/*****************************************************************************
 * audio.c: audio decoder using libavcodec library
 *****************************************************************************
 * Copyright (C) 1999-2003 VLC authors and VideoLAN
 *
 * Authors: Laurent Aimar <fenrir@via.ecp.fr>
 *          Gildas Bazin <gbazin@videolan.org>
 *
 * 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.
 *****************************************************************************/

/*****************************************************************************
 * Preamble
 *****************************************************************************/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>

#include <vlc_common.h>
#include <vlc_aout.h>
#include <vlc_codec.h>
#include <vlc_avcodec.h>

#include "avcodec.h"
#include "../../demux/xiph.h"

#include <stdbit.h>

#include <libavcodec/avcodec.h>
#include <libavutil/mem.h>

#define API_CHANNEL_LAYOUT_STRUCT (LIBAVCODEC_VERSION_CHECK(59, 24, 100)) // AVCodecContext.ch_layout

#include <libavutil/channel_layout.h>


/*****************************************************************************
 * decoder_sys_t : decoder descriptor
 *****************************************************************************/
typedef struct
{
    AVCodecContext *p_context;
    const AVCodec  *p_codec;

    /*
     * Output properties
     */
    audio_sample_format_t aout_format;
    date_t                end_date;

    /* */
    int     i_reject_count;

    /* */
    bool    b_extract;
    bool    discontinuity;
    int     pi_extraction[AOUT_CHAN_MAX];
    int     i_previous_channels;
    uint64_t i_previous_layout;
} decoder_sys_t;

#define BLOCK_FLAG_PRIVATE_REALLOCATED (1 << BLOCK_FLAG_PRIVATE_SHIFT)

static void SetupOutputFormat( decoder_t *p_dec, bool b_trust );
static block_t * ConvertAVFrame( decoder_t *p_dec, AVFrame *frame );
static int  DecodeAudio( decoder_t *, block_t * );
static void Flush( decoder_t * );

static void InitDecoderConfig( decoder_t *p_dec, AVCodecContext *p_context )
{
    if( p_dec->fmt_in->i_extra > 0 )
    {
        const uint8_t * const p_src = p_dec->fmt_in->p_extra;

        int i_offset = 0;
        int i_size = p_dec->fmt_in->i_extra;

        if( p_dec->fmt_in->i_codec == VLC_CODEC_ALAC )
        {
            static const uint8_t p_pattern[] = { 0, 0, 0, 36, 'a', 'l', 'a', 'c' };
            /* Find alac atom XXX it is a bit ugly */
            for( i_offset = 0; i_offset < i_size - (int)sizeof(p_pattern); i_offset++ )
            {
                if( !memcmp( &p_src[i_offset], p_pattern, sizeof(p_pattern) ) )
                    break;
            }
            i_size = __MIN( p_dec->fmt_in->i_extra - i_offset, 36 );
            if( i_size < 36 )
                i_size = 0;
        }
        else if( p_dec->fmt_in->i_codec == VLC_CODEC_OPUS &&
                 i_size > 21 && !memcmp( &p_src[2], "OpusHead", 8 ) )
        {
            /* see opus.c decoder */
            size_t hdr_size[XIPH_MAX_HEADER_COUNT];
            const void *hdr[XIPH_MAX_HEADER_COUNT];
            size_t i_count;
            if( !xiph_SplitHeaders( hdr_size, hdr, &i_count,
                                    i_size, p_src ) && i_count >= 1 )
            {
                i_offset = (const uint8_t *)hdr[0] - p_src;
                i_size = hdr_size[0];
            }
        }

        if( i_size > 0 )
        {
            p_context->extradata =
                av_malloc( i_size + AV_INPUT_BUFFER_PADDING_SIZE );
            if( p_context->extradata )
            {
                uint8_t *p_dst = p_context->extradata;

                p_context->extradata_size = i_size;

