Ticket #4804: libs_libmyth-preamp-patch-ticket-4804

Ticket 4804 is an enhancement to MythTV to provide a pre-amp feature. This is

From: Erik Hovland <erik@hovland.org>

the first step towards having native ReplayGain support in MythMusic.
---

 mythtv/libs/libmyth/audiooutput.h       |   15 ++++
 mythtv/libs/libmyth/audiooutputbase.cpp |  120 +++++++++++++++++++++++++++++++
 mythtv/libs/libmyth/audiooutputbase.h   |   22 +++++-
 3 files changed, 155 insertions(+), 2 deletions(-)


diff --git a/mythtv/libs/libmyth/audiooutput.h b/mythtv/libs/libmyth/audiooutput.h
index e89147c..e3014c4 100644
--- a/mythtv/libs/libmyth/audiooutput.h
+++ b/mythtv/libs/libmyth/audiooutput.h
@@ -33,6 +33,21 @@ class MPUBLIC AudioOutput : public VolumeBase, public OutputListeners
     virtual void SetStretchFactor(float factor);
     virtual float GetStretchFactor(void) const { return 1.0f; }
 
+    // For software pre-amplification.
+    virtual bool IsPreAmpEnabled() const { return false; }
+    virtual void SetPreAmp(bool enabled) { return; }
+    virtual void EnablePreAmp() { return; }
+    virtual void DisablePreAmp() { return; }
+    virtual void SetPreAmpGain(float gain) { return; }
+    virtual void SetPreAmpFactor(float factor) { return; }
+    virtual float GetPreAmpGain() const { return 0.0; }
+    virtual float GetPreAmpFactor() const { return 1.0; }
+    virtual void ResetClippingMonitor() { return; }
+    virtual bool HasClippingOccurred() const { return false; }
+    virtual float GetMaxOutput() const { return 1.0; }
+    virtual float GetMaxClipFreePreAmpGain() const { return 0.0; }
+    virtual float GetMaxClipFreePreAmpFactor() const { return 1.0; }
+
     // do AddSamples calls block?
     virtual void SetBlocking(bool blocking) = 0;
     
diff --git a/mythtv/libs/libmyth/audiooutputbase.cpp b/mythtv/libs/libmyth/audiooutputbase.cpp
index 6db02f2..c71d2ad 100644
--- a/mythtv/libs/libmyth/audiooutputbase.cpp
+++ b/mythtv/libs/libmyth/audiooutputbase.cpp
@@ -44,6 +44,9 @@ AudioOutputBase::AudioOutputBase(const AudioSettings &settings) :
     need_resampler(false),
 
     src_ctx(NULL),
+    
+    pre_amp_enabled(false),     pre_amp_factor(1.0),
+    pre_amp_max_output(0.0),
 
     pSoundStretch(NULL),
     encoder(NULL),
@@ -790,6 +793,36 @@ bool AudioOutputBase::AddSamples(char *buffers[], int samples,
     return true;
 }
 
+#define __APPLY_PRE_AMP(TYPE,MIN,MAX) \
+{ \
+    TYPE *buf = (TYPE *)buffer; \
+    for ( int i = 0; i < samples; ++i ) \
+    { \
+        float f = (float)buf[i] / (float)MAX; \
+        f *= pre_amp_factor; \
+        float a = abs(f); \
+        if ( a > pre_amp_max_output ) pre_amp_max_output = a; \
+        if ( f >= 1.0 ) buf[i] = MAX; \
+        else if ( f <= -1.0 ) buf[i] = MIN; \
+        else buf[i] = (TYPE)round(f*MAX); \
+    } \
+}
+
+void AudioOutputBase::ApplyPreAmp(void *buffer, int samples, int sample_bytes)
+{
+    if ( !pre_amp_enabled ) return;
+    // NOTE: This only handles 1, 2 or 4 byte samples.
+    if ( sample_bytes == 4 )
+        __APPLY_PRE_AMP(int,INT_MIN,INT_MAX)
+    else if ( sample_bytes == 2 )
+        __APPLY_PRE_AMP(short,SHRT_MIN,SHRT_MAX)
+    else if ( sample_bytes == 1 )
+        __APPLY_PRE_AMP(char,CHAR_MIN,CHAR_MAX)
+
+    return;
+}
+#undef __APPLY_PRE_AMP
+
 bool AudioOutputBase::AddSamples(char *buffer, int samples, long long timecode)
 {
     // NOTE: This function is not threadsafe
@@ -928,6 +961,17 @@ void AudioOutputBase::_AddSamples(void *buffer, bool interleaved, int samples,
     int audio_bytes = audio_bits / 8;
     int org_waud = waud;
 
