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Use the fast transcription API with Azure AI Speech

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Fast transcription API is used to transcribe audio files with returning results synchronously and faster than real-time. Use fast transcription in the scenarios that you need the transcript of an audio recording as quickly as possible with predictable latency, such as:

  • Quick audio or video transcription, subtitles, and edit.
  • Video translation

Unlike the batch transcription API, fast transcription API only produces transcriptions in the display (not lexical) form. The display form is a more human-readable form of the transcription that includes punctuation and capitalization.

Prerequisites

  • An Azure AI Speech resource in one of the regions where the fast transcription API is available. The supported regions are: Australia East, Brazil South, Central India, East US, East US 2, French Central, Japan East, North Central US, North Europe, South Central US, Southeast Asia, Sweden Central, West Europe, West US, West US 2, West US 3. For more information about regions supported for other Speech service features, see Speech service regions.

  • An audio file (less than 2 hours long and less than 200 MB in size) in one of the formats and codecs supported by the batch transcription API. For more information about supported audio formats, see supported audio formats.

Use the fast transcription API

Tip

Try out fast transcription in the Azure AI Foundry portal.

We learn how to use the fast transcription API (via Transcriptions - Transcribe) with the following scenarios:

  • Known locale specified: Transcribe an audio file with a specified locale. If you know the locale of the audio file, you can specify it to improve transcription accuracy and minimize the latency.
  • Language identification on: Transcribe an audio file with language identification on. If you're not sure about the locale of the audio file, you can turn on language identification to let the Speech service identify the locale.
  • Diarization on: Transcribe an audio file with diarization on. Diarization distinguishes between different speakers in the conversation. The Speech service provides information about which speaker was speaking a particular part of the transcribed speech.
  • Multi-channel on: Transcribe an audio file that has one or two channels. Multi-channel transcriptions are useful for audio files with multiple channels, such as audio files with multiple speakers or audio files with background noise. By default, the fast transcription API merges all input channels into a single channel and then performs the transcription. If this isn't desirable, channels can be transcribed independently without merging.

Make a multipart/form-data POST request to the transcriptions endpoint with the audio file and the request body properties.

The following example shows how to transcribe an audio file with a specified locale. If you know the locale of the audio file, you can specify it to improve transcription accuracy and minimize the latency.

  • Replace YourSubscriptionKey with your Speech resource key.
  • Replace YourServiceRegion with your Speech resource region.
  • Replace YourAudioFile with the path to your audio file.
curl --location 'https://YourServiceRegion.api.cognitive.microsoft.com/speechtotext/transcriptions:transcribe?api-version=2024-11-15' \
--header 'Content-Type: multipart/form-data' \
--header 'Ocp-Apim-Subscription-Key: YourSubscriptionKey' \
--form 'audio=@"YourAudioFile"' \
--form 'definition="{
    "locales":["en-US"]}"'

Construct the form definition according to the following instructions:

  • Set the optional (but recommended) locales property that should match the expected locale of the audio data to transcribe. In this example, the locale is set to en-US. The supported locales that you can specify are: de-DE, en-IN, en-US, es-ES, es-MX, fr-FR, hi-IN, it-IT, ja-JP, ko-KR, pt-BR, and zh-CN.

For more information about locales and other properties for the fast transcription API, see the request configuration options section later in this guide.

The response includes durationMilliseconds, offsetMilliseconds, and more. The combinedPhrases property contains the full transcriptions for all speakers.