                memcpy( &p_dst[0],            &p_src[i_offset], i_size );
                memset( &p_dst[i_size], 0, AV_INPUT_BUFFER_PADDING_SIZE );
            }
        }
    }
    else
    {
        p_context->extradata_size = 0;
        p_context->extradata = NULL;
    }
}

static int OpenAudioCodec( decoder_t *p_dec )
{
    decoder_sys_t *p_sys = p_dec->p_sys;
    AVCodecContext *ctx = p_sys->p_context;
    const AVCodec *codec = p_sys->p_codec;

    if( ctx->extradata_size <= 0 )
    {
        if( codec->id == AV_CODEC_ID_VORBIS ||
            ( codec->id == AV_CODEC_ID_AAC &&
              !p_dec->fmt_in->b_packetized ) )
        {
            msg_Warn( p_dec, "waiting for extra data for codec %s",
                      codec->name );
            return 1;
        }
    }

    ctx->sample_rate = p_dec->fmt_in->audio.i_rate;
#if API_CHANNEL_LAYOUT_STRUCT && LIBAVUTIL_VERSION_CHECK(57, 24, 100)
    av_channel_layout_default( &ctx->ch_layout, p_dec->fmt_in->audio.i_channels );
#else
    ctx->channels = p_dec->fmt_in->audio.i_channels;
#endif
    ctx->block_align = p_dec->fmt_in->audio.i_blockalign;
    ctx->bit_rate = p_dec->fmt_in->i_bitrate;
    ctx->bits_per_coded_sample = p_dec->fmt_in->audio.i_bitspersample;

    if( codec->id == AV_CODEC_ID_ADPCM_G726 &&
        ctx->bit_rate > 0 &&
        ctx->sample_rate >  0)
        ctx->bits_per_coded_sample = ctx->bit_rate / ctx->sample_rate;

    return ffmpeg_OpenCodec( p_dec, ctx, codec );
}

/**
 * Allocates decoded audio buffer for libavcodec to use.
 */
typedef struct
{
    block_t self;
    AVFrame *frame;
} vlc_av_frame_t;

static void vlc_av_frame_Release(block_t *block)
{
    vlc_av_frame_t *b = (void *)block;

    av_frame_free(&b->frame);
    free(b);
}

static const struct vlc_block_callbacks vlc_av_frame_cbs =
{
    vlc_av_frame_Release,
};

static block_t *vlc_av_frame_Wrap(AVFrame *frame)
{
    for (unsigned i = 1; i < AV_NUM_DATA_POINTERS; i++)
        assert(frame->linesize[i] == 0); /* only packed frame supported */

    if (av_frame_make_writable(frame)) /* TODO: read-only block_t */
        return NULL;

    vlc_av_frame_t *b = malloc(sizeof (*b));
    if (unlikely(b == NULL))
        return NULL;

    block_t *block = &b->self;

    block_Init(block, &vlc_av_frame_cbs,
               frame->extended_data[0], frame->linesize[0]);
    block->i_nb_samples = frame->nb_samples;
    b->frame = frame;
    return block;
}

/*****************************************************************************
 * EndAudio: decoder destruction
 *****************************************************************************
 * This function is called when the thread ends after a successful
 * initialization.
 *****************************************************************************/
void EndAudioDec( vlc_object_t *obj )
{
    decoder_t *p_dec = (decoder_t *)obj;
    decoder_sys_t *sys = p_dec->p_sys;
    AVCodecContext *ctx = sys->p_context;

    avcodec_free_context( &ctx );
    free( sys );
}

/*****************************************************************************
 * InitAudioDec: initialize audio decoder
 *****************************************************************************
 * The avcodec codec will be opened, some memory allocated.
 *****************************************************************************/
int InitAudioDec( vlc_object_t *obj )
{
    decoder_t *p_dec = (decoder_t *)obj;
    const AVCodec *codec;
    AVCodecContext *avctx = ffmpeg_AllocContext( p_dec, &codec, false );
    if( avctx == NULL )
        return VLC_EGENERIC;

