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 Amazon Web Services Management Console
In this example, each line is the partial result of an audio segment.
The
The Amazon.
The Amazon is
The Amazon is the law.
The Amazon is the largest
The Amazon is the largest ray
The Amazon is the largest rain for
The Amazon is the largest rainforest.
The Amazon is the largest rainforest on the
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 rainforest." "EndTime": 4.545, "IsPartial": true, "ResultId": "12345a67-8bc9-0de1-2f34-a5b678c90d12", "StartTime": 0.025"IsPartial": false (complete segment)"Transcript": "The Amazon is the largest rainforest on the planet." "EndTime": 6.025, "IsPartial": false, "ResultId": "34567e89-0fa1-2bc3-4d56-78e90123456f", "StartTime": 0.025
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.
Tip
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 may be beneficial when 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.
"Transcript": |
"EndTime": |
"IsPartial": |
|---|---|---|
Partial-result stabilization not enabled |
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|
Partial-result stabilization enabled (high stability) |
||
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When you activate partial-result stabilization, Amazon Transcribe uses a
Stable field to indicate whether an item is stable, where 'item' refers to a
transcribed word or punctuation mark. Values for Stable are
true or false. Items flagged as false (not
stable) are more likely to change as your segment is transcribed. Conversely, items flagged as
true (stable) won'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 "to" and
"Amazon" are not stable and therefore could change before the segment is
finalized.
"Transcript": { "Results": [ { "Alternatives": [ { "Items": [ { "Content": "Welcome", "EndTime": 2.4225, "Stable": true, "StartTime": 1.65, "Type": "pronunciation", "VocabularyFilterMatch": false }, { "Content": "to", "EndTime": 2.8325, "Stable": false, "StartTime": 2.4225, "Type": "pronunciation", "VocabularyFilterMatch": false }, { "Content": "Amazon", "EndTime": 3.635, "Stable": false, "StartTime": 2.8325, "Type": "pronunciation", "VocabularyFilterMatch": false }, { "Content": ".", "EndTime": 3.635, "Stable": false, "StartTime": 3.635, "Type": "punctuation", "VocabularyFilterMatch": false } ], "Transcript": "Welcome to Amazon." } ], "EndTime": 4.165, "IsPartial": true, "ResultId": "12345a67-8bc9-0de1-2f34-a5b678c90d12", "StartTime": 1.65 } ] }