[pulseaudio] / src / pulsecore / resampler.c

/***
  This file is part of PulseAudio.

  Copyright 2004-2006 Lennart Poettering

  PulseAudio is free software; you can redistribute it and/or modify
  it under the terms of the GNU Lesser General Public License as published
  by the Free Software Foundation; either version 2.1 of the License,
  or (at your option) any later version.

  PulseAudio 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
  General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with PulseAudio; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  USA.
***/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <string.h>

#ifdef HAVE_LIBSAMPLERATE
#include <samplerate.h>
#endif

#include <speex/speex_resampler.h>

#include <pulse/xmalloc.h>
#include <pulsecore/sconv.h>
#include <pulsecore/log.h>
#include <pulsecore/macro.h>
#include <pulsecore/strbuf.h>
#include <pulsecore/remap.h>

#include "ffmpeg/avcodec.h"

#include "resampler.h"

/* Number of samples of extra space we allow the resamplers to return */
#define EXTRA_FRAMES 128

struct pa_resampler {
    pa_resample_method_t method;
    pa_resample_flags_t flags;

    pa_sample_spec i_ss, o_ss;
    pa_channel_map i_cm, o_cm;
    size_t i_fz, o_fz, w_sz;
    pa_mempool *mempool;

    pa_memchunk buf1, buf2, buf3, buf4;
    unsigned buf1_samples, buf2_samples, buf3_samples, buf4_samples;

    pa_sample_format_t work_format;

    pa_convert_func_t to_work_format_func;
    pa_convert_func_t from_work_format_func;

    pa_remap_t remap;
    pa_bool_t map_required;

    void (*impl_free)(pa_resampler *r);
    void (*impl_update_rates)(pa_resampler *r);
    void (*impl_resample)(pa_resampler *r, const pa_memchunk *in, unsigned in_samples, pa_memchunk *out, unsigned *out_samples);
    void (*impl_reset)(pa_resampler *r);

    struct { /* data specific to the trivial resampler */
        unsigned o_counter;
        unsigned i_counter;
    } trivial;

    struct { /* data specific to the peak finder pseudo resampler */
        unsigned o_counter;
        unsigned i_counter;

        float max_f[PA_CHANNELS_MAX];
        int16_t max_i[PA_CHANNELS_MAX];

    } peaks;

#ifdef HAVE_LIBSAMPLERATE
    struct { /* data specific to libsamplerate */
        SRC_STATE *state;
    } src;
#endif

    struct { /* data specific to speex */
        SpeexResamplerState* state;
    } speex;

    struct { /* data specific to ffmpeg */
        struct AVResampleContext *state;
        pa_memchunk buf[PA_CHANNELS_MAX];
    } ffmpeg;
};

static int copy_init(pa_resampler *r);
static int trivial_init(pa_resampler*r);
static int speex_init(pa_resampler*r);
static int ffmpeg_init(pa_resampler*r);
static int peaks_init(pa_resampler*r);
#ifdef HAVE_LIBSAMPLERATE
static int libsamplerate_init(pa_resampler*r);
#endif

static void calc_map_table(pa_resampler *r);

static int (* const init_table[])(pa_resampler*r) = {
#ifdef HAVE_LIBSAMPLERATE
    [PA_RESAMPLER_SRC_SINC_BEST_QUALITY]   = libsamplerate_init,
    [PA_RESAMPLER_SRC_SINC_MEDIUM_QUALITY] = libsamplerate_init,
    [PA_RESAMPLER_SRC_SINC_FASTEST]        = libsamplerate_init,
    [PA_RESAMPLER_SRC_ZERO_ORDER_HOLD]     = libsamplerate_init,
    [PA_RESAMPLER_SRC_LINEAR]              = libsamplerate_init,
#else
    [PA_RESAMPLER_SRC_SINC_BEST_QUALITY]   = NULL,
    [PA_RESAMPLER_SRC_SINC_MEDIUM_QUALITY] = NULL,
    [PA_RESAMPLER_SRC_SINC_FASTEST]        = NULL,
    [PA_RESAMPLER_SRC_ZERO_ORDER_HOLD]     = NULL,
    [PA_RESAMPLER_SRC_LINEAR]              = NULL,
#endif
    [PA_RESAMPLER_TRIVIAL]                 = trivial_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+0]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+1]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+2]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+3]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+4]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+5]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+6]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+7]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+8]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+9]      = speex_init,
    [PA_RESAMPLER_SPEEX_FLOAT_BASE+10]     = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+0]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+1]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+2]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+3]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+4]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+5]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+6]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+7]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+8]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+9]      = speex_init,
    [PA_RESAMPLER_SPEEX_FIXED_BASE+10]     = speex_init,
    [PA_RESAMPLER_FFMPEG]                  = ffmpeg_init,
    [PA_RESAMPLER_AUTO]                    = NULL,
    [PA_RESAMPLER_COPY]                    = copy_init,
    [PA_RESAMPLER_PEAKS]                   = peaks_init,
};

pa_resampler* pa_resampler_new(
        pa_mempool *pool,
        const pa_sample_spec *a,
        const pa_channel_map *am,
        const pa_sample_spec *b,
        const pa_channel_map *bm,
        pa_resample_method_t method,
        pa_resample_flags_t flags) {

    pa_resampler *r = NULL;

    pa_assert(pool);
    pa_assert(a);
    pa_assert(b);
    pa_assert(pa_sample_spec_valid(a));
    pa_assert(pa_sample_spec_valid(b));
    pa_assert(method >= 0);
    pa_assert(method < PA_RESAMPLER_MAX);

    /* Fix method */

    if (!(flags & PA_RESAMPLER_VARIABLE_RATE) && a->rate == b->rate) {
        pa_log_info("Forcing resampler 'copy', because of fixed, identical sample rates.");
        method = PA_RESAMPLER_COPY;
    }

    if (!pa_resample_method_supported(method)) {
        pa_log_warn("Support for resampler '%s' not compiled in, reverting to 'auto'.", pa_resample_method_to_string(method));
        method = PA_RESAMPLER_AUTO;
    }

    if (method == PA_RESAMPLER_FFMPEG && (flags & PA_RESAMPLER_VARIABLE_RATE)) {
        pa_log_info("Resampler 'ffmpeg' cannot do variable rate, reverting to resampler 'auto'.");
        method = PA_RESAMPLER_AUTO;
    }

    if (method == PA_RESAMPLER_COPY && ((flags & PA_RESAMPLER_VARIABLE_RATE) || a->rate != b->rate)) {
        pa_log_info("Resampler 'copy' cannot change sampling rate, reverting to resampler 'auto'.");
        method = PA_RESAMPLER_AUTO;
    }

    if (method == PA_RESAMPLER_AUTO)
        method = PA_RESAMPLER_SPEEX_FLOAT_BASE + 3;

    r = pa_xnew(pa_resampler, 1);
    r->mempool = pool;
    r->method = method;
    r->flags = flags;

    r->impl_free = NULL;
    r->impl_update_rates = NULL;
    r->impl_resample = NULL;
    r->impl_reset = NULL;

    /* Fill sample specs */
    r->i_ss = *a;
    r->o_ss = *b;

