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Values: URL


Enables you to specify the URL of a callback server to which each utterance in a transcription result will be POSTed as it is transcribed. Using this option is mandatory for real-time speech processing. As used in the ASR engine, a callback is the address and (optionally) method name and parameters of a web application that can receive data via HTTP or HTTPS. In the ASR engine, callbacks are usually used to enable another application to receive and directly interact with the transcripts produced by the ASR engine.

By default, ASR engine results are returned by calling the /transcribe/result API with the requestid that was returned by the /transcribe call. When a callback is specified, the result can still be retrieved using the requestid that was returned by the /transcribe call, but only if the callback has not succeeded (indicated by HTTP code 200). Once the callback returns success, the result is no longer available from ASR engine. If a callback fails, it will be retried until it succeeds or until a maximum number of retries is reached.

ASR engine transcriptions are normally returned immediately and directly to the user or application that submitted the audio file for transcription. When a callback is specified, the transcription result is POSTed to the specified callback address and cannot be retrieved subsequently unless the application that is listening on the callback address somehow makes it available. The ASR engine does not check the return code from the callback to verify that the transcription was sent to a valid address or that it was received correctly.