+    if ( interleaved )
+        // Apply to the single buffer if we're interleaved.
+        ApplyPreAmp(buffer,samples*source_audio_channels,audio_bytes);
+    else
+    {
+        // Otherwise, apply to each channel individually.
+        void **bufs = (void**)buffer;
+        for ( int i = 0; i < source_audio_channels; ++i )
+            ApplyPreAmp(bufs[i],samples,audio_bytes);
+    }
+
     int afree = audiofree(false);
 
     int abps = (encoder) ?
@@ -1408,5 +1452,79 @@ int AudioOutputBase::readOutputData(unsigned char*, int)
     return 0;
 }
 
-/* vim: set expandtab tabstop=4 shiftwidth=4: */
+bool AudioOutputBase::IsPreAmpEnabled() const
+{
+    return pre_amp_enabled;
+}
+
+void AudioOutputBase::SetPreAmp(bool enabled)
+{
+       pre_amp_enabled = enabled;
+       return;
+}
+
+void AudioOutputBase::EnablePreAmp()
+{
+    pre_amp_enabled = true;
+    return;
+}
+
+void AudioOutputBase::DisablePreAmp()
+{
+    pre_amp_enabled = false;
+    return;
+}
+
+void AudioOutputBase::SetPreAmpGain(float gain)
+{
+    pre_amp_factor = pow(10.0,gain/20.0);
+    return;
+}
 
+void AudioOutputBase::SetPreAmpFactor(float factor)
+{
+    if ( factor >= 0 ) pre_amp_factor = factor;
+    return;
+}
+
+float AudioOutputBase::GetPreAmpGain() const
+{
+    if ( pre_amp_factor <= 0 ) return -1.0*numeric_limits<float>::max();
+    return 20.0*log(pre_amp_factor)/log(10.0);
+}
+
+float AudioOutputBase::GetPreAmpFactor() const
+{
+    return pre_amp_factor;
+}
+
+void AudioOutputBase::ResetClippingMonitor()
+{
+    pre_amp_max_output = 0.0;
+    return;
+}
+
+bool AudioOutputBase::HasClippingOccurred() const
+{
+    return pre_amp_max_output > 1.0;
+}
+
+float AudioOutputBase::GetMaxOutput() const
+{
+    return pre_amp_max_output;
+}
+
+float AudioOutputBase::GetMaxClipFreePreAmpGain() const
+{
+    float max_factor = GetMaxClipFreePreAmpFactor();
+    if ( max_factor <= 0 ) return -1.0*numeric_limits<float>::max();
+    return 20.0*log(max_factor)/log(10.0);
+}
+
+float AudioOutputBase::GetMaxClipFreePreAmpFactor() const
+{
+    if ( pre_amp_max_output == 0 ) return numeric_limits<float>::max();
+    return pre_amp_factor / pre_amp_max_output;
+}
+
+/* vim: set expandtab tabstop=4 shiftwidth=4: */
diff --git a/mythtv/libs/libmyth/audiooutputbase.h b/mythtv/libs/libmyth/audiooutputbase.h
index 8d9e86b..1732d97 100644
--- a/mythtv/libs/libmyth/audiooutputbase.h
+++ b/mythtv/libs/libmyth/audiooutputbase.h
@@ -71,8 +71,22 @@ class AudioOutputBase : public AudioOutput, public QThread
 
     virtual void GetBufferStatus(uint &fill, uint &total);
 
-    //  Only really used by the AudioOutputNULL object
+     // For software pre-amplification.
+     virtual bool IsPreAmpEnabled() const;
+     virtual void SetPreAmp(bool enabled);
+     virtual void EnablePreAmp();
+     virtual void DisablePreAmp();
+     virtual void SetPreAmpGain(float gain);
+     virtual void SetPreAmpFactor(float factor);
+     virtual float GetPreAmpGain() const;
+     virtual float GetPreAmpFactor() const;
+     virtual void ResetClippingMonitor();
+     virtual bool HasClippingOccurred() const;
+     virtual float GetMaxOutput() const;
+     virtual float GetMaxClipFreePreAmpGain() const;
+     virtual float GetMaxClipFreePreAmpFactor() const;
 
+    //  Only really used by the AudioOutputNULL object
     virtual void bufferOutputData(bool y){ buffer_output_data_for_use = y; }
     virtual int readOutputData(unsigned char *read_buffer, int max_length);
 
@@ -100,6 +114,7 @@ class AudioOutputBase : public AudioOutput, public QThread
 
     int GetAudioData(unsigned char *buffer, int buf_size, bool fill_buffer);
 
+    void ApplyPreAmp(void *buffer, int samples, int sample_bytes);
     void _AddSamples(void *buffer, bool interleaved, int samples, long long timecode);
 
     void OutputAudioLoop(void);
@@ -165,6 +180,11 @@ class AudioOutputBase : public AudioOutput, public QThread
     bool need_resampler;
     SRC_STATE *src_ctx;
 
+    // pre-amplification
+    bool pre_amp_enabled;
+    float pre_amp_factor;
+    float pre_amp_max_output;
+
     // timestretch
     soundtouch::SoundTouch    *pSoundStretch;
     AudioOutputDigitalEncoder *encoder;