    /* set up the remap structure */
    r->remap.i_ss = &r->i_ss;
    r->remap.o_ss = &r->o_ss;
    r->remap.format = &r->work_format;

    if (am)
        r->i_cm = *am;
    else if (!pa_channel_map_init_auto(&r->i_cm, r->i_ss.channels, PA_CHANNEL_MAP_DEFAULT))
        goto fail;

    if (bm)
        r->o_cm = *bm;
    else if (!pa_channel_map_init_auto(&r->o_cm, r->o_ss.channels, PA_CHANNEL_MAP_DEFAULT))
        goto fail;

    r->i_fz = pa_frame_size(a);
    r->o_fz = pa_frame_size(b);

    pa_memchunk_reset(&r->buf1);
    pa_memchunk_reset(&r->buf2);
    pa_memchunk_reset(&r->buf3);
    pa_memchunk_reset(&r->buf4);

    r->buf1_samples = r->buf2_samples = r->buf3_samples = r->buf4_samples = 0;

    calc_map_table(r);

    pa_log_info("Using resampler '%s'", pa_resample_method_to_string(method));

    if ((method >= PA_RESAMPLER_SPEEX_FIXED_BASE && method <= PA_RESAMPLER_SPEEX_FIXED_MAX) ||
        (method == PA_RESAMPLER_FFMPEG))
        r->work_format = PA_SAMPLE_S16NE;
    else if (method == PA_RESAMPLER_TRIVIAL || method == PA_RESAMPLER_COPY || method == PA_RESAMPLER_PEAKS) {

        if (r->map_required || a->format != b->format || method == PA_RESAMPLER_PEAKS) {

            if (a->format == PA_SAMPLE_S32NE || a->format == PA_SAMPLE_S32RE ||
                a->format == PA_SAMPLE_FLOAT32NE || a->format == PA_SAMPLE_FLOAT32RE ||
                a->format == PA_SAMPLE_S24NE || a->format == PA_SAMPLE_S24RE ||
                a->format == PA_SAMPLE_S24_32NE || a->format == PA_SAMPLE_S24_32RE ||
                b->format == PA_SAMPLE_S32NE || b->format == PA_SAMPLE_S32RE ||
                b->format == PA_SAMPLE_FLOAT32NE || b->format == PA_SAMPLE_FLOAT32RE ||
                b->format == PA_SAMPLE_S24NE || b->format == PA_SAMPLE_S24RE ||
                b->format == PA_SAMPLE_S24_32NE || b->format == PA_SAMPLE_S24_32RE)
                r->work_format = PA_SAMPLE_FLOAT32NE;
            else
                r->work_format = PA_SAMPLE_S16NE;

        } else
            r->work_format = a->format;

    } else
        r->work_format = PA_SAMPLE_FLOAT32NE;

    pa_log_info("Using %s as working format.", pa_sample_format_to_string(r->work_format));

    r->w_sz = pa_sample_size_of_format(r->work_format);

    if (r->i_ss.format == r->work_format)
        r->to_work_format_func = NULL;
    else if (r->work_format == PA_SAMPLE_FLOAT32NE) {
        if (!(r->to_work_format_func = pa_get_convert_to_float32ne_function(r->i_ss.format)))
            goto fail;
    } else {
        pa_assert(r->work_format == PA_SAMPLE_S16NE);
        if (!(r->to_work_format_func = pa_get_convert_to_s16ne_function(r->i_ss.format)))
            goto fail;
    }

    if (r->o_ss.format == r->work_format)
        r->from_work_format_func = NULL;
    else if (r->work_format == PA_SAMPLE_FLOAT32NE) {
        if (!(r->from_work_format_func = pa_get_convert_from_float32ne_function(r->o_ss.format)))
            goto fail;
    } else {
        pa_assert(r->work_format == PA_SAMPLE_S16NE);
        if (!(r->from_work_format_func = pa_get_convert_from_s16ne_function(r->o_ss.format)))
            goto fail;
    }

    /* initialize implementation */
    if (init_table[method](r) < 0)
        goto fail;

    return r;

fail:
    pa_xfree(r);

    return NULL;
}

void pa_resampler_free(pa_resampler *r) {
    pa_assert(r);

    if (r->impl_free)
        r->impl_free(r);

    if (r->buf1.memblock)
        pa_memblock_unref(r->buf1.memblock);
    if (r->buf2.memblock)
        pa_memblock_unref(r->buf2.memblock);
    if (r->buf3.memblock)
        pa_memblock_unref(r->buf3.memblock);
    if (r->buf4.memblock)
        pa_memblock_unref(r->buf4.memblock);

    pa_xfree(r);
}

void pa_resampler_set_input_rate(pa_resampler *r, uint32_t rate) {
    pa_assert(r);
    pa_assert(rate > 0);

    if (r->i_ss.rate == rate)
        return;

    r->i_ss.rate = rate;

    r->impl_update_rates(r);
}

void pa_resampler_set_output_rate(pa_resampler *r, uint32_t rate) {
    pa_assert(r);
    pa_assert(rate > 0);

    if (r->o_ss.rate == rate)
        return;

    r->o_ss.rate = rate;

    r->impl_update_rates(r);
}

size_t pa_resampler_request(pa_resampler *r, size_t out_length) {
    pa_assert(r);

    /* Let's round up here */

    return (((((out_length + r->o_fz-1) / r->o_fz) * r->i_ss.rate) + r->o_ss.rate-1) / r->o_ss.rate) * r->i_fz;
}

size_t pa_resampler_result(pa_resampler *r, size_t in_length) {
    pa_assert(r);

    /* Let's round up here */

    return (((((in_length + r->i_fz-1) / r->i_fz) * r->o_ss.rate) + r->i_ss.rate-1) / r->i_ss.rate) * r->o_fz;
}

size_t pa_resampler_max_block_size(pa_resampler *r) {
    size_t block_size_max;
    pa_sample_spec ss;
    size_t fs;

    pa_assert(r);

    block_size_max = pa_mempool_block_size_max(r->mempool);

    /* We deduce the "largest" sample spec we're using during the
     * conversion */
    ss.channels = (uint8_t) (PA_MAX(r->i_ss.channels, r->o_ss.channels));

    /* We silently assume that the format enum is ordered by size */
    ss.format = PA_MAX(r->i_ss.format, r->o_ss.format);
    ss.format = PA_MAX(ss.format, r->work_format);

    ss.rate = PA_MAX(r->i_ss.rate, r->o_ss.rate);

    fs = pa_frame_size(&ss);

    return (((block_size_max/fs - EXTRA_FRAMES)*r->i_ss.rate)/ss.rate)*r->i_fz;
}

void pa_resampler_reset(pa_resampler *r) {
    pa_assert(r);

    if (r->impl_reset)
        r->impl_reset(r);
}

pa_resample_method_t pa_resampler_get_method(pa_resampler *r) {
    pa_assert(r);

    return r->method;
}

const pa_channel_map* pa_resampler_input_channel_map(pa_resampler *r) {
    pa_assert(r);

    return &r->i_cm;
}

const pa_sample_spec* pa_resampler_input_sample_spec(pa_resampler *r) {
    pa_assert(r);

    return &r->i_ss;
}

const pa_channel_map* pa_resampler_output_channel_map(pa_resampler *r) {
    pa_assert(r);

