - (hyphen/minus), (space).
The boost value must be between -30 and 30 inclusive.

Basic Transcription
Asynchronous Transcription
Speech Context