gstreamer/gst-libs/gst/audio/audio-channel-mixer.c

/* GStreamer
 * Copyright (C) 2004 Ronald Bultje <rbultje@ronald.bitfreak.net>
 * Copyright (C) 2008 Sebastian Dröge <slomo@circular-chaos.org>
 *
 * audio-channel-mixer.c: setup of channel conversion matrices
 *
 * 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.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <math.h>
#include <string.h>

#include "audio-channel-mixer.h"

#ifndef GST_DISABLE_GST_DEBUG
#define GST_CAT_DEFAULT ensure_debug_category()
static GstDebugCategory *
ensure_debug_category (void)
{
  static gsize cat_gonce = 0;

  if (g_once_init_enter (&cat_gonce)) {
    gsize cat_done;

    cat_done = (gsize) _gst_debug_category_new ("audio-channel-mixer", 0,
        "audio-channel-mixer object");

    g_once_init_leave (&cat_gonce, cat_done);
  }

  return (GstDebugCategory *) cat_gonce;
}
#else
#define ensure_debug_category() /* NOOP */
#endif /* GST_DISABLE_GST_DEBUG */


#define PRECISION_INT 10

typedef void (*MixerFunc) (GstAudioChannelMixer * mix, const gpointer src,
    gpointer dst, gint samples);

struct _GstAudioChannelMixer
{
  GstAudioChannelMixerFlags flags;
  GstAudioFormat format;

  gint in_channels;
  gint out_channels;

  GstAudioChannelPosition in_position[64];
  GstAudioChannelPosition out_position[64];

  /* channel conversion matrix, m[in_channels][out_channels].
   * If identity matrix, passthrough applies. */
  gfloat **matrix;

  /* channel conversion matrix with int values, m[in_channels][out_channels].
   * this is matrix * (2^10) as integers */
  gint **matrix_int;

  MixerFunc func;

  gpointer tmp;
};

/**
 * gst_audio_channel_mixer_free:
 * @mix: a #GstAudioChannelMixer
 *
 * Free memory allocated by @mix.
 */
void
gst_audio_channel_mixer_free (GstAudioChannelMixer * mix)
{
  gint i;

  /* free */
  for (i = 0; i < mix->in_channels; i++)
    g_free (mix->matrix[i]);
  g_free (mix->matrix);
  mix->matrix = NULL;

  for (i = 0; i < mix->in_channels; i++)
    g_free (mix->matrix_int[i]);
  g_free (mix->matrix_int);
  mix->matrix_int = NULL;

  g_free (mix->tmp);
  mix->tmp = NULL;

  g_slice_free (GstAudioChannelMixer, mix);
}

/*
 * Detect and fill in identical channels. E.g.
 * forward the left/right front channels in a
 * 5.1 to 2.0 conversion.
 */

static void
gst_audio_channel_mixer_fill_identical (GstAudioChannelMixer * mix)
{
  gint ci, co;

  /* Apart from the compatible channel assignments, we can also have
   * same channel assignments. This is much simpler, we simply copy
   * the value from source to dest! */
  for (co = 0; co < mix->out_channels; co++) {
    /* find a channel in input with same position */
    for (ci = 0; ci < mix->in_channels; ci++) {
      if (mix->in_position[ci] == mix->out_position[co]) {
        mix->matrix[ci][co] = 1.0;
      }
    }
  }
}

/*
 * Detect and fill in compatible channels. E.g.
 * forward left/right front to mono (or the other
 * way around) when going from 2.0 to 1.0.
 */

static void
gst_audio_channel_mixer_fill_compatible (GstAudioChannelMixer * mix)
{
  /* Conversions from one-channel to compatible two-channel configs */
  struct
  {
    GstAudioChannelPosition pos1[2];
    GstAudioChannelPosition pos2[1];
  } conv[] = {
    /* front: mono <-> stereo */
    { {
    GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT,
            GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT}, {
    GST_AUDIO_CHANNEL_POSITION_MONO}},
        /* front center: 2 <-> 1 */
    { {
    GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT_OF_CENTER,
            GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT_OF_CENTER}, {
    GST_AUDIO_CHANNEL_POSITION_FRONT_CENTER}},
        /* rear: 2 <-> 1 */
    { {
    GST_AUDIO_CHANNEL_POSITION_REAR_LEFT,
            GST_AUDIO_CHANNEL_POSITION_REAR_RIGHT}, {
    GST_AUDIO_CHANNEL_POSITION_REAR_CENTER}}, { {
    GST_AUDIO_CHANNEL_POSITION_INVALID}}
  };
  gint c;