    /* Allocate the memory needed to store the decoder's structure */
    decoder_sys_t *p_sys = malloc(sizeof(*p_sys));
    if( unlikely(p_sys == NULL) )
    {
        avcodec_free_context( &avctx );
        return VLC_ENOMEM;
    }

    p_dec->p_sys = p_sys;
    p_sys->p_context = avctx;
    p_sys->p_codec = codec;

    // Initialize decoder extradata
    InitDecoderConfig( p_dec, avctx );

    /* ***** Open the codec ***** */
    if( OpenAudioCodec( p_dec ) < 0 )
    {
        free( p_sys );
        avcodec_free_context( &avctx );
        return VLC_EGENERIC;
    }

    p_sys->i_reject_count = 0;
    p_sys->b_extract = false;
    p_sys->i_previous_channels = 0;
    p_sys->i_previous_layout = 0;
    p_sys->discontinuity = false;

    /* */
    /* Try to set as much information as possible but do not trust it */
    SetupOutputFormat( p_dec, false );

    if( !p_dec->fmt_out.audio.i_rate )
        p_dec->fmt_out.audio.i_rate = p_dec->fmt_in->audio.i_rate;
    if( p_dec->fmt_out.audio.i_rate )
        date_Init( &p_sys->end_date, p_dec->fmt_out.audio.i_rate, 1 );
    p_dec->fmt_out.audio.i_chan_mode = p_dec->fmt_in->audio.i_chan_mode;

    p_dec->pf_decode = DecodeAudio;
    p_dec->pf_flush  = Flush;

    return VLC_SUCCESS;
}

/*****************************************************************************
 * Flush:
 *****************************************************************************/
static void Flush( decoder_t *p_dec )
{
    decoder_sys_t *p_sys = p_dec->p_sys;
    AVCodecContext *ctx = p_sys->p_context;

    if( avcodec_is_open( ctx ) )
        avcodec_flush_buffers( ctx );
    date_Set( &p_sys->end_date, VLC_TICK_INVALID );

    if( ctx->codec_id == AV_CODEC_ID_MP2 ||
        ctx->codec_id == AV_CODEC_ID_MP3 )
        p_sys->i_reject_count = 3;
    p_sys->discontinuity = false;
}

/*****************************************************************************
 * DecodeBlock: Called to decode one frame
 *****************************************************************************/
static int DecodeBlock( decoder_t *p_dec, block_t **pp_block )
{
    decoder_sys_t *p_sys = p_dec->p_sys;
    AVCodecContext *ctx = p_sys->p_context;
    AVFrame *frame = NULL;
    block_t *p_block = NULL;
    bool b_error = false;

    if( !ctx->extradata_size && p_dec->fmt_in->i_extra
     && !avcodec_is_open( ctx ) )
    {
        InitDecoderConfig( p_dec, ctx );
        if( OpenAudioCodec( p_dec ) < 0 )
        {
            if( pp_block != NULL && *pp_block != NULL )
                block_Release( *pp_block );
            return VLCDEC_ECRITICAL;
        }
    }

    if( !avcodec_is_open( ctx ) )
    {
        if( pp_block )
            p_block = *pp_block;
        goto drop;
    }

    if( pp_block == NULL ) /* Drain request */
    {
        /* we don't need to care about return val */
        (void) avcodec_send_packet( ctx, NULL );
    }
    else
    {
        p_block = *pp_block;
    }

    if( p_block )
    {
        if( p_block->i_flags & BLOCK_FLAG_CORRUPTED )
        {
            Flush( p_dec );
            goto drop;
        }

        if( p_block->i_flags & BLOCK_FLAG_DISCONTINUITY )
        {
            date_Set( &p_sys->end_date, VLC_TICK_INVALID );
        }

