LINE DC Generative AI Meetup #6 で「LINE Messaging API × OpenAI APIで入力音声の文字起こしBot作ってみた」というテーマで登壇しました

line-transcriptions-bot/ ├── infra/ // インフラ │ ├── lib/ │ │ └── infra-stack.ts // スタック定義 │ ├── bin/ │ │ └── infra.ts │ └── config.ts ├── server/ // バックエンド │ ├── src/ │ │ ├── index.ts // handler │ │ └── services/ │ │ └── openai.ts └── └── package.json 

import * as cdk from 'aws-cdk-lib'; import * as lambda from 'aws-cdk-lib/aws-lambda'; import { NodejsFunction } from 'aws-cdk-lib/aws-lambda-nodejs'; import * as apigateway from 'aws-cdk-lib/aws-apigateway'; import { Construct } from 'constructs'; import { Config } from '../config-type'; type InfraStackProps = cdk.StackProps & {   config: Config; }; export class InfraStack extends cdk.Stack {   constructor(scope: Construct, id: string, props: InfraStackProps) {   super(scope, id, props);    // Lambda関数の作成   const lineTranscriptionLambda = new NodejsFunction(this, 'LineTranscriptionFunction', {   runtime: lambda.Runtime.NODEJS_LATEST,   entry: '../server/src/index.ts',   handler: 'handler',   timeout: cdk.Duration.seconds(30),   environment: { + LINE_CHANNEL_ACCESS_TOKEN: props.config.LINE_CHANNEL_ACCESS_TOKEN, + LINE_CHANNEL_SECRET: props.config.LINE_CHANNEL_SECRET, + OPENAI_API_KEY: props.config.OPENAI_API_KEY,   },   });    // API Gatewayの作成   const api = new apigateway.RestApi(this, 'LineTranscriptionApi', {   restApiName: 'LINE Transcription Bot API',   description: 'LINE音声文字起こしBot用のAPI Gateway',   defaultCorsPreflightOptions: {   allowOrigins: apigateway.Cors.ALL_ORIGINS,   allowMethods: apigateway.Cors.ALL_METHODS,   },   });    // Webhookエンドポイントの作成   const webhookIntegration = new apigateway.LambdaIntegration(lineTranscriptionLambda);   // https://domain/webhook にPOSTリクエストを受け付ける + api.root.addResource('webhook').addMethod('POST', webhookIntegration);   } } 

import { APIGatewayProxyEvent, APIGatewayProxyResult } from 'aws-lambda'; import { WebhookEvent, MessageEvent, validateSignature, messagingApi, middleware, LINE_SIGNATURE_HTTP_HEADER_NAME } from '@line/bot-sdk'; import { transcribeAudio } from './services/openai'; const LINE_CHANNEL_ACCESS_TOKEN = process.env.LINE_CHANNEL_ACCESS_TOKEN ?? ""; const LINE_CHANNEL_SECRET = process.env.LINE_CHANNEL_SECRET ?? ""; const client = new messagingApi.MessagingApiClient({   channelAccessToken: LINE_CHANNEL_ACCESS_TOKEN, }); const blobClient = new messagingApi.MessagingApiBlobClient({   channelAccessToken: LINE_CHANNEL_ACCESS_TOKEN, }); middleware({   channelSecret: LINE_CHANNEL_SECRET, }); export const handler = async (   event: APIGatewayProxyEvent ): Promise<APIGatewayProxyResult> => {   console.debug("handler開始", event);   try {   // リクエストボディの取得   const body = event.body;   if (!body) {   return {   statusCode: 400,   body: JSON.stringify({ message: 'Request body is required' }),   };   }    // LINEのWebhookからのリクエストであることを検証 @see: https://dev.classmethod.jp/articles/line-messaging-api-for-nodejs/ + const signature = event.headers[LINE_SIGNATURE_HTTP_HEADER_NAME] + if (!validateSignature(event.body!, LINE_CHANNEL_SECRET, signature!)) { + console.error("Invalid signature"); + return { + statusCode: 403, + body: 'Invalid signature', + }; + }    // Webhookイベントの解析   const webhookEvents: WebhookEvent[] = JSON.parse(body).events;    // 各イベントを処理   await Promise.all(   webhookEvents.map(async (webhookEvent) => {   if (webhookEvent.type === 'message' && webhookEvent.message.type === 'audio') { + await handleAudioMessage(webhookEvent);   }   })   );    const response = {   statusCode: 200,   body: JSON.stringify({ message: 'OK' }),   };    console.debug("handler終了", response);   return response;   } catch (error) {   console.error('Error processing webhook:', error);   return {   statusCode: 500,   body: JSON.stringify({ message: 'Internal server error' }),   };   } }; async function handleAudioMessage(event: MessageEvent) {   console.debug("handleAudioMessage開始", event);   try {   const messageId = event.message.id;   const replyToken = event.replyToken;    // LINEから音声データを取得   const audioStream = await blobClient.getMessageContent(messageId);    // 音声データをバッファに変換   const audioBuffer = await streamToBuffer(audioStream);   // OpenAI APIで文字起こし + const transcription = await transcribeAudio(audioBuffer);    // 結果をLINEに返信 + await client.replyMessage({ + replyToken: replyToken, + messages: [{ + type: 'text', + text: `🗣️\n${transcription}`, + }] + });    } catch (error) {   console.error('Error handling audio message:', error);    // エラーメッセージを返信   if ('replyToken' in event) {   await client.replyMessage({   replyToken: event.replyToken,   messages: [{   type: 'text',   text: '音声の文字起こしに失敗しました。もう一度お試しください。',   }]   });   }   } } async function streamToBuffer(stream: NodeJS.ReadableStream): Promise<Buffer> {   return new Promise((resolve, reject) => {   const chunks: Buffer[] = [];   stream.on('data', (chunk) => chunks.push(chunk));   stream.on('end', () => resolve(Buffer.concat(chunks)));   stream.on('error', reject);   }); } 

import OpenAI from 'openai'; import { toFile } from 'openai'; const openai = new OpenAI({   apiKey: process.env.OPENAI_API_KEY!, }); export async function transcribeAudio(audioBuffer: Buffer): Promise<string> {   try {   // BufferをOpenAI SDKが期待するFile形式に変換   const audioFile = await toFile(audioBuffer, 'audio.m4a', {   type: 'audio/m4a'   });    // OpenAI gpt-4o-transcribeで文字起こし + const transcription = await openai.audio.transcriptions.create({ + file: audioFile, + model: 'gpt-4o-transcribe', + response_format: 'text', + language: 'ja', // 日本語を指定 + prompt: '以下は日本語の音声です。正確に文字起こししてください。', + });    return transcription;   } catch (error) {   console.error('Error transcribing audio:', error);    // フォールバックとして異なる音声形式を試す（mp3）   try {   const audioFile = await toFile(audioBuffer, 'audio.mp3', {   type: 'audio/mp3'   });    const transcription = await openai.audio.transcriptions.create({   file: audioFile,   model: 'gpt-4o-transcribe',   response_format: 'text',   language: 'ja',   prompt: '以下は日本語の音声です。正確に文字起こししてください。',   });    return transcription;   } catch (fallbackError) {   console.error('Error with fallback transcription:', fallbackError);   throw new Error('音声の文字起こしに失敗しました');   }   } }