  /* conversions from compatible (but not the same) channel schemes */
  for (c = 0; conv[c].pos1[0] != GST_AUDIO_CHANNEL_POSITION_INVALID; c++) {
    gint pos1_0 = -1, pos1_1 = -1, pos1_2 = -1;
    gint pos2_0 = -1, pos2_1 = -1, pos2_2 = -1;
    gint n;

    for (n = 0; n < mix->in_channels; n++) {
      if (mix->in_position[n] == conv[c].pos1[0])
        pos1_0 = n;
      else if (mix->in_position[n] == conv[c].pos1[1])
        pos1_1 = n;
      else if (mix->in_position[n] == conv[c].pos2[0])
        pos1_2 = n;
    }
    for (n = 0; n < mix->out_channels; n++) {
      if (mix->out_position[n] == conv[c].pos1[0])
        pos2_0 = n;
      else if (mix->out_position[n] == conv[c].pos1[1])
        pos2_1 = n;
      else if (mix->out_position[n] == conv[c].pos2[0])
        pos2_2 = n;
    }

    /* The general idea here is to fill in channels from the same position
     * as good as possible. This means mixing left<->center and right<->center.
     */

    /* left -> center */
    if (pos1_0 != -1 && pos1_2 == -1 && pos2_0 == -1 && pos2_2 != -1)
      mix->matrix[pos1_0][pos2_2] = 1.0;
    else if (pos1_0 != -1 && pos1_2 != -1 && pos2_0 == -1 && pos2_2 != -1)
      mix->matrix[pos1_0][pos2_2] = 0.5;
    else if (pos1_0 != -1 && pos1_2 == -1 && pos2_0 != -1 && pos2_2 != -1)
      mix->matrix[pos1_0][pos2_2] = 1.0;

    /* right -> center */
    if (pos1_1 != -1 && pos1_2 == -1 && pos2_1 == -1 && pos2_2 != -1)
      mix->matrix[pos1_1][pos2_2] = 1.0;
    else if (pos1_1 != -1 && pos1_2 != -1 && pos2_1 == -1 && pos2_2 != -1)
      mix->matrix[pos1_1][pos2_2] = 0.5;
    else if (pos1_1 != -1 && pos1_2 == -1 && pos2_1 != -1 && pos2_2 != -1)
      mix->matrix[pos1_1][pos2_2] = 1.0;

    /* center -> left */
    if (pos1_2 != -1 && pos1_0 == -1 && pos2_2 == -1 && pos2_0 != -1)
      mix->matrix[pos1_2][pos2_0] = 1.0;
    else if (pos1_2 != -1 && pos1_0 != -1 && pos2_2 == -1 && pos2_0 != -1)
      mix->matrix[pos1_2][pos2_0] = 0.5;
    else if (pos1_2 != -1 && pos1_0 == -1 && pos2_2 != -1 && pos2_0 != -1)
      mix->matrix[pos1_2][pos2_0] = 1.0;

    /* center -> right */
    if (pos1_2 != -1 && pos1_1 == -1 && pos2_2 == -1 && pos2_1 != -1)
      mix->matrix[pos1_2][pos2_1] = 1.0;
    else if (pos1_2 != -1 && pos1_1 != -1 && pos2_2 == -1 && pos2_1 != -1)
      mix->matrix[pos1_2][pos2_1] = 0.5;
    else if (pos1_2 != -1 && pos1_1 == -1 && pos2_2 != -1 && pos2_1 != -1)
      mix->matrix[pos1_2][pos2_1] = 1.0;
  }
}

