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diff --git a/engine/audio/public/ivoicecodec.h b/engine/audio/public/ivoicecodec.h
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+++ b/engine/audio/public/ivoicecodec.h
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+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// Purpose: Define the IVoiceCodec interface.
+//
+// $NoKeywords: $
+//=============================================================================//
+
+#ifndef IVOICECODEC_H
+#define IVOICECODEC_H
+#pragma once
+
+
+#include "interface.h"
+
+
+#define BYTES_PER_SAMPLE	2
+
+
+// This interface is for voice codecs to implement.
+
+// Codecs are guaranteed to be called with the exact output from Compress into Decompress (ie:
+// data won't be stuck together and sent to Decompress).
+
+// Decompress is not guaranteed to be called in any specific order relative to Compress, but 
+// Codecs maintain state between calls, so it is best to call Compress with consecutive voice data
+// and decompress likewise. If you call it out of order, it will sound wierd. 
+
+// In the same vein, calling Decompress twice with the same data is a bad idea since the state will be
+// expecting the next block of data, not the same block.
+
+class IVoiceCodec
+{
+protected:
+	virtual			~IVoiceCodec() {}
+
+public:
+	// Initialize the object. The uncompressed format is always 8-bit signed mono.
+	virtual bool	Init( int quality )=0;
+
+	// Use this to delete the object.
+	virtual void	Release()=0;
+
+
+	// Compress the voice data.
+	// pUncompressed		-	16-bit signed mono voice data.
+	// maxCompressedBytes	-	The length of the pCompressed buffer. Don't exceed this.
+	// bFinal        		-	Set to true on the last call to Compress (the user stopped talking).
+	//							Some codecs like big block sizes and will hang onto data you give them in Compress calls.
+	//							When you call with bFinal, the codec will give you compressed data no matter what.
+	// Return the number of bytes you filled into pCompressed.
+	virtual int		Compress(const char *pUncompressed, int nSamples, char *pCompressed, int maxCompressedBytes, bool bFinal)=0;
+
+	// Decompress voice data. pUncompressed is 16-bit signed mono.
+	virtual int		Decompress(const char *pCompressed, int compressedBytes, char *pUncompressed, int maxUncompressedBytes)=0;
+
+	// Some codecs maintain state between Compress and Decompress calls. This should clear that state.
+	virtual bool	ResetState()=0;
+};
+
+
+#endif // IVOICECODEC_H