audiomixmatrix: New element that mixes audio channels

This element transforms a given number of input channels into a given number of
output channels according to a given transformation matrix. The matrix
coefficients must be between -1 and 1. In the auto mode, input/output channels
are automatically negotiated and the transformation matrix is a truncated or
zero-padded identity matrix.

https://bugzilla.gnome.org/show_bug.cgi?id=777376

3 files changed, 901 insertions, 0 deletions

diff --git a/gst/audiomixmatrix/Makefile.am b/gst/audiomixmatrix/Makefile.am
new file mode 100644
index 000000000..e54eb9d03
--- /dev/null
+++ b/gst/audiomixmatrix/Makefile.am
@@ -0,0 +1,10 @@
+plugin_LTLIBRARIES = libgstaudiomixmatrix.la
+
+libgstaudiomixmatrix_la_SOURCES = gstaudiomixmatrix.c
+
+libgstaudiomixmatrix_la_CFLAGS = $(GST_PLUGINS_BASE_CFLAGS) $(GST_BASE_CFLAGS) $(GST_CFLAGS)
+libgstaudiomixmatrix_la_LIBADD = $(GST_PLUGINS_BASE_LIBS) -lgstaudio-$(GST_API_VERSION) $(GST_BASE_LIBS) $(GST_LIBS) $(LIBM)
+libgstaudiomixmatrix_la_LDFLAGS = $(GST_PLUGIN_LDFLAGS)
+libgstaudiomixmatrix_la_LIBTOOLFLAGS = $(GST_PLUGIN_LIBTOOLFLAGS)
+
+noinst_HEADERS = gstaudiomixmatrix.h
diff --git a/gst/audiomixmatrix/gstaudiomixmatrix.c b/gst/audiomixmatrix/gstaudiomixmatrix.c
new file mode 100644
index 000000000..5604d064b
--- /dev/null
+++ b/gst/audiomixmatrix/gstaudiomixmatrix.c
@@ -0,0 +1,813 @@
+/*
+ * GStreamer
+ * Copyright (C) 2017 Vivia Nikolaidou <vivia@toolsonair.com>
+ *
+ * gstaudiomixmatrix.c
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+/**
+ * SECTION:element-audiomixmatrix
+ * @short_description: Transform input/output channels according to a matrix
+ *
+ * This element transforms a given number of input channels into a given
+ * number of output channels according to a given transformation matrix. The
+ * matrix coefficients must be between -1 and 1: the number of rows is equal
+ * to the number of output channels and the number of columns is equal to the
+ * number of input channels. In the first-channels mode, input/output channels
+ * are automatically negotiated and the transformation matrix is a truncated
+ * identity matrix.
+ *
+ * <refsect2>
+ * <title>Example matrix generation code</title>
+ * To generate the matrix using code:
+ *
+ * |[
+ * GValue v = G_VALUE_INIT;
+ * GValue v2 = G_VALUE_INIT;
+ * GValue v3 = G_VALUE_INIT;
+ *
+ * g_value_init (&v2, GST_TYPE_ARRAY);
+ * g_value_init (&v3, G_TYPE_DOUBLE);
+ * g_value_set_double (&v3, 1);
+ * gst_value_array_append_value (&v2, &v3);
+ * g_value_unset (&v3);
+ * [ Repeat for as many double as your input channels - unset and reinit v3 ]
+ * g_value_init (&v, GST_TYPE_ARRAY);
+ * gst_value_array_append_value (&v, &v2);
+ * g_value_unset (&v2);
+ * [ Repeat for as many v2's as your output channels - unset and reinit v2]
+ * g_object_set_property (G_OBJECT (audiomixmatrix), "matrix", &v);
+ * g_value_unset (&v);
+ * ]|
+ * </refsect2>
+ *
+ * <refsect2>
+ * <title>Example launch line</title>
+ * |[
+ * gst-launch-1.0 audiotestsrc ! audio/x-raw,channels=4 ! audiomixmatrix in-channels=4 out-channels=2 channel-mask=-1 matrix="<<(double)1, (double)0, (double)0, (double)0>, <0.0, 1.0, 0.0, 0.0>>" ! audio/x-raw,channels=2 ! autoaudiosink
+ * ]|
+ * </refsect2>
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+/* FIXME 2.0: suppress warnings for deprecated API such as GValueArray
+ * with newer GLib versions (>= 2.31.0) */
+#define GLIB_DISABLE_DEPRECATION_WARNINGS
+
+#include "gstaudiomixmatrix.h"
+
+#include <gst/gst.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+
+GST_DEBUG_CATEGORY_STATIC (audiomixmatrix_debug);
+#define GST_CAT_DEFAULT audiomixmatrix_debug
+
+/* GstAudioMixMatrix properties */
+enum
+{
+  PROP_0,
+  PROP_IN_CHANNELS,
+  PROP_OUT_CHANNELS,
+  PROP_MATRIX,
+  PROP_MATRIX_VALUE_ARRAY,
+  PROP_CHANNEL_MASK,
