从 Wooji-Juice ，多媒体Wiki 和 Apple ，这是我的建议（可能需要一些实验）：

After gathering all the data from Wooji-Juice, Multimedia Wiki and Apple, here is my proposal (may need some experiment):

文件结构

• Apple IMA4文件由34个字节的数据包组成。这是用于构建文件的数据包单元。


• 每个34字节的数据包有两部分：
  
  
  
  
  • 第一部分2个字节包含前导码：初始预测器和步骤索引
  
  
  • 剩下的32个字节包含声音半字节（4位的半字节用于检索16位样本）
  
  

  解码

  每个34字节的数据包将导致64位16位样本的解压缩。因此，未压缩数据的大小为每个数据包128个字节。

  Each packet of 34 bytes will lead to the decompression of 64 samples of 16 bits. So the size of the uncompressed data is 128 bytes per packet.

  解码伪代码如下所示：

  int[] ima_index_table = ... // Index table from [Multimedia Wiki][2]
  int[] step_table = ... // Step table from [Multimedia Wiki][2]
  byte[] packet = ... // A packet of 34 bytes compressed
  short[] output = ... // The output buffer of 128 bytes
  int preamble = (packet[0] << 8) | packet[1];
  int predictor = preamble && 0xFF80; // See [Multimedia Wiki][2]
  int step_index = preamble && 0x007F; // See [Multimedia Wiki][2]
  int i;
  int j = 0;
  for(i = 2; i < 34; i++) {
      byte data = packet[i];
      int lower_nibble = data && 0x0F;
      int upper_nibble = (data && 0xF0) >> 4;
  
      // Decode the lower nibble
      step_index += ima_index_table[lower_nibble];
      diff = ((signed)nibble + 0.5f) * step / 4;
      predictor += diff;
      step = ima_step_table[step index];
  
      // Clamp the predictor value to stay in range
      if (predictor > 65535)
          output[j++] = 65535;
      else if (predictor < -65536)
          output[j++] = -65536;
      else
          output[j++] = (short) predictor;
  
      // Decode the uppper nibble
      step_index += ima_index_table[upper_nibble];
      diff = ((signed)nibble + 0.5f) * step / 4;
      predictor += diff;
      step = ima_step_table[step index];
  
      // Clamp the predictor value to stay in range
      if (predictor > 65535)
          output[j++] = 65535;
      else if (predictor < -65536)
          output[j++] = -65536;
      else
          output[j++] = (short) predictor;
  }