文件 AWS 開發套件範例 GitHub 儲存庫中有更多可用的 [AWS SDK 範例](https://github.com/awsdocs/aws-doc-sdk-examples)。

本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 使用適用於 Swift 的 SDK 的 Amazon Transcribe 串流範例
<a name="swift_1_transcribe-streaming_code_examples"></a>

下列程式碼範例示範如何使用適用於 Swift 的 AWS SDK 搭配 Amazon Transcribe Streaming 來執行動作和實作常見案例。

*Actions* 是大型程式的程式碼摘錄，必須在內容中執行。雖然動作會告訴您如何呼叫個別服務函數，但您可以在其相關情境中查看內容中的動作。

*案例*是向您展示如何呼叫服務中的多個函數或與其他 AWS 服務組合來完成特定任務的程式碼範例。

每個範例均包含完整原始碼的連結，您可在連結中找到如何設定和執行內容中程式碼的相關指示。

**Topics**
+ [動作](#actions)
+ [案例](#scenarios)

## 動作
<a name="actions"></a>

### `StartStreamTranscription`
<a name="transcribe-streaming_StartStreamTranscription_swift_1_topic"></a>

以下程式碼範例顯示如何使用 `StartStreamTranscription`。

**適用於 Swift 的 SDK**  
 GitHub 上提供更多範例。尋找完整範例，並了解如何在 [AWS 程式碼範例儲存庫](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/swift/example_code/transcribe-streaming#code-examples)中設定和執行。

```
        let client = TranscribeStreamingClient(
            config: try await TranscribeStreamingClient.TranscribeStreamingClientConfiguration(
                region: region
            )
        )

        // Start the transcription running on the audio stream.

        let output = try await client.startStreamTranscription(
            input: StartStreamTranscriptionInput(
                audioStream: try await createAudioStream(),
                languageCode: TranscribeStreamingClientTypes.LanguageCode(rawValue: lang),
                mediaEncoding: encoding,
                mediaSampleRateHertz: sampleRate
            )
        )
```
+  如需 API 詳細資訊，請參閱《適用於 Swift 的AWS SDK API 參考》**中的 [StartStreamTranscription](https://sdk.amazonaws.com/swift/api/awstranscribestreaming/latest/documentation/awstranscribestreaming/transcribestreamingclient/startstreamtranscription(input:))。