{
	"durationMilliseconds": 182439,
	"combinedPhrases": [
		{
			"text": "Good afternoon. This is Sam. Thank you for calling Contoso. How can I help? Hi there. My name is Mary. I'm currently living in Los Angeles, but I'm planning to move to Las Vegas. I would like to apply for a loan. Okay. I see you're currently living in California. Let me make sure I understand you correctly. Uh You'd like to apply for a loan even though you'll be moving soon. Is that right? Yes, exactly. So I'm planning to relocate soon, but I would like to apply for the loan first so that I can purchase a new home once I move there. And are you planning to sell your current home? Yes, I will be listing it on the market soon and hopefully it'll sell quickly. That's why I'm applying for a loan now, so that I can purchase a new house in Nevada and close on it quickly as well once my current home sells. I see. Would you mind holding for a moment while I take your information down? Yeah, no problem. Thank you for your help. Mm-hmm. Just one moment. All right. Thank you for your patience, ma'am. May I have your first and last name, please? Yes, my name is Mary Smith. Thank you, Ms. Smith. May I have your current address, please? Yes. So my address is 123 Main Street in Los Angeles, California, and the zip code is 90923. Sorry, that was a 90 what? 90923. 90923 on Main Street. Got it. Thank you. May I have your phone number as well, please? Uh Yes, my phone number is 504-529-2351 and then yeah. 2351. Got it. And do you have an e-mail address we I can associate with this application? uh Yes, so my e-mail address is mary.a.sm78@gmail.com. Mary.a, was that a S-N as in November or M as in Mike? M as in Mike. Mike78, got it. Thank you. Ms. Smith, do you currently have any other loans? Uh Yes, so I currently have two other loans through Contoso. So my first one is my car loan and then my other is my student loan. They total about 1400 per month combined and my interest rate is 8%. I see. And you're currently paying those loans off monthly, is that right? Yes, of course I do. OK, thank you. Here's what I suggest we do. Let me place you on a brief hold again so that I can talk with one of our loan officers and get this started for you immediately. In the meantime, it would be great if you could take a few minutes and complete the remainder of the secure application online at www.contosoloans.com. Yeah, that sounds good. I can go ahead and get started. Thank you for your help. Thank you."
		}
	],
	"phrases": [
		{
			"offsetMilliseconds": 960,
			"durationMilliseconds": 640,
			"text": "Good afternoon.",
			"words": [
				{
					"text": "Good",
					"offsetMilliseconds": 960,
					"durationMilliseconds": 240
				},
				{
					"text": "afternoon.",
					"offsetMilliseconds": 1200,
					"durationMilliseconds": 400
				}
			],
			"locale": "en-US",
			"confidence": 0.93616915
		},
		{
			"offsetMilliseconds": 1600,
			"durationMilliseconds": 640,
			"text": "This is Sam.",
			"words": [
				{
					"text": "This",
					"offsetMilliseconds": 1600,
					"durationMilliseconds": 240
				},
				{
					"text": "is",
					"offsetMilliseconds": 1840,
					"durationMilliseconds": 120
				},
				{
					"text": "Sam.",
					"offsetMilliseconds": 1960,
					"durationMilliseconds": 280
				}
			],
			"locale": "en-US",
			"confidence": 0.93616915
		},
		{
			"offsetMilliseconds": 2240,
			"durationMilliseconds": 1040,
			"text": "Thank you for calling Contoso.",
			"words": [
				{
					"text": "Thank",
					"offsetMilliseconds": 2240,
					"durationMilliseconds": 200
				},
				{
					"text": "you",
					"offsetMilliseconds": 2440,
					"durationMilliseconds": 80
				},
				{
					"text": "for",
					"offsetMilliseconds": 2520,
					"durationMilliseconds": 120
				},
				{
					"text": "calling",
					"offsetMilliseconds": 2640,
					"durationMilliseconds": 200
				},
				{
					"text": "Contoso.",
					"offsetMilliseconds": 2840,
					"durationMilliseconds": 440
				}
			],
			"locale": "en-US",
			"confidence": 0.93616915
		},
		{
			"offsetMilliseconds": 3280,
			"durationMilliseconds": 640,
			"text": "How can I help?",
			"words": [
				{
					"text": "How",
					"offsetMilliseconds": 3280,
					"durationMilliseconds": 120
				},
				{
					"text": "can",
					"offsetMilliseconds": 3440,
					"durationMilliseconds": 120
				},
				{
					"text": "I",
					"offsetMilliseconds": 3560,
					"durationMilliseconds": 40
				},
				{
					"text": "help?",
					"offsetMilliseconds": 3600,
					"durationMilliseconds": 320
				}
			],
			"locale": "en-US",
			"confidence": 0.93616915
		},
		{
			"offsetMilliseconds": 5040,
			"durationMilliseconds": 400,
			"text": "Hi there.",
			"words": [
				{
					"text": "Hi",
					"offsetMilliseconds": 5040,
					"durationMilliseconds": 240
				},
				{
					"text": "there.",
					"offsetMilliseconds": 5280,
					"durationMilliseconds": 160
				}
			],
			"locale": "en-US",
			"confidence": 0.93616915
		},
		{
			"offsetMilliseconds": 5440,
			"durationMilliseconds": 800,
			"text": "My name is Mary.",
			"words": [
				{
					"text": "My",
					"offsetMilliseconds": 5440,
					"durationMilliseconds": 80
				},
				{
					"text": "name",
					"offsetMilliseconds": 5520,
					"durationMilliseconds": 120
				},
				{
					"text": "is",
					"offsetMilliseconds": 5640,
					"durationMilliseconds": 80
				},
				{
					"text": "Mary.",
					"offsetMilliseconds": 5720,
					"durationMilliseconds": 520
				}
			],
			"locale": "en-US",
			"confidence": 0.93616915
		},
		// More transcription results...
	    // Redacted for brevity
		{
			"offsetMilliseconds": 180320,
			"durationMilliseconds": 680,
			"text": "Thank you for your help.",
			"words": [
				{
					"text": "Thank",
					"offsetMilliseconds": 180320,
					"durationMilliseconds": 160
				},
				{
					"text": "you",
					"offsetMilliseconds": 180480,
					"durationMilliseconds": 80
				},
				{
					"text": "for",
					"offsetMilliseconds": 180560,
					"durationMilliseconds": 120
				},
				{
					"text": "your",
					"offsetMilliseconds": 180680,
					"durationMilliseconds": 120
				},
				{
					"text": "help.",
					"offsetMilliseconds": 180800,
					"durationMilliseconds": 200
				}
			],
			"locale": "en-US",
			"confidence": 0.9314801
		},
		{
			"offsetMilliseconds": 181960,
			"durationMilliseconds": 280,
			"text": "Thank you.",
			"words": [
				{
					"text": "Thank",
					"offsetMilliseconds": 181960,
					"durationMilliseconds": 200
				},
				{
					"text": "you.",
					"offsetMilliseconds": 182160,
					"durationMilliseconds": 80
				}
			],
			"locale": "en-US",
			"confidence": 0.9314801
		}
	]
}

