vlc/modules/audio_output/coreaudio_common.c

/*****************************************************************************
 * coreaudio_common.c: Common AudioUnit code for iOS and macOS
 *****************************************************************************
 * Copyright (C) 2005 - 2017 VLC authors and VideoLAN
 *
 * Authors: Derk-Jan Hartman <hartman at videolan dot org>
 *          Felix Paul Kühne <fkuehne at videolan dot org>
 *          David Fuhrmann <david dot fuhrmann at googlemail dot com>
 *
 * This program 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.
 *
 * This program 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

#import "coreaudio_common.h"
#import <CoreAudio/CoreAudioTypes.h>

static inline uint64_t
BytesToFrames(struct aout_sys_common *p_sys, size_t i_bytes)
{
    return i_bytes * p_sys->i_frame_length / p_sys->i_bytes_per_frame;
}

static inline mtime_t
FramesToUs(struct aout_sys_common *p_sys, uint64_t i_nb_frames)
{
    return i_nb_frames * CLOCK_FREQ / p_sys->i_rate;
}

static inline size_t
FramesToBytes(struct aout_sys_common *p_sys, uint64_t i_frames)
{
    return i_frames * p_sys->i_bytes_per_frame / p_sys->i_frame_length;
}

static inline uint64_t
UsToFrames(struct aout_sys_common *p_sys, vlc_tick_t i_us)
{
    return i_us * p_sys->i_rate / CLOCK_FREQ;
}

static inline mtime_t
HostTimeToTick(struct aout_sys_common *p_sys, uint64_t i_host_time)
{
    return i_host_time * p_sys->tinfo.numer / p_sys->tinfo.denom / 1000;
}

static inline uint64_t
TickToHostTime(struct aout_sys_common *p_sys, vlc_tick_t i_us)
{
    return i_us * 1000 * p_sys->tinfo.denom / p_sys->tinfo.numer;
}

static void
ca_ClearOutBuffers(audio_output_t *p_aout)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    block_ChainRelease(p_sys->p_out_chain);
    p_sys->p_out_chain = NULL;
    p_sys->pp_out_last = &p_sys->p_out_chain;

    p_sys->i_out_size = 0;
}

static void
lock_init(struct aout_sys_common *p_sys)
{
    if (likely(os_unfair_lock_lock))
        p_sys->lock.unfair = OS_UNFAIR_LOCK_INIT;
    else
        vlc_mutex_init(&p_sys->lock.mutex);
}

static inline void
lock_destroy(struct aout_sys_common *p_sys)
{
    if (unlikely(!os_unfair_lock_lock))
        vlc_mutex_destroy(&p_sys->lock.mutex);
}

static inline void
lock_lock(struct aout_sys_common *p_sys)
{
    if (likely(os_unfair_lock_lock))
        os_unfair_lock_lock(&p_sys->lock.unfair);
    else
        vlc_mutex_lock(&p_sys->lock.mutex);
}

static inline void
lock_unlock(struct aout_sys_common *p_sys)
{
    if (likely(os_unfair_lock_lock))
        os_unfair_lock_unlock(&p_sys->lock.unfair);
    else
        vlc_mutex_unlock(&p_sys->lock.mutex);
}

int
ca_Open(audio_output_t *p_aout)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    if (mach_timebase_info(&p_sys->tinfo) != KERN_SUCCESS)
        return VLC_EGENERIC;

    assert(p_sys->tinfo.denom != 0 && p_sys->tinfo.numer != 0);

    vlc_sem_init(&p_sys->flush_sem, 0);
    lock_init(p_sys);
    p_sys->p_out_chain = NULL;
    p_sys->pp_out_last = &p_sys->p_out_chain;
    p_sys->chans_to_reorder = 0;

    p_aout->play = ca_Play;
    p_aout->pause = ca_Pause;
    p_aout->flush = ca_Flush;
    p_aout->time_get = ca_TimeGet;

    return VLC_SUCCESS;
}

void
ca_Close(audio_output_t *p_aout)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    vlc_sem_destroy(&p_sys->flush_sem);
    lock_destroy(p_sys);
}