/*
 * Detect and fill in channels not handled by the
 * above two, e.g. center to left/right front in
 * 5.1 to 2.0 (or the other way around).
 *
 * Unfortunately, limited to static conversions
 * for now.
 */

static void
gst_audio_channel_mixer_detect_pos (gint channels,
    GstAudioChannelPosition position[64], gint * f, gboolean * has_f, gint * c,
    gboolean * has_c, gint * r, gboolean * has_r, gint * s, gboolean * has_s,
    gint * b, gboolean * has_b)
{
  gint n;

  for (n = 0; n < channels; n++) {
    switch (position[n]) {
      case GST_AUDIO_CHANNEL_POSITION_MONO:
        f[1] = n;
        *has_f = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT:
        f[0] = n;
        *has_f = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT:
        f[2] = n;
        *has_f = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_FRONT_CENTER:
        c[1] = n;
        *has_c = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT_OF_CENTER:
        c[0] = n;
        *has_c = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT_OF_CENTER:
        c[2] = n;
        *has_c = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_REAR_CENTER:
        r[1] = n;
        *has_r = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_REAR_LEFT:
        r[0] = n;
        *has_r = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_REAR_RIGHT:
        r[2] = n;
        *has_r = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_SIDE_LEFT:
        s[0] = n;
        *has_s = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_SIDE_RIGHT:
        s[2] = n;
        *has_s = TRUE;
        break;
      case GST_AUDIO_CHANNEL_POSITION_LFE1:
        *has_b = TRUE;
        b[1] = n;
        break;
      default:
        break;
    }
  }
}

static void
gst_audio_channel_mixer_fill_one_other (gfloat ** matrix,
    gint * from_idx, gint * to_idx, gfloat ratio)
{

  /* src & dst have center => passthrough */
  if (from_idx[1] != -1 && to_idx[1] != -1) {
    matrix[from_idx[1]][to_idx[1]] = ratio;
  }

  /* src & dst have left => passthrough */
  if (from_idx[0] != -1 && to_idx[0] != -1) {
    matrix[from_idx[0]][to_idx[0]] = ratio;
  }

  /* src & dst have right => passthrough */
  if (from_idx[2] != -1 && to_idx[2] != -1) {
    matrix[from_idx[2]][to_idx[2]] = ratio;
  }

  /* src has left & dst has center => put into center */
  if (from_idx[0] != -1 && to_idx[1] != -1 && from_idx[1] != -1) {
    matrix[from_idx[0]][to_idx[1]] = 0.5 * ratio;
  } else if (from_idx[0] != -1 && to_idx[1] != -1 && from_idx[1] == -1) {
    matrix[from_idx[0]][to_idx[1]] = ratio;
  }

  /* src has right & dst has center => put into center */
  if (from_idx[2] != -1 && to_idx[1] != -1 && from_idx[1] != -1) {
    matrix[from_idx[2]][to_idx[1]] = 0.5 * ratio;
  } else if (from_idx[2] != -1 && to_idx[1] != -1 && from_idx[1] == -1) {
    matrix[from_idx[2]][to_idx[1]] = ratio;
  }

  /* src has center & dst has left => passthrough */
  if (from_idx[1] != -1 && to_idx[0] != -1 && from_idx[0] != -1) {
    matrix[from_idx[1]][to_idx[0]] = 0.5 * ratio;
  } else if (from_idx[1] != -1 && to_idx[0] != -1 && from_idx[0] == -1) {
    matrix[from_idx[1]][to_idx[0]] = ratio;
  }

  /* src has center & dst has right => passthrough */
  if (from_idx[1] != -1 && to_idx[2] != -1 && from_idx[2] != -1) {
    matrix[from_idx[1]][to_idx[2]] = 0.5 * ratio;
  } else if (from_idx[1] != -1 && to_idx[2] != -1 && from_idx[2] == -1) {
    matrix[from_idx[1]][to_idx[2]] = ratio;
  }
}