    return &r->o_cm;
}

const pa_sample_spec* pa_resampler_output_sample_spec(pa_resampler *r) {
    pa_assert(r);

    return &r->o_ss;
}

static const char * const resample_methods[] = {
    "src-sinc-best-quality",
    "src-sinc-medium-quality",
    "src-sinc-fastest",
    "src-zero-order-hold",
    "src-linear",
    "trivial",
    "speex-float-0",
    "speex-float-1",
    "speex-float-2",
    "speex-float-3",
    "speex-float-4",
    "speex-float-5",
    "speex-float-6",
    "speex-float-7",
    "speex-float-8",
    "speex-float-9",
    "speex-float-10",
    "speex-fixed-0",
    "speex-fixed-1",
    "speex-fixed-2",
    "speex-fixed-3",
    "speex-fixed-4",
    "speex-fixed-5",
    "speex-fixed-6",
    "speex-fixed-7",
    "speex-fixed-8",
    "speex-fixed-9",
    "speex-fixed-10",
    "ffmpeg",
    "auto",
    "copy",
    "peaks"
};

const char *pa_resample_method_to_string(pa_resample_method_t m) {

    if (m < 0 || m >= PA_RESAMPLER_MAX)
        return NULL;

    return resample_methods[m];
}

int pa_resample_method_supported(pa_resample_method_t m) {

    if (m < 0 || m >= PA_RESAMPLER_MAX)
        return 0;

#ifndef HAVE_LIBSAMPLERATE
    if (m <= PA_RESAMPLER_SRC_LINEAR)
        return 0;
#endif

    return 1;
}

pa_resample_method_t pa_parse_resample_method(const char *string) {
    pa_resample_method_t m;

    pa_assert(string);

    for (m = 0; m < PA_RESAMPLER_MAX; m++)
        if (!strcmp(string, resample_methods[m]))
            return m;

    if (!strcmp(string, "speex-fixed"))
        return PA_RESAMPLER_SPEEX_FIXED_BASE + 3;

    if (!strcmp(string, "speex-float"))
        return PA_RESAMPLER_SPEEX_FLOAT_BASE + 3;

    return PA_RESAMPLER_INVALID;
}

static pa_bool_t on_left(pa_channel_position_t p) {

    return
        p == PA_CHANNEL_POSITION_FRONT_LEFT ||
        p == PA_CHANNEL_POSITION_REAR_LEFT ||
        p == PA_CHANNEL_POSITION_FRONT_LEFT_OF_CENTER ||
        p == PA_CHANNEL_POSITION_SIDE_LEFT ||
        p == PA_CHANNEL_POSITION_TOP_FRONT_LEFT ||
        p == PA_CHANNEL_POSITION_TOP_REAR_LEFT;
}

static pa_bool_t on_right(pa_channel_position_t p) {

    return
        p == PA_CHANNEL_POSITION_FRONT_RIGHT ||
        p == PA_CHANNEL_POSITION_REAR_RIGHT ||
        p == PA_CHANNEL_POSITION_FRONT_RIGHT_OF_CENTER ||
        p == PA_CHANNEL_POSITION_SIDE_RIGHT ||
        p == PA_CHANNEL_POSITION_TOP_FRONT_RIGHT ||
        p == PA_CHANNEL_POSITION_TOP_REAR_RIGHT;
}

static pa_bool_t on_center(pa_channel_position_t p) {

    return
        p == PA_CHANNEL_POSITION_FRONT_CENTER ||
        p == PA_CHANNEL_POSITION_REAR_CENTER ||
        p == PA_CHANNEL_POSITION_TOP_CENTER ||
        p == PA_CHANNEL_POSITION_TOP_FRONT_CENTER ||
        p == PA_CHANNEL_POSITION_TOP_REAR_CENTER;
}

static pa_bool_t on_lfe(pa_channel_position_t p) {
    return
        p == PA_CHANNEL_POSITION_LFE;
}

static pa_bool_t on_front(pa_channel_position_t p) {
    return
        p == PA_CHANNEL_POSITION_FRONT_LEFT ||
        p == PA_CHANNEL_POSITION_FRONT_RIGHT ||
        p == PA_CHANNEL_POSITION_FRONT_CENTER ||
        p == PA_CHANNEL_POSITION_TOP_FRONT_LEFT ||
        p == PA_CHANNEL_POSITION_TOP_FRONT_RIGHT ||
        p == PA_CHANNEL_POSITION_TOP_FRONT_CENTER ||
        p == PA_CHANNEL_POSITION_FRONT_LEFT_OF_CENTER ||
        p == PA_CHANNEL_POSITION_FRONT_RIGHT_OF_CENTER;
}

static pa_bool_t on_rear(pa_channel_position_t p) {
    return
        p == PA_CHANNEL_POSITION_REAR_LEFT ||
        p == PA_CHANNEL_POSITION_REAR_RIGHT ||
        p == PA_CHANNEL_POSITION_REAR_CENTER ||
        p == PA_CHANNEL_POSITION_TOP_REAR_LEFT ||
        p == PA_CHANNEL_POSITION_TOP_REAR_RIGHT ||
        p == PA_CHANNEL_POSITION_TOP_REAR_CENTER;
}

static pa_bool_t on_side(pa_channel_position_t p) {
    return
        p == PA_CHANNEL_POSITION_SIDE_LEFT ||
        p == PA_CHANNEL_POSITION_SIDE_RIGHT ||
        p == PA_CHANNEL_POSITION_TOP_CENTER;
}

enum {
    ON_FRONT,
    ON_REAR,
    ON_SIDE,
    ON_OTHER
};

static int front_rear_side(pa_channel_position_t p) {
    if (on_front(p))
        return ON_FRONT;
    if (on_rear(p))
        return ON_REAR;
    if (on_side(p))
        return ON_SIDE;
    return ON_OTHER;
}

static void calc_map_table(pa_resampler *r) {
    unsigned oc, ic;
    unsigned n_oc, n_ic;
    pa_bool_t ic_connected[PA_CHANNELS_MAX];
    pa_bool_t remix;
    pa_strbuf *s;
    char *t;
    pa_remap_t *m;

    pa_assert(r);

    if (!(r->map_required = (r->i_ss.channels != r->o_ss.channels || (!(r->flags & PA_RESAMPLER_NO_REMAP) && !pa_channel_map_equal(&r->i_cm, &r->o_cm)))))
        return;

    m = &r->remap;

    n_oc = r->o_ss.channels;
    n_ic = r->i_ss.channels;

    memset(m->map_table_f, 0, sizeof(m->map_table_f));
    memset(m->map_table_i, 0, sizeof(m->map_table_i));

    memset(ic_connected, 0, sizeof(ic_connected));
    remix = (r->flags & (PA_RESAMPLER_NO_REMAP|PA_RESAMPLER_NO_REMIX)) == 0;

    for (oc = 0; oc < n_oc; oc++) {
        pa_bool_t oc_connected = FALSE;
        pa_channel_position_t b = r->o_cm.map[oc];

        for (ic = 0; ic < n_ic; ic++) {
            pa_channel_position_t a = r->i_cm.map[ic];

            if (r->flags & PA_RESAMPLER_NO_REMAP) {
                /* We shall not do any remapping. Hence, just check by index */

                if (ic == oc)
                    m->map_table_f[oc][ic] = 1.0;

                continue;
            }

            if (r->flags & PA_RESAMPLER_NO_REMIX) {
                /* We shall not do any remixing. Hence, just check by name */

                if (a == b)
                    m->map_table_f[oc][ic] = 1.0;

                continue;
            }

            pa_assert(remix);