/* Called from render callbacks. No lock, wait, and IO here */
void
ca_Render(audio_output_t *p_aout, uint32_t i_frames, uint64_t i_host_time,
          uint8_t *p_output, size_t i_requested)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    lock_lock(p_sys);

    if (p_sys->b_do_flush)
    {
        ca_ClearOutBuffers(p_aout);
        /* Signal that the renderer is flushed */
        p_sys->b_do_flush = false;
        vlc_sem_post(&p_sys->flush_sem);
    }

    if (unlikely(p_sys->i_first_render_host_time == 0))
        goto drop;

    if (p_sys->b_paused)
    {
        p_sys->i_render_host_time = i_host_time;
        goto drop;
    }

    /* Start deferred: write silence (zeros) until we reach the first render
     * host time. */
    if (unlikely(p_sys->i_first_render_host_time > i_host_time ))
    {
        /* Convert the requested bytes into host time and check that it does
         * not overlap between the first_render host time and the current one.
         * */
        const size_t i_requested_us =
            FramesToUs(p_sys, BytesToFrames(p_sys, i_requested));
        const uint64_t i_requested_host_time =
            TickToHostTime(p_sys, i_requested_us);
        if (p_sys->i_first_render_host_time >= i_host_time + i_requested_host_time)
        {
            /* Fill the buffer with silence */
            goto drop;
        }

        /* Write silence to reach the first_render host time */
        const vlc_tick_t i_silence_us =
            HostTimeToTick(p_sys, p_sys->i_first_render_host_time - i_host_time);

        const uint64_t i_silence_bytes =
            FramesToBytes(p_sys, UsToFrames(p_sys, i_silence_us));
        assert(i_silence_bytes <= i_requested);
        memset(p_output, 0, i_silence_bytes);

        i_requested -= i_silence_bytes;
        p_output += i_silence_bytes;

        /* Start the first rendering */
    }

    p_sys->i_render_host_time = i_host_time;
    p_sys->i_render_frames = i_frames;

    size_t i_copied = 0;
    block_t *p_block = p_sys->p_out_chain;
    while (p_block != NULL && i_requested != 0)
    {
        size_t i_tocopy = __MIN(i_requested, p_block->i_buffer);
        memcpy(p_output, p_block->p_buffer, i_tocopy);
        i_requested -= i_tocopy;
        i_copied += i_tocopy;
        p_output += i_tocopy;

        if (i_tocopy == p_block->i_buffer)
        {
            block_t *p_release = p_block;
            p_block = p_block->p_next;
            block_Release(p_release);
        }
        else
        {
            assert(i_requested == 0);

            p_block->p_buffer += i_tocopy;
            p_block->i_buffer -= i_tocopy;
        }
    }
    p_sys->p_out_chain = p_block;
    if (!p_sys->p_out_chain)
        p_sys->pp_out_last = &p_sys->p_out_chain;
    p_sys->i_out_size -= i_copied;

    /* Pad with 0 */
    if (i_requested > 0)
    {
        assert(p_sys->i_out_size == 0);
        p_sys->i_underrun_size += i_requested;
        memset(p_output, 0, i_requested);
    }

    lock_unlock(p_sys);
    return;

drop:
    memset(p_output, 0, i_requested);
    lock_unlock(p_sys);
}

static mtime_t
ca_GetLatencyLocked(audio_output_t *p_aout)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    const int64_t i_out_frames = BytesToFrames(p_sys, p_sys->i_out_size);
    return FramesToUs(p_sys, i_out_frames + p_sys->i_render_frames)
           + p_sys->i_dev_latency_us;
}

int
ca_TimeGet(audio_output_t *p_aout, vlc_tick_t *delay)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    lock_lock(p_sys);

    if (p_sys->i_render_host_time == 0 || p_sys->i_first_render_host_time == 0)
    {
        /* Not yet started (or reached the first_render host time) */
        lock_unlock(p_sys);
        return -1;
    }

    const vlc_tick_t i_render_time_us =
        HostTimeToTick(p_sys, p_sys->i_render_host_time);
    const vlc_tick_t i_render_delay = i_render_time_us - mdate();

