From 35522eb0f4d54741d47dca4c1058f3590bf17caf Mon Sep 17 00:00:00 2001
From: Ralph Gasser <rg@pontius.ch>
Date: Fri, 19 Apr 2024 13:57:53 +0200
Subject: [PATCH] Adds a utilities class that can handle WAVE files.

Signed-off-by: Ralph Gasser <rg@pontius.ch>
---
 .../engine/index/util/WaveUtilities.kt        | 83 +++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 vitrivr-engine-index/src/main/kotlin/org/vitrivr/engine/index/util/WaveUtilities.kt

diff --git a/vitrivr-engine-index/src/main/kotlin/org/vitrivr/engine/index/util/WaveUtilities.kt b/vitrivr-engine-index/src/main/kotlin/org/vitrivr/engine/index/util/WaveUtilities.kt
new file mode 100644
index 00000000..bd69083c
--- /dev/null
+++ b/vitrivr-engine-index/src/main/kotlin/org/vitrivr/engine/index/util/WaveUtilities.kt
@@ -0,0 +1,83 @@
+package org.vitrivr.engine.index.util
+
+import org.vitrivr.engine.core.model.content.element.AudioContent
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+import java.nio.channels.ByteChannel
+import java.nio.file.Files
+import java.nio.file.Path
+import java.nio.file.StandardOpenOption
+
+/**
+ * A collection of utilities for handling WAVE files.
+ *
+ * @author Ralph Gasser
+ * @version 1.0.0
+ */
+object WaveUtilities {
+    /**
+     * Exports a list of [AudioContent] as WAVE file (.wav).
+     *
+     * @param content List of [AudioContent] to export.
+     * @param path The path to the file.
+     *
+     */
+    fun export(content: List<AudioContent>, path: Path) {
+        if (content.isEmpty()) return
+        Files.newByteChannel(path, StandardOpenOption.WRITE, StandardOpenOption.CREATE_NEW).use { channel ->
+            /* Write audio data. */
+            var bytes = 0
+            channel.position(44)
+            content.forEach { audio ->
+                val buffer = ByteBuffer.allocate(audio.size).order(ByteOrder.LITTLE_ENDIAN)
+                buffer.asShortBuffer().put(audio.content)
+                bytes += channel.write(buffer)
+            }
+
+            /* Write header. */
+            channel.position(0)
+            writeWaveHeader(channel, content.first().channels, content.first().samplingRate, bytes)
+        }
+    }
+
+    /**
+     * Exports a single [AudioContent] as WAVE file (.wav).
+     *
+     * @param content [AudioContent] to export.
+     * @param path The path to the file.
+     */
+    fun export(content: AudioContent, path: Path) = export(listOf(content), path)
+
+    /**
+     * Writes the WAV header to the ByteBuffer.
+     *
+     * @param channels     The number of channels in the WAV file.
+     * @param sampleRate   Sample rate of the output file.
+     * @param length       Length in bytes of the frames data
+     */
+    private fun writeWaveHeader(channel: ByteChannel, channels: Short, sampleRate: Int, length: Int) {
+        /* Length of the subChunk2. */
+        val subChunk2Length: Int = length * channels * Short.SIZE_BYTES  /* Number of bytes for audio data: NumSamples * NumChannels * BytesPerSample. */
+        val buffer = ByteBuffer.allocate(44).order(ByteOrder.LITTLE_ENDIAN)
+
+        /* RIFF Chunk. */
+        buffer.put("RIFF".toByteArray(Charsets.US_ASCII))
+        buffer.putInt(36 + subChunk2Length)
+        buffer.put("WAVE".toByteArray(Charsets.US_ASCII)) /* WAV format. */
+
+        /* Format chunk. */
+        buffer.put("fmt ".toByteArray(Charsets.US_ASCII)) /* Begin of the format chunk. */
+        buffer.putInt(16) /* Length of the Format chunk. */
+        buffer.putShort(1.toShort()) /* Format: 1 = Raw PCM (linear quantization). */
+        buffer.putShort(channels) /* Number of channels. */
+        buffer.putInt(sampleRate) /* sampleRate. */
+        buffer.putInt((sampleRate * channels * Short.SIZE_BYTES)) /* Byte rate: SampleRate * NumChannels * BytesPerSample */
+        buffer.putShort((channels * Short.SIZE_BYTES).toShort()) /* Block align: NumChannels * BytesPerSample. */
+        buffer.putShort(Short.SIZE_BITS.toShort()) /* Bits per sample. */
+
+        /* Data chunk */
+        buffer.put("data".toByteArray(Charsets.US_ASCII)) /* Begin of the data chunk. */
+        buffer.putInt(subChunk2Length) /* Length of the data chunk. */
+        channel.write(buffer.flip())
+    }
+}
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