Audio transcoding (#82)

* Adding audio transcoding.

* Audio transcoding working, some interferance is present.

* Implementing Resample.

* Audio transcoding working, resample do not work.

* code format.

* log properly

---------

Co-authored-by: Emily Dixon <edixon@mux.com>

library/src/main/java/com/mux/video/upload/internal/Resample.kt

@@ -0,0 +1,176 @@
+package com.mux.video.upload.internal
+
+class Resample {
+    fun resample(
+        data: ByteArray,
+        length: Int,
+        stereo: Boolean,
+        inFrequency: Int,
+        outFrequency: Int
+    ): ByteArray? {
+        if (inFrequency < outFrequency) return upsample(
+            data,
+            length,
+            stereo,
+            inFrequency,
+            outFrequency
+        )
+        return if (inFrequency > outFrequency) downsample(
+            data,
+            length,
+            stereo,
+            inFrequency,
+            outFrequency
+        ) else trimArray(data, length)
+    }
+
+    /**
+     * Basic upsampling algorithm. Uses linear approximation to fill in the
+     * missing data.
+     *
+     * @param data          Input data
+     * @param length        The current size of the input array (usually, data.length)
+     * @param inputIsStereo True if input is inputIsStereo
+     * @param inFrequency   Frequency of input
+     * @param outFrequency  Frequency of output
+     *
+     * @return Upsampled audio data
+     */
+    private fun upsample(
+        data: ByteArray,
+        length: Int,
+        inputIsStereo: Boolean,
+        inFrequency: Int,
+        outFrequency: Int
+    ): ByteArray? {
+
+        // Special case for no action
+        if (inFrequency == outFrequency) return trimArray(data, length)
+        val scale = inFrequency.toDouble() / outFrequency.toDouble()
+        var pos = 0.0
+        val output: ByteArray
+        if (!inputIsStereo) {
+            output = ByteArray((length / scale).toInt())
+            for (i in output.indices) {
+                var inPos = pos.toInt()
+                var proportion = pos - inPos
+                if (inPos >= length - 1) {
+                    inPos = length - 2
+                    proportion = 1.0
+                }
+                output[i] =
+                    Math.round(data[inPos] * (1 - proportion) + data[inPos + 1] * proportion)
+                        .toByte()
+                pos += scale
+            }
+        } else {
+            output = ByteArray(2 * (length / 2 / scale).toInt())
+            for (i in 0 until output.size / 2) {
+                val inPos = pos.toInt()
+                var proportion = pos - inPos
+                var inRealPos = inPos * 2
+                if (inRealPos >= length - 3) {
+                    inRealPos = length - 4
+                    proportion = 1.0
+                }
+                output[i * 2] =
+                    Math.round(data[inRealPos] * (1 - proportion) + data[inRealPos + 2] * proportion)
+                        .toByte()
+                output[i * 2 + 1] =
+                    Math.round(data[inRealPos + 1] * (1 - proportion) + data[inRealPos + 3] * proportion)
+                        .toByte()
+                pos += scale
+            }
+        }
+        return output
+    }
+
+    /**
+     * Basic downsampling algorithm. Uses linear approximation to reduce data.
+     *
+     * @param data          Input data
+     * @param length        The current size of the input array (usually, data.length)
+     * @param inputIsStereo True if input is inputIsStereo
+     * @param inFrequency   Frequency of input
+     * @param outFrequency  Frequency of output
+     *
+     * @return Downsampled audio data
+     */
+    private fun downsample(
+        data: ByteArray,
+        length: Int,
+        inputIsStereo: Boolean,
+        inFrequency: Int,
+        outFrequency: Int
+    ): ByteArray? {
+
+        // Special case for no action
+        if (inFrequency == outFrequency) return trimArray(data, length)
+        val scale = outFrequency.toDouble() / inFrequency.toDouble()
+        val output: ByteArray
+        var pos = 0.0
+        var outPos = 0
+        if (!inputIsStereo) {
+            var sum = 0.0
+            output = ByteArray((length * scale).toInt())
+            var inPos = 0
+            while (outPos < output.size) {
+                val firstVal = data[inPos++].toDouble()
+                var nextPos = pos + scale
+                if (nextPos >= 1) {
+                    sum += firstVal * (1 - pos)
+                    output[outPos++] = Math.round(sum).toByte()
+                    nextPos -= 1.0
+                    sum = nextPos * firstVal
+                } else {
+                    sum += scale * firstVal
+                }
+                pos = nextPos
+                if (inPos >= length && outPos < output.size) {
+                    output[outPos++] = Math.round(sum / pos).toByte()
+                }
+            }
+        } else {
+            var sum1 = 0.0
+            var sum2 = 0.0
+            output = ByteArray(2 * (length / 2 * scale).toInt())
+            var inPos = 0
+            while (outPos < output.size) {
+                val firstVal = data[inPos++].toDouble()
+                val nextVal = data[inPos++].toDouble()
+                var nextPos = pos + scale
+                if (nextPos >= 1) {
+                    sum1 += firstVal * (1 - pos)
+                    sum2 += nextVal * (1 - pos)
+                    output[outPos++] = Math.round(sum1).toByte()
+                    output[outPos++] = Math.round(sum2).toByte()
+                    nextPos -= 1.0
+                    sum1 = nextPos * firstVal
+                    sum2 = nextPos * nextVal
+                } else {
+                    sum1 += scale * firstVal
+                    sum2 += scale * nextVal
+                }
+                pos = nextPos
+                if (inPos >= length && outPos < output.size) {
+                    output[outPos++] = Math.round(sum1 / pos).toByte()
+                    output[outPos++] = Math.round(sum2 / pos).toByte()
+                }
+            }
+        }
+        return output
+    }
+
+    /**
+     * @param data   Data
+     * @param length Length of valid data
+     *
+     * @return Array trimmed to length (or same array if it already is)
+     */
+    fun trimArray(data: ByteArray, length: Int): ByteArray? {
+        if (data.size == length) return data
+        val output = ByteArray(length)
+        System.arraycopy(output, 0, data, 0, length)
+        return output
+    }
+}