path: root/audio/out/ao_alsa.c

/*
 * ALSA 0.9.x-1.x audio output driver
 *
 * Copyright (C) 2004 Alex Beregszaszi
 * Zsolt Barat <joy@streamminister.de>
 *
 * modified for real ALSA 0.9.0 support by Zsolt Barat <joy@streamminister.de>
 * additional AC-3 passthrough support by Andy Lo A Foe <andy@alsaplayer.org>
 * 08/22/2002 iec958-init rewritten and merged with common init, zsolt
 * 04/13/2004 merged with ao_alsa1.x, fixes provided by Jindrich Makovicka
 * 04/25/2004 printfs converted to mp_msg, Zsolt.
 *
 * This file is part of mpv.
 *
 * mpv is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * mpv 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 General Public License along
 * with mpv.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <errno.h>
#include <sys/time.h>
#include <stdlib.h>
#include <stdarg.h>
#include <math.h>
#include <string.h>

#include "config.h"
#include "options/options.h"
#include "options/m_option.h"
#include "common/msg.h"
#include "osdep/endian.h"

#include <alsa/asoundlib.h>

#define HAVE_CHMAP_API \
    (defined(SND_CHMAP_API_VERSION) && SND_CHMAP_API_VERSION >= (1 << 16))

#include "ao.h"
#include "internal.h"
#include "audio/format.h"

struct priv {
    snd_pcm_t *alsa;
    bool device_lost;
    snd_pcm_format_t alsa_fmt;
    int can_pause;
    snd_pcm_sframes_t prepause_frames;
    double delay_before_pause;
    int buffersize; // in frames
    int outburst; // in frames

    char *cfg_device;
    char *cfg_mixer_device;
    char *cfg_mixer_name;
    int cfg_mixer_index;
    int cfg_resample;
    int cfg_ni;
    int cfg_ignore_chmap;
};

#define BUFFER_TIME 250000  // 250ms
#define FRAGCOUNT 16

#define CHECK_ALSA_ERROR(message) \
    do { \
        if (err < 0) { \
            MP_ERR(ao, "%s: %s\n", (message), snd_strerror(err)); \
            goto alsa_error; \
        } \
    } while (0)

#define CHECK_ALSA_WARN(message) \
    do { \
        if (err < 0) \
            MP_WARN(ao, "%s: %s\n", (message), snd_strerror(err)); \
    } while (0)

// Common code for handling ENODEV, which happens if a device gets "lost", and
// can't be used anymore. Returns true if alsa_err is not ENODEV.
static bool check_device_present(struct ao *ao, int alsa_err)
{
    struct priv *p = ao->priv;
    if (alsa_err != -ENODEV)
        return true;
    if (!p->device_lost) {
        MP_WARN(ao, "Device lost, trying to recover...\n");
        ao_request_reload(ao);
        p->device_lost = true;
    }
    return false;
}

static int control(struct ao *ao, enum aocontrol cmd, void *arg)
{
    struct priv *p = ao->priv;
    snd_mixer_t *handle = NULL;
    switch (cmd) {
    case AOCONTROL_GET_MUTE:
    case AOCONTROL_SET_MUTE:
    case AOCONTROL_GET_VOLUME:
    case AOCONTROL_SET_VOLUME:
    {
        int err;
        snd_mixer_elem_t *elem;
        snd_mixer_selem_id_t *sid;

        long pmin, pmax;
        long get_vol, set_vol;
        float f_multi;

        if (!af_fmt_is_pcm(ao->format))
            return CONTROL_FALSE;

        snd_mixer_selem_id_alloca(&sid);

        snd_mixer_selem_id_set_index(sid, p->cfg_mixer_index);
        snd_mixer_selem_id_set_name(sid, p->cfg_mixer_name);

        err = snd_mixer_open(&handle, 0);
        CHECK_ALSA_ERROR("Mixer open error");

        err = snd_mixer_attach(handle, p->cfg_mixer_device);
        CHECK_ALSA_ERROR("Mixer attach error");

        err = snd_mixer_selem_register(handle, NULL, NULL);
        CHECK_ALSA_ERROR("Mixer register error");

        err = snd_mixer_load(handle);
        CHECK_ALSA_ERROR("Mixer load error");