            /* OK, we shall do the full monty: upmixing and
             * downmixing. Our algorithm is relatively simple, does
             * not do spacialization, delay elements or apply lowpass
             * filters for LFE. Patches are always welcome,
             * though. Oh, and it doesn't do any matrix
             * decoding. (Which probably wouldn't make any sense
             * anyway.)
             *
             * This code is not idempotent: downmixing an upmixed
             * stereo stream is not identical to the original. The
             * volume will not match, and the two channels will be a
             * linear combination of both.
             *
             * This is loosely based on random suggestions found on the
             * Internet, such as this:
             * http://www.halfgaar.net/surround-sound-in-linux and the
             * alsa upmix plugin.
             *
             * The algorithm works basically like this:
             *
             * 1) Connect all channels with matching names.
             *
             * 2) Mono Handling:
             *    S:Mono: Copy into all D:channels
             *    D:Mono: Copy in all S:channels
             *
             * 3) Mix D:Left, D:Right:
             *    D:Left: If not connected, avg all S:Left
             *    D:Right: If not connected, avg all S:Right
             *
             * 4) Mix D:Center
             *       If not connected, avg all S:Center
             *       If still not connected, avg all S:Left, S:Right
             *
             * 5) Mix D:LFE
             *       If not connected, avg all S:*
             *
             * 6) Make sure S:Left/S:Right is used: S:Left/S:Right: If
             *    not connected, mix into all D:left and all D:right
             *    channels. Gain is 0.1, the current left and right
             *    should be multiplied by 0.9.
             *
             * 7) Make sure S:Center, S:LFE is used:
             *
             *    S:Center, S:LFE: If not connected, mix into all
             *    D:left, all D:right, all D:center channels, gain is
             *    0.375. The current (as result of 1..6) factors
             *    should be multiplied by 0.75. (Alt. suggestion: 0.25
             *    vs. 0.5) If C-front is only mixed into
             *    L-front/R-front if available, otherwise into all L/R
             *    channels. Similarly for C-rear.
             *
             * S: and D: shall relate to the source resp. destination channels.
             *
             * Rationale: 1, 2 are probably obvious. For 3: this
             * copies front to rear if needed. For 4: we try to find
             * some suitable C source for C, if we don't find any, we
             * avg L and R. For 5: LFE is mixed from all channels. For
             * 6: the rear channels should not be dropped entirely,
             * however have only minimal impact. For 7: movies usually
             * encode speech on the center channel. Thus we have to
             * make sure this channel is distributed to L and R if not
             * available in the output. Also, LFE is used to achieve a
             * greater dynamic range, and thus we should try to do our
             * best to pass it to L+R.
             */

            if (a == b || a == PA_CHANNEL_POSITION_MONO || b == PA_CHANNEL_POSITION_MONO) {
                m->map_table_f[oc][ic] = 1.0;

                oc_connected = TRUE;
                ic_connected[ic] = TRUE;
            }
        }

        if (!oc_connected && remix) {
            /* OK, we shall remix */

            /* Try to find matching input ports for this output port */

            if (on_left(b)) {
                unsigned n = 0;

                /* We are not connected and on the left side, let's
                 * average all left side input channels. */

                for (ic = 0; ic < n_ic; ic++)
                    if (on_left(r->i_cm.map[ic]))
                        n++;

                if (n > 0)
                    for (ic = 0; ic < n_ic; ic++)
                        if (on_left(r->i_cm.map[ic])) {
                            m->map_table_f[oc][ic] = 1.0f / (float) n;
                            ic_connected[ic] = TRUE;
                        }

                /* We ignore the case where there is no left input
                 * channel. Something is really wrong in this case
                 * anyway. */

            } else if (on_right(b)) {
                unsigned n = 0;

                /* We are not connected and on the right side, let's
                 * average all right side input channels. */

                for (ic = 0; ic < n_ic; ic++)
                    if (on_right(r->i_cm.map[ic]))
                        n++;

                if (n > 0)
                    for (ic = 0; ic < n_ic; ic++)
                        if (on_right(r->i_cm.map[ic])) {
                            m->map_table_f[oc][ic] = 1.0f / (float) n;
                            ic_connected[ic] = TRUE;
                        }

                /* We ignore the case where there is no right input
                 * channel. Something is really wrong in this case
                 * anyway. */

            } else if (on_center(b)) {
                unsigned n = 0;

                /* We are not connected and at the center. Let's
                 * average all center input channels. */

                for (ic = 0; ic < n_ic; ic++)
                    if (on_center(r->i_cm.map[ic]))
                        n++;

                if (n > 0) {
                    for (ic = 0; ic < n_ic; ic++)
                        if (on_center(r->i_cm.map[ic])) {
                            m->map_table_f[oc][ic] = 1.0f / (float) n;
                            ic_connected[ic] = TRUE;
                        }
                } else {

                    /* Hmm, no center channel around, let's synthesize
                     * it by mixing L and R.*/

                    n = 0;

                    for (ic = 0; ic < n_ic; ic++)
                        if (on_left(r->i_cm.map[ic]) || on_right(r->i_cm.map[ic]))
                            n++;

                    if (n > 0)
                        for (ic = 0; ic < n_ic; ic++)
                            if (on_left(r->i_cm.map[ic]) || on_right(r->i_cm.map[ic])) {
                                m->map_table_f[oc][ic] = 1.0f / (float) n;
                                ic_connected[ic] = TRUE;
                            }

                    /* We ignore the case where there is not even a
                     * left or right input channel. Something is
                     * really wrong in this case anyway. */
                }

            } else if (on_lfe(b)) {

                /* We are not connected and an LFE. Let's average all
                 * channels for LFE. */

                for (ic = 0; ic < n_ic; ic++) {

                    if (!(r->flags & PA_RESAMPLER_NO_LFE))
                        m->map_table_f[oc][ic] = 1.0f / (float) n_ic;
                    else
                        m->map_table_f[oc][ic] = 0;

