Why use Batch transcription?

• 2/20/2019
• 6 minutes to read
• Contributors
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Batch transcription is ideal if you want to transcribe a large quantity of audio in storage, such as Azure Blobs. By using the dedicated REST API, you can point to audio files with a shared access signature (SAS) URI and asynchronously receive transcriptions.

Prerequisites

Subscription Key

As with all features of the Speech service, you create a subscription key from the Azure portal by following our Get started guide. If you plan to get transcriptions from our baseline models, creating a key is all you need to do.

Custom models

If you plan to customize acoustic or language models, follow the steps in Customize acoustic models and Customizing language models. To use the created models in batch transcription you need their model IDs. This ID is not the endpoint ID that you find on the Endpoint Details view, it is the model ID that you can retrieve when you select the details of the models.

The Batch Transcription API

The Batch Transcription API offers asynchronous speech-to-text transcription, along with additional features. It is a REST API that exposes methods for:

1. Creating batch processing requests
2. Query Status
3. Downloading transcriptions

Supported formats

The Batch Transcription API supports the following formats:

For stereo audio streams, the Batch transcription API splits the left and right channel during the transcription. The two JSON files with the result are each created from a single channel. The timestamps per utterance enable the developer to create an ordered final transcript. This sample request includes properties for profanity filtering, punctuation, and word level timestamps.

Configuration

Configuration parameters are provided as JSON:

{
  "recordingsUrl": "<URL to the Azure blob to transcribe>",
  "models": ["<optional acoustic model ID>, <optional language model ID>"],
  "locale": "<local to us, for example en-US>",
  "name": "<user define name of the transcription batch>",
  "description": "<optional description of the transcription>",
  "properties": {
    "ProfanityFilterMode": "Masked",
    "PunctuationMode": "DictatedAndAutomatic",
    "AddWordLevelTimestamps" : "True"
  }
}

Configuration properties

Storage

Batch transcription supports Azure Blob storage for reading audio and writing transcriptions to storage.

Webhooks

Polling for transcription status may not be the most performant, or provide the best user experience. To poll for status, you can register callbacks, which will notify the client when long-running transcription tasks have completed.

For more details, see Webhooks.

Sample code

The complete sample is available in the GitHub sample repository inside the samples/batch subdirectory.

You have to customize the sample code with your subscription information, the service region, the SAS URI pointing to the audio file to transcribe, and model IDs in case you want to use a custom acoustic or language model.

      // Replace with your subscription key
      private const string SubscriptionKey = "<YourSubscriptionKey>";

      // Update with your service region
      private const string HostName = "<YourServiceRegion>.cris.ai";
      private const int Port = 443;

      // recordings and locale
      private const string Locale = "en-US";
      private const string RecordingsBlobUri = "<URI pointing to an audio file stored in Azure Blob Storage>";

      // For usage of baseline models, no acoustic and language model needs to be specified.
      private static Guid[] modelList = new Guid[0];

      // For use of specific acoustic and language models:
      // - comment the previous line
      // - uncomment the next lines to create an array containing the guids of your required model(s)
      // private static Guid AdaptedAcousticId = new Guid("<id of the custom acoustic model>");
      // private static Guid AdaptedLanguageId = new Guid("<id of the custom language model>");
      // private static Guid[] modelList = new[] { AdaptedAcousticId, AdaptedLanguageId };

      //name and description
      private const string Name = "Simple transcription";
      private const string Description = "Simple transcription description";

The sample code will setup the client and submit the transcription request. It will then poll for status information and print details about the transcription progress.

// get all transcriptions for the user
transcriptions = await client.GetTranscriptionsAsync().ConfigureAwait(false);

completed = 0; running = 0; notStarted = 0;
// for each transcription in the list we check the status
foreach (var transcription in transcriptions)
{
    switch (transcription.Status)
    {
        case "Failed":
        case "Succeeded":
            // we check to see if it was one of the transcriptions we created from this client.
            if (!createdTranscriptions.Contains(transcription.Id))
            {
                // not created form here, continue
                continue;
            }
            completed++;

            // if the transcription was successfull, check the results
            if (transcription.Status == "Succeeded")
            {
                var resultsUri = transcription.ResultsUrls["channel_0"];

                WebClient webClient = new WebClient();

                var filename = Path.GetTempFileName();
                webClient.DownloadFile(resultsUri, filename);

                var results = File.ReadAllText(filename);
                Console.WriteLine("Transcription succeeded. Results: ");
                Console.WriteLine(results);
            }
            break;

        case "Running":
            running++;
            break;

        case "NotStarted":
            notStarted++;
            break;
    }
}

For full details about the preceding calls, see our Swagger document. For the full sample shown here, go to GitHub in the samples/batch subdirectory.

Take note of the asynchronous setup for posting audio and receiving transcription status. The client that you create is a .NET HTTP client. There's a PostTranscriptions method for sending the audio file details and a GetTranscriptions method for receiving the results. PostTranscriptions returns a handle, and GetTranscriptions uses it to create a handle to get the transcription status.

The current sample code doesn't specify a custom model. The service uses the baseline models for transcribing the file or files. To specify the models, you can pass on the same method as the model IDs for the acoustic and the language model.

Download the sample

You can find the sample in the samples/batch directory in the GitHub sample repository.

Next steps

• Get your Speech trial subscription