+  PROP_MODE
+};
+
+GType
+gst_audio_mix_matrix_mode_get_type (void)
+{
+  static GType gst_audio_mix_matrix_mode_type = 0;
+  static const GEnumValue gst_audio_mix_matrix_mode[] = {
+    {GST_AUDIO_MIX_MATRIX_MODE_MANUAL,
+          "Manual mode: please specify input/output channels and transformation matrix",
+        "manual"},
+    {GST_AUDIO_MIX_MATRIX_MODE_FIRST_CHANNELS,
+          "First channels mode: input/output channels are auto-negotiated, transformation matrix is a truncated identity matrix",
+        "first-channels"},
+    {0, NULL, NULL}
+
+  };
+
+  if (!gst_audio_mix_matrix_mode_type) {
+    gst_audio_mix_matrix_mode_type =
+        g_enum_register_static ("GstAudioMixMatrixModeType",
+        gst_audio_mix_matrix_mode);
+  }
+  return gst_audio_mix_matrix_mode_type;
+}
+
+static GstStaticPadTemplate gst_audio_mix_matrix_src_template =
+GST_STATIC_PAD_TEMPLATE ("src",
+    GST_PAD_SRC,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS
+    ("audio/x-raw, channels = [1, max], layout = (string) interleaved, format = (string) {"
+        GST_AUDIO_NE (F32) "," GST_AUDIO_NE (F64) "," GST_AUDIO_NE (S16) ","
+        GST_AUDIO_NE (S32) "}")
+    );
+
+static GstStaticPadTemplate gst_audio_mix_matrix_sink_template =
+GST_STATIC_PAD_TEMPLATE ("sink",
+    GST_PAD_SINK,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS
+    ("audio/x-raw, channels = [1, max], layout = (string) interleaved, format = (string) {"
+        GST_AUDIO_NE (F32) "," GST_AUDIO_NE (F64) "," GST_AUDIO_NE (S16) ","
+        GST_AUDIO_NE (S32) "}")
+    );
+
+static void gst_audio_mix_matrix_set_property (GObject * object, guint prop_id,
+    const GValue * value, GParamSpec * pspec);
+static void gst_audio_mix_matrix_get_property (GObject * object, guint prop_id,
+    GValue * value, GParamSpec * pspec);
+static void gst_audio_mix_matrix_dispose (GObject * object);
+static gboolean gst_audio_mix_matrix_get_unit_size (GstBaseTransform * trans,
+    GstCaps * caps, gsize * size);
+static gboolean gst_audio_mix_matrix_set_caps (GstBaseTransform * trans,
+    GstCaps * incaps, GstCaps * outcaps);
+static GstFlowReturn gst_audio_mix_matrix_transform (GstBaseTransform * trans,
+    GstBuffer * inbuf, GstBuffer * outbuf);
+static GstCaps *gst_audio_mix_matrix_transform_caps (GstBaseTransform * trans,
+    GstPadDirection direction, GstCaps * caps, GstCaps * filter);
+static GstCaps *gst_audio_mix_matrix_fixate_caps (GstBaseTransform * trans,
+    GstPadDirection direction, GstCaps * caps, GstCaps * othercaps);
+static GstStateChangeReturn gst_audio_mix_matrix_change_state (GstElement *
+    element, GstStateChange transition);
+
+G_DEFINE_TYPE (GstAudioMixMatrix, gst_audio_mix_matrix,
+    GST_TYPE_BASE_TRANSFORM);
+
+static void
+gst_audio_mix_matrix_class_init (GstAudioMixMatrixClass * klass)
+{
+  GObjectClass *gobject_class = (GObjectClass *) klass;
+  GstElementClass *element_class = (GstElementClass *) klass;
+  GstBaseTransformClass *trans_class = (GstBaseTransformClass *) klass;
+
+  GST_DEBUG_CATEGORY_INIT (audiomixmatrix_debug, "audiomixmatrix", 0,
+      "audiomixmatrix");
+  gst_element_class_set_static_metadata (element_class, "Matrix audio mix",
+      "Filter/Audio",
+      "Mixes a number of input channels into a number of output channels according to a transformation matrix",
+      "Vivia Nikolaidou <vivia@toolsonair.com>");
+
+  gobject_class->set_property = gst_audio_mix_matrix_set_property;
+  gobject_class->get_property = gst_audio_mix_matrix_get_property;
+  gobject_class->dispose = gst_audio_mix_matrix_dispose;
+
+  g_object_class_install_property (gobject_class, PROP_IN_CHANNELS,
+      g_param_spec_uint ("in-channels", "Input audio channels",
+          "How many audio channels we have on the input side",
