@omnimedia/omnitool/s/features/speech/transcribe/parts/prep-audio.ts

open source video processing tools

import {Driver} from "../../../../driver/driver.js"

export async function prepAudio(driver: Driver, source: Blob) {
	const arrayBuffer = await source.arrayBuffer()
	const audioCTX = new AudioContext({sampleRate: 16000})
	try {
		const audioData = await audioCTX.decodeAudioData(arrayBuffer)
		let audio: Float32Array

		if (audioData.numberOfChannels === 2) {
			const SCALING_FACTOR = Math.sqrt(2)
			const left = audioData.getChannelData(0)
			const right = audioData.getChannelData(1)
			audio = new Float32Array(left.length)

			for (let i = 0; i < audioData.length; ++i)
				audio[i] = (SCALING_FACTOR * (left[i] + right[i])) / 2
		} else {
			audio = audioData.getChannelData(0)
		}

		const duration = await driver.getAudioDuration(source)
		return {audio, duration}
	} finally {
		await audioCTX.close()
	}
}