/// <summary>
/// Get decoded audio track for the BGM using a specified samplerate.
/// could probably work with different samplerates but i don't know why you'd try
/// </summary>
/// <param name="dstFreq"></param>
/// <param name="track">The type of Audio Track</param>
/// <returns>Signed 16-Bit PCM audio</returns>
public short[] getAudioTrackPcm(int dstFreq, PPMAudioTrack track)
{
var srcPcm = Decode(track);
var srcFreq = 8192;
double soundspeed = Flipnote.BGMRate;
double framerate = Flipnote.Framerate;
if (track == PPMAudioTrack.BGM)
{
var bgmAdjust = (1.0 / soundspeed) / (1.0 / framerate);
srcFreq = ((int)(srcFreq * bgmAdjust));
}
if ((int)srcFreq != dstFreq)
{
return(pcmResampleNearestNeighbour(srcPcm, srcFreq, dstFreq));
}
return(srcPcm);
}
/// <summary>
/// Get decoded audio track for a given track
/// </summary>
/// <param name="track">Which type of Audio Track to decode</param>
/// <returns>Signed 16-Bit PCM audio</returns>
private short[] Decode(PPMAudioTrack track)
{
_SoundData sounds = Flipnote.Audio.SoundData;
byte[] src = null;
switch (track)
{
case PPMAudioTrack.BGM:
src = sounds.RawBGM; break;
case PPMAudioTrack.SE1:
src = sounds.RawSE1; break;
case PPMAudioTrack.SE2:
src = sounds.RawSE2; break;
case PPMAudioTrack.SE3:
src = sounds.RawSE3; break;
default:
src = sounds.RawBGM; break;
}
var srcSize = src.Length;
var dst = new short[srcSize * 2];
var srcPtr = 0;
var dstPtr = 0;
var sample = 0;
step_index = 0;
var predictor = 0;
var lowNibble = true;
while (srcPtr < srcSize)
{
// switch between high and low nibble each loop iteration
// increments srcPtr after every high nibble
if (lowNibble)
{
sample = src[srcPtr] & 0xF;
}
else
{
sample = src[srcPtr++] >> 4;
}
lowNibble = !lowNibble;
var step = ADPCM_STEP_TABLE[step_index];
var diff = step >> 3;
if ((sample & 1) != 0)
{
diff += step >> 2;
}
if ((sample & 2) != 0)
{
diff += step >> 1;
}
if ((sample & 4) != 0)
{
diff += step;
}
if ((sample & 8) != 0)
{
diff = -diff;
}
predictor += diff;
predictor = Utils.NumClamp(predictor, -32768, 32767);
step_index += IndexTable[sample];
step_index = Utils.NumClamp(step_index, 0, 88);
dst[dstPtr++] = (short)predictor;
}
return(dst);
}