        /* We've just started the stream, wait for the first PTS. */
        if( p_block->i_pts == VLC_TICK_INVALID &&
            date_Get( &p_sys->end_date ) == VLC_TICK_INVALID )
            goto drop;

        if( p_block->i_buffer <= 0 )
            goto drop;

        if( (p_block->i_flags & BLOCK_FLAG_PRIVATE_REALLOCATED) == 0 )
        {
            *pp_block = p_block = block_Realloc( p_block, 0, p_block->i_buffer + AV_INPUT_BUFFER_PADDING_SIZE );
            if( !p_block )
                goto end;
            p_block->i_buffer -= AV_INPUT_BUFFER_PADDING_SIZE;
            memset( &p_block->p_buffer[p_block->i_buffer], 0, AV_INPUT_BUFFER_PADDING_SIZE );

            p_block->i_flags |= BLOCK_FLAG_PRIVATE_REALLOCATED;
        }
    }

    frame = av_frame_alloc();
    if (unlikely(frame == NULL))
        goto end;

    bool send_failed = false;
    for( int ret = 0; ret == 0; )
    {
        /* Feed in the loop as buffer could have been full on first iterations */
        if( p_block )
        {
            AVPacket *pkt = av_packet_alloc();
            if( !pkt )
                goto end;
            pkt->data = p_block->p_buffer;
            pkt->size = p_block->i_buffer;
            ret = avcodec_send_packet( ctx, pkt );
            av_packet_free(&pkt);
            if( ret == 0 ) /* Block has been consumed */
            {
                /* Only set new pts from input block if it has been used,
                 * otherwise let it be through interpolation */
                if( p_block->i_pts > date_Get( &p_sys->end_date ) )
                {
                    date_Set( &p_sys->end_date, p_block->i_pts );
                }

                block_Release( p_block );
                *pp_block = p_block = NULL;
            }
            else if ( ret != AVERROR(EAGAIN) ) /* Errors other than buffer full */
            {
                if( ret == AVERROR(ENOMEM) || ret == AVERROR(EINVAL) )
                    goto end;
                else
                {
                    char errorstring[AV_ERROR_MAX_STRING_SIZE];
                    if( !av_strerror( ret, errorstring, AV_ERROR_MAX_STRING_SIZE ) )
                        msg_Err( p_dec, "%s", errorstring );

                    /* Signal an error, but continue to receive all output
                     * frames. A discontinuity will be triggered for the
                     * output frame coming right after the dropped one. */
                    send_failed = true;
                    block_Release( p_block );
                    *pp_block = p_block = NULL;
                }
            }
        }

        /* Try to read one or multiple frames */
        ret = avcodec_receive_frame( ctx, frame );
        if( ret == 0 )
        {
#if LIBAVUTIL_VERSION_CHECK(57, 24, 100)
            int channels = frame->ch_layout.nb_channels;
#else
            int channels = ctx->channels;
#endif
            /* checks and init from first decoded frame */
            if( channels <= 0 || channels > INPUT_CHAN_MAX
             || ctx->sample_rate <= 0 )
            {
                msg_Warn( p_dec, "invalid audio properties channels count %d, sample rate %d",
                          channels, ctx->sample_rate );
                goto drop;
            }
            else if( p_dec->fmt_out.audio.i_rate != (unsigned int)ctx->sample_rate )
            {
                date_Init( &p_sys->end_date, ctx->sample_rate, 1 );
            }

            SetupOutputFormat( p_dec, true );
            if( decoder_UpdateAudioFormat( p_dec ) )
                goto drop;

            block_t *p_converted = ConvertAVFrame( p_dec, frame ); /* Consumes frame */
            if( p_converted )
            {
                /* Silent unwanted samples */
                if( p_sys->i_reject_count > 0 )
                {
                    memset( p_converted->p_buffer, 0, p_converted->i_buffer );
                    p_sys->i_reject_count--;
                }
                p_converted->i_buffer = p_converted->i_nb_samples
                                      * p_dec->fmt_out.audio.i_bytes_per_frame;
                p_converted->i_pts = date_Get( &p_sys->end_date );
                p_converted->i_length = date_Increment( &p_sys->end_date,
                                                      p_converted->i_nb_samples ) - p_converted->i_pts;

                if (p_sys->discontinuity)
                {
                    p_sys->discontinuity = false;
                    p_converted->i_flags |= BLOCK_FLAG_DISCONTINUITY;
                }
                decoder_QueueAudio( p_dec, p_converted );
            }