                    /* Please note that a channel connected to LFE
                     * doesn't really count as connected. */
                }
            }
        }
    }

    if (remix) {
        unsigned
            ic_unconnected_left = 0,
            ic_unconnected_right = 0,
            ic_unconnected_center = 0,
            ic_unconnected_lfe = 0;

        for (ic = 0; ic < n_ic; ic++) {
            pa_channel_position_t a = r->i_cm.map[ic];

            if (ic_connected[ic])
                continue;

            if (on_left(a))
                ic_unconnected_left++;
            else if (on_right(a))
                ic_unconnected_right++;
            else if (on_center(a))
                ic_unconnected_center++;
            else if (on_lfe(a))
                ic_unconnected_lfe++;
        }

        if (ic_unconnected_left > 0) {

            /* OK, so there are unconnected input channels on the
             * left. Let's multiply all already connected channels on
             * the left side by .9 and add in our averaged unconnected
             * channels multiplied by .1 */

            for (oc = 0; oc < n_oc; oc++) {

                if (!on_left(r->o_cm.map[oc]))
                    continue;

                for (ic = 0; ic < n_ic; ic++) {

                    if (ic_connected[ic]) {
                        m->map_table_f[oc][ic] *= .9f;
                        continue;
                    }

                    if (on_left(r->i_cm.map[ic]))
                        m->map_table_f[oc][ic] = .1f / (float) ic_unconnected_left;
                }
            }
        }

        if (ic_unconnected_right > 0) {

            /* OK, so there are unconnected input channels on the
             * right. Let's multiply all already connected channels on
             * the right side by .9 and add in our averaged unconnected
             * channels multiplied by .1 */

            for (oc = 0; oc < n_oc; oc++) {

                if (!on_right(r->o_cm.map[oc]))
                    continue;

                for (ic = 0; ic < n_ic; ic++) {

                    if (ic_connected[ic]) {
                        m->map_table_f[oc][ic] *= .9f;
                        continue;
                    }

                    if (on_right(r->i_cm.map[ic]))
                        m->map_table_f[oc][ic] = .1f / (float) ic_unconnected_right;
                }
            }
        }

        if (ic_unconnected_center > 0) {
            pa_bool_t mixed_in = FALSE;

            /* OK, so there are unconnected input channels on the
             * center. Let's multiply all already connected channels on
             * the center side by .9 and add in our averaged unconnected
             * channels multiplied by .1 */

            for (oc = 0; oc < n_oc; oc++) {

                if (!on_center(r->o_cm.map[oc]))
                    continue;

                for (ic = 0; ic < n_ic; ic++) {

                    if (ic_connected[ic]) {
                        m->map_table_f[oc][ic] *= .9f;
                        continue;
                    }

                    if (on_center(r->i_cm.map[ic])) {
                        m->map_table_f[oc][ic] = .1f / (float) ic_unconnected_center;
                        mixed_in = TRUE;
                    }
                }
            }

            if (!mixed_in) {
                unsigned ncenter[PA_CHANNELS_MAX];
                pa_bool_t found_frs[PA_CHANNELS_MAX];

                memset(ncenter, 0, sizeof(ncenter));
                memset(found_frs, 0, sizeof(found_frs));

                /* Hmm, as it appears there was no center channel we
                   could mix our center channel in. In this case, mix
                   it into left and right. Using .375 and 0.75 as
                   factors. */

                for (ic = 0; ic < n_ic; ic++) {

                    if (ic_connected[ic])
                        continue;

                    if (!on_center(r->i_cm.map[ic]))
                        continue;

                    for (oc = 0; oc < n_oc; oc++) {

                        if (!on_left(r->o_cm.map[oc]) && !on_right(r->o_cm.map[oc]))
                            continue;

                        if (front_rear_side(r->i_cm.map[ic]) == front_rear_side(r->o_cm.map[oc])) {
                            found_frs[ic] = TRUE;
                            break;
                        }
                    }

                    for (oc = 0; oc < n_oc; oc++) {

                        if (!on_left(r->o_cm.map[oc]) && !on_right(r->o_cm.map[oc]))
                            continue;

                        if (!found_frs[ic] || front_rear_side(r->i_cm.map[ic]) == front_rear_side(r->o_cm.map[oc]))
                            ncenter[oc]++;
                    }
                }

                for (oc = 0; oc < n_oc; oc++) {

                    if (!on_left(r->o_cm.map[oc]) && !on_right(r->o_cm.map[oc]))
                        continue;

                    if (ncenter[oc] <= 0)
                        continue;

                    for (ic = 0; ic < n_ic; ic++) {

                        if (ic_connected[ic]) {
                            m->map_table_f[oc][ic] *= .75f;
                            continue;
                        }

                        if (!on_center(r->i_cm.map[ic]))
                            continue;

                        if (!found_frs[ic] || front_rear_side(r->i_cm.map[ic]) == front_rear_side(r->o_cm.map[oc]))
                            m->map_table_f[oc][ic] = .375f / (float) ncenter[oc];
                    }
                }
            }
        }

        if (ic_unconnected_lfe > 0 && !(r->flags & PA_RESAMPLER_NO_LFE)) {

            /* OK, so there is an unconnected LFE channel. Let's mix
             * it into all channels, with factor 0.375 */

            for (ic = 0; ic < n_ic; ic++) {

                if (!on_lfe(r->i_cm.map[ic]))
                    continue;

                for (oc = 0; oc < n_oc; oc++)
                    m->map_table_f[oc][ic] = 0.375f / (float) ic_unconnected_lfe;
            }
        }
    }
    /* make an 16:16 int version of the matrix */
    for (oc = 0; oc < n_oc; oc++)
        for (ic = 0; ic < n_ic; ic++)
            m->map_table_i[oc][ic] = (int32_t) (m->map_table_f[oc][ic] * 0x10000);

    s = pa_strbuf_new();

    pa_strbuf_printf(s, "     ");
    for (ic = 0; ic < n_ic; ic++)
        pa_strbuf_printf(s, "  I%02u ", ic);
    pa_strbuf_puts(s, "\n    +");

    for (ic = 0; ic < n_ic; ic++)
        pa_strbuf_printf(s, "------");
    pa_strbuf_puts(s, "\n");

    for (oc = 0; oc < n_oc; oc++) {
        pa_strbuf_printf(s, "O%02u |", oc);

        for (ic = 0; ic < n_ic; ic++)
            pa_strbuf_printf(s, " %1.3f", m->map_table_f[oc][ic]);

        pa_strbuf_puts(s, "\n");
    }

    pa_log_debug("Channel matrix:\n%s", t = pa_strbuf_tostring_free(s));
    pa_xfree(t);

    /* initialize the remapping function */
    pa_init_remap(m);
}

static pa_memchunk* convert_to_work_format(pa_resampler *r, pa_memchunk *input) {
    unsigned n_samples;
    void *src, *dst;

    pa_assert(r);
    pa_assert(input);
    pa_assert(input->memblock);

    /* Convert the incoming sample into the work sample format and place them in buf1 */

    if (!r->to_work_format_func || !input->length)
        return input;

    n_samples = (unsigned) ((input->length / r->i_fz) * r->i_ss.channels);

    r->buf1.index = 0;
    r->buf1.length = r->w_sz * n_samples;

    if (!r->buf1.memblock || r->buf1_samples < n_samples) {
        if (r->buf1.memblock)
            pa_memblock_unref(r->buf1.memblock);

        r->buf1_samples = n_samples;
        r->buf1.memblock = pa_memblock_new(r->mempool, r->buf1.length);
    }

    src = (uint8_t*) pa_memblock_acquire(input->memblock) + input->index;
    dst = (uint8_t*) pa_memblock_acquire(r->buf1.memblock);

    r->to_work_format_func(n_samples, src, dst);

    pa_memblock_release(input->memblock);
    pa_memblock_release(r->buf1.memblock);

    return &r->buf1;
}

static pa_memchunk *remap_channels(pa_resampler *r, pa_memchunk *input) {
    unsigned in_n_samples, out_n_samples, n_frames;
    void *src, *dst;
    pa_remap_t *remap;

    pa_assert(r);
    pa_assert(input);
    pa_assert(input->memblock);

