Centralize fallback sample rate with kFallbackSampleRate

Replaces hardcoded 44100Hz values (used as fallbacks or for the "Default" sample rate preference) with a new constant `constexpr int kFallbackSampleRate = 44100;` defined in RageSound.h.

This constant is now used in:
- RageSoundReader_Silence
- RageSoundManager (for unloaded driver scenarios)
- All sound drivers' initialization logic for the "Default (0)" preference (DSound, WaveOut, AU, PulseAudio, OSS, WDMKS, Null)
- DSound primary buffer setup.

src/RageSound.cpp

@@ -147,7 +147,7 @@ public:
 	int SetPosition( int iFrame )  { return 1; }
 	int Read( float *pBuf, int iFrames ) { return RageSoundReader::END_OF_FILE; }
 	RageSoundReader *Copy() const { return new RageSoundReader_Silence; }
-	int GetSampleRate() const { return 44100; } // Hardcoded to 44100
+	int GetSampleRate() const { return kFallbackSampleRate; }
 	unsigned GetNumChannels() const { return 1; }
 	int GetNextSourceFrame() const { return 0; }
 	float GetStreamToSourceRatio() const { return 1.0f; }

src/RageSound.h

@@ -9,6 +9,8 @@
 
 #include <cstdint>
 
+constexpr int kFallbackSampleRate = 44100;
+
 class RageSoundReader;
 struct lua_State;
 

src/RageSoundManager.cpp

@@ -133,7 +133,7 @@ float RageSoundManager::GetPlayLatency() const
 int RageSoundManager::GetDriverSampleRate() const
 {
 	if( m_pDriver == nullptr )
-		return 44100; // Fallback if no driver is loaded
+		return kFallbackSampleRate;
 
 	return m_pDriver->GetSampleRate(); // Returns the *actual* operating rate of the loaded driver
 }

src/arch/Sound/ALSA9Helpers.cpp

@@ -1,4 +1,5 @@
 #include "global.h"
+#include "RageSound.h"
 #include "RageLog.h"
 #include "RageUtil.h"
 #include "ALSA9Helpers.h"
@@ -229,7 +230,7 @@ RString Alsa9Buf::Init( int channels_,
 	preferred_writeahead = iWriteahead;
 	preferred_chunksize = iChunkSize;
 	if( iSampleRate == 0 )
-		samplerate = 44100;
+		samplerate = kFallbackSampleRate;
 	else
 		samplerate = iSampleRate;
 

src/arch/Sound/DSoundHelpers.cpp

@@ -65,7 +65,7 @@ void DSound::SetPrimaryBufferMode()
 	int preferredSampleRate = PREFSMAN->m_iSoundPreferredSampleRate;
 	if (preferredSampleRate == 0)
 	{
-		preferredSampleRate = 44100; // Default to 44100 Hz if preference is 0
+		preferredSampleRate = kFallbackSampleRate;
 	}
 	waveformat.nSamplesPerSec = preferredSampleRate;
 	waveformat.nBlockAlign = 4;
@@ -202,7 +202,7 @@ RString DSoundBuf::Init( DSound &ds, DSoundBuf::hw hardware,
 	bool bNeedCtrlFrequency = false;
 	if( m_iSampleRate == DYNAMIC_SAMPLERATE ) // DYNAMIC_SAMPLERATE is usually 0 or some special value
 	{
-		m_iSampleRate = 44100; // If dynamic, default to 44100 for now
+		m_iSampleRate = kFallbackSampleRate;
 		bNeedCtrlFrequency = true;
 	}
 

src/arch/Sound/RageSoundDriver.h

@@ -6,13 +6,14 @@
 #include "RageThreads.h"
 #include "RageTimer.h"
 #include "RageUtil_CircularBuffer.h"
+#include "RageSound.h"
 
 #include <cstdint>
 
 class RageSoundBase;
 class RageTimer;
 class RageSoundMixBuffer;
-static const int samples_per_block = 512;
+static const int samples_per_block = 512; // This should probably be kSamplesPerBlock or similar if it's truly const and static
 
 class RageSoundDriver: public RageDriver
 {
@@ -66,7 +67,7 @@ public:
 	 * hearing it.  (This isn't necessarily the same as the buffer latency.) */
 	virtual float GetPlayLatency() const { return 0.0f; }
 
-	virtual int GetSampleRate() const { return 44100; }
+	virtual int GetSampleRate() const { return kFallbackSampleRate; }
 
 protected:
 	/* Start the decoding.  This should be called once the hardware is set up and

src/arch/Sound/RageSoundDriver_DSound_Software.cpp

@@ -97,7 +97,7 @@ RString RageSoundDriver_DSound_Software::Init()
 	m_pPCM = new DSoundBuf;
 	m_iSampleRate = PREFSMAN->m_iSoundPreferredSampleRate;
 	if( m_iSampleRate == 0 )
-		m_iSampleRate = 44100;
+		m_iSampleRate = kFallbackSampleRate;
 	// This m_iSampleRate (driver's) is then passed as the iSampleRate parameter to DSoundBuf::Init()
 	sError = m_pPCM->Init( ds, DSoundBuf::HW_DONT_CARE, channels, m_iSampleRate, 16, g_iMaxWriteahead );
 	if( sError != "" )

src/arch/Sound/RageSoundDriver_Null.cpp

@@ -32,7 +32,7 @@ RageSoundDriver_Null::RageSoundDriver_Null()
 {
 	m_iSampleRate = PREFSMAN->m_iSoundPreferredSampleRate;
 	if( m_iSampleRate == 0 )
-		m_iSampleRate = 44100;
+		m_iSampleRate = kFallbackSampleRate;
 	m_iLastCursorPos = GetPosition();
 	StartDecodeThread();
 }

src/arch/Sound/RageSoundDriver_OSS.cpp

@@ -196,7 +196,7 @@ RString RageSoundDriver_OSS::Init()
 	// Determine the target sample rate based on preference
 	int targetSampleRate = PREFSMAN->m_iSoundPreferredSampleRate;
 	if (targetSampleRate == 0) {
-		targetSampleRate = 44100; // Default to 44100 if preference is 0
+		targetSampleRate = kFallbackSampleRate;
 	}
 	
 	samplerate = targetSampleRate; // Attempt to set this rate

src/arch/Sound/RageSoundDriver_PulseAudio.cpp

@@ -29,7 +29,7 @@ m_PulseMainLoop(nullptr), m_PulseCtx(nullptr), m_PulseStream(nullptr)
 {
 	m_ss.rate = PREFSMAN->m_iSoundPreferredSampleRate;
 	if( m_ss.rate == 0 )
-		m_ss.rate = 44100;
+		m_ss.rate = kFallbackSampleRate;
 }
 
 RageSoundDriver_PulseAudio::~RageSoundDriver_PulseAudio()

src/arch/Sound/RageSoundDriver_WaveOut.cpp

@@ -125,7 +125,7 @@ RString RageSoundDriver_WaveOut::Init()
 	b_InitSuccess = false;
 	m_iSampleRate = PREFSMAN->m_iSoundPreferredSampleRate;
 	if( m_iSampleRate == 0 )
-		m_iSampleRate = 44100;
+		m_iSampleRate = kFallbackSampleRate;
 
 	WAVEFORMATEX fmt;
 	fmt.wFormatTag = WAVE_FORMAT_PCM;