    *delay = ca_GetLatencyLocked(p_aout) + i_render_delay;
    lock_unlock(p_sys);
    return 0;
}

void
ca_Flush(audio_output_t *p_aout, bool wait)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    lock_lock(p_sys);
    if (wait)
    {
        while (p_sys->i_out_size > 0)
        {
            if (p_sys->b_paused)
            {
                ca_ClearOutBuffers(p_aout);
                break;
            }

            /* Calculate the duration of the circular buffer, in order to wait
             * for the render thread to play it all */
            const vlc_tick_t i_frame_us =
                FramesToUs(p_sys, BytesToFrames(p_sys, p_sys->i_out_size)) + 10000;
            lock_unlock(p_sys);
            msleep(i_frame_us);
            lock_lock(p_sys);
        }
    }
    else
    {
        assert(!p_sys->b_do_flush);
        if (p_sys->b_paused)
            ca_ClearOutBuffers(p_aout);
        else
        {
            p_sys->b_do_flush = true;
            lock_unlock(p_sys);
            vlc_sem_wait(&p_sys->flush_sem);
            lock_lock(p_sys);
        }
    }

    p_sys->i_render_host_time = p_sys->i_first_render_host_time = 0;
    p_sys->i_render_frames = 0;
    lock_unlock(p_sys);

    p_sys->b_played = false;
}

void
ca_Pause(audio_output_t * p_aout, bool pause, vlc_tick_t date)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;
    VLC_UNUSED(date);

    lock_lock(p_sys);
    p_sys->b_paused = pause;
    lock_unlock(p_sys);
}

void
ca_Play(audio_output_t * p_aout, block_t * p_block)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    /* Do the channel reordering */
    if (p_sys->chans_to_reorder)
       aout_ChannelReorder(p_block->p_buffer, p_block->i_buffer,
                           p_sys->chans_to_reorder, p_sys->chan_table,
                           VLC_CODEC_FL32);

    lock_lock(p_sys);

    if (p_sys->i_render_host_time == 0)
    {
        /* Setup the first render time, this date must be updated until the
         * first (non-silence/zero) frame is rendered by the render callback.
         * Once the rendering is truly started, the date can be ignored. */

        const vlc_tick_t first_render_time = p_block->i_pts - ca_GetLatencyLocked(p_aout);
        p_sys->i_first_render_host_time =
            TickToHostTime(p_sys, first_render_time);
    }

    do
    {
        const size_t i_avalaible_bytes =
            __MIN(p_block->i_buffer, p_sys->i_out_max_size - p_sys->i_out_size);

        if (unlikely(i_avalaible_bytes != p_block->i_buffer))
        {
            /* Not optimal but unlikely code path. */

            lock_unlock(p_sys);

            block_t *p_new = block_Alloc(i_avalaible_bytes);
            if (!p_new)
            {
                block_Release(p_block);
                return;
            }

            memcpy(p_new->p_buffer, p_block->p_buffer, i_avalaible_bytes);

            p_block->p_buffer += i_avalaible_bytes;
            p_block->i_buffer -= i_avalaible_bytes;

            lock_lock(p_sys);

            block_ChainLastAppend(&p_sys->pp_out_last, p_new);
            p_sys->i_out_size += i_avalaible_bytes;

            if (p_sys->b_paused)
            {
                lock_unlock(p_sys);
                block_Release(p_block);
                return;
            }

            const vlc_tick_t i_frame_us =
                FramesToUs(p_sys, BytesToFrames(p_sys, p_block->i_buffer));