    /* Remap channels and place the result int buf2 */

    if (!r->map_required || !input->length)
        return input;

    in_n_samples = (unsigned) (input->length / r->w_sz);
    n_frames = in_n_samples / r->i_ss.channels;
    out_n_samples = n_frames * r->o_ss.channels;

    r->buf2.index = 0;
    r->buf2.length = r->w_sz * out_n_samples;

    if (!r->buf2.memblock || r->buf2_samples < out_n_samples) {
        if (r->buf2.memblock)
            pa_memblock_unref(r->buf2.memblock);

        r->buf2_samples = out_n_samples;
        r->buf2.memblock = pa_memblock_new(r->mempool, r->buf2.length);
    }

    src = ((uint8_t*) pa_memblock_acquire(input->memblock) + input->index);
    dst = pa_memblock_acquire(r->buf2.memblock);

    remap = &r->remap;

    pa_assert(remap->do_remap);
    remap->do_remap(remap, dst, src, n_frames);

    pa_memblock_release(input->memblock);
    pa_memblock_release(r->buf2.memblock);

    return &r->buf2;
}

static pa_memchunk *resample(pa_resampler *r, pa_memchunk *input) {
    unsigned in_n_frames, in_n_samples;
    unsigned out_n_frames, out_n_samples;

    pa_assert(r);
    pa_assert(input);

    /* Resample the data and place the result in buf3 */

    if (!r->impl_resample || !input->length)
        return input;

    in_n_samples = (unsigned) (input->length / r->w_sz);
    in_n_frames = (unsigned) (in_n_samples / r->o_ss.channels);

    out_n_frames = ((in_n_frames*r->o_ss.rate)/r->i_ss.rate)+EXTRA_FRAMES;
    out_n_samples = out_n_frames * r->o_ss.channels;

    r->buf3.index = 0;
    r->buf3.length = r->w_sz * out_n_samples;

    if (!r->buf3.memblock || r->buf3_samples < out_n_samples) {
        if (r->buf3.memblock)
            pa_memblock_unref(r->buf3.memblock);

        r->buf3_samples = out_n_samples;
        r->buf3.memblock = pa_memblock_new(r->mempool, r->buf3.length);
    }

    r->impl_resample(r, input, in_n_frames, &r->buf3, &out_n_frames);
    r->buf3.length = out_n_frames * r->w_sz * r->o_ss.channels;

    return &r->buf3;
}

static pa_memchunk *convert_from_work_format(pa_resampler *r, pa_memchunk *input) {
    unsigned n_samples, n_frames;
    void *src, *dst;

    pa_assert(r);
    pa_assert(input);

    /* Convert the data into the correct sample type and place the result in buf4 */

    if (!r->from_work_format_func || !input->length)
        return input;

    n_samples = (unsigned) (input->length / r->w_sz);
    n_frames = n_samples / r->o_ss.channels;

    r->buf4.index = 0;
    r->buf4.length = r->o_fz * n_frames;

    if (!r->buf4.memblock || r->buf4_samples < n_samples) {
        if (r->buf4.memblock)
            pa_memblock_unref(r->buf4.memblock);

        r->buf4_samples = n_samples;
        r->buf4.memblock = pa_memblock_new(r->mempool, r->buf4.length);
    }

    src = (uint8_t*) pa_memblock_acquire(input->memblock) + input->index;
    dst = pa_memblock_acquire(r->buf4.memblock);
    r->from_work_format_func(n_samples, src, dst);
    pa_memblock_release(input->memblock);
    pa_memblock_release(r->buf4.memblock);

    r->buf4.length = r->o_fz * n_frames;

    return &r->buf4;
}

void pa_resampler_run(pa_resampler *r, const pa_memchunk *in, pa_memchunk *out) {
    pa_memchunk *buf;

    pa_assert(r);
    pa_assert(in);
    pa_assert(out);
    pa_assert(in->length);
    pa_assert(in->memblock);
    pa_assert(in->length % r->i_fz == 0);

    buf = (pa_memchunk*) in;
    buf = convert_to_work_format(r, buf);
    buf = remap_channels(r, buf);
    buf = resample(r, buf);

    if (buf->length) {
        buf = convert_from_work_format(r, buf);
        *out = *buf;

        if (buf == in)
            pa_memblock_ref(buf->memblock);
        else
            pa_memchunk_reset(buf);
    } else
        pa_memchunk_reset(out);
}

/*** libsamplerate based implementation ***/

#ifdef HAVE_LIBSAMPLERATE
static void libsamplerate_resample(pa_resampler *r, const pa_memchunk *input, unsigned in_n_frames, pa_memchunk *output, unsigned *out_n_frames) {
    SRC_DATA data;

    pa_assert(r);
    pa_assert(input);
    pa_assert(output);
    pa_assert(out_n_frames);

    memset(&data, 0, sizeof(data));

    data.data_in = (float*) ((uint8_t*) pa_memblock_acquire(input->memblock) + input->index);
    data.input_frames = (long int) in_n_frames;

    data.data_out = (float*) ((uint8_t*) pa_memblock_acquire(output->memblock) + output->index);
    data.output_frames = (long int) *out_n_frames;

    data.src_ratio = (double) r->o_ss.rate / r->i_ss.rate;
    data.end_of_input = 0;

    pa_assert_se(src_process(r->src.state, &data) == 0);
    pa_assert((unsigned) data.input_frames_used == in_n_frames);

    pa_memblock_release(input->memblock);
    pa_memblock_release(output->memblock);

    *out_n_frames = (unsigned) data.output_frames_gen;
}

static void libsamplerate_update_rates(pa_resampler *r) {
    pa_assert(r);

    pa_assert_se(src_set_ratio(r->src.state, (double) r->o_ss.rate / r->i_ss.rate) == 0);
}

static void libsamplerate_reset(pa_resampler *r) {
    pa_assert(r);

    pa_assert_se(src_reset(r->src.state) == 0);
}

static void libsamplerate_free(pa_resampler *r) {
    pa_assert(r);

    if (r->src.state)
        src_delete(r->src.state);
}

static int libsamplerate_init(pa_resampler *r) {
    int err;

    pa_assert(r);

    if (!(r->src.state = src_new(r->method, r->o_ss.channels, &err)))
        return -1;

    r->impl_free = libsamplerate_free;
    r->impl_update_rates = libsamplerate_update_rates;
    r->impl_resample = libsamplerate_resample;
    r->impl_reset = libsamplerate_reset;

    return 0;
}
#endif

/*** speex based implementation ***/

static void speex_resample_float(pa_resampler *r, const pa_memchunk *input, unsigned in_n_frames, pa_memchunk *output, unsigned *out_n_frames) {
    float *in, *out;
    uint32_t inf = in_n_frames, outf = *out_n_frames;

    pa_assert(r);
    pa_assert(input);
    pa_assert(output);
    pa_assert(out_n_frames);

    in = (float*) ((uint8_t*) pa_memblock_acquire(input->memblock) + input->index);
    out = (float*) ((uint8_t*) pa_memblock_acquire(output->memblock) + output->index);

    pa_assert_se(speex_resampler_process_interleaved_float(r->speex.state, in, &inf, out, &outf) == 0);

