audio-ui/lib/audio/buffer-utils.ts

/**
 * AudioBuffer manipulation utilities
 */

import { getAudioContext } from './context';

/**
 * Extract a portion of an AudioBuffer
 */
export function extractBufferSegment(
  buffer: AudioBuffer,
  startTime: number,
  endTime: number
): AudioBuffer {
  const audioContext = getAudioContext();
  const startSample = Math.floor(startTime * buffer.sampleRate);
  const endSample = Math.floor(endTime * buffer.sampleRate);
  const length = endSample - startSample;

  const segment = audioContext.createBuffer(
    buffer.numberOfChannels,
    length,
    buffer.sampleRate
  );

  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
    const sourceData = buffer.getChannelData(channel);
    const targetData = segment.getChannelData(channel);

    for (let i = 0; i < length; i++) {
      targetData[i] = sourceData[startSample + i];
    }
  }

  return segment;
}

/**
 * Delete a portion of an AudioBuffer
 */
export function deleteBufferSegment(
  buffer: AudioBuffer,
  startTime: number,
  endTime: number
): AudioBuffer {
  const audioContext = getAudioContext();
  const startSample = Math.floor(startTime * buffer.sampleRate);
  const endSample = Math.floor(endTime * buffer.sampleRate);

  const beforeLength = startSample;
  const afterLength = buffer.length - endSample;
  const newLength = beforeLength + afterLength;

  const newBuffer = audioContext.createBuffer(
    buffer.numberOfChannels,
    newLength,
    buffer.sampleRate
  );

  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
    const sourceData = buffer.getChannelData(channel);
    const targetData = newBuffer.getChannelData(channel);

    // Copy before segment
    for (let i = 0; i < beforeLength; i++) {
      targetData[i] = sourceData[i];
    }

    // Copy after segment
    for (let i = 0; i < afterLength; i++) {
      targetData[beforeLength + i] = sourceData[endSample + i];
    }
  }

  return newBuffer;
}

/**
 * Insert an AudioBuffer at a specific position
 */
export function insertBufferSegment(
  buffer: AudioBuffer,
  insertBuffer: AudioBuffer,
  insertTime: number
): AudioBuffer {
  const audioContext = getAudioContext();
  const insertSample = Math.floor(insertTime * buffer.sampleRate);
  const newLength = buffer.length + insertBuffer.length;

  const newBuffer = audioContext.createBuffer(
    buffer.numberOfChannels,
    newLength,
    buffer.sampleRate
  );

  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
    const sourceData = buffer.getChannelData(channel);
    const insertData = insertBuffer.getChannelData(
      Math.min(channel, insertBuffer.numberOfChannels - 1)
    );
    const targetData = newBuffer.getChannelData(channel);

    // Copy before insert point
    for (let i = 0; i < insertSample; i++) {
      targetData[i] = sourceData[i];
    }

    // Copy insert buffer
    for (let i = 0; i < insertBuffer.length; i++) {
      targetData[insertSample + i] = insertData[i];
    }

    // Copy after insert point
    for (let i = insertSample; i < buffer.length; i++) {
      targetData[insertSample + insertBuffer.length + (i - insertSample)] = sourceData[i];
    }
  }

  return newBuffer;
}

/**
 * Trim buffer to selection
 */
export function trimBuffer(
  buffer: AudioBuffer,
  startTime: number,
  endTime: number
): AudioBuffer {
  return extractBufferSegment(buffer, startTime, endTime);
}

/**
 * Concatenate two audio buffers
 */
export function concatenateBuffers(
  buffer1: AudioBuffer,
  buffer2: AudioBuffer
): AudioBuffer {
  const audioContext = getAudioContext();
  const newLength = buffer1.length + buffer2.length;
  const channels = Math.max(buffer1.numberOfChannels, buffer2.numberOfChannels);

  const newBuffer = audioContext.createBuffer(
    channels,
    newLength,
    buffer1.sampleRate
  );

  for (let channel = 0; channel < channels; channel++) {
    const targetData = newBuffer.getChannelData(channel);

    // Copy first buffer
    if (channel < buffer1.numberOfChannels) {
      const data1 = buffer1.getChannelData(channel);
      targetData.set(data1, 0);
    }

    // Copy second buffer
    if (channel < buffer2.numberOfChannels) {
      const data2 = buffer2.getChannelData(channel);
      targetData.set(data2, buffer1.length);
    }
  }

  return newBuffer;
}

/**
 * Duplicate a segment of audio buffer (extract and insert it after the selection)
 */
export function duplicateBufferSegment(
  buffer: AudioBuffer,
  startTime: number,
  endTime: number
): AudioBuffer {
  const segment = extractBufferSegment(buffer, startTime, endTime);
  return insertBufferSegment(buffer, segment, endTime);
}