        elem = snd_mixer_find_selem(handle, sid);
        if (!elem) {
            MP_VERBOSE(ao, "Unable to find simple control '%s',%i.\n",
                       snd_mixer_selem_id_get_name(sid),
                       snd_mixer_selem_id_get_index(sid));
            goto alsa_error;
        }

        snd_mixer_selem_get_playback_volume_range(elem, &pmin, &pmax);
        f_multi = (100 / (float)(pmax - pmin));

        switch (cmd) {
        case AOCONTROL_SET_VOLUME: {
            ao_control_vol_t *vol = arg;
            set_vol = vol->left / f_multi + pmin + 0.5;

            err = snd_mixer_selem_set_playback_volume
                    (elem, SND_MIXER_SCHN_FRONT_LEFT, set_vol);
            CHECK_ALSA_ERROR("Error setting left channel");
            MP_DBG(ao, "left=%li, ", set_vol);

            set_vol = vol->right / f_multi + pmin + 0.5;

            err = snd_mixer_selem_set_playback_volume
                    (elem, SND_MIXER_SCHN_FRONT_RIGHT, set_vol);
            CHECK_ALSA_ERROR("Error setting right channel");
            MP_DBG(ao, "right=%li, pmin=%li, pmax=%li, mult=%f\n",
                   set_vol, pmin, pmax, f_multi);
            break;
        }
        case AOCONTROL_GET_VOLUME: {
            ao_control_vol_t *vol = arg;
            snd_mixer_selem_get_playback_volume
                (elem, SND_MIXER_SCHN_FRONT_LEFT, &get_vol);
            vol->left = (get_vol - pmin) * f_multi;
            snd_mixer_selem_get_playback_volume
                (elem, SND_MIXER_SCHN_FRONT_RIGHT, &get_vol);
            vol->right = (get_vol - pmin) * f_multi;
            MP_DBG(ao, "left=%f, right=%f\n", vol->left, vol->right);
            break;
        }
        case AOCONTROL_SET_MUTE: {
            bool *mute = arg;
            if (!snd_mixer_selem_has_playback_switch(elem))
                goto alsa_error;
            if (!snd_mixer_selem_has_playback_switch_joined(elem)) {
                snd_mixer_selem_set_playback_switch
                    (elem, SND_MIXER_SCHN_FRONT_RIGHT, !*mute);
            }
            snd_mixer_selem_set_playback_switch
                (elem, SND_MIXER_SCHN_FRONT_LEFT, !*mute);
            break;
        }
        case AOCONTROL_GET_MUTE: {
            bool *mute = arg;
            if (!snd_mixer_selem_has_playback_switch(elem))
                goto alsa_error;
            int tmp = 1;
            snd_mixer_selem_get_playback_switch
                (elem, SND_MIXER_SCHN_FRONT_LEFT, &tmp);
            *mute = !tmp;
            if (!snd_mixer_selem_has_playback_switch_joined(elem)) {
                snd_mixer_selem_get_playback_switch
                    (elem, SND_MIXER_SCHN_FRONT_RIGHT, &tmp);
                *mute &= !tmp;
            }
            break;
        }
        }
        snd_mixer_close(handle);
        return CONTROL_OK;
    }

    } //end switch
    return CONTROL_UNKNOWN;

alsa_error:
    if (handle)
        snd_mixer_close(handle);
    return CONTROL_ERROR;
}

static const int mp_to_alsa_format[][2] = {
    {AF_FORMAT_U8,          SND_PCM_FORMAT_U8},
    {AF_FORMAT_S16,         SND_PCM_FORMAT_S16},
    {AF_FORMAT_S32,         SND_PCM_FORMAT_S32},
    {AF_FORMAT_S24,
            MP_SELECT_LE_BE(SND_PCM_FORMAT_S24_3LE, SND_PCM_FORMAT_S24_3BE)},
    {AF_FORMAT_FLOAT,       SND_PCM_FORMAT_FLOAT},
    {AF_FORMAT_DOUBLE,      SND_PCM_FORMAT_FLOAT64},
    {AF_FORMAT_UNKNOWN,     SND_PCM_FORMAT_UNKNOWN},
};

static int find_alsa_format(int af_format)
{
    if (af_fmt_is_spdif(af_format)) {
        if (af_format == AF_FORMAT_S_MP3) {
            return SND_PCM_FORMAT_MPEG;
        } else {
            return SND_PCM_FORMAT_S16;
        }
    }

    af_format = af_fmt_from_planar(af_format);
    for (int n = 0; mp_to_alsa_format[n][0] != AF_FORMAT_UNKNOWN; n++) {
        if (mp_to_alsa_format[n][0] == af_format)
            return mp_to_alsa_format[n][1];
    }
    return SND_PCM_FORMAT_UNKNOWN;
}