    pa_memblock_release(input->memblock);
    pa_memblock_release(output->memblock);

    pa_assert(inf == in_n_frames);
    *out_n_frames = outf;
}

static void speex_resample_int(pa_resampler *r, const pa_memchunk *input, unsigned in_n_frames, pa_memchunk *output, unsigned *out_n_frames) {
    int16_t *in, *out;
    uint32_t inf = in_n_frames, outf = *out_n_frames;

    pa_assert(r);
    pa_assert(input);
    pa_assert(output);
    pa_assert(out_n_frames);

    in = (int16_t*) ((uint8_t*) pa_memblock_acquire(input->memblock) + input->index);
    out = (int16_t*) ((uint8_t*) pa_memblock_acquire(output->memblock) + output->index);

    pa_assert_se(speex_resampler_process_interleaved_int(r->speex.state, in, &inf, out, &outf) == 0);

    pa_memblock_release(input->memblock);
    pa_memblock_release(output->memblock);

    pa_assert(inf == in_n_frames);
    *out_n_frames = outf;
}

static void speex_update_rates(pa_resampler *r) {
    pa_assert(r);

    pa_assert_se(speex_resampler_set_rate(r->speex.state, r->i_ss.rate, r->o_ss.rate) == 0);
}

static void speex_reset(pa_resampler *r) {
    pa_assert(r);

    pa_assert_se(speex_resampler_reset_mem(r->speex.state) == 0);
}

static void speex_free(pa_resampler *r) {
    pa_assert(r);

    if (!r->speex.state)
        return;

    speex_resampler_destroy(r->speex.state);
}

static int speex_init(pa_resampler *r) {
    int q, err;

    pa_assert(r);

    r->impl_free = speex_free;
    r->impl_update_rates = speex_update_rates;
    r->impl_reset = speex_reset;

    if (r->method >= PA_RESAMPLER_SPEEX_FIXED_BASE && r->method <= PA_RESAMPLER_SPEEX_FIXED_MAX) {

        q = r->method - PA_RESAMPLER_SPEEX_FIXED_BASE;
        r->impl_resample = speex_resample_int;

    } else {
        pa_assert(r->method >= PA_RESAMPLER_SPEEX_FLOAT_BASE && r->method <= PA_RESAMPLER_SPEEX_FLOAT_MAX);

        q = r->method - PA_RESAMPLER_SPEEX_FLOAT_BASE;
        r->impl_resample = speex_resample_float;
    }

    pa_log_info("Choosing speex quality setting %i.", q);

    if (!(r->speex.state = speex_resampler_init(r->o_ss.channels, r->i_ss.rate, r->o_ss.rate, q, &err)))
        return -1;

    return 0;
}

/* Trivial implementation */

static void trivial_resample(pa_resampler *r, const pa_memchunk *input, unsigned in_n_frames, pa_memchunk *output, unsigned *out_n_frames) {
    size_t fz;
    unsigned i_index, o_index;
    void *src, *dst;

    pa_assert(r);
    pa_assert(input);
    pa_assert(output);
    pa_assert(out_n_frames);
    pa_assert(r->i_ss.channels == r->o_ss.channels);

    fz = r->w_sz * r->o_ss.channels;

    src = (uint8_t*) pa_memblock_acquire(input->memblock) + input->index;
    dst = (uint8_t*) pa_memblock_acquire(output->memblock) + output->index;

    for (o_index = 0;; o_index++, r->trivial.o_counter++) {
        i_index = (r->trivial.o_counter * r->i_ss.rate) / r->o_ss.rate;
        i_index = i_index > r->trivial.i_counter ? i_index - r->trivial.i_counter : 0;

        if (i_index >= in_n_frames)
            break;

        pa_assert_fp(o_index * fz < pa_memblock_get_length(output->memblock));

        /* Directly assign some common sample sizes, use memcpy as fallback */
        if (r->w_sz == 2) {
            for (unsigned c = 0; c < r->o_ss.channels; c++)
                ((uint16_t *) dst)[o_index+c] = ((uint16_t *) src)[i_index+c];
        } else if (r->w_sz == 4) {
            for (unsigned c = 0; c < r->o_ss.channels; c++)
                ((uint32_t *) dst)[o_index+c] = ((uint32_t *) src)[i_index+c];
        } else {
            memcpy((uint8_t *) dst + fz * o_index, (uint8_t *) src + fz * i_index, (int) fz);
        }
    }

    pa_memblock_release(input->memblock);
    pa_memblock_release(output->memblock);

    *out_n_frames = o_index;

    r->trivial.i_counter += in_n_frames;

    /* Normalize counters */
    while (r->trivial.i_counter >= r->i_ss.rate) {
        pa_assert(r->trivial.o_counter >= r->o_ss.rate);

        r->trivial.i_counter -= r->i_ss.rate;
        r->trivial.o_counter -= r->o_ss.rate;
    }
}

static void trivial_update_rates_or_reset(pa_resampler *r) {
    pa_assert(r);

    r->trivial.i_counter = 0;
    r->trivial.o_counter = 0;
}

static int trivial_init(pa_resampler*r) {
    pa_assert(r);

    r->trivial.o_counter = r->trivial.i_counter = 0;

    r->impl_resample = trivial_resample;
    r->impl_update_rates = trivial_update_rates_or_reset;
    r->impl_reset = trivial_update_rates_or_reset;

    return 0;
}

/* Peak finder implementation */

static void peaks_resample(pa_resampler *r, const pa_memchunk *input, unsigned in_n_frames, pa_memchunk *output, unsigned *out_n_frames) {
    unsigned c, o_index = 0;
    unsigned i, i_end = 0;
    void *src, *dst;

    pa_assert(r);
    pa_assert(input);
    pa_assert(output);
    pa_assert(out_n_frames);
    pa_assert(r->i_ss.rate >= r->o_ss.rate);
    pa_assert(r->i_ss.channels == r->o_ss.channels);
    pa_assert(r->work_format == PA_SAMPLE_S16NE || r->work_format == PA_SAMPLE_FLOAT32NE);

    src = (uint8_t*) pa_memblock_acquire(input->memblock) + input->index;
    dst = (uint8_t*) pa_memblock_acquire(output->memblock) + output->index;

    i = (r->peaks.o_counter * r->i_ss.rate) / r->o_ss.rate;
    i = i > r->peaks.i_counter ? i - r->peaks.i_counter : 0;

    while (i_end < in_n_frames) {
        i_end = ((r->peaks.o_counter+1) * r->i_ss.rate) / r->o_ss.rate;
        i_end = i_end > r->peaks.i_counter ? i_end - r->peaks.i_counter : 0;

        pa_assert_fp(o_index * r->w_sz * r->o_ss.channels < pa_memblock_get_length(output->memblock));

