Bing Speech API overview

Microsoft’s Speech to Text and Text to Speech cloud offerings help you put speech to work in your application. Microsoft's Speech APIs can transcribe speech to text and can generate speech from text. These APIs enable you to create powerful experiences that delight your users.

  • Speech to Text APIs convert human speech to text that can be used as input or commands to control your application.
  • Text to Speech APIs convert text to audio streams that can be played back to the user of your application.

Speech to text (speech recognition)

The Speech to Text APIs transcribe audio streams into text that your application can display to the user or act upon as command input. The Speech To Text APIs come in two flavors.

  • A REST API, useful for apps that need to convert short spoken commands to text but do not need simultaneous user feedback. The REST API uses HTTP chunked-transfer encoding to send the audio bytes to the service.
  • A WebSocket API, useful for apps need an improved user experience by using the power of the full-duplex WebSocket connection. Apps using this API get access to advanced features like speech recognition hypotheses. This API choice is also better for apps that need to transcribe longer audio passages.

Both Speech to Text APIs enrich the transcribed text by adding capitalization and punctuation, masking profanity, and text normalization.

Comparing API options for speech recognition

Feature WebSocket API REST API
Speech hypotheses Yes No
Continuous recognition Yes No
Maximum audio input 10 minutes of audio 15 seconds of audio
Service detects when speech ends Yes No
Subscription key authorization Yes No

Speech recognition modes

Microsoft's Speech to Text APIs support multiple modes of speech recognition. Choose the mode that produces the best recognition results for your application.

Mode Description
interactive "Command and control" recognition for interactive user application scenarios. Users speak short phrases intended as commands to an application.
dictation Continuous recognition for dictation scenarios. Users speak longer sentences that are displayed as text. Users adopt a more formal speaking style.
conversation Continuous recognition for transcribing conversations between humans. Users adopt a less formal speaking style and may alternate between longer sentences and shorter phrases.

For more information, see Recognition Modes in the API reference.

Speech recognition supported languages

The Speech to Text APIs support many spoken languages in multiple dialects. For the full list of supported languages in each recognition mode, see Recognition Languages.

Text to speech (speech synthesis)

Text to Speech APIs use REST to convert structured text to an audio stream. The APIs provide fast text to speech conversion in various voices and languages. For the full list of supported languages and voices, see Supported Locales and Voice Fonts.

Text to speech API

The maximum amount of audio returned for any single request is 15 seconds.