#if HAVE_CHMAP_API

static const int alsa_to_mp_channels[][2] = {
    {SND_CHMAP_FL,      MP_SP(FL)},
    {SND_CHMAP_FR,      MP_SP(FR)},
    {SND_CHMAP_RL,      MP_SP(BL)},
    {SND_CHMAP_RR,      MP_SP(BR)},
    {SND_CHMAP_FC,      MP_SP(FC)},
    {SND_CHMAP_LFE,     MP_SP(LFE)},
    {SND_CHMAP_SL,      MP_SP(SL)},
    {SND_CHMAP_SR,      MP_SP(SR)},
    {SND_CHMAP_RC,      MP_SP(BC)},
    {SND_CHMAP_FLC,     MP_SP(FLC)},
    {SND_CHMAP_FRC,     MP_SP(FRC)},
    {SND_CHMAP_FLW,     MP_SP(WL)},
    {SND_CHMAP_FRW,     MP_SP(WR)},
    {SND_CHMAP_TC,      MP_SP(TC)},
    {SND_CHMAP_TFL,     MP_SP(TFL)},
    {SND_CHMAP_TFR,     MP_SP(TFR)},
    {SND_CHMAP_TFC,     MP_SP(TFC)},
    {SND_CHMAP_TRL,     MP_SP(TBL)},
    {SND_CHMAP_TRR,     MP_SP(TBR)},
    {SND_CHMAP_TRC,     MP_SP(TBC)},
    {SND_CHMAP_RRC,     MP_SP(SDR)},
    {SND_CHMAP_RLC,     MP_SP(SDL)},
    {SND_CHMAP_MONO,    MP_SP(FC)},
    {SND_CHMAP_NA,      MP_SPEAKER_ID_NA},
    {SND_CHMAP_UNKNOWN, MP_SPEAKER_ID_NA},
    {SND_CHMAP_LAST,    MP_SPEAKER_ID_COUNT}
};

static int find_mp_channel(int alsa_channel)
{
    for (int i = 0; alsa_to_mp_channels[i][1] != MP_SPEAKER_ID_COUNT; i++) {
        if (alsa_to_mp_channels[i][0] == alsa_channel)
            return alsa_to_mp_channels[i][1];
    }

    return MP_SPEAKER_ID_COUNT;
}

static int find_alsa_channel(int mp_channel)
{
    for (int i = 0; alsa_to_mp_channels[i][1] != MP_SPEAKER_ID_COUNT; i++) {
        if (alsa_to_mp_channels[i][1] == mp_channel)
            return alsa_to_mp_channels[i][0];
    }

    return SND_CHMAP_UNKNOWN;
}

static int mp_chmap_from_alsa(struct mp_chmap *dst, snd_pcm_chmap_t *src)
{
    *dst = (struct mp_chmap) {0};

    if (src->channels > MP_NUM_CHANNELS)
        return -1;

    dst->num = src->channels;
    for (int c = 0; c < dst->num; c++)
        dst->speaker[c] = find_mp_channel(src->pos[c]);

    return 0;
}

static bool query_chmaps(struct ao *ao, struct mp_chmap *chmap)
{
    struct priv *p = ao->priv;
    struct mp_chmap_sel chmap_sel = {.tmp = p};

    snd_pcm_chmap_query_t **maps = snd_pcm_query_chmaps(p->alsa);
    if (!maps)
        return false;

    for (int i = 0; maps[i] != NULL; i++) {
        struct mp_chmap entry;
        mp_chmap_from_alsa(&entry, &maps[i]->map);

        if (mp_chmap_is_valid(&entry)) {
            if (maps[i]->type == SND_CHMAP_TYPE_VAR)
                mp_chmap_reorder_norm(&entry);
            MP_DBG(ao, "Got supported channel map: %s (type %s)\n",
                   mp_chmap_to_str(&entry),
                   snd_pcm_chmap_type_name(maps[i]->type));
            mp_chmap_sel_add_map(&chmap_sel, &entry);
        } else {
            char tmp[128];
            if (snd_pcm_chmap_print(&maps[i]->map, sizeof(tmp), tmp) > 0)
                MP_VERBOSE(ao, "skipping unknown ALSA channel map: %s\n", tmp);
        }
    }

    snd_pcm_free_chmaps(maps);

    return ao_chmap_sel_adjust(ao, &chmap_sel, chmap);
}

#else /* HAVE_CHMAP_API */

static bool query_chmaps(struct ao *ao, struct mp_chmap *chmap)
{
    return false;
}

