app-starlock/lib/talk/call/g711.dart

import 'dart:async';
import 'dart:math';
import 'package:flutter/services.dart';

class G711 {

   List<int> _aLawTable = [
    1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7
  ];

  Future<List<int>> readAssetFile(String assetPath) async {
    final ByteData data = await rootBundle.load(assetPath);
    final List<int> bytes = data.buffer.asUint8List();
    return bytes;
  }

  List<int> encodeALaw(List<int> pcmSamples) {
    final List<int> aLawSamples = [];

    for (final sample in pcmSamples) {
      // 将 16 位 PCM 样本归一化为 13 位有符号整数
      int normalizedSample = sample >> 3;

      // 获取样本的符号位
      int sign = (normalizedSample & 0x8000) != 0 ? 0x80 : 0x00;

      // 取绝对值
      normalizedSample = normalizedSample.abs();

      // 查找编码表中的段
      int segment = _aLawTable[normalizedSample >> 8];

      // 计算量化值
      int quantizedValue = (normalizedSample >> (segment + 3)) & 0x0F;

      // 生成 A-law 编码
      int aLawSample = sign | (segment << 4) | quantizedValue;

      // 添加到结果列表
      aLawSamples.add(aLawSample);
    }

    return aLawSamples;
  }


  int ALawToLinear(int aVal) {
    // 取反
    aVal = ~aVal;

    // 计算偏移
    int t = ((aVal & 0x0F) << 3) + 0x84;
    t <<= (aVal & 0x70) >> 4;

    // 根据符号位决定返回值的正负
    return (aVal & 0x80) != 0 ? 0x84 - t : t - 0x84;
  }

  int decodeG711(int encodedValue, bool isALaw) {
    if (isALaw) {
      // A律解码
      encodedValue = ~encodedValue;
      int t = ((encodedValue & 0x0F) << 3) + 0x84;
      t <<= (encodedValue & 0x70) >> 4;
      return (encodedValue & 0x80) != 0 ? 0x84 - t : t - 0x84;
    } else {
      // μ律解码
      encodedValue = ~encodedValue;
      int t = ((encodedValue & 0x0F) << 3) + 0x84;
      t <<= (encodedValue & 0x70) >> 4;
      return (encodedValue & 0x80) != 0 ? 0x84 - t : t - 0x84;
    }
  }

  /// 高通滤波
  List<int> highPassFilter(
      List<int> audioData, int sampleRate, double cutoffFreq) {
    final double rc = 1.0 / (2 * pi * cutoffFreq);
    final double dt = 1.0 / sampleRate;
    final double alpha = rc / (rc + dt);

    List<int> filteredData = [];
    int prevInput = 0;
    int prevOutput = 0;

    for (int sample in audioData) {
      int output = (alpha * (prevOutput + sample - prevInput)).round();
      filteredData.add(output);
      prevInput = sample;
      prevOutput = output;
    }

    return filteredData;
  }

  /// 噪声门
  List<int> noiseGate(List<int> audioData, int threshold) {
    return audioData
        .map((sample) => sample.abs() > threshold ? sample : 0)
        .toList();
  }

  /// 解码并降噪
  List<int> decodeAndDenoise(List<int> encodedData, bool isALaw, int sampleRate,
      double cutoffFreq, int threshold) {
    // 解码 G.711 数据
    List<int> decodedData =
        encodedData.map((value) => decodeG711(value, isALaw)).toList();

    // 高通滤波
    List<int> filteredData =
        highPassFilter(decodedData, sampleRate, cutoffFreq);

    // 噪声门
    List<int> denoisedData = noiseGate(filteredData, threshold);

    return denoisedData;
  }

//711解码为pcm数据
  List<int> convertList(List<int> aLawList) {
    // 将 ALawToLinear 函数应用于 List<int>
    final List<int> linearList = aLawList.map(ALawToLinear).toList();
    return linearList;
  }

//List<int>转为Uint8List
  Uint8List convertToInt8ListLittleEndian(List<int> intList) {
    final List<int> int8List = [];

    for (int intValue in intList) {
      intValue = intValue * 2;
      // 将 int 拆分为两个字节，采用小端序
      int8List.add(intValue & 0xFF); // 低 8 位
      int8List.add((intValue & 0xFF00) >> 8); // 高 8 位
    }

    return Uint8List.fromList(int8List);
  }
}