Creating long audio files - Amazon Polly

Creating long audio files

To create TTS files for large passages of text, use Amazon Polly's asynchronous synthesis functionality. This uses the three SpeechSynthesisTask APIs:

  • StartSpeechSynthesisTask: starts a new synthesis task.

  • GetSpeechSynthesisTask: returns details about a previously submitted synthesis task.

  • ListSpeechSynthesisTasks: lists all submitted synthesis tasks.

The SynthesizeSpeech operation produces audio in near-real time, with relatively little latency in most cases. To do this, the operation can only synthesize 3000 characters.

Amazon Polly's Asynchronous Synthesis feature overcomes the challenge of processing a larger text document by changing the way the document is both synthesized and returned. When a synthesis request is made by submitting input text using the StartSpeechSynthesisTask, Amazon Polly queues the requests, and then asynchronously processes them in the background as soon as the system resources are available. Amazon Polly then uploads the resulting speech or speech marks stream directly to your (required) Amazon Simple Storage Service (Amazon S3) bucket, and notifies you about the completed file's availability through your (optional) SNS topic.

In this way, all of the functionality except near-real time processing is available for texts of up to 100,000 billable characters (or 200,000 total characters) in length.

To synthesize a document using this method, you must have an Amazon S3 bucket that is writable to which the audio file can be saved. You can be notified when the synthesized audio is ready by providing an optional SNS Topic identifier. When the synthesis task is complete, Amazon Polly will publish a message on that topic. This message may also contain useful error information in cases where the synthesis task didn't succeed. To do this, make sure that the user creating the synthesis task can also publish to the SNS Topic. See the Amazon SNS documentation for more information on how to create and subscribe to an SNS Topic.


You can store the output file in an encrypted form in your S3 bucket if desired. To do this, you enable Amazon S3 bucket encryption, which use one of the strongest block ciphers available, 256-bit Advanced Encryption Standard (AES-256).