#define RATIO_CENTER_FRONT (1.0 / sqrt (2.0))
#define RATIO_CENTER_SIDE (1.0 / 2.0)
#define RATIO_CENTER_REAR (1.0 / sqrt (8.0))

#define RATIO_FRONT_CENTER (1.0 / sqrt (2.0))
#define RATIO_FRONT_SIDE (1.0 / sqrt (2.0))
#define RATIO_FRONT_REAR (1.0 / 2.0)

#define RATIO_SIDE_CENTER (1.0 / 2.0)
#define RATIO_SIDE_FRONT (1.0 / sqrt (2.0))
#define RATIO_SIDE_REAR (1.0 / sqrt (2.0))

#define RATIO_CENTER_BASS (1.0 / sqrt (2.0))
#define RATIO_FRONT_BASS (1.0)
#define RATIO_SIDE_BASS (1.0 / sqrt (2.0))
#define RATIO_REAR_BASS (1.0 / sqrt (2.0))

static void
gst_audio_channel_mixer_fill_others (GstAudioChannelMixer * mix)
{
  gboolean in_has_front = FALSE, out_has_front = FALSE,
      in_has_center = FALSE, out_has_center = FALSE,
      in_has_rear = FALSE, out_has_rear = FALSE,
      in_has_side = FALSE, out_has_side = FALSE,
      in_has_bass = FALSE, out_has_bass = FALSE;
  /* LEFT, RIGHT, MONO */
  gint in_f[3] = { -1, -1, -1 };
  gint out_f[3] = { -1, -1, -1 };
  /* LOC, ROC, CENTER */
  gint in_c[3] = { -1, -1, -1 };
  gint out_c[3] = { -1, -1, -1 };
  /* RLEFT, RRIGHT, RCENTER */
  gint in_r[3] = { -1, -1, -1 };
  gint out_r[3] = { -1, -1, -1 };
  /* SLEFT, INVALID, SRIGHT */
  gint in_s[3] = { -1, -1, -1 };
  gint out_s[3] = { -1, -1, -1 };
  /* INVALID, LFE, INVALID */
  gint in_b[3] = { -1, -1, -1 };
  gint out_b[3] = { -1, -1, -1 };

  /* First see where (if at all) the various channels from/to
   * which we want to convert are located in our matrix/array. */
  gst_audio_channel_mixer_detect_pos (mix->in_channels, mix->in_position,
      in_f, &in_has_front,
      in_c, &in_has_center, in_r, &in_has_rear,
      in_s, &in_has_side, in_b, &in_has_bass);
  gst_audio_channel_mixer_detect_pos (mix->out_channels, mix->out_position,
      out_f, &out_has_front,
      out_c, &out_has_center, out_r, &out_has_rear,
      out_s, &out_has_side, out_b, &out_has_bass);

  /* The general idea here is:
   * - if the source has a channel that the destination doesn't have mix
   *   it into the nearest available destination channel
   * - if the destination has a channel that the source doesn't have mix
   *   the nearest source channel into the destination channel
   *
   * The ratio for the mixing becomes lower as the distance between the
   * channels gets larger
   */

  /* center <-> front/side/rear */
  if (!in_has_center && in_has_front && out_has_center) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_c,
        RATIO_CENTER_FRONT);
  } else if (!in_has_center && !in_has_front && in_has_side && out_has_center) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_c,
        RATIO_CENTER_SIDE);
  } else if (!in_has_center && !in_has_front && !in_has_side && in_has_rear
      && out_has_center) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_c,
        RATIO_CENTER_REAR);
  } else if (in_has_center && !out_has_center && out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_f,
        RATIO_CENTER_FRONT);
  } else if (in_has_center && !out_has_center && !out_has_front && out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_s,
        RATIO_CENTER_SIDE);
  } else if (in_has_center && !out_has_center && !out_has_front && !out_has_side
      && out_has_rear) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_r,
        RATIO_CENTER_REAR);
  }