            /* Prepare new frame */
            frame = av_frame_alloc();
            if (unlikely(frame == NULL))
                break;
        }
        else
        {
            /* After draining, we need to reset decoder with a flush */
            if( ret == AVERROR_EOF )
                avcodec_flush_buffers( p_sys->p_context );
            av_frame_free( &frame );
        }
    };

    if (send_failed)
    {
        /* Signal a discontinuity for the next output frame. */
        p_sys->discontinuity = true;
    }

    return VLCDEC_SUCCESS;

end:
    b_error = true;
drop:
    /* Signal a discontinuity for the next output frame. */
    p_sys->discontinuity = true;
    if( pp_block )
    {
        assert( *pp_block == p_block );
        *pp_block = NULL;
    }
    if( p_block != NULL )
        block_Release(p_block);
    if( frame != NULL )
        av_frame_free( &frame );

    return (b_error) ? VLCDEC_ECRITICAL : VLCDEC_SUCCESS;
}

static int DecodeAudio( decoder_t *p_dec, block_t *p_block )
{
    block_t **pp_block = p_block ? &p_block : NULL;
    int i_ret;
    do
    {
        i_ret = DecodeBlock( p_dec, pp_block );
    }
    while( i_ret == VLCDEC_SUCCESS && pp_block && *pp_block );

    return i_ret;
}

static block_t * ConvertAVFrame( decoder_t *p_dec, AVFrame *frame )
{
    decoder_sys_t *p_sys = p_dec->p_sys;
    AVCodecContext *ctx = p_sys->p_context;
    block_t *p_block;

    /* Interleave audio if required */
    if( av_sample_fmt_is_planar( ctx->sample_fmt ) )
    {
        p_block = block_Alloc(frame->linesize[0] * p_dec->fmt_out.audio.i_channels );
        if ( likely(p_block) )
        {
            const void *planes[p_dec->fmt_out.audio.i_channels];
            for (int i = 0; i < p_dec->fmt_out.audio.i_channels; i++)
                planes[i] = frame->extended_data[i];

            aout_Interleave(p_block->p_buffer, planes, frame->nb_samples,
                            p_dec->fmt_out.audio.i_channels, p_dec->fmt_out.audio.i_format);
            p_block->i_nb_samples = frame->nb_samples;
        }
        av_frame_free(&frame);
    }
    else
    {
        p_block = vlc_av_frame_Wrap(frame);
        frame = NULL;
    }

    if (p_sys->b_extract && p_block)
    {   /* TODO: do not drop channels... at least not here */
        block_t *p_buffer = block_Alloc( p_dec->fmt_out.audio.i_bytes_per_frame
                                         * p_block->i_nb_samples );
        if( likely(p_buffer) )
        {
            aout_ChannelExtract( p_buffer->p_buffer,
                                 p_dec->fmt_out.audio.i_channels,
                                 p_block->p_buffer, p_dec->fmt_out.audio.i_channels,
                                 p_block->i_nb_samples, p_sys->pi_extraction,
                                 p_dec->fmt_out.audio.i_bitspersample );
            p_buffer->i_nb_samples = p_block->i_nb_samples;
        }
        block_Release( p_block );
        p_block = p_buffer;
    }

    return p_block;
}

/*****************************************************************************
 *
 *****************************************************************************/