            /* Wait for the render buffer to play the remaining data */
            lock_unlock(p_sys);
            msleep(i_frame_us);
            lock_lock(p_sys);
        }
        else
        {
            block_ChainLastAppend(&p_sys->pp_out_last, p_block);
            p_sys->i_out_size += i_avalaible_bytes;
            p_block = NULL;
        }
    } while (p_block != NULL);

    size_t i_underrun_size = p_sys->i_underrun_size;
    p_sys->i_underrun_size = 0;

    lock_unlock(p_sys);

    if (!p_sys->b_played)
        p_sys->b_played = true;
    else if (i_underrun_size > 0)
        msg_Warn(p_aout, "underrun of %zu bytes", i_underrun_size);
}

int
ca_Initialize(audio_output_t *p_aout, const audio_sample_format_t *fmt,
              vlc_tick_t i_dev_latency_us)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    p_sys->i_underrun_size = 0;
    p_sys->b_paused = false;
    p_sys->i_render_host_time = p_sys->i_first_render_host_time = 0;
    p_sys->i_render_frames = 0;

    p_sys->i_rate = fmt->i_rate;
    p_sys->i_bytes_per_frame = fmt->i_bytes_per_frame;
    p_sys->i_frame_length = fmt->i_frame_length;

    /* TODO VLC can't handle latency higher than 1 seconds */
    if (i_dev_latency_us > 1000000)
    {
        i_dev_latency_us = 1000000;
        msg_Warn(p_aout, "VLC can't handle this device latency, lowering it to "
                 "%lld", i_dev_latency_us);
    }
    p_sys->i_dev_latency_us = i_dev_latency_us;

    /* setup circular buffer */
    size_t i_audiobuffer_size = fmt->i_rate * fmt->i_bytes_per_frame
                              / p_sys->i_frame_length;
    if (fmt->channel_type == AUDIO_CHANNEL_TYPE_AMBISONICS)
    {
        /* lower latency: 200 ms of buffering. XXX: Decrease when VLC's core
         * can handle lower audio latency */
        p_sys->i_out_max_size = i_audiobuffer_size / 5;
    }
    else
    {
        /* 2 seconds of buffering */
        p_sys->i_out_max_size = i_audiobuffer_size * 2;
    }

    ca_ClearOutBuffers(p_aout);
    p_sys->b_played = false;

    return VLC_SUCCESS;
}

void
ca_Uninitialize(audio_output_t *p_aout)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;
    ca_ClearOutBuffers(p_aout);
    p_sys->i_out_max_size = 0;
    p_sys->chans_to_reorder = 0;
}

void
ca_SetAliveState(audio_output_t *p_aout, bool alive)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    lock_lock(p_sys);

    bool b_sem_post = false;
    p_sys->b_paused = !alive;
    if (!alive && p_sys->b_do_flush)
    {
        ca_ClearOutBuffers(p_aout);
        p_sys->b_played = false;
        p_sys->b_do_flush = false;
        b_sem_post = true;
    }

    lock_unlock(p_sys);

    if (b_sem_post)
        vlc_sem_post(&p_sys->flush_sem);
}

void ca_SetDeviceLatency(audio_output_t *p_aout, vlc_tick_t i_dev_latency_us)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;

    lock_lock(p_sys);
    /* cf. TODO in ca_Initialize */
    p_sys->i_dev_latency_us = i_dev_latency_us > 1000000 ? 1000000 : i_dev_latency_us;
    lock_unlock(p_sys);
}

AudioUnit
au_NewOutputInstance(audio_output_t *p_aout, OSType comp_sub_type)
{
    AudioComponentDescription desc = {
        .componentType = kAudioUnitType_Output,
        .componentSubType = comp_sub_type,
        .componentManufacturer = kAudioUnitManufacturer_Apple,
        .componentFlags = 0,
        .componentFlagsMask = 0,
    };

    AudioComponent au_component;
    au_component = AudioComponentFindNext(NULL, &desc);
    if (au_component == NULL)
    {
        msg_Err(p_aout, "cannot find any AudioComponent, PCM output failed");
        return NULL;
    }

    AudioUnit au;
    OSStatus err = AudioComponentInstanceNew(au_component, &au);
    if (err != noErr)
    {
        ca_LogErr("cannot open AudioComponent, PCM output failed");
        return NULL;
    }
    return au;
}

