70 lines
1.6 KiB
Dart
70 lines
1.6 KiB
Dart
import 'dart:typed_data';
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enum G711Type {
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uLaw,
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aLaw,
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}
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class G711Decoder {
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Uint8List g711Encode(Uint8List pcmData, G711Type g711Type) {
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List<int> g711Data = [];
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for (int sample in pcmData) {
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int sign = (sample < 0) ? 0x80 : 0;
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int magnitude = (sample < 0) ? -sample : sample;
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int exponent = 7;
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while (magnitude < (1 << exponent) && exponent > 0) {
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exponent--;
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}
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int mantissa = (magnitude >> (exponent - 4)) & 0x0F;
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if (g711Type == G711Type.uLaw) {
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// μ-law encoding
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int value = ~(sign | ((exponent << 4) & 0x70) | (mantissa >> 4));
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g711Data.add(value & 0xFF);
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} else {
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// A-law encoding
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int value = sign | ((exponent << 4) & 0x70) | (mantissa >> 4);
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g711Data.add(value & 0xFF);
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}
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}
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return Uint8List.fromList(g711Data);
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}
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List<int> pcm16ToG711u(List<int> pcm16Data) {
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List<int> g711uData = [];
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for (int i = 0; i < pcm16Data.length; i += 2) {
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int pcmSample = (pcm16Data[i + 1] << 8) | pcm16Data[i];
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int g711Sample = pcmToG711u(pcmSample);
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// 将 G.711 样本拆分成两个字节
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g711uData.add(g711Sample & 0xFF);
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g711uData.add((g711Sample >> 8) & 0xFF);
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}
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return g711uData;
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}
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int pcmToG711u(int pcmSample) {
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const int MULAW_BIAS = 0x84;
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const int CLIP = 32635;
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// 剪裁 PCM 样本
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if (pcmSample > CLIP) {
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pcmSample = CLIP;
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} else if (pcmSample < -CLIP) {
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pcmSample = -CLIP;
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}
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// 增加偏置并取反
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pcmSample += MULAW_BIAS;
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pcmSample = ~pcmSample & 0xFF;
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return pcmSample;
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}
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}
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