Add experimental echo cancellation to qTox

It compiles with modified OpenAL (unchanged logic otherwise), but effectiveness needs testing (like uTox)

src/audio.cpp

@@ -333,3 +333,23 @@ bool Audio::tryCaptureSamples(uint8_t* buf, int framesize)
     alcCaptureSamples(Audio::alInDev, buf, framesize);
     return true;
 }
+
+#ifdef QTOX_FILTER_AUDIO
+#include "audiofilterer.h"
+#include <AL/alext.h>
+
+void Audio::getEchoesToFilter(AudioFilterer* filterer, int framesize)
+{
+#ifdef ALC_LOOPBACK_CAPTURE_SAMPLES
+    ALint samples;
+    alcGetIntegerv(Audio::alOutDev, ALC_LOOPBACK_CAPTURE_SAMPLES, sizeof(samples), &samples);
+    if (samples >= framesize)
+    {
+        int16_t buf[framesize];
+        alcCaptureSamplesLoopback(Audio::alOutDev, buf, framesize);
+        filterer->passAudioOutput(buf, framesize);
+        filterer->setEchoDelayMs(5); // This 5ms is configurable I believe
+    }
+#endif
+}
+#endif

src/audio.h

@@ -36,6 +36,7 @@ class QTimer;
 class QThread;
 class QMutex;
 struct Tox;
+class AudioFilterer;
 
 class Audio : QObject
 {
@@ -64,6 +65,11 @@ public:
     static void playGroupAudioQueued(Tox*, int group, int peer, const int16_t* data,
                         unsigned samples, uint8_t channels, unsigned sample_rate, void*);
 
+#ifdef QTOX_FILTER_AUDIO
+    static void getEchoesToFilter(AudioFilterer* filter, int framesize);
+    // is a null op #ifndef ALC_LOOPBACK_CAPTURE_SAMPLES
+#endif
+
 public slots:
     /// Must be called from the audio thread, plays a group call's received audio
     void playGroupAudio(int group, int peer, const int16_t* data,

src/audiofilterer.cpp

@@ -35,15 +35,28 @@ void AudioFilterer::closeFilter()
     filter = nullptr;
 }
 
+bool AudioFilterer::filterAudio(int16_t* data, int framesize)
+{
+    return filter && 0 == filter_audio(filter, (int16_t*) data, framesize);
+}
 
-void AudioFilterer::filterAudio(int16_t* data, int framesize)
+/* Enable/disable filters. 1 to enable, 0 to disable. */
+bool AudioFilterer::enableDisableFilters(int echo, int noise, int gain)
 {
-    if (!filter)
-        return;
+    return filter && 0 == enable_disable_filters(filter, echo, noise, gain);
+}
 
-    filter_audio(filter, (int16_t*) data, framesize);
+/* Give the audio output from your software to this function so it knows what echo to cancel from the frame */
+bool AudioFilterer::passAudioOutput(const int16_t *data, int samples)
+{
+    return filter && 0 == pass_audio_output(filter, data, samples);
 }
 
+/* Tell the echo canceller how much time in ms it takes for audio to be played and recorded back after. */
+bool AudioFilterer::setEchoDelayMs(int16_t msInSndCardBuf)
+{
+    return filter && 0 == set_echo_delay_ms(filter, msInSndCardBuf);
+}
 
 AudioFilterer::~AudioFilterer()
 {

src/audiofilterer.h

@@ -28,11 +28,20 @@ class AudioFilterer
 public:
     explicit AudioFilterer() = default;
     ~AudioFilterer();
-
     void startFilter(unsigned int fs);
-    void filterAudio(int16_t* data, int framesize);
     void closeFilter();
 
+    /* Enable/disable filters. 1 to enable, 0 to disable. */
+    bool enableDisableFilters(int echo, int noise, int gain);
+
+    bool filterAudio(int16_t* data, int samples);
+
+    /* Give the audio output from your software to this function so it knows what echo to cancel from the frame */
+    bool passAudioOutput(const int16_t *data, int samples);
+
+    /* Tell the echo canceller how much time in ms it takes for audio to be played and recorded back after. */
+    bool setEchoDelayMs(int16_t msInSndCardBuf);
+
 private:
     struct Filter_Audio* filter{nullptr};
 };

src/coreav.cpp

@@ -258,7 +258,12 @@ void Core::sendCallAudio(int callId, ToxAv* toxav)
     {
 #ifdef QTOX_FILTER_AUDIO
         if (filterer[callId])
+        {
+            // is a null op #ifndef ALC_LOOPBACK_CAPTURE_SAMPLES
+            Audio::getEchoesToFilter(filterer[callId], framesize);
+
             filterer[callId]->filterAudio((int16_t*) buf, framesize);
+        }
 #endif
 
         uint8_t dest[bufsize];