/*****************************************************************************
 * RenderCallback: This function is called every time the AudioUnit wants
 * us to provide some more audio data.
 * Don't print anything during normal playback, calling blocking function from
 * this callback is not allowed.
 *****************************************************************************/
static OSStatus
RenderCallback(void *p_data, AudioUnitRenderActionFlags *ioActionFlags,
               const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber,
               UInt32 inNumberFrames, AudioBufferList *ioData)
{
    VLC_UNUSED(ioActionFlags);
    VLC_UNUSED(inTimeStamp);
    VLC_UNUSED(inBusNumber);

    uint64_t i_host_time = (inTimeStamp->mFlags & kAudioTimeStampHostTimeValid)
                         ? inTimeStamp->mHostTime : 0;

    ca_Render(p_data, inNumberFrames, i_host_time, ioData->mBuffers[0].mData,
              ioData->mBuffers[0].mDataByteSize);

    return noErr;
}

static AudioChannelLayout *
GetLayoutDescription(audio_output_t *p_aout,
                     const AudioChannelLayout *outlayout)
{
    AudioFormatPropertyID id;
    UInt32 size;
    const void *data;
    /* We need to "fill out" the ChannelLayout, because there are multiple
     * ways that it can be set */
    if (outlayout->mChannelLayoutTag == kAudioChannelLayoutTag_UseChannelBitmap)
    {
        id = kAudioFormatProperty_ChannelLayoutForBitmap;
        size = sizeof(UInt32);
        data = &outlayout->mChannelBitmap;
    }
    else
    {
        id = kAudioFormatProperty_ChannelLayoutForTag;
        size = sizeof(AudioChannelLayoutTag);
        data = &outlayout->mChannelLayoutTag;
    }

    UInt32 param_size;
    OSStatus err = AudioFormatGetPropertyInfo(id, size, data, &param_size);
    if (err != noErr)
        return NULL;

    AudioChannelLayout *reslayout = malloc(param_size);
    if (reslayout == NULL)
        return NULL;

    err = AudioFormatGetProperty(id, size, data, &param_size, reslayout);
    if (err != noErr || reslayout->mNumberChannelDescriptions == 0)
    {
        msg_Err(p_aout, "insufficient number of output channels");
        free(reslayout);
        return NULL;
    }

    return reslayout;
}

static unsigned
AudioChannelLabelToVlcChan(AudioChannelLabel chan, bool swap_rear_surround)
{
    /* maps auhal channels to vlc ones */
    switch (chan)
    {
        case kAudioChannelLabel_Left:
            return AOUT_CHAN_LEFT;
        case kAudioChannelLabel_Right:
            return AOUT_CHAN_RIGHT;
        case kAudioChannelLabel_Center:
            return AOUT_CHAN_CENTER;
        case kAudioChannelLabel_LFEScreen:
            return AOUT_CHAN_LFE;
        case kAudioChannelLabel_LeftSurround:
            return swap_rear_surround ? AOUT_CHAN_MIDDLELEFT
                                      : AOUT_CHAN_REARLEFT;
        case kAudioChannelLabel_RightSurround:
            return swap_rear_surround ? AOUT_CHAN_MIDDLERIGHT
                                      : AOUT_CHAN_REARRIGHT;
        case kAudioChannelLabel_RearSurroundLeft:
            return swap_rear_surround ? AOUT_CHAN_REARLEFT
                                      : AOUT_CHAN_MIDDLELEFT;
        case kAudioChannelLabel_RearSurroundRight:
            return swap_rear_surround ? AOUT_CHAN_REARRIGHT
                                      : AOUT_CHAN_MIDDLERIGHT;
        case kAudioChannelLabel_CenterSurround:
            return AOUT_CHAN_REARCENTER;
        case kAudioChannelLabel_LeftSurroundDirect:
            return AOUT_CHAN_MIDDLELEFT;
        case kAudioChannelLabel_RightSurroundDirect:
            return AOUT_CHAN_MIDDLERIGHT;
        default:
            return 0;
    }
}