#endif /* else HAVE_CHMAP_API */

static int map_iec958_srate(int srate)
{
    switch (srate) {
    case 44100:     return IEC958_AES3_CON_FS_44100;
    case 48000:     return IEC958_AES3_CON_FS_48000;
    case 32000:     return IEC958_AES3_CON_FS_32000;
    case 22050:     return IEC958_AES3_CON_FS_22050;
    case 24000:     return IEC958_AES3_CON_FS_24000;
    case 88200:     return IEC958_AES3_CON_FS_88200;
    case 768000:    return IEC958_AES3_CON_FS_768000;
    case 96000:     return IEC958_AES3_CON_FS_96000;
    case 176400:    return IEC958_AES3_CON_FS_176400;
    case 192000:    return IEC958_AES3_CON_FS_192000;
    default:        return IEC958_AES3_CON_FS_NOTID;
    }
}

// ALSA device strings can have parameters. They are usually appended to the
// device name. Since there can be various forms, and we (sometimes) want to
// append them to unknown device strings, which possibly already include params.
static char *append_params(void *ta_parent, const char *device, const char *p)
{
    if (!p || !p[0])
        return talloc_strdup(ta_parent, device);

    int len = strlen(device);
    char *end = strchr(device, ':');
    if (!end) {
        /* no existing parameters: add it behind device name */
        return talloc_asprintf(ta_parent, "%s:%s", device, p);
    } else if (end[1] == '\0') {
        /* ":" but no parameters */
        return talloc_asprintf(ta_parent, "%s%s", device, p);
    } else if (end[1] == '{' && device[len - 1] == '}') {
        /* parameters in config syntax: add it inside the { } block */
        return talloc_asprintf(ta_parent, "%.*s %s}", len - 1, device, p);
    } else {
        /* a simple list of parameters: add it at the end of the list */
        return talloc_asprintf(ta_parent, "%s,%s", device, p);
    }
    abort();
}

static int try_open_device(struct ao *ao, const char *device)
{
    struct priv *p = ao->priv;
    int err;

    if (af_fmt_is_spdif(ao->format)) {
        void *tmp = talloc_new(NULL);
        char *params = talloc_asprintf(tmp,
                        "AES0=%d,AES1=%d,AES2=0,AES3=%d",
                        IEC958_AES0_NONAUDIO | IEC958_AES0_PRO_EMPHASIS_NONE,
                        IEC958_AES1_CON_ORIGINAL | IEC958_AES1_CON_PCM_CODER,
                        map_iec958_srate(ao->samplerate));
        const char *ac3_device = append_params(tmp, device, params);
        MP_VERBOSE(ao, "opening device '%s' => '%s'\n", device, ac3_device);
        err = snd_pcm_open(&p->alsa, ac3_device, SND_PCM_STREAM_PLAYBACK, 0);
        if (err < 0) {
            // Some spdif-capable devices do not accept the AES0 parameter,
            // and instead require the iec958 pseudo-device (they will play
            // noise otherwise). Unfortunately, ALSA gives us no way to map
            // these devices, so try it for the default device only.
            bstr dev;
            bstr_split_tok(bstr0(device), ":", &dev, &(bstr){0});
            if (bstr_equals0(dev, "default")) {
                ac3_device = append_params(tmp, "iec958", params);
                MP_VERBOSE(ao, "got error %d; opening iec fallback device '%s'\n",
                           err, ac3_device);
                err = snd_pcm_open
                            (&p->alsa, ac3_device, SND_PCM_STREAM_PLAYBACK, 0);
            }
        }
        talloc_free(tmp);
    } else {
        MP_VERBOSE(ao, "opening device '%s'\n", device);
        err = snd_pcm_open(&p->alsa, device, SND_PCM_STREAM_PLAYBACK, 0);
    }