        /* 1ch float is treated separately, because that is the common case */
        if (r->o_ss.channels == 1 && r->work_format == PA_SAMPLE_FLOAT32NE) {
            float *s = (float*) src + i;
            float *d = (float*) dst + o_index;

            for (; i < i_end && i < in_n_frames; i++) {
                float n = fabsf(*s++);

                if (n > r->peaks.max_f[0])
                    r->peaks.max_f[0] = n;
            }

            if (i == i_end) {
                *d = r->peaks.max_f[0];
                r->peaks.max_f[0] = 0;
                o_index++, r->peaks.o_counter++;
            }
        } else if (r->work_format == PA_SAMPLE_S16NE) {
            int16_t *s = (int16_t*) src + r->i_ss.channels * i;
            int16_t *d = (int16_t*) dst + r->o_ss.channels * o_index;

            for (; i < i_end && i < in_n_frames; i++)
                for (c = 0; c < r->o_ss.channels; c++) {
                    int16_t n = abs(*s++);

                    if (n > r->peaks.max_i[c])
                        r->peaks.max_i[c] = n;
                }

            if (i == i_end) {
                for (c = 0; c < r->o_ss.channels; c++, d++) {
                    *d = r->peaks.max_i[c];
                    r->peaks.max_i[c] = 0;
                }
                o_index++, r->peaks.o_counter++;
            }
        } else {
            float *s = (float*) src + r->i_ss.channels * i;
            float *d = (float*) dst + r->o_ss.channels * o_index;

            for (; i < i_end && i < in_n_frames; i++)
                for (c = 0; c < r->o_ss.channels; c++) {
                    float n = fabsf(*s++);

                    if (n > r->peaks.max_f[c])
                        r->peaks.max_f[c] = n;
                }

            if (i == i_end) {
                for (c = 0; c < r->o_ss.channels; c++, d++) {
                    *d = r->peaks.max_f[c];
                    r->peaks.max_f[c] = 0;
                }
                o_index++, r->peaks.o_counter++;
            }
        }
    }

    pa_memblock_release(input->memblock);
    pa_memblock_release(output->memblock);

    *out_n_frames = o_index;

    r->peaks.i_counter += in_n_frames;

    /* Normalize counters */
    while (r->peaks.i_counter >= r->i_ss.rate) {
        pa_assert(r->peaks.o_counter >= r->o_ss.rate);

        r->peaks.i_counter -= r->i_ss.rate;
        r->peaks.o_counter -= r->o_ss.rate;
    }
}

static void peaks_update_rates_or_reset(pa_resampler *r) {
    pa_assert(r);

    r->peaks.i_counter = 0;
    r->peaks.o_counter = 0;
}

static int peaks_init(pa_resampler*r) {
    pa_assert(r);

    r->peaks.o_counter = r->peaks.i_counter = 0;
    memset(r->peaks.max_i, 0, sizeof(r->peaks.max_i));
    memset(r->peaks.max_f, 0, sizeof(r->peaks.max_f));

    r->impl_resample = peaks_resample;
    r->impl_update_rates = peaks_update_rates_or_reset;
    r->impl_reset = peaks_update_rates_or_reset;

    return 0;
}

/*** ffmpeg based implementation ***/

static void ffmpeg_resample(pa_resampler *r, const pa_memchunk *input, unsigned in_n_frames, pa_memchunk *output, unsigned *out_n_frames) {
    unsigned used_frames = 0, c;

    pa_assert(r);
    pa_assert(input);
    pa_assert(output);
    pa_assert(out_n_frames);

    for (c = 0; c < r->o_ss.channels; c++) {
        unsigned u;
        pa_memblock *b, *w;
        int16_t *p, *t, *k, *q, *s;
        int consumed_frames;
        unsigned in, l;

        /* Allocate a new block */
        b = pa_memblock_new(r->mempool, r->ffmpeg.buf[c].length + in_n_frames * sizeof(int16_t));
        p = pa_memblock_acquire(b);

        /* Copy the remaining data into it */
        l = (unsigned) r->ffmpeg.buf[c].length;
        if (r->ffmpeg.buf[c].memblock) {
            t = (int16_t*) ((uint8_t*) pa_memblock_acquire(r->ffmpeg.buf[c].memblock) + r->ffmpeg.buf[c].index);
            memcpy(p, t, l);
            pa_memblock_release(r->ffmpeg.buf[c].memblock);
            pa_memblock_unref(r->ffmpeg.buf[c].memblock);
            pa_memchunk_reset(&r->ffmpeg.buf[c]);
        }

        /* Now append the new data, splitting up channels */
        t = ((int16_t*) ((uint8_t*) pa_memblock_acquire(input->memblock) + input->index)) + c;
        k = (int16_t*) ((uint8_t*) p + l);
        for (u = 0; u < in_n_frames; u++) {
            *k = *t;
            t += r->o_ss.channels;
            k ++;
        }
        pa_memblock_release(input->memblock);

        /* Calculate the resulting number of frames */
        in = (unsigned) in_n_frames + l / (unsigned) sizeof(int16_t);

        /* Allocate buffer for the result */
        w = pa_memblock_new(r->mempool, *out_n_frames * sizeof(int16_t));
        q = pa_memblock_acquire(w);

        /* Now, resample */
        used_frames = (unsigned) av_resample(r->ffmpeg.state,
                                             q, p,
                                             &consumed_frames,
                                             (int) in, (int) *out_n_frames,
                                             c >= (unsigned) (r->o_ss.channels-1));

        pa_memblock_release(b);

        /* Now store the remaining samples away */
        pa_assert(consumed_frames <= (int) in);
        if (consumed_frames < (int) in) {
            r->ffmpeg.buf[c].memblock = b;
            r->ffmpeg.buf[c].index = (size_t) consumed_frames * sizeof(int16_t);
            r->ffmpeg.buf[c].length = (size_t) (in - (unsigned) consumed_frames) * sizeof(int16_t);
        } else
            pa_memblock_unref(b);

        /* And place the results in the output buffer */
        s = (short*) ((uint8_t*) pa_memblock_acquire(output->memblock) + output->index) + c;
        for (u = 0; u < used_frames; u++) {
            *s = *q;
            q++;
            s += r->o_ss.channels;
        }
        pa_memblock_release(output->memblock);
        pa_memblock_release(w);
        pa_memblock_unref(w);
    }

    *out_n_frames = used_frames;
}

static void ffmpeg_free(pa_resampler *r) {
    unsigned c;

    pa_assert(r);

    if (r->ffmpeg.state)
        av_resample_close(r->ffmpeg.state);

    for (c = 0; c < PA_ELEMENTSOF(r->ffmpeg.buf); c++)
        if (r->ffmpeg.buf[c].memblock)
            pa_memblock_unref(r->ffmpeg.buf[c].memblock);
}

static int ffmpeg_init(pa_resampler *r) {
    unsigned c;

    pa_assert(r);

    /* We could probably implement different quality levels by
     * adjusting the filter parameters here. However, ffmpeg
     * internally only uses these hardcoded values, so let's use them
     * here for now as well until ffmpeg makes this configurable. */

    if (!(r->ffmpeg.state = av_resample_init((int) r->o_ss.rate, (int) r->i_ss.rate, 16, 10, 0, 0.8)))
        return -1;

    r->impl_free = ffmpeg_free;
    r->impl_resample = ffmpeg_resample;

    for (c = 0; c < PA_ELEMENTSOF(r->ffmpeg.buf); c++)
        pa_memchunk_reset(&r->ffmpeg.buf[c]);

    return 0;
}

/*** copy (noop) implementation ***/

static int copy_init(pa_resampler *r) {
    pa_assert(r);

    pa_assert(r->o_ss.rate == r->i_ss.rate);

    return 0;
}