#1351 Restores semi-accurate timestamps of sample buffers to ensure P25 & DMR decoded messages have accurate timestamps and MBE recording voice frames have accurate timestamps. (#1357)

Co-authored-by: Dennis Sheirer <dsheirer@github.com>

src/main/java/io/github/dsheirer/buffer/AbstractNativeBuffer.java

@@ -0,0 +1,70 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2022 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.buffer;
+
+/**
+ * Base native buffer class.
+ */
+public abstract class AbstractNativeBuffer implements INativeBuffer
+{
+    private long mTimestamp;
+    private float mSamplesPerMillisecond;
+
+    /**
+     * Constructs an instance
+     * @param timestamp for the start of this buffer
+     * @param samplesPerMillisecond to calculate the time offset of sub-buffers extracted from this native buffer.
+     */
+    public AbstractNativeBuffer(long timestamp, float samplesPerMillisecond)
+    {
+        mTimestamp = timestamp;
+        mSamplesPerMillisecond = samplesPerMillisecond;
+    }
+
+    /**
+     * Timestamp for the start of this buffer
+     * @return timestamp in milliseconds
+     */
+    @Override
+    public long getTimestamp()
+    {
+        return mTimestamp;
+    }
+
+    /**
+     * Quantity of samples representing one millisecond of sample data, used for calculating fragment timestamp offsets.
+     * @return samples per millisecond count.
+     */
+    public float getSamplesPerMillisecond()
+    {
+        return mSamplesPerMillisecond;
+    }
+
+    /**
+     * Calculates the timestamp for a samples buffer fragment based on where it is extracted from relative to the
+     * native buffer starting timestamp.
+     * @param samplesPointer for the start of the fragment.  Note: this value will be divided by 2 to account for I/Q sample pairs.
+     * @return timestamp adjusted to the fragment or sub-buffer start sample.
+     */
+    protected long getFragmentTimestamp(int samplesPointer)
+    {
+        return getTimestamp() + (long)(samplesPointer / 2 / getSamplesPerMillisecond());
+    }
+}