  /* front <-> center/side/rear */
  if (!in_has_front && in_has_center && !in_has_side && out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_f,
        RATIO_CENTER_FRONT);
  } else if (!in_has_front && !in_has_center && in_has_side && out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_f,
        RATIO_FRONT_SIDE);
  } else if (!in_has_front && in_has_center && in_has_side && out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_f,
        0.5 * RATIO_CENTER_FRONT);
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_f,
        0.5 * RATIO_FRONT_SIDE);
  } else if (!in_has_front && !in_has_center && !in_has_side && in_has_rear
      && out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_f,
        RATIO_FRONT_REAR);
  } else if (in_has_front && out_has_center && !out_has_side && !out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix,
        in_f, out_c, RATIO_CENTER_FRONT);
  } else if (in_has_front && !out_has_center && out_has_side && !out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_s,
        RATIO_FRONT_SIDE);
  } else if (in_has_front && out_has_center && out_has_side && !out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_c,
        0.5 * RATIO_CENTER_FRONT);
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_s,
        0.5 * RATIO_FRONT_SIDE);
  } else if (in_has_front && !out_has_center && !out_has_side && !out_has_front
      && out_has_rear) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_r,
        RATIO_FRONT_REAR);
  }

  /* side <-> center/front/rear */
  if (!in_has_side && in_has_front && !in_has_rear && out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_s,
        RATIO_FRONT_SIDE);
  } else if (!in_has_side && !in_has_front && in_has_rear && out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_s,
        RATIO_SIDE_REAR);
  } else if (!in_has_side && in_has_front && in_has_rear && out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_s,
        0.5 * RATIO_FRONT_SIDE);
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_s,
        0.5 * RATIO_SIDE_REAR);
  } else if (!in_has_side && !in_has_front && !in_has_rear && in_has_center
      && out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_s,
        RATIO_CENTER_SIDE);
  } else if (in_has_side && out_has_front && !out_has_rear && !out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_f,
        RATIO_FRONT_SIDE);
  } else if (in_has_side && !out_has_front && out_has_rear && !out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_r,
        RATIO_SIDE_REAR);
  } else if (in_has_side && out_has_front && out_has_rear && !out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_f,
        0.5 * RATIO_FRONT_SIDE);
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_r,
        0.5 * RATIO_SIDE_REAR);
  } else if (in_has_side && !out_has_front && !out_has_rear && out_has_center
      && !out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_c,
        RATIO_CENTER_SIDE);
  }

  /* rear <-> center/front/side */
  if (!in_has_rear && in_has_side && out_has_rear) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_r,
        RATIO_SIDE_REAR);
  } else if (!in_has_rear && !in_has_side && in_has_front && out_has_rear) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_r,
        RATIO_FRONT_REAR);
  } else if (!in_has_rear && !in_has_side && !in_has_front && in_has_center
      && out_has_rear) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_r,
        RATIO_CENTER_REAR);
  } else if (in_has_rear && !out_has_rear && out_has_side) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_s,
        RATIO_SIDE_REAR);
  } else if (in_has_rear && !out_has_rear && !out_has_side && out_has_front) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_f,
        RATIO_FRONT_REAR);
  } else if (in_has_rear && !out_has_rear && !out_has_side && !out_has_front
      && out_has_center) {
    gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_c,
        RATIO_CENTER_REAR);
  }

  /* bass <-> any */
  if (in_has_bass && !out_has_bass) {
    if (out_has_center) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_b, out_c,
          RATIO_CENTER_BASS);
    }
    if (out_has_front) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_b, out_f,
          RATIO_FRONT_BASS);
    }
    if (out_has_side) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_b, out_s,
          RATIO_SIDE_BASS);
    }
    if (out_has_rear) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_b, out_r,
          RATIO_REAR_BASS);
    }
  } else if (!in_has_bass && out_has_bass) {
    if (in_has_center) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_c, out_b,
          RATIO_CENTER_BASS);
    }
    if (in_has_front) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_f, out_b,
          RATIO_FRONT_BASS);
    }
    if (in_has_side) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_s, out_b,
          RATIO_REAR_BASS);
    }
    if (in_has_rear) {
      gst_audio_channel_mixer_fill_one_other (mix->matrix, in_r, out_b,
          RATIO_REAR_BASS);
    }
  }
}