static AudioChannelLabel
VlcChanToAudioChannelLabel(unsigned chan, bool swap_rear_surround)
{
    /* maps auhal channels to vlc ones */
    switch (chan)
    {
        case AOUT_CHAN_LEFT:
            return kAudioChannelLabel_Left;
        case AOUT_CHAN_RIGHT:
            return kAudioChannelLabel_Right;
        case AOUT_CHAN_CENTER:
            return kAudioChannelLabel_Center;
        case AOUT_CHAN_LFE:
            return kAudioChannelLabel_LFEScreen;
        case AOUT_CHAN_REARLEFT:
            return swap_rear_surround ? kAudioChannelLabel_RearSurroundLeft
                                      : kAudioChannelLabel_LeftSurround;
        case AOUT_CHAN_REARRIGHT:
            return swap_rear_surround ? kAudioChannelLabel_RearSurroundRight
                                      : kAudioChannelLabel_RightSurround;
        case AOUT_CHAN_MIDDLELEFT:
            return swap_rear_surround ? kAudioChannelLabel_LeftSurround
                                      : kAudioChannelLabel_RearSurroundLeft;
        case AOUT_CHAN_MIDDLERIGHT:
            return swap_rear_surround ? kAudioChannelLabel_RightSurround
                                      : kAudioChannelLabel_RearSurroundRight;
        case AOUT_CHAN_REARCENTER:
            return kAudioChannelLabel_CenterSurround;
        default:
            vlc_assert_unreachable();
    }
}

static int
MapOutputLayout(audio_output_t *p_aout, audio_sample_format_t *fmt,
                const AudioChannelLayout *outlayout, bool *warn_configuration)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;
    /* Fill VLC physical_channels from output layout */
    uint32_t i_original = fmt->i_physical_channels;
    fmt->i_physical_channels = 0;
    AudioChannelLayout *reslayout = NULL;
    assert(outlayout != NULL);

    if (outlayout->mChannelLayoutTag !=
        kAudioChannelLayoutTag_UseChannelDescriptions)
    {
        reslayout = GetLayoutDescription(p_aout, outlayout);
        if (reslayout == NULL)
            return VLC_EGENERIC;
        outlayout = reslayout;
    }

    if (i_original == AOUT_CHAN_CENTER
     || outlayout->mNumberChannelDescriptions < 2)
    {
        /* We only need Mono or cannot output more than 1 channel */
        fmt->i_physical_channels = AOUT_CHAN_CENTER;
        msg_Dbg(p_aout, "output layout of AUHAL has 1 channel");
    }
    else if (i_original == (AOUT_CHAN_LEFT | AOUT_CHAN_RIGHT)
          || outlayout->mNumberChannelDescriptions < 3)
    {
        /* We only need Stereo or cannot output more than 2 channels */
        fmt->i_physical_channels = AOUT_CHANS_STEREO;
        msg_Dbg(p_aout, "output layout of AUHAL is Stereo");
    }
    else
    {
        assert(outlayout->mNumberChannelDescriptions > 0);

        msg_Dbg(p_aout, "output layout of AUHAL has %i channels",
                outlayout->mNumberChannelDescriptions);
        uint32_t chans_out[AOUT_CHAN_MAX];

        /* For 7.1, AOUT_CHAN_MIDDLELEFT/RIGHT needs to be swapped with
         * AOUT_CHAN_REARLEFT/RIGHT. Auhal
         * kAudioChannelLabel_Left/RightSurround are used as surround for 5.1,
         * but as middle speakers for rear 7.1. */
        unsigned swap_rear_surround = 0;
        if (outlayout->mNumberChannelDescriptions == 8)
        {
            for (unsigned i = 0; i < outlayout->mNumberChannelDescriptions; i++)
            {
                AudioChannelLabel chan =
                    outlayout->mChannelDescriptions[i].mChannelLabel;
                if (chan == kAudioChannelLabel_RearSurroundLeft
                 || chan == kAudioChannelLabel_RearSurroundRight)
                    swap_rear_surround++;
            }
            if (swap_rear_surround == 2)
                msg_Dbg(p_aout, "swapping Surround and RearSurround channels "
                        "for 7.1 Rear Surround");
        }