    return err;
}

static void uninit(struct ao *ao)
{
    struct priv *p = ao->priv;

    if (p->alsa) {
        int err;

        err = snd_pcm_close(p->alsa);
        CHECK_ALSA_ERROR("pcm close error");
    }

alsa_error: ;
}

#define INIT_OK 0
#define INIT_ERROR -1
#define INIT_BRAINDEATH -2
static int init_device(struct ao *ao, bool second_try)
{
    struct priv *p = ao->priv;
    int err;

    const char *device = "default";
    if (ao->device)
        device = ao->device;
    if (p->cfg_device && p->cfg_device[0])
        device = p->cfg_device;

    err = try_open_device(ao, device);
    CHECK_ALSA_ERROR("Playback open error");

    err = snd_pcm_nonblock(p->alsa, 0);
    CHECK_ALSA_WARN("Unable to set blocking mode");

    snd_pcm_hw_params_t *alsa_hwparams;
    snd_pcm_sw_params_t *alsa_swparams;

    snd_pcm_hw_params_alloca(&alsa_hwparams);
    snd_pcm_sw_params_alloca(&alsa_swparams);

    err = snd_pcm_hw_params_any(p->alsa, alsa_hwparams);
    CHECK_ALSA_ERROR("Unable to get initial parameters");

    bool found_format = false;
    int try_formats[AF_FORMAT_COUNT];
    af_get_best_sample_formats(ao->format, try_formats);
    for (int n = 0; try_formats[n]; n++) {
        p->alsa_fmt = find_alsa_format(try_formats[n]);
        MP_VERBOSE(ao, "trying format %s\n", af_fmt_to_str(try_formats[n]));
        if (snd_pcm_hw_params_test_format(p->alsa, alsa_hwparams, p->alsa_fmt) >= 0) {
            ao->format = try_formats[n];
            found_format = true;
            break;
        }
    }

    if (!found_format) {
        MP_ERR(ao, "Can't find appropriate sample format.\n");
        goto alsa_error;
    }

    err = snd_pcm_hw_params_set_format(p->alsa, alsa_hwparams, p->alsa_fmt);
    CHECK_ALSA_ERROR("Unable to set format");

    snd_pcm_access_t access = af_fmt_is_planar(ao->format)
                                    ? SND_PCM_ACCESS_RW_NONINTERLEAVED
                                    : SND_PCM_ACCESS_RW_INTERLEAVED;
    err = snd_pcm_hw_params_set_access(p->alsa, alsa_hwparams, access);
    if (err < 0 && af_fmt_is_planar(ao->format)) {
        ao->format = af_fmt_from_planar(ao->format);
        access = SND_PCM_ACCESS_RW_INTERLEAVED;
        err = snd_pcm_hw_params_set_access(p->alsa, alsa_hwparams, access);
    }
    CHECK_ALSA_ERROR("Unable to set access type");

    struct mp_chmap dev_chmap = ao->channels;
    if (af_fmt_is_spdif(ao->format) || p->cfg_ignore_chmap) {
        dev_chmap.num = 0; // disable chmap API
    } else if (dev_chmap.num == 1 && dev_chmap.speaker[0] == MP_SPEAKER_ID_FC) {
        // As yet another ALSA API inconsistency, mono is not reported correctly.
        dev_chmap.num = 0;
    } else if (query_chmaps(ao, &dev_chmap)) {
        ao->channels = dev_chmap;
    } else {
        // Assume only stereo and mono are supported.
        mp_chmap_from_channels(&ao->channels, MPMIN(2, dev_chmap.num));
        dev_chmap.num = 0;
    }

    int num_channels = ao->channels.num;
    err = snd_pcm_hw_params_set_channels_near
            (p->alsa, alsa_hwparams, &num_channels);
    CHECK_ALSA_ERROR("Unable to set channels");

    if (num_channels > MP_NUM_CHANNELS) {
        MP_FATAL(ao, "Too many audio channels (%d).\n", num_channels);
        goto alsa_error;
    }

    if (num_channels != ao->channels.num) {
        int req = ao->channels.num;
        mp_chmap_from_channels_alsa(&ao->channels, num_channels);
        if (!mp_chmap_is_valid(&ao->channels))
            mp_chmap_from_channels(&ao->channels, 2);
        MP_ERR(ao, "Asked for %d channels, got %d - fallback to %s.\n", req,
               num_channels, mp_chmap_to_str(&ao->channels));
    }