/*
 * Normalize output values.
 */

static void
gst_audio_channel_mixer_fill_normalize (GstAudioChannelMixer * mix)
{
  gfloat sum, top = 0;
  gint i, j;

  for (j = 0; j < mix->out_channels; j++) {
    /* calculate sum */
    sum = 0.0;
    for (i = 0; i < mix->in_channels; i++) {
      sum += fabs (mix->matrix[i][j]);
    }
    if (sum > top) {
      top = sum;
    }
  }

  /* normalize to mix */
  if (top == 0.0)
    return;

  for (j = 0; j < mix->out_channels; j++) {
    for (i = 0; i < mix->in_channels; i++) {
      mix->matrix[i][j] /= top;
    }
  }
}

static gboolean
gst_audio_channel_mixer_fill_special (GstAudioChannelMixer * mix)
{
  /* Special, standard conversions here */

  /* Mono<->Stereo, just a fast-path */
  if (mix->in_channels == 2 && mix->out_channels == 1 &&
      ((mix->in_position[0] == GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT &&
              mix->in_position[1] == GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT) ||
          (mix->in_position[0] == GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT &&
              mix->in_position[1] == GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT)) &&
      mix->out_position[0] == GST_AUDIO_CHANNEL_POSITION_MONO) {
    mix->matrix[0][0] = 0.5;
    mix->matrix[1][0] = 0.5;
    return TRUE;
  } else if (mix->in_channels == 1 && mix->out_channels == 2 &&
      ((mix->out_position[0] == GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT &&
              mix->out_position[1] == GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT) ||
          (mix->out_position[0] == GST_AUDIO_CHANNEL_POSITION_FRONT_RIGHT &&
              mix->out_position[1] == GST_AUDIO_CHANNEL_POSITION_FRONT_LEFT)) &&
      mix->in_position[0] == GST_AUDIO_CHANNEL_POSITION_MONO) {
    mix->matrix[0][0] = 1.0;
    mix->matrix[0][1] = 1.0;
    return TRUE;
  }

  /* TODO: 5.1 <-> Stereo and other standard conversions */

  return FALSE;
}

/*
 * Automagically generate conversion matrix.
 */

static void
gst_audio_channel_mixer_fill_matrix (GstAudioChannelMixer * mix)
{
  if (gst_audio_channel_mixer_fill_special (mix))
    return;

  gst_audio_channel_mixer_fill_identical (mix);

  if (!(mix->flags & GST_AUDIO_CHANNEL_MIXER_FLAGS_UNPOSITIONED_IN)) {
    gst_audio_channel_mixer_fill_compatible (mix);
    gst_audio_channel_mixer_fill_others (mix);
    gst_audio_channel_mixer_fill_normalize (mix);
  }
}

/* only call mix after mix->matrix is fully set up and normalized */
static void
gst_audio_channel_mixer_setup_matrix_int (GstAudioChannelMixer * mix)
{
  gint i, j;
  gfloat tmp;
  gfloat factor = (1 << PRECISION_INT);

  mix->matrix_int = g_new0 (gint *, mix->in_channels);

  for (i = 0; i < mix->in_channels; i++) {
    mix->matrix_int[i] = g_new (gint, mix->out_channels);

    for (j = 0; j < mix->out_channels; j++) {
      tmp = mix->matrix[i][j] * factor;
      mix->matrix_int[i][j] = (gint) tmp;
    }
  }
}

static void
gst_audio_channel_mixer_setup_matrix (GstAudioChannelMixer * mix)
{
  gint i, j;

  mix->tmp = (gpointer) g_new (gdouble, mix->out_channels);

  /* allocate */
  mix->matrix = g_new0 (gfloat *, mix->in_channels);
  for (i = 0; i < mix->in_channels; i++) {
    mix->matrix[i] = g_new (gfloat, mix->out_channels);
    for (j = 0; j < mix->out_channels; j++)
      mix->matrix[i][j] = 0.;
  }