+          0, 64, 0, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+  g_object_class_install_property (gobject_class, PROP_OUT_CHANNELS,
+      g_param_spec_uint ("out-channels", "Output audio channels",
+          "How many audio channels we have on the output side",
+          0, 64, 0, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+  g_object_class_install_property (gobject_class, PROP_MATRIX,
+      gst_param_spec_array ("matrix",
+          "Input/output channel matrix",
+          "Transformation matrix for input/output channels",
+          gst_param_spec_array ("matrix-in1", "rows", "rows",
+              g_param_spec_double ("matrix-in2", "cols", "cols",
+                  -1, 1, 0,
+                  G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS),
+              G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS),
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+  g_object_class_install_property (gobject_class, PROP_MATRIX_VALUE_ARRAY,
+      g_param_spec_value_array ("matrix-value-array",
+          "Input/output channel matrix (GValueArray)",
+          "Transformation matrix (GValueArray) for input/output channels",
+          g_param_spec_value_array ("matrix-va-in1", "rows", "rows",
+              g_param_spec_double ("matrix-va-in2", "cols", "cols",
+                  -1, 1, 0,
+                  G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS),
+              G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS),
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+  g_object_class_install_property (gobject_class, PROP_CHANNEL_MASK,
+      g_param_spec_uint64 ("channel-mask",
+          "Output channel mask",
+          "Output channel mask (-1 means \"default for these channels\")",
+          0, G_MAXUINT64, 0, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+  g_object_class_install_property (gobject_class, PROP_MODE,
+      g_param_spec_enum ("mode",
+          "Channel/matrix mode",
+          "Whether to auto-negotiate input/output channels and matrix",
+          GST_TYPE_AUDIO_MIX_MATRIX_MODE,
+          GST_AUDIO_MIX_MATRIX_MODE_MANUAL,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
+  gst_element_class_add_pad_template (element_class,
+      gst_static_pad_template_get (&gst_audio_mix_matrix_sink_template));
+  gst_element_class_add_pad_template (element_class,
+      gst_static_pad_template_get (&gst_audio_mix_matrix_src_template));
+
+  trans_class->get_unit_size =
+      GST_DEBUG_FUNCPTR (gst_audio_mix_matrix_get_unit_size);
+  trans_class->set_caps = GST_DEBUG_FUNCPTR (gst_audio_mix_matrix_set_caps);
+  trans_class->transform = GST_DEBUG_FUNCPTR (gst_audio_mix_matrix_transform);
+  trans_class->transform_caps =
+      GST_DEBUG_FUNCPTR (gst_audio_mix_matrix_transform_caps);
+  trans_class->fixate_caps =
+      GST_DEBUG_FUNCPTR (gst_audio_mix_matrix_fixate_caps);
+
+  element_class->change_state =
+      GST_DEBUG_FUNCPTR (gst_audio_mix_matrix_change_state);
+}
+
+static void
+gst_audio_mix_matrix_init (GstAudioMixMatrix * self)
+{
+  self->in_channels = 0;
+  self->out_channels = 0;
+  self->matrix = NULL;
+  self->channel_mask = 0;
+  self->s16_conv_matrix = NULL;
+  self->s32_conv_matrix = NULL;
+  self->mode = GST_AUDIO_MIX_MATRIX_MODE_MANUAL;
+}
+
+static void
+gst_audio_mix_matrix_dispose (GObject * object)
+{
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (object);
+
+  if (self->matrix) {
+    g_free (self->matrix);
+    self->matrix = NULL;
+  }
+
+  G_OBJECT_CLASS (gst_audio_mix_matrix_parent_class)->dispose (object);
+}
+
+static void
+gst_audio_mix_matrix_convert_s16_matrix (GstAudioMixMatrix * self)
+{
+  gint i;
+
+  /* converted bits - input bits - sign - bits needed for channel */
+  self->shift_bytes = 32 - 16 - 1 - ceil (log (self->in_channels) / log (2));
+
+  if (self->s16_conv_matrix)
+    g_free (self->s16_conv_matrix);