    // Some ALSA drivers have broken delay reporting, so disable the ALSA
    // resampling plugin by default.
    if (!p->cfg_resample) {
        err = snd_pcm_hw_params_set_rate_resample(p->alsa, alsa_hwparams, 0);
        CHECK_ALSA_ERROR("Unable to disable resampling");
    }

    err = snd_pcm_hw_params_set_rate_near
            (p->alsa, alsa_hwparams, &ao->samplerate, NULL);
    CHECK_ALSA_ERROR("Unable to set samplerate-2");

    err = snd_pcm_hw_params_set_buffer_time_near
            (p->alsa, alsa_hwparams, &(unsigned int){BUFFER_TIME}, NULL);
    CHECK_ALSA_WARN("Unable to set buffer time near");

    err = snd_pcm_hw_params_set_periods_near
            (p->alsa, alsa_hwparams, &(unsigned int){FRAGCOUNT}, NULL);
    CHECK_ALSA_WARN("Unable to set periods");

    /* finally install hardware parameters */
    err = snd_pcm_hw_params(p->alsa, alsa_hwparams);
    CHECK_ALSA_ERROR("Unable to set hw-parameters");

    /* end setting hw-params */

#if HAVE_CHMAP_API
    if (mp_chmap_is_valid(&dev_chmap)) {
        snd_pcm_chmap_t *alsa_chmap =
            calloc(1, sizeof(*alsa_chmap) +
                      sizeof(alsa_chmap->pos[0]) * dev_chmap.num);
        if (!alsa_chmap)
            goto alsa_error;

        alsa_chmap->channels = dev_chmap.num;
        for (int c = 0; c < dev_chmap.num; c++)
            alsa_chmap->pos[c] = find_alsa_channel(dev_chmap.speaker[c]);

        // mpv and ALSA use different conventions for mono
        if (dev_chmap.num == 1 && dev_chmap.speaker[0] == MP_SP(FC))
            alsa_chmap->pos[0] = SND_CHMAP_MONO;

        char tmp[128];
        if (snd_pcm_chmap_print(alsa_chmap, sizeof(tmp), tmp) > 0)
            MP_VERBOSE(ao, "trying to set ALSA channel map: %s\n", tmp);

        err = snd_pcm_set_chmap(p->alsa, alsa_chmap);
        if (err == -ENXIO) {
            // A device my not be able to set any channel map, even channel maps
            // that were reported as supported. This is either because the ALSA
            // device is broken (dmix), or because the driver has only 1
            // channel map per channel count, and setting the map is not needed.
            MP_VERBOSE(ao, "device returned ENXIO when setting channel map %s\n",
                       mp_chmap_to_str(&dev_chmap));
        } else {
            CHECK_ALSA_WARN("Channel map setup failed");
        }

        free(alsa_chmap);
    }

    snd_pcm_chmap_t *alsa_chmap = snd_pcm_get_chmap(p->alsa);
    if (alsa_chmap) {
        char tmp[128];
        if (snd_pcm_chmap_print(alsa_chmap, sizeof(tmp), tmp) > 0)
            MP_VERBOSE(ao, "channel map reported by ALSA: %s\n", tmp);

        struct mp_chmap chmap;
        mp_chmap_from_alsa(&chmap, alsa_chmap);

        MP_VERBOSE(ao, "which we understand as: %s\n", mp_chmap_to_str(&chmap));

        if (p->cfg_ignore_chmap) {
            MP_VERBOSE(ao, "user set ignore-chmap; ignoring the channel map.\n");
        } else if (af_fmt_is_spdif(ao->format)) {
            MP_VERBOSE(ao, "using spdif passthrough; ignoring the channel map.\n");
        } else if (mp_chmap_is_valid(&chmap)) {
            // Is it one that contains NA channels?
            struct mp_chmap without_na = chmap;
            mp_chmap_remove_na(&without_na);