  /* setup the matrix' internal values */
  gst_audio_channel_mixer_fill_matrix (mix);

  gst_audio_channel_mixer_setup_matrix_int (mix);

#ifndef GST_DISABLE_GST_DEBUG
  /* debug */
  {
    GString *s;
    s = g_string_new ("Matrix for");
    g_string_append_printf (s, " %d -> %d: ",
        mix->in_channels, mix->out_channels);
    g_string_append (s, "{");
    for (i = 0; i < mix->in_channels; i++) {
      if (i != 0)
        g_string_append (s, ",");
      g_string_append (s, " {");
      for (j = 0; j < mix->out_channels; j++) {
        if (j != 0)
          g_string_append (s, ",");
        g_string_append_printf (s, " %f", mix->matrix[i][j]);
      }
      g_string_append (s, " }");
    }
    g_string_append (s, " }");
    GST_DEBUG ("%s", s->str);
    g_string_free (s, TRUE);
  }
#endif
}

static void
gst_audio_channel_mixer_mix_int16 (GstAudioChannelMixer * mix,
    const gint16 * in_data, gint16 * out_data, gint samples)
{
  gint in, out, n;
  gint32 res;
  gint inchannels, outchannels;

  inchannels = mix->in_channels;
  outchannels = mix->out_channels;

  for (n = 0; n < samples; n++) {
    for (out = 0; out < outchannels; out++) {
      /* convert */
      res = 0;
      for (in = 0; in < inchannels; in++)
        res += in_data[n * inchannels + in] * mix->matrix_int[in][out];

      /* remove factor from int matrix */
      res = (res + (1 << (PRECISION_INT - 1))) >> PRECISION_INT;
      out_data[n * outchannels + out] = CLAMP (res, G_MININT16, G_MAXINT16);
    }
  }
}

static void
gst_audio_channel_mixer_mix_int32 (GstAudioChannelMixer * mix,
    const gint32 * in_data, gint32 * out_data, gint samples)
{
  gint in, out, n;
  gint64 res;
  gint inchannels, outchannels;

  inchannels = mix->in_channels;
  outchannels = mix->out_channels;

  for (n = 0; n < samples; n++) {
    for (out = 0; out < outchannels; out++) {
      /* convert */
      res = 0;
      for (in = 0; in < inchannels; in++)
        res += in_data[n * inchannels + in] * (gint64) mix->matrix_int[in][out];

      /* remove factor from int matrix */
      res = (res + (1 << (PRECISION_INT - 1))) >> PRECISION_INT;
      out_data[n * outchannels + out] = CLAMP (res, G_MININT32, G_MAXINT32);
    }
  }
}

static void
gst_audio_channel_mixer_mix_float (GstAudioChannelMixer * mix,
    const gfloat * in_data, gfloat * out_data, gint samples)
{
  gint in, out, n;
  gfloat res;
  gint inchannels, outchannels;

  inchannels = mix->in_channels;
  outchannels = mix->out_channels;

  for (n = 0; n < samples; n++) {
    for (out = 0; out < outchannels; out++) {
      /* convert */
      res = 0.0;
      for (in = 0; in < inchannels; in++)
        res += in_data[n * inchannels + in] * mix->matrix[in][out];

      out_data[n * outchannels + out] = res;
    }
  }
}

static void
gst_audio_channel_mixer_mix_double (GstAudioChannelMixer * mix,
    const gdouble * in_data, gdouble * out_data, gint samples)
{
  gint in, out, n;
  gdouble res;
  gint inchannels, outchannels;

  inchannels = mix->in_channels;
  outchannels = mix->out_channels;

  for (n = 0; n < samples; n++) {
    for (out = 0; out < outchannels; out++) {
      /* convert */
      res = 0.0;
      for (in = 0; in < inchannels; in++)
        res += in_data[n * inchannels + in] * mix->matrix[in][out];