+  self->s16_conv_matrix =
+      g_new (gint32, self->in_channels * self->out_channels);
+  for (i = 0; i < self->in_channels * self->out_channels; i++) {
+    self->s16_conv_matrix[i] =
+        (gint32) ((self->matrix[i]) * (1 << self->shift_bytes));
+  }
+}
+
+static void
+gst_audio_mix_matrix_convert_s32_matrix (GstAudioMixMatrix * self)
+{
+  gint i;
+
+  /* converted bits - input bits - sign - bits needed for channel */
+  self->shift_bytes = 64 - 32 - 1 - (gint) (log (self->in_channels) / log (2));
+
+  if (self->s32_conv_matrix)
+    g_free (self->s32_conv_matrix);
+  self->s32_conv_matrix =
+      g_new (gint64, self->in_channels * self->out_channels);
+  for (i = 0; i < self->in_channels * self->out_channels; i++) {
+    self->s32_conv_matrix[i] =
+        (gint64) ((self->matrix[i]) * (1 << self->shift_bytes));
+  }
+}
+
+
+static void
+gst_audio_mix_matrix_set_property (GObject * object, guint prop_id,
+    const GValue * value, GParamSpec * pspec)
+{
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (object);
+
+  switch (prop_id) {
+    case PROP_IN_CHANNELS:
+      self->in_channels = g_value_get_uint (value);
+      if (self->matrix) {
+        gst_audio_mix_matrix_convert_s16_matrix (self);
+        gst_audio_mix_matrix_convert_s32_matrix (self);
+      }
+      break;
+    case PROP_OUT_CHANNELS:
+      self->out_channels = g_value_get_uint (value);
+      if (self->matrix) {
+        gst_audio_mix_matrix_convert_s16_matrix (self);
+        gst_audio_mix_matrix_convert_s32_matrix (self);
+      }
+      break;
+    case PROP_MATRIX:{
+      gint in, out;
+
+      if (self->matrix)
+        g_free (self->matrix);
+      self->matrix = g_new (gdouble, self->in_channels * self->out_channels);
+
+      g_return_if_fail (gst_value_array_get_size (value) == self->out_channels);
+      for (out = 0; out < self->out_channels; out++) {
+        const GValue *row = gst_value_array_get_value (value, out);
+        g_return_if_fail (gst_value_array_get_size (row) == self->in_channels);
+        for (in = 0; in < self->in_channels; in++) {
+          const GValue *itm;
+          gdouble coefficient;
+
+          itm = gst_value_array_get_value (row, in);
+          g_return_if_fail (G_VALUE_HOLDS_DOUBLE (itm));
+          coefficient = g_value_get_double (itm);
+          self->matrix[out * self->in_channels + in] = coefficient;
+        }
+      }
+      gst_audio_mix_matrix_convert_s16_matrix (self);
+      gst_audio_mix_matrix_convert_s32_matrix (self);
+      break;
+    }
+    case PROP_MATRIX_VALUE_ARRAY:{
+      gint in, out;
+      GValueArray *a;
+
+      if (self->matrix)
+        g_free (self->matrix);
+      self->matrix = g_new (gdouble, self->in_channels * self->out_channels);
+
+      a = g_value_get_boxed (value);
+      g_return_if_fail (a->n_values == self->out_channels);
+      for (out = 0; out < self->out_channels; out++) {
+        const GValue *row = g_value_array_get_nth (a, out);
+        GValueArray *ra = g_value_get_boxed (row);
+
+        g_return_if_fail (ra->n_values == self->in_channels);
+        for (in = 0; in < self->in_channels; in++) {
+          const GValue *itm;
+          gdouble coefficient;
+
+          itm = g_value_array_get_nth (ra, in);
+          g_return_if_fail (G_VALUE_HOLDS_DOUBLE (itm));
+          coefficient = g_value_get_double (itm);
+          self->matrix[out * self->in_channels + in] = coefficient;
+        }
+      }
+      gst_audio_mix_matrix_convert_s16_matrix (self);
+      gst_audio_mix_matrix_convert_s32_matrix (self);
+      break;
+    }
+    case PROP_CHANNEL_MASK:
+      self->channel_mask = g_value_get_uint64 (value);
+      break;
+    case PROP_MODE:
+      self->mode = g_value_get_enum (value);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
+gst_audio_mix_matrix_get_property (GObject * object, guint prop_id,