            if (mp_chmap_is_valid(&without_na) &&
                !mp_chmap_equals(&without_na, &chmap) &&
                !mp_chmap_equals(&chmap, &ao->channels) &&
                !second_try)
            {
                // Sometimes, ALSA will advertise certain chmaps, but it's not
                // possible to set them. This can happen with dmix: as of
                // alsa 1.0.28, dmix can do stereo only, but advertises the
                // surround chmaps of the underlying device. In this case,
                // e.g. setting 6 channels will succeed, but requesting  5.1
                // afterwards will fail. Then it will return something like
                // "FL FR NA NA NA NA" as channel map. This means we would
                // have to pad stereo output to 6 channels with silence, which
                // would require lots of extra processing. You can't change
                // the number of channels to 2 either, because the hw params
                // are already set! So just fuck it and reopen the device with
                // the chmap "cleaned out" of NA entries.
                MP_VERBOSE(ao, "Working around braindead ALSA behavior.\n");
                err = snd_pcm_close(p->alsa);
                p->alsa = NULL;
                CHECK_ALSA_ERROR("pcm close error");
                ao->channels = without_na;
                return INIT_BRAINDEATH;
            }

            if (mp_chmap_equals(&chmap, &ao->channels)) {
                MP_VERBOSE(ao, "which is what we requested.\n");
            } else if (chmap.num == ao->channels.num) {
                MP_VERBOSE(ao, "using the ALSA channel map.\n");
                ao->channels = chmap;
            } else {
                MP_WARN(ao, "ALSA channel map conflicts with channel count!\n");
            }
        } else {
            MP_WARN(ao, "Got unknown channel map from ALSA.\n");
        }

        // mpv and ALSA use different conventions for mono
        if (ao->channels.num == 1) {
            MP_VERBOSE(ao, "assuming we actually got MONO from ALSA.\n");
            ao->channels.speaker[0] = MP_SP(FC);
        }

        free(alsa_chmap);
    }
#endif

    snd_pcm_uframes_t bufsize;
    err = snd_pcm_hw_params_get_buffer_size(alsa_hwparams, &bufsize);
    CHECK_ALSA_ERROR("Unable to get buffersize");

    p->buffersize = bufsize;
    MP_VERBOSE(ao, "got buffersize=%i samples\n", p->buffersize);

    snd_pcm_uframes_t chunk_size;
    err = snd_pcm_hw_params_get_period_size(alsa_hwparams, &chunk_size, NULL);
    CHECK_ALSA_ERROR("Unable to get period size");

    MP_VERBOSE(ao, "got period size %li\n", chunk_size);
    p->outburst = chunk_size;

    /* setting software parameters */
    err = snd_pcm_sw_params_current(p->alsa, alsa_swparams);
    CHECK_ALSA_ERROR("Unable to get sw-parameters");

    snd_pcm_uframes_t boundary;
    err = snd_pcm_sw_params_get_boundary(alsa_swparams, &boundary);
    CHECK_ALSA_ERROR("Unable to get boundary");

    /* start playing when one period has been written */
    err = snd_pcm_sw_params_set_start_threshold
            (p->alsa, alsa_swparams, chunk_size);
    CHECK_ALSA_ERROR("Unable to set start threshold");

    /* disable underrun reporting */
    err = snd_pcm_sw_params_set_stop_threshold
            (p->alsa, alsa_swparams, boundary);
    CHECK_ALSA_ERROR("Unable to set stop threshold");

    /* play silence when there is an underrun */
    err = snd_pcm_sw_params_set_silence_size
            (p->alsa, alsa_swparams, boundary);
    CHECK_ALSA_ERROR("Unable to set silence size");

    err = snd_pcm_sw_params(p->alsa, alsa_swparams);
    CHECK_ALSA_ERROR("Unable to set sw-parameters");

    /* end setting sw-params */

    p->can_pause = snd_pcm_hw_params_can_pause(alsa_hwparams);
    if (p->can_pause)
        MP_VERBOSE(ao, "pausing supported by device\n");

    return INIT_OK;

alsa_error:
    uninit(ao);
    return INIT_ERROR;
}

static int init(struct ao *ao)
{
    struct priv *p = ao->priv;
    if (!p->cfg_ni)
        ao->format = af_fmt_from_planar(ao->format);

    MP_VERBOSE(ao, "using ALSA version: %s\n", snd_asoundlib_version());

    int r = init_device(ao, false);
    if (r == INIT_BRAINDEATH)
        r = init_device(ao, true); // retry with normalized channel layout
    return r == INIT_OK ? 0 : -1;
}

static void drain(struct ao *ao)
{
    struct priv *p = ao->priv;
    snd_pcm_drain(p->alsa);
}

static in