        size_t chans_out_idx = 0;
        for (unsigned i = 0; i < outlayout->mNumberChannelDescriptions; i++)
        {
            AudioChannelLabel chan =
                outlayout->mChannelDescriptions[i].mChannelLabel;
#ifndef NDEBUG
            msg_Dbg(p_aout, "this is channel: %d", (int) chan);
#endif
            unsigned mapped_chan =
                AudioChannelLabelToVlcChan(chan, swap_rear_surround == 2);
            if (mapped_chan != 0)
            {
                chans_out[chans_out_idx++] = mapped_chan;
                fmt->i_physical_channels |= mapped_chan;
            }
            else
                msg_Dbg(p_aout, "found nonrecognized channel %d at index "
                        "%d", chan, i);
        }
        if (fmt->i_physical_channels == 0)
        {
            fmt->i_physical_channels = AOUT_CHANS_STEREO;
            if (warn_configuration)
                *warn_configuration = true;
        }
        else
        {
            p_sys->chans_to_reorder =
                aout_CheckChannelReorder(NULL, chans_out,
                                         fmt->i_physical_channels,
                                         p_sys->chan_table);
            if (p_sys->chans_to_reorder)
                msg_Dbg(p_aout, "channel reordering needed");
        }
    }

    free(reslayout);
    aout_FormatPrepare(fmt);

    msg_Dbg(p_aout, "VLC will output: %s", aout_FormatPrintChannels(fmt));

    return VLC_SUCCESS;
}

static int
MapInputLayout(audio_output_t *p_aout, const audio_sample_format_t *fmt,
               AudioChannelLayout **inlayoutp, size_t *inlayout_size)
{
    struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;
    uint32_t chans_out[AOUT_CHAN_MAX] = { 0, };

    unsigned channels = aout_FormatNbChannels(fmt);

    size_t size;
    if (mul_overflow(channels, sizeof(AudioChannelDescription), &size))
        return VLC_ENOMEM;
    if (add_overflow(size, sizeof(AudioChannelLayout), &size))
        return VLC_ENOMEM;
    AudioChannelLayout *inlayout = malloc(size);
    if (inlayout == NULL)
        return VLC_ENOMEM;

    *inlayoutp = inlayout;
    *inlayout_size = size;
    inlayout->mChannelLayoutTag = kAudioChannelLayoutTag_UseChannelDescriptions;
    inlayout->mNumberChannelDescriptions = aout_FormatNbChannels(fmt);

    bool swap_rear_surround = (fmt->i_physical_channels & AOUT_CHANS_7_0) == AOUT_CHANS_7_0;
    if (swap_rear_surround)
        msg_Dbg(p_aout, "swapping Surround and RearSurround channels "
                "for 7.1 Rear Surround");
    unsigned chan_idx = 0;
    for (unsigned i = 0; i < AOUT_CHAN_MAX; ++i)
    {
        unsigned vlcchan = pi_vlc_chan_order_wg4[i];
        if ((vlcchan & fmt->i_physical_channels) == 0)
            continue;

        inlayout->mChannelDescriptions[chan_idx].mChannelLabel =
            VlcChanToAudioChannelLabel(vlcchan, swap_rear_surround);
        inlayout->mChannelDescriptions[chan_idx].mChannelFlags =
            kAudioChannelFlags_AllOff;
        chan_idx++;
    }

    msg_Dbg(p_aout, "VLC keeping the same input layout");

    return VLC_SUCCESS;
}

int
au_Initialize(audio_output_t *p_aout, AudioUnit au, audio_sample_format_t *fmt,
              const AudioChannelLayout *outlayout, vlc_tick_t i_dev_latency_us,
              bool *warn_configuration)
{
    int ret;
    AudioChannelLayout *inlayout_buf = NULL;
    const AudioChannelLayout *inlayout = NULL;
    size_t inlayout_size = 0;

    if (warn_configuration)
        *warn_configuration = false;