Request configuration options

Here are some property options to configure a transcription when you call the Transcriptions - Transcribe operation.

Property Description Required or optional
channels The list of zero-based indices of the channels to be transcribed separately. Up to two channels are supported unless diarization is enabled. By default, the fast transcription API merges all input channels into a single channel and then performs the transcription. If this isn't desirable, channels can be transcribed independently without merging.

If you want to transcribe the channels from a stereo audio file separately, you need to specify [0,1], [0], or [1]. Otherwise, stereo audio is merged to mono and only a single channel is transcribed.

If the audio is stereo and diarization is enabled, then you can't set the channels property to [0,1]. The Speech service doesn't support diarization of multiple channels.

For mono audio, the channels property is ignored, and the audio is always transcribed as a single channel.		 Optional
diarization The diarization configuration. Diarization is the process of recognizing and separating multiple speakers in one audio channel. For example, specify "diarization": {"maxSpeakers": 2, "enabled": true}. Then the transcription file contains speaker entries (such as "speaker": 0 or "speaker": 1) for each transcribed phrase. Optional
locales The list of locales that should match the expected locale of the audio data to transcribe.

If you know the locale of the audio file, you can specify it to improve transcription accuracy and minimize the latency. If a single locale is specified, that locale is used for transcription.

But if you're not sure about the locale, you can specify multiple locales. Language identification might be more accurate with a more precise list of candidate locales.

If you don't specify any locale, or if the locales that you specify aren't in the audio file, then the Speech service still tries to identify the language. If the language can't be identified, an error is returned.

The supported locales that you can specify are: de-DE, en-IN, en-US, es-ES, es-MX, fr-FR, hi-IN, it-IT, ja-JP, ko-KR, pt-BR, and zh-CN. You can get the latest supported languages via the Transcriptions - List Supported Locales REST API. For more information about locales, see the Speech service language support documentation.		 Optional but recommended if you know the expected locale.
profanityFilterMode Specifies how to handle profanity in recognition results. Accepted values are None to disable profanity filtering, Masked to replace profanity with asterisks, Removed to remove all profanity from the result, or Tags to add profanity tags. The default value is Masked. Optional

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