+    GValue * value, GParamSpec * pspec)
+{
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (object);
+
+  switch (prop_id) {
+    case PROP_IN_CHANNELS:
+      g_value_set_uint (value, self->in_channels);
+      break;
+    case PROP_OUT_CHANNELS:
+      g_value_set_uint (value, self->out_channels);
+      break;
+    case PROP_MATRIX:{
+      gint in, out;
+
+      for (out = 0; out < self->out_channels; out++) {
+        GValue row = G_VALUE_INIT;
+        g_value_init (&row, GST_TYPE_ARRAY);
+        for (in = 0; in < self->in_channels; in++) {
+          GValue itm = G_VALUE_INIT;
+          g_value_init (&itm, G_TYPE_DOUBLE);
+          g_value_set_double (&itm, self->matrix[out * self->in_channels + in]);
+          gst_value_array_append_value (&row, &itm);
+          g_value_unset (&itm);
+        }
+        gst_value_array_append_value (value, &row);
+        g_value_unset (&row);
+      }
+      break;
+    }
+    case PROP_MATRIX_VALUE_ARRAY:{
+      gint in, out;
+      GValueArray *a = g_value_array_new (self->out_channels);
+
+      for (out = 0; out < self->out_channels; out++) {
+        GValue row = G_VALUE_INIT;
+        GValueArray *ra = g_value_array_new (self->in_channels);
+
+        g_value_init (&row, G_TYPE_VALUE_ARRAY);
+        for (in = 0; in < self->in_channels; in++) {
+          GValue itm = G_VALUE_INIT;
+          g_value_init (&itm, G_TYPE_DOUBLE);
+          g_value_set_double (&itm, self->matrix[out * self->in_channels + in]);
+          g_value_array_append (ra, &itm);
+          g_value_unset (&itm);
+        }
+        g_value_take_boxed (&row, ra);
+        g_value_array_append (a, &row);
+        g_value_unset (&row);
+      }
+      g_value_take_boxed (value, a);
+      break;
+    }
+    case PROP_CHANNEL_MASK:
+      g_value_set_uint64 (value, self->channel_mask);
+      break;
+    case PROP_MODE:
+      g_value_set_enum (value, self->mode);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static GstStateChangeReturn
+gst_audio_mix_matrix_change_state (GstElement * element,
+    GstStateChange transition)
+{
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (element);
+  GstStateChangeReturn s;
+
+  s = GST_ELEMENT_CLASS (gst_audio_mix_matrix_parent_class)->change_state
+      (element, transition);
+
+  if (transition == GST_STATE_CHANGE_PAUSED_TO_READY) {
+    if (self->s16_conv_matrix) {
+      g_free (self->s16_conv_matrix);
+      self->s16_conv_matrix = NULL;
+    }
+
+    if (self->s32_conv_matrix) {
+      g_free (self->s32_conv_matrix);
+      self->s32_conv_matrix = NULL;
+    }
+  }
+
+  return s;
+}
+
+
+static GstFlowReturn
+gst_audio_mix_matrix_transform (GstBaseTransform * vfilter,
+    GstBuffer * inbuf, GstBuffer * outbuf)
+{
+  GstMapInfo inmap, outmap;
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (vfilter);
+  gint in, out, sample;
+  guint inchannels = self->in_channels;
+  guint outchannels = self->out_channels;
+  gdouble *matrix = self->matrix;
+
+  if (!gst_buffer_map (inbuf, &inmap, GST_MAP_READ)) {
+    return GST_FLOW_ERROR;
+  }
+  if (!gst_buffer_map (outbuf, &outmap, GST_MAP_WRITE)) {
+    gst_buffer_unmap (inbuf, &inmap);
+    return GST_FLOW_ERROR;
+  }
+
+  switch (self->format) {
+    case GST_AUDIO_FORMAT_F32LE:
+    case GST_AUDIO_FORMAT_F32BE:{
+      const gfloat *inarray;
+      gfloat *outarray;
+      guint n_samples = outmap.size / (sizeof (gfloat) * outchannels);
+
+      inarray = (gfloat *) inmap.data;
+      outarray = (gfloat *) outmap.data;
+
+      for (sample = 0; sample < n_samples; sample++) {
+        for (out = 0; out < outchannels; out++) {
+          gfloat outval = 0;
+          for (in = 0; in < inchannels; in++) {
+            outval +=
+                inarray[sample * inchannels +
+                in] * matrix[out * inchannels + in];
