Created
December 31, 2013 02:32
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| private int downSample(float factor, byte [] in, byte [] out) { | |
| int bytes = 4; // one audio sample is 32bits | |
| factor = 1.0f / factor; | |
| int downSampleCount = (int) (((in.length / bytes)) * factor); | |
| int ouputSampleCount = 0; | |
| for (int i = 0; i < downSampleCount; ++i) { | |
| float scaledIndex = i * factor; | |
| int floorIndex = (int)(scaledIndex); | |
| float alpha = scaledIndex - floorIndex; | |
| float rev_alpha = (float) (1.0 - alpha); | |
| floorIndex = (floorIndex << 2); // x4 | |
| int nextIndex = floorIndex + 4; | |
| // left channel: floor sample | |
| short left = in[floorIndex + 1]; // Swap for little endian | |
| left <<= 8; | |
| short tmp = (short) (in[floorIndex] & 0xff); | |
| left |= tmp; | |
| // left channel: next sample | |
| int nIndex = nextIndex; | |
| short leftNext = in[nIndex + 1]; // Swap for little endian | |
| leftNext <<= 8; | |
| tmp = (short) (in[nIndex] & 0xff); | |
| leftNext |= tmp; | |
| short resampleValue = (short) (left * rev_alpha + leftNext * alpha); | |
| byte leftLSB = (byte) (short) (resampleValue >> 8); | |
| byte leftMSB = (byte) ((resampleValue & 0x00ff)); | |
| // right channel: floor sample | |
| short right = in[floorIndex + 3]; | |
| right <<= 8; | |
| tmp = (short) (in[floorIndex + 2] & 0xff); | |
| right |= tmp; | |
| // right channel: next sample | |
| short rightNext = in[nIndex + 3]; | |
| rightNext <<= 8; | |
| tmp = (short) (in[nIndex + 2] & 0xff); | |
| rightNext |= tmp; | |
| resampleValue = (short) (right * rev_alpha + rightNext * alpha); | |
| byte rightLSB = (byte) (short) (resampleValue >> 8); | |
| byte rightMSB = (byte) ((resampleValue & 0x00ff)); | |
| int outIndex = (i << 2); // i * 4 | |
| int base = outIndex; | |
| out[base] = leftMSB; out[base + 1] = leftLSB; | |
| out[base + 2] = rightMSB; out[base + 3] = rightLSB; | |
| ouputSampleCount++; | |
| } | |
| return ouputSampleCount; | |
| } |
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