    /* Set the desired format */
    AudioStreamBasicDescription desc;
    if (aout_BitsPerSample(fmt->i_format) != 0)
    {
        /* PCM */
        fmt->i_format = VLC_CODEC_FL32;
        if (outlayout != NULL)
        {
            ret = MapOutputLayout(p_aout, fmt, outlayout, warn_configuration);
            if (ret != VLC_SUCCESS)
                return ret;
        }
        else
        {
            aout_FormatPrepare(fmt);
            ret = MapInputLayout(p_aout, fmt, &inlayout_buf, &inlayout_size);
            if (ret != VLC_SUCCESS)
                return ret;
            inlayout = inlayout_buf;
        }

        desc.mFormatFlags = kAudioFormatFlagsNativeFloatPacked;
        desc.mChannelsPerFrame = aout_FormatNbChannels(fmt);
        desc.mBitsPerChannel = 32;
    }
    else if (AOUT_FMT_SPDIF(fmt))
    {
        /* Passthrough */
        fmt->i_format = VLC_CODEC_SPDIFL;
        fmt->i_bytes_per_frame = 4;
        fmt->i_frame_length = 1;

        static const AudioChannelLayout inlayout_spdif = {
            .mChannelLayoutTag = kAudioChannelLayoutTag_Stereo,
        };
        inlayout = &inlayout_spdif;
        inlayout_size = sizeof(inlayout_spdif);

        desc.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger |
                            kLinearPCMFormatFlagIsPacked; /* S16LE */
        desc.mChannelsPerFrame = 2;
        desc.mBitsPerChannel = 16;
    }
    else
        return VLC_EGENERIC;

    desc.mSampleRate = fmt->i_rate;
    desc.mFormatID = kAudioFormatLinearPCM;
    desc.mFramesPerPacket = 1;
    desc.mBytesPerFrame = desc.mBitsPerChannel * desc.mChannelsPerFrame / 8;
    desc.mBytesPerPacket = desc.mBytesPerFrame * desc.mFramesPerPacket;

    OSStatus err = AudioUnitSetProperty(au, kAudioUnitProperty_StreamFormat,
                                        kAudioUnitScope_Input, 0, &desc,
                                        sizeof(desc));
    if (err != noErr)
    {
        ca_LogErr("failed to set stream format");
        free(inlayout_buf);
        return VLC_EGENERIC;
    }
    msg_Dbg(p_aout, STREAM_FORMAT_MSG("Current AU format: " , desc));

    /* Retrieve actual format */
    err = AudioUnitGetProperty(au, kAudioUnitProperty_StreamFormat,
                               kAudioUnitScope_Input, 0, &desc,
                               &(UInt32) { sizeof(desc) });
    if (err != noErr)
    {
        ca_LogErr("failed to set stream format");
        free(inlayout_buf);
        return VLC_EGENERIC;
    }

    /* Set the IOproc callback */
    const AURenderCallbackStruct callback = {
        .inputProc = RenderCallback,
        .inputProcRefCon = p_aout,
    };

    err = AudioUnitSetProperty(au, kAudioUnitProperty_SetRenderCallback,
                               kAudioUnitScope_Input, 0, &callback,
                               sizeof(callback));
    if (err != noErr)
    {
        ca_LogErr("failed to setup render callback");
        free(inlayout_buf);
        return VLC_EGENERIC;
    }

    if (inlayout != NULL)
    {
        /* Set the input_layout as the layout VLC will use to feed the AU unit.
         * Yes, it must be the INPUT scope */
        err = AudioUnitSetProperty(au, kAudioUnitProperty_AudioChannelLayout,
                                   kAudioUnitScope_Input, 0, inlayout,
                                   inlayout_size);
        free(inlayout_buf);
        if (err != noErr)
        {
            ca_LogErr("failed to setup input layout");
            return VLC_EGENERIC;
        }
    }

    /* AU init */
    err = AudioUnitInitialize(au);

    if (err != noErr)
    {
        ca_LogErr("AudioUnitInitialize failed");
        return VLC_EGENERIC;
    }

    ret = ca_Initialize(p_aout, fmt, i_dev_latency_us);
    if (ret != VLC_SUCCESS)
    {
        AudioUnitUninitialize(au);
        return VLC_EGENERIC;
    }

    return VLC_SUCCESS;
}

void
au_Uninitialize(audio_output_t *p_aout, AudioUnit au)
{
    OSStatus err = AudioUnitUninitialize(au);
    if (err != noErr)
        ca_LogWarn("AudioUnitUninitialize failed");

    ca_Uninitialize(p_aout);
}