Aurora-SpotiRip/helpers/audioProcessing.tsx

import {
  ALL_FORMATS,
  BlobSource,
  BufferTarget,
  canEncodeAudio,
  Conversion,
  Input,
  Mp3OutputFormat,
  Output,
  Quality,
} from "mediabunny";
import { registerMp3Encoder } from "@mediabunny/mp3-encoder";

type DecodedAudio = {
  sampleRate: number;
  channelCount: number;
  channelData: Float32Array[];
};

export async function decodeAudio(file: File): Promise<AudioBuffer> {
  const AudioContextCtor =
    window.AudioContext ||
    (window as typeof window & { webkitAudioContext?: typeof AudioContext }).webkitAudioContext;
  if (!AudioContextCtor) throw new Error("This browser does not support local audio decoding.");
  const context = new AudioContextCtor();
  try {
    const data = await file.arrayBuffer();
    return await context.decodeAudioData(data.slice(0));
  } finally {
    await context.close();
  }
}

function clamp16(value: number) {
  const sample = Math.max(-1, Math.min(1, value));
  return sample < 0 ? Math.round(sample * 0x8000) : Math.round(sample * 0x7fff);
}

function writeAscii(view: DataView, offset: number, value: string) {
  for (let index = 0; index < value.length; index += 1) {
    view.setUint8(offset + index, value.charCodeAt(index));
  }
}

function makeWavBlob(audio: DecodedAudio) {
  const channels = Math.min(audio.channelCount, 2);
  const frameCount = audio.channelData[0]?.length || 0;
  const bytesPerSample = 2;
  const blockAlign = channels * bytesPerSample;
  const dataSize = frameCount * blockAlign;
  const buffer = new ArrayBuffer(44 + dataSize);
  const view = new DataView(buffer);
  writeAscii(view, 0, "RIFF");
  view.setUint32(4, 36 + dataSize, true);
  writeAscii(view, 8, "WAVE");
  writeAscii(view, 12, "fmt ");
  view.setUint32(16, 16, true);
  view.setUint16(20, 1, true);
  view.setUint16(22, channels, true);
  view.setUint32(24, audio.sampleRate, true);
  view.setUint32(28, audio.sampleRate * blockAlign, true);
  view.setUint16(32, blockAlign, true);
  view.setUint16(34, 16, true);
  writeAscii(view, 36, "data");
  view.setUint32(40, dataSize, true);

  let offset = 44;
  for (let frame = 0; frame < frameCount; frame += 1) {
    for (let channel = 0; channel < channels; channel += 1) {
      view.setInt16(offset, clamp16(audio.channelData[channel][frame] || 0), true);
      offset += 2;
    }
  }

  return new Blob([buffer], { type: "audio/wav" });
}

export async function createRecognitionSnippet(file: File) {
  const decoded = await decodeAudio(file);
  const duration = decoded.duration;
  const snippetSeconds = Math.min(12, Math.max(4, duration));
  const preferredStart = duration > 35 ? 20 : duration > 20 ? 8 : 0;
  const startSeconds = Math.min(preferredStart, Math.max(0, duration - snippetSeconds));
  const startFrame = Math.floor(startSeconds * decoded.sampleRate);
  const snippetFrames = Math.min(
    Math.floor(snippetSeconds * decoded.sampleRate),
    Math.max(0, decoded.length - startFrame),
  );
  const channels = Math.min(decoded.numberOfChannels, 2);
  const channelData: Float32Array[] = [];
  for (let channel = 0; channel < channels; channel += 1) {
    const source = decoded.getChannelData(channel);
    channelData.push(source.slice(startFrame, startFrame + snippetFrames));
  }

  const blob = makeWavBlob({
    sampleRate: decoded.sampleRate,
    channelCount: channels,
    channelData,
  });
  return new File([blob], "recognition-snippet.wav", {
    type: "audio/wav",
    lastModified: Date.now(),
  });
}

export async function convertAudioFileToMp3(file: File, bitrateKbps = 192) {
  if (file.type === "audio/mpeg" || file.name.toLowerCase().endsWith(".mp3")) {
    return new Blob([await file.arrayBuffer()], { type: "audio/mpeg" });
  }

  if (!(await canEncodeAudio("mp3"))) {
    registerMp3Encoder();
  }

  const input = new Input({
    source: new BlobSource(file),
    formats: ALL_FORMATS,
  });
  const target = new BufferTarget();
  const output = new Output({
    format: new Mp3OutputFormat(),
    target,
  });
  const conversion = await Conversion.init({
    input,
    output,
    tracks: "primary",
    video: { discard: true },
    audio: {
      codec: "mp3",
      quality: new Quality({ bitrate: bitrateKbps * 1000 }),
      forceTranscode: true,
    },
  });

  if (!conversion.isValid) {
    const reasons = conversion.discardedTracks.map((entry) => entry.reason).join(", ");
    throw new Error(
      reasons
        ? `This audio file cannot be converted in this browser (${reasons}).`
        : "This audio file cannot be converted in this browser.",
    );
  }

  await conversion.execute();
  if (!target.buffer) throw new Error("MP3 conversion produced no output.");
  return new Blob([target.buffer], { type: "audio/mpeg" });
}