+          }
+          outarray[sample * outchannels + out] = outval;
+        }
+      }
+      break;
+    }
+    case GST_AUDIO_FORMAT_F64LE:
+    case GST_AUDIO_FORMAT_F64BE:{
+      const gdouble *inarray;
+      gdouble *outarray;
+      guint n_samples = outmap.size / (sizeof (gdouble) * outchannels);
+
+      inarray = (gdouble *) inmap.data;
+      outarray = (gdouble *) outmap.data;
+
+      for (sample = 0; sample < n_samples; sample++) {
+        for (out = 0; out < outchannels; out++) {
+          gdouble outval = 0;
+          for (in = 0; in < inchannels; in++) {
+            outval +=
+                inarray[sample * inchannels +
+                in] * matrix[out * inchannels + in];
+          }
+          outarray[sample * outchannels + out] = outval;
+        }
+      }
+      break;
+    }
+    case GST_AUDIO_FORMAT_S16LE:
+    case GST_AUDIO_FORMAT_S16BE:{
+      const gint16 *inarray;
+      gint16 *outarray;
+      guint n_samples = outmap.size / (sizeof (gint16) * outchannels);
+      guint n = self->shift_bytes;
+      gint32 *conv_matrix = self->s16_conv_matrix;
+
+      inarray = (gint16 *) inmap.data;
+      outarray = (gint16 *) outmap.data;
+
+      for (sample = 0; sample < n_samples; sample++) {
+        for (out = 0; out < outchannels; out++) {
+          gint32 outval = 0;
+          for (in = 0; in < inchannels; in++) {
+            outval += (gint32) (inarray[sample * inchannels + in] *
+                conv_matrix[out * inchannels + in]);
+          }
+          outarray[sample * outchannels + out] = (gint16) (outval >> n);
+        }
+      }
+      break;
+    }
+    case GST_AUDIO_FORMAT_S32LE:
+    case GST_AUDIO_FORMAT_S32BE:{
+      const gint32 *inarray;
+      gint32 *outarray;
+      guint n_samples = outmap.size / (sizeof (gint32) * outchannels);
+      guint n = self->shift_bytes;
+      gint64 *conv_matrix = self->s32_conv_matrix;
+
+      inarray = (gint32 *) inmap.data;
+      outarray = (gint32 *) outmap.data;
+
+      for (sample = 0; sample < n_samples; sample++) {
+        for (out = 0; out < outchannels; out++) {
+          gint64 outval = 0;
+          for (in = 0; in < inchannels; in++) {
+            outval += (gint64) (inarray[sample * inchannels + in] *
+                conv_matrix[out * inchannels + in]);
+          }
+          outarray[sample * outchannels + out] = (gint32) (outval >> n);
+        }
+      }
+      break;
+    }
+    default:
+      gst_buffer_unmap (inbuf, &inmap);
+      gst_buffer_unmap (outbuf, &outmap);
+      return GST_FLOW_NOT_SUPPORTED;
+
+  }
+
+  gst_buffer_unmap (inbuf, &inmap);
+  gst_buffer_unmap (outbuf, &outmap);
+  return GST_FLOW_OK;
+}
+
+static gboolean
+gst_audio_mix_matrix_get_unit_size (GstBaseTransform * trans,
+    GstCaps * caps, gsize * size)
+{
+  GstAudioInfo info;
+
+  if (!gst_audio_info_from_caps (&info, caps))
+    return FALSE;
+
+  *size = GST_AUDIO_INFO_BPF (&info);
+
+  return TRUE;
+}
+
+static gboolean
+gst_audio_mix_matrix_set_caps (GstBaseTransform * trans, GstCaps * incaps,
+    GstCaps * outcaps)
+{
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (trans);
+  GstAudioInfo info, out_info;
+
+  if (!gst_audio_info_from_caps (&info, incaps))
+    return FALSE;
+
+  if (!gst_audio_info_from_caps (&out_info, outcaps))
+    return FALSE;
+
+  self->format = info.finfo->format;
+
+  if (self->mode == GST_AUDIO_MIX_MATRIX_MODE_FIRST_CHANNELS) {
+    gint in, out;
+
+    self->in_channels = info.channels;
+    self->out_channels = out_info.channels;
+
+    self->matrix = g_new (gdouble, self->in_channels * self->out_channels);
+
+    for (out = 0; out < self->out_channels; out++) {
+      for (in = 0; in < self->in_channels; in++) {
+        self->matrix[out * self->in_channels + in] = (out == in);
+      }
+    }