## 案例
<a name="scenarios"></a>

### 轉錄音訊檔案
<a name="transcribe-streaming_Scenario_StreamEvents_File_swift_1_topic"></a>

下列程式碼範例示範如何使用 Amazon Transcribe 串流產生來源音訊檔案的轉錄。

**適用於 Swift 的 SDK**  
 GitHub 上提供更多範例。尋找完整範例，並了解如何在 [AWS 程式碼範例儲存庫](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/swift/example_code/transcribe-streaming#code-examples)中設定和執行。
使用 Amazon Transcribe 串流轉錄音訊檔案中的口頭語。  

```
/// An example that demonstrates how to watch an transcribe event stream to
/// transcribe audio from a file to the console.

import ArgumentParser
import AWSClientRuntime
import AWSTranscribeStreaming
import Foundation

/// Identify one of the media file formats supported by Amazon Transcribe.
enum TranscribeFormat: String, ExpressibleByArgument {
    case ogg = "ogg"
    case pcm = "pcm"
    case flac = "flac"
}

// -MARK: - Async command line tool

struct ExampleCommand: ParsableCommand {
    // -MARK: Command arguments
    @Flag(help: "Show partial results")
    var showPartial = false
    @Option(help: "Language code to transcribe into")
    var lang: String = "en-US"
    @Option(help: "Format of the source audio file")
    var format: TranscribeFormat
    @Option(help: "Sample rate of the source audio file in Hertz")
    var sampleRate: Int = 16000
    @Option(help: "Path of the source audio file")
    var path: String
    @Option(help: "Name of the Amazon S3 Region to use (default: us-east-1)")
    var region = "us-east-1"

    static var configuration = CommandConfiguration(
        commandName: "tsevents",
        abstract: """
        This example shows how to use event streaming with Amazon Transcribe.
        """,
        discussion: """
        """
    )

    /// Create and return an Amazon Transcribe audio stream from the file
    /// specified in the arguments.
    /// 
    /// - Throws: Errors from `TranscribeError`.
    ///
    /// - Returns: `AsyncThrowingStream<TranscribeStreamingClientTypes.AudioStream, Error>`
    func createAudioStream() async throws
                -> AsyncThrowingStream<TranscribeStreamingClientTypes.AudioStream, Error> {

        let fileURL: URL = URL(fileURLWithPath: path)
        let audioData = try Data(contentsOf: fileURL)

        // Properties defining the size of audio chunks and the total size of
        // the audio file in bytes. You should try to send chunks that last on
        // average 125 milliseconds.

        let chunkSizeInMilliseconds = 125.0
        let chunkSize = Int(chunkSizeInMilliseconds  / 1000.0 * Double(sampleRate) * 2.0)
        let audioDataSize = audioData.count

        // Create an audio stream from the source data. The stream's job is
        // to send the audio in chunks to Amazon Transcribe as
        // `AudioStream.audioevent` events.

        let audioStream = AsyncThrowingStream<TranscribeStreamingClientTypes.AudioStream,
                                Error> { continuation in
            Task {
                var currentStart = 0
                var currentEnd = min(chunkSize, audioDataSize - currentStart)

                // Generate and send chunks of audio data as `audioevent`
                // events until the entire file has been sent. Each event is
                // yielded to the SDK after being created.

                while currentStart < audioDataSize {
                    let dataChunk = audioData[currentStart ..< currentEnd]
                    
                    let audioEvent = TranscribeStreamingClientTypes.AudioStream.audioevent(
                        .init(audioChunk: dataChunk)
                    )
                    let yieldResult = continuation.yield(audioEvent)
                    switch yieldResult {
                        case .enqueued(_):
                            // The chunk was successfully enqueued into the
                            // stream. The `remaining` parameter estimates how
                            // much room is left in the queue, but is ignored here.
                            break
                        case .dropped(_):
                            // The chunk was dropped because the queue buffer
                            // is full. This will cause transcription errors.
                            print("Warning: Dropped audio! The transcription will be incomplete.")
                        case .terminated:
                            print("Audio stream terminated.")
                            continuation.finish()
                            return
                        default:
                            print("Warning: Unrecognized response during audio streaming.")
                    }

                    currentStart = currentEnd
                    currentEnd = min(currentStart + chunkSize, audioDataSize)
                }

                // Let the SDK's continuation block know the stream is over.

                continuation.finish()
            }
        }

        return audioStream
    }

    /// Run the transcription process.
    ///
    /// - Throws: An error from `TranscribeError`.
    func transcribe(encoding: TranscribeStreamingClientTypes.MediaEncoding) async throws {
        // Create the Transcribe Streaming client.

        let client = TranscribeStreamingClient(
            config: try await TranscribeStreamingClient.TranscribeStreamingClientConfiguration(
                region: region
            )
        )

        // Start the transcription running on the audio stream.

        let output = try await client.startStreamTranscription(
            input: StartStreamTranscriptionInput(
                audioStream: try await createAudioStream(),
                languageCode: TranscribeStreamingClientTypes.LanguageCode(rawValue: lang),
                mediaEncoding: encoding,
                mediaSampleRateHertz: sampleRate
            )
        )

        // Iterate over the events in the returned transcript result stream.
        // Each `transcriptevent` contains a list of result fragments which
        // need to be concatenated together to build the final transcript.
        for try await event in output.transcriptResultStream! {
            switch event {
            case .transcriptevent(let event):
            for result in event.transcript?.results ?? [] {
                guard let transcript = result.alternatives?.first?.transcript else {
                    continue
                }

                // If showing partial results is enabled and the result is
                // partial, show it. Partial results may be incomplete, and
                // may be inaccurate, with upcoming audio making the
                // transcription complete or by giving more context to make
                // transcription make more sense.

                if (result.isPartial && showPartial) {
                    print("[Partial] \(transcript)")
                }

                // When the complete fragment of transcribed text is ready,
                // print it. This could just as easily be used to draw the
                // text as a subtitle over a playing video, though timing
                // would need to be managed.

                if !result.isPartial {
                    if (showPartial) {
                        print("[Final  ] ", terminator: "")
                    }
                    print(transcript)
                }
            }
            default:
                print("Error: Unexpected message from Amazon Transcribe:")
            }
        }
    }

    /// Convert the value of the `--format` command line option into the
    /// corresponding Transcribe Streaming `MediaEncoding` type.
    ///
    /// - Returns: The `MediaEncoding` equivalent of the format specified on
    ///   the command line.
    func getMediaEncoding() -> TranscribeStreamingClientTypes.MediaEncoding {
        let mediaEncoding: TranscribeStreamingClientTypes.MediaEncoding
        
        switch format {
        case .flac:
            mediaEncoding = .flac
        case .ogg:
            mediaEncoding = .oggOpus
        case .pcm:
            mediaEncoding = .pcm
        }

        return mediaEncoding
    }
}

// -MARK: - Entry point

/// The program's asynchronous entry point.
@main
struct Main {
    static func main() async {
        let args = Array(CommandLine.arguments.dropFirst())

        do {
            let command = try ExampleCommand.parse(args)
            try await command.transcribe(encoding: command.getMediaEncoding())
        } catch let error as TranscribeError {
            print("ERROR: \(error.errorDescription ?? "Unknown error")")
        } catch {
            ExampleCommand.exit(withError: error)
        }
    }    
}

/// Errors thrown by the example's functions.
enum TranscribeError: Error {
    /// No transcription stream available.
    case noTranscriptionStream
    /// The source media file couldn't be read.
    case readError

    var errorDescription: String? {
        switch self {
        case .noTranscriptionStream:
            return "No transcription stream returned by Amazon Transcribe."
        case .readError:
            return "Unable to read the source audio file."
        }
    }
}
```
+  如需 API 詳細資訊，請參閱《適用於 Swift 的AWS SDK API 參考》**中的 [StartStreamTranscription](https://sdk.amazonaws.com/swift/api/awstranscribestreaming/latest/documentation/awstranscribestreaming/transcribestreamingclient/startstreamtranscription(input:))。