      out_data[n * outchannels + out] = res;
    }
  }
}

/**
 * gst_audio_channel_mixer_new: (skip):
 * @flags: #GstAudioChannelMixerFlags
 * @in_channels: number of input channels
 * @in_position: positions of input channels
 * @out_channels: number of output channels
 * @out_position: positions of output channels
 *
 * Create a new channel mixer object for the given parameters.
 *
 * Returns: a new #GstAudioChannelMixer object. Free with gst_audio_channel_mixer_free()
 * after usage.
 */
GstAudioChannelMixer *
gst_audio_channel_mixer_new (GstAudioChannelMixerFlags flags,
    GstAudioFormat format,
    gint in_channels,
    GstAudioChannelPosition * in_position,
    gint out_channels, GstAudioChannelPosition * out_position)
{
  GstAudioChannelMixer *mix;
  gint i;

  g_return_val_if_fail (format == GST_AUDIO_FORMAT_S16
      || format == GST_AUDIO_FORMAT_S32
      || format == GST_AUDIO_FORMAT_F32
      || format == GST_AUDIO_FORMAT_F64, NULL);
  g_return_val_if_fail (in_channels > 0 && in_channels < 64, NULL);
  g_return_val_if_fail (out_channels > 0 && out_channels < 64, NULL);

  mix = g_slice_new0 (GstAudioChannelMixer);
  mix->flags = flags;
  mix->format = format;
  mix->in_channels = in_channels;
  mix->out_channels = out_channels;

  for (i = 0; i < in_channels; i++)
    mix->in_position[i] = in_position[i];
  for (i = 0; i < out_channels; i++)
    mix->out_position[i] = out_position[i];

  gst_audio_channel_mixer_setup_matrix (mix);

  switch (mix->format) {
    case GST_AUDIO_FORMAT_S16:
      mix->func = (MixerFunc) gst_audio_channel_mixer_mix_int16;
      break;
    case GST_AUDIO_FORMAT_S32:
      mix->func = (MixerFunc) gst_audio_channel_mixer_mix_int32;
      break;
    case GST_AUDIO_FORMAT_F32:
      mix->func = (MixerFunc) gst_audio_channel_mixer_mix_float;
      break;
    case GST_AUDIO_FORMAT_F64:
      mix->func = (MixerFunc) gst_audio_channel_mixer_mix_double;
      break;
    default:
      g_assert_not_reached ();
      break;
  }
  return mix;
}

/**
 * gst_audio_channel_mixer_is_passthrough:
 * @mix: a #GstAudioChannelMixer
 *
 * Check if @mix is in passthrough.
 *
 * Returns: %TRUE is @mix is passthrough.
 */
gboolean
gst_audio_channel_mixer_is_passthrough (GstAudioChannelMixer * mix)
{
  gint i;
  guint64 in_mask, out_mask;

  /* only NxN matrices can be identities */
  if (mix->in_channels != mix->out_channels)
    return FALSE;

  /* passthrough for 1->1 channels (MONO and NONE position are the same here) */
  if (mix->in_channels == 1 && mix->out_channels == 1)
    return TRUE;

  /* passthrough if both channel masks are the same */
  in_mask = out_mask = 0;
  for (i = 0; i < mix->in_channels; i++) {
    in_mask |= mix->in_position[i];
    out_mask |= mix->out_position[i];
  }
  return in_mask == out_mask;
}

/**
 * gst_audio_channel_mixer_samples:
 * @mix: a #GstAudioChannelMixer
 * @in: input samples
 * @out: output samples
 * @samples: number of samples
 *
 * In case the samples are interleaved, @in and @out must point to an
 * array with a single element pointing to a block of interleaved samples.
 *
 * If non-interleaved samples are used, @in and @out must point to an
 * array with pointers to memory blocks, one for each channel.
 *
 * Perform channel mixing on @in_data and write the result to @out_data.
 * @in_data and @out_data need to be in @format and @layout.
 */
void
gst_audio_channel_mixer_samples (GstAudioChannelMixer * mix,
    const gpointer in[], gpointer out[], gint samples)
{
  g_return_if_fail (mix != NULL);
  g_return_if_fail (mix->matrix != NULL);

  mix->func (mix, in[0], out[0], samples);
}