Transcribing streaming audio - Amazon Transcribe

Transcribing streaming audio

Using Amazon Transcribe streaming, you can produce real-time transcriptions for your media content. Unlike batch transcriptions, which involve uploading media files, streaming media is delivered to Amazon Transcribe in real time. Amazon Transcribe then returns a transcript, also in real time.

Streaming can include pre-recorded media (movies, music, and podcasts) and real-time media (live news broadcasts). Common streaming use cases for Amazon Transcribe include live closed captioning for sporting events and real-time monitoring of call center audio.

Streaming content is delivered as a series of sequential data packets, or 'chunks,' that Amazon Transcribe transcribes instantaneously. The advantages to using streaming over batch include real-time speech-to-text capabilities in your applications and faster transcription times. However, this increased speed may have accuracy limitations in some cases.

Amazon Transcribe offers the following options for streaming:

We recommend using the AWS Management Console or an SDK, rather than using HTTP/2 or WebSockets directly.

Audio formats supported for streaming transcriptions are:

  • FLAC

  • OPUS-encoded audio in an Ogg container

  • PCM (only signed 16-bit little-endian audio formats, which does not include WAV)

Lossless formats (FLAC or PCM) are recommended.


Streaming transcriptions are not supported with all languages. See Supported languages and language-specific features for details.

Streaming and partial results

Because streaming works in real time, transcripts are produced in partial results. Amazon Transcribe breaks up the incoming audio stream based on natural speech segments, such as a change in speaker or a pause in the audio. The transcription is returned to your application in a stream of transcription events, with each response containing more transcribed speech until an entire segment is transcribed.

An approximation of this is shown in the following code block. You can view this process in action by signing into the AWS Management Console, selecting Real-time transcription, and speaking into your microphone. Watch the Transcription output pane as you speak.

In this example, each line is the partial result of an audio segment.

The The ad. The and The Amazon. The Amazon is The Amazon is the The Amazon is the law. The Amazon is the lar. The Amazon is the large The Amazon is the largest The Amazon is the largest ray The Amazon is the largest rain The Amazon is the largest rain for The Amazon is the largest rainforest. The Amazon is the largest rainforest on the planet.

These partial results are present in your transcription output within the Results objects. Also in this object block is an IsPartial field. If this field is true, your transcription segment is not yet complete. You can view the difference between an incomplete and a complete segment below:

"IsPartial": true (incomplete segment) "Transcript": "The Amazon is the largest" } ], "EndTime": 3.275, "IsPartial": true, "ResultId": "55421b61-7cc6-4ef1-8d55-08a97159870e", "StartTime": 1.26 } "IsPartial": false (complete segment) "Transcript": "The Amazon is the largest rain forest on the planet." } ], "EndTime": 5.735, "IsPartial": false, "ResultId": "55421b61-7cc6-4ef1-8d55-08a97159870e", "StartTime": 1.26 }

Each word within a complete segment has an associated confidence score, which is a value between 0 and 1. A larger value indicates a greater likelihood that the word is correctly transcribed.


The StartTime and EndTime of an audio segment can be used to synchronize transcription output with video dialogue.

If you're running an application that requires low latency, you may want to use partial-result stabilization.

Partial-result stabilization

Amazon Transcribe starts returning transcription results as soon as you start streaming your audio. It returns these partial results incrementally until it generates a finished result at the level of a natural speech segment. A natural speech segment is continuous speech that contains a pause or a change in speaker.

Amazon Transcribe continues outputting partial results until it generates the final transcription result for a speech segment. Because speech recognition may revise words as it gains more context, streaming transcriptions can change slightly with each new partial result output.

This process gives you two options for each speech segment:

  • Wait for the finished segment

  • Use the segment's partial results

Partial result stabilization changes how Amazon Transcribe produces the final transcription result for each complete segment. When activated, only the last few words from the partial results can change. Because of this, transcription accuracy may be affected. However, your transcript is returned faster than without partial-results stabilization. This reduction in latency can help use cases, such as subtitling videos or generating captions for live streams.

The following examples show how the same audio stream is handled when partial-results stabilization is not activated and when it is. Note that you can set the stability level to low, medium, or high. Low stability provides the highest accuracy. High stability transcribes faster, but with slightly lower accuracy. You can also see that by the end of the segment, transcription time is quite similar.

Transcription output


Partial-result stabilization not enabled

The The Amazon. The Amazon is the large The Amazon is the largest The Amazon is the largest The Amazon is the largest rainforest on The Amazon is the largest rainforest on the planet. The Amazon is the largest rainforest on the planet.
0.515 1.015 1.515 2.015 2.515 3.015 3.515 3.885

Partial-result stabilization enabled (high stability)

The The Amazon. The Amazon is the large The Amazon is the largest The Amazon is the largest rain for The Amazon is the largest rain forest on The Amazon is the largest rain forest on the plan. The Amazon is the largest rain forest on the planet.
0.095 1.015 1.515 2.015 2.495 3.015 3.515 4.015

When you activate partial-result stabilization, Amazon Transcribe uses the Stable field to indicate whether an 'item' is stable, where 'item' refers to a transcribed word or phrase. Values for Stable are either true, indicating that the item is stable, or false, indicating that the item is not stable.

Items flagged as false (not stable) are more likely to change as your segment is transcribed. Conversely, items flagged as true (stable) don't change.

You can choose to render non-stable words so your captions align with speech. Even if captions change slightly as context is added, this is a better user experience than periodic text bursts, which may or may not align with speech.

You can also choose to display non-stable words in a different format, such as italics, to indicate to viewers that these words may change. Displaying partial results limits the amount of text displayed at a given time. This can be important when you're dealing with space constraints, as with video captions.

Partial-result stabilization example output

The following example output shows Stable flags for an incomplete segment ("IsPartial": true). You can see that the words "the large" are not stable and therefore could change before the segment is finalized.

"Transcript": { "Results": [ { "Alternatives": [ { "Items": [ { "Content": "The", "EndTime": 1.4475, "Stable": true, "StartTime": 1.26, "Type": "pronunciation", "VocabularyFilterMatch": false }, { "Content": "Amazon", "EndTime": 2.1725, "Stable": true, "StartTime": 1.4475, "Type": "pronunciation", "VocabularyFilterMatch": false }, { "Content": "is", "EndTime": 2.3975, "Stable": true, "StartTime": 2.1725, "Type": "pronunciation", "VocabularyFilterMatch": false }, { "Content": "the", "EndTime": 2.5875, "Stable": false, "StartTime": 2.3975, "Type": "pronunciation", "VocabularyFilterMatch": false }, { "Content": "large", "EndTime": 2.775, "Stable": false, "StartTime": 2.5875, "Type": "pronunciation", "VocabularyFilterMatch": false } ], "Transcript": "The Amazon is the large" } ], "EndTime": 2.775, "IsPartial": true, "ResultId": "55421b61-7cc6-4ef1-8d55-08a97159870e", "StartTime": 1.26 } ] }