+  } else if (!self->matrix || info.channels != self->in_channels ||
+      out_info.channels != self->out_channels) {
+    GST_ELEMENT_ERROR (self, LIBRARY, SETTINGS,
+        ("Erroneous matrix detected"),
+        ("Please enter a matrix with the correct input and output channels"));
+    return FALSE;
+  }
+
+  switch (self->format) {
+    case GST_AUDIO_FORMAT_S16LE:
+    case GST_AUDIO_FORMAT_S16BE:{
+      gst_audio_mix_matrix_convert_s16_matrix (self);
+      break;
+    }
+    case GST_AUDIO_FORMAT_S32LE:
+    case GST_AUDIO_FORMAT_S32BE:{
+      gst_audio_mix_matrix_convert_s32_matrix (self);
+      break;
+    }
+    default:
+      break;
+  }
+  return TRUE;
+}
+
+static GstCaps *
+gst_audio_mix_matrix_fixate_caps (GstBaseTransform * trans,
+    GstPadDirection direction, GstCaps * caps, GstCaps * othercaps)
+{
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (trans);
+  GstStructure *s, *s2;
+  guint capssize = gst_caps_get_size (othercaps);
+  gint i;
+  gint channels;
+
+  if (self->mode == GST_AUDIO_MIX_MATRIX_MODE_FIRST_CHANNELS) {
+    s2 = gst_caps_get_structure (caps, 0);
+
+    /* Try to keep channel configuration as much as possible */
+    if (gst_structure_get_int (s2, "channels", &channels)) {
+      gint mindiff = channels;
+      othercaps = gst_caps_make_writable (othercaps);
+      for (i = 0; i < capssize; i++) {
+        s = gst_caps_get_structure (othercaps, i);
+        if (!gst_structure_has_field (s, "channels")) {
+          mindiff = 0;
+          gst_structure_set (s, "channels", G_TYPE_INT, channels, NULL);
+        } else {
+          gint outchannels;
+          gint diff;
+
+          gst_structure_fixate_field_nearest_int (s, "channels", channels);
+          if (gst_structure_get_int (s, "channels", &outchannels)) {
+            diff = ABS (channels - outchannels);
+            if (diff < mindiff)
+              mindiff = diff;
+          }
+        }
+      }
+
+      for (i = 0; i < capssize; i++) {
+        gint outchannels, diff;
+        s = gst_caps_get_structure (othercaps, i);
+        if (gst_structure_get_int (s, "channels", &outchannels)) {
+          diff = ABS (channels - outchannels);
+          if (diff > mindiff) {
+            gst_caps_remove_structure (othercaps, i--);
+            capssize--;
+          }
+        }
+      }
+    }
+  }
+
+  othercaps =
+      GST_BASE_TRANSFORM_CLASS (gst_audio_mix_matrix_parent_class)->fixate_caps
+      (trans, direction, caps, othercaps);
+
+  s = gst_caps_get_structure (othercaps, 0);
+
+  if (!gst_structure_has_field (s, "channel-mask")) {
+    if (self->mode == GST_AUDIO_MIX_MATRIX_MODE_FIRST_CHANNELS ||
+        self->channel_mask == -1) {
+      gint channels;
+
+      g_assert (gst_structure_get_int (s, "channels", &channels));
+      gst_structure_set (s, "channel-mask", GST_TYPE_BITMASK,
+          gst_audio_channel_get_fallback_mask (channels), NULL);
+    } else {
+      gst_structure_set (s, "channel-mask", GST_TYPE_BITMASK,
+          self->channel_mask, NULL);
+    }
+  }
+
+  return othercaps;
+
+}
+
+static GstCaps *
+gst_audio_mix_matrix_transform_caps (GstBaseTransform * trans,
+    GstPadDirection direction, GstCaps * caps, GstCaps * filter)
+{
+  GstAudioMixMatrix *self = GST_AUDIO_MIX_MATRIX (trans);
+  GstCaps *outcaps = gst_caps_copy (caps);
+  GstCaps *ret;
+  GstStructure *s;
+  gint i;
+  guint capssize = gst_caps_get_size (outcaps);
+
+  if (self->mode == GST_AUDIO_MIX_MATRIX_MODE_FIRST_CHANNELS) {
+    for (i = 0; i < capssize; i++) {
+      s = gst_caps_get_structure (outcaps, i);
+      if (gst_structure_has_field (s, "channels")) {
+        gst_structure_remove_field (s, "channels");
+      }
+      if (gst_structure_has_field (s, "channel-mask")) {
+        gst_structure_remove_field (s, "channel-mask");
+      }
+    }
+    goto beach;
+  }
+
