AUDIO: Fix Oki ADPCM to work with Mono streams using odd sized buffers.

2 files changed, 15 insertions, 5 deletions

diff --git a/audio/decoders/adpcm.cpp b/audio/decoders/adpcm.cpp
index 5c96d5245a..e7297423f6 100644
--- a/audio/decoders/adpcm.cpp
+++ b/audio/decoders/adpcm.cpp
@@ -71,13 +71,19 @@ int Oki_ADPCMStream::readBuffer(int16 *buffer, const int numSamples) {
 	int samples;
 	byte data;
 
-	assert(numSamples % 2 == 0);
+	for (samples = 0; samples < numSamples && !_stream->eos() && (_stream->pos() < _endpos); samples++) {
+		if (_decodedSampleCount == 0) {
+			data = _stream->readByte();
+			_decodedSamples[0] = decodeOKI((data >> 4) & 0x0f);
+			_decodedSamples[1] = decodeOKI((data >> 0) & 0x0f);
+			_decodedSampleCount = 2;
+		}
 
-	for (samples = 0; samples < numSamples && !_stream->eos() && _stream->pos() < _endpos; samples += 2) {
-		data = _stream->readByte();
-		buffer[samples] = decodeOKI((data >> 4) & 0x0f);
-		buffer[samples + 1] = decodeOKI(data & 0x0f);
+		// (1 - (count - 1)) ensures that _decodedSamples acts as a FIFO of depth 2
+		buffer[samples] = _decodedSamples[1 - (_decodedSampleCount - 1)];
+		_decodedSampleCount--;
 	}
+
 	return samples;
 }
 
diff --git a/audio/decoders/adpcm_intern.h b/audio/decoders/adpcm_intern.h
index 537ae023ef..423c4af267 100644
--- a/audio/decoders/adpcm_intern.h
+++ b/audio/decoders/adpcm_intern.h
@@ -89,6 +89,10 @@ public:
 
 protected:
 	int16 decodeOKI(byte);
+
+private:
+	uint8 _decodedSampleCount;
+	int16 _decodedSamples[2];
 };
 
 class Ima_ADPCMStream : public ADPCMStream {