+  if (self->in_channels == 0 || self->out_channels == 0 || self->matrix == NULL) {
+    /* Not dispatching element error because we return empty caps anyway and
+     * we should let it fail to link. Additionally, the element error would be
+     * printed as WARN, so a possible gst-launch pipeline would appear to
+     * hang. */
+    GST_ERROR_OBJECT (self, "Invalid settings detected in manual mode. "
+        "Please specify in-channels, out-channels and matrix.");
+    return gst_caps_new_empty ();
+  }
+
+  if (self->in_channels == self->out_channels) {
+    goto beach;
+  }
+
+  for (i = 0; i < capssize; i++) {
+    s = gst_caps_get_structure (outcaps, i);
+    if (direction == GST_PAD_SRC) {
+      gst_structure_set (s, "channels", G_TYPE_INT, self->in_channels, NULL);
+      gst_structure_remove_field (s, "channel-mask");
+    } else if (direction == GST_PAD_SINK) {
+      gst_structure_set (s, "channels", G_TYPE_INT, self->out_channels,
+          "channel-mask", GST_TYPE_BITMASK, self->channel_mask, NULL);
+    } else {
+      g_assert_not_reached ();
+    }
+  }
+
+beach:
+  if (filter) {
+    ret = gst_caps_intersect_full (filter, outcaps, GST_CAPS_INTERSECT_FIRST);
+    gst_caps_unref (outcaps);
+  } else {
+    ret = outcaps;
+  }
+  return ret;
+}
+
+static gboolean
+plugin_init (GstPlugin * plugin)
+{
+  return gst_element_register (plugin, "audiomixmatrix", GST_RANK_NONE,
+      GST_TYPE_AUDIO_MIX_MATRIX);
+}
+
+GST_PLUGIN_DEFINE (GST_VERSION_MAJOR,
+    GST_VERSION_MINOR,
+    audiomixmatrix,
+    "Audio matrix mix",
+    plugin_init, VERSION, GST_LICENSE, GST_PACKAGE_NAME, GST_PACKAGE_ORIGIN);
diff --git a/gst/audiomixmatrix/gstaudiomixmatrix.h b/gst/audiomixmatrix/gstaudiomixmatrix.h
new file mode 100644
index 000000000..5321954b4
--- /dev/null
+++ b/gst/audiomixmatrix/gstaudiomixmatrix.h
@@ -0,0 +1,78 @@
+/*
+ * GStreamer
+ * Copyright (C) 2017 Vivia Nikolaidou <vivia@toolsonair.com>
+ *
+ * gstaudiomixmatrix.h
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __GST_AUDIO_MIX_MATRIX_H__
+#define __GST_AUDIO_MIX_MATRIX_H__
+
+#include <gst/gst.h>
+#include <gst/audio/audio.h>
+
+#define GST_TYPE_AUDIO_MIX_MATRIX            (gst_audio_mix_matrix_get_type())
+#define GST_AUDIO_MIX_MATRIX(obj)            (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_AUDIO_MIX_MATRIX,GstAudioMixMatrix))
+#define GST_AUDIO_MIX_MATRIX_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST((klass), GST_TYPE_AUDIO_MIX_MATRIX,GstAudioMixMatrixClass))
+#define GST_AUDIO_MIX_MATRIX_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS((obj), GST_TYPE_AUDIO_MIX_MATRIX,GstAudioMixMatrixClass))
+#define GST_IS_AUDIO_MIX_MATRIX(obj)         (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_AUDIO_MIX_MATRIX))
+#define GST_IS_AUDIO_MIX_MATRIX_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE((klass), GST_TYPE_AUDIO_MIX_MATRIX))
+#define GST_TYPE_AUDIO_MIX_MATRIX_MODE (gst_audio_mix_matrix_mode_get_type())
+
+typedef struct _GstAudioMixMatrix GstAudioMixMatrix;
+typedef struct _GstAudioMixMatrixClass GstAudioMixMatrixClass;
+
+typedef enum _GstAudioMixMatrixMode
+{
+  GST_AUDIO_MIX_MATRIX_MODE_MANUAL = 0,
+  GST_AUDIO_MIX_MATRIX_MODE_FIRST_CHANNELS = 1
+} GstAudioMixMatrixMode;
+
+/**
+ * GstAudioMixMatrix:
+ *
+ * Opaque data structure.
+ */
+struct _GstAudioMixMatrix
+{
+  GstBaseTransform audiofilter;
+
+  /* < private > */
+  guint in_channels;
+  guint out_channels;
+  gdouble *matrix;
+  guint64 channel_mask;
+  GstAudioMixMatrixMode mode;
+  gint32 *s16_conv_matrix;
+  gint64 *s32_conv_matrix;
+  gint shift_bytes;
+
+  GstAudioFormat format;
+};
+
+struct _GstAudioMixMatrixClass
+{
+  GstBaseTransformClass parent_class;
+};
+
+GType gst_audio_mix_matrix_get_type (void);
+
+GType gst_audio_mix_matrix_mode_get_type (void);
+
+G_END_DECLS
+#endif /* __GST_AUDIO_MIX_MATRIX_H__ */