vlc_fourcc_t GetVlcAudioFormat( int fmt )
{
    static const vlc_fourcc_t fcc[] = {
        [AV_SAMPLE_FMT_U8]    = VLC_CODEC_U8,
        [AV_SAMPLE_FMT_S16]   = VLC_CODEC_S16N,
        [AV_SAMPLE_FMT_S32]   = VLC_CODEC_S32N,
        [AV_SAMPLE_FMT_FLT]   = VLC_CODEC_FL32,
        [AV_SAMPLE_FMT_DBL]   = VLC_CODEC_FL64,
        [AV_SAMPLE_FMT_U8P]   = VLC_CODEC_U8,
        [AV_SAMPLE_FMT_S16P]  = VLC_CODEC_S16N,
        [AV_SAMPLE_FMT_S32P]  = VLC_CODEC_S32N,
        [AV_SAMPLE_FMT_FLTP]  = VLC_CODEC_FL32,
        [AV_SAMPLE_FMT_DBLP]  = VLC_CODEC_FL64,
    };
    if( ARRAY_SIZE(fcc) > (unsigned)fmt )
        return fcc[fmt];
    return VLC_CODEC_S16N;
}

static const uint64_t pi_channels_map[][2] =
{
    { AV_CH_FRONT_LEFT,        AOUT_CHAN_LEFT },
    { AV_CH_FRONT_RIGHT,       AOUT_CHAN_RIGHT },
    { AV_CH_FRONT_CENTER,      AOUT_CHAN_CENTER },
    { AV_CH_LOW_FREQUENCY,     AOUT_CHAN_LFE },
    { AV_CH_BACK_LEFT,         AOUT_CHAN_REARLEFT },
    { AV_CH_BACK_RIGHT,        AOUT_CHAN_REARRIGHT },
    { AV_CH_FRONT_LEFT_OF_CENTER, 0 },
    { AV_CH_FRONT_RIGHT_OF_CENTER, 0 },
    { AV_CH_BACK_CENTER,       AOUT_CHAN_REARCENTER },
    { AV_CH_SIDE_LEFT,         AOUT_CHAN_MIDDLELEFT },
    { AV_CH_SIDE_RIGHT,        AOUT_CHAN_MIDDLERIGHT },
    { AV_CH_TOP_CENTER,        0 },
    { AV_CH_TOP_FRONT_LEFT,    0 },
    { AV_CH_TOP_FRONT_CENTER,  0 },
    { AV_CH_TOP_FRONT_RIGHT,   0 },
    { AV_CH_TOP_BACK_LEFT,     0 },
    { AV_CH_TOP_BACK_CENTER,   0 },
    { AV_CH_TOP_BACK_RIGHT,    0 },
    { AV_CH_STEREO_LEFT,       0 },
    { AV_CH_STEREO_RIGHT,      0 },
    { 0, 0 },
};

static void SetupOutputFormat( decoder_t *p_dec, bool b_trust )
{
    decoder_sys_t *p_sys = p_dec->p_sys;

    p_dec->fmt_out.i_codec = GetVlcAudioFormat( p_sys->p_context->sample_fmt );
    p_dec->fmt_out.audio.channel_type = p_dec->fmt_in->audio.channel_type;
    p_dec->fmt_out.audio.i_format = p_dec->fmt_out.i_codec;
    p_dec->fmt_out.audio.i_rate = p_sys->p_context->sample_rate;

    /* */
#if API_CHANNEL_LAYOUT_STRUCT
    if( p_sys->i_previous_channels == p_sys->p_context->ch_layout.nb_channels &&
        p_sys->i_previous_layout == p_sys->p_context->ch_layout.u.mask )
        return;
    if( b_trust )
    {
        p_sys->i_previous_channels = p_sys->p_context->ch_layout.nb_channels;
        p_sys->i_previous_layout = p_sys->p_context->ch_layout.u.mask;
    }
#else
    if( p_sys->i_previous_channels == p_sys->p_context->channels &&
        p_sys->i_previous_layout == p_sys->p_context->channel_layout )
        return;
    if( b_trust )
    {
        p_sys->i_previous_channels = p_sys->p_context->channels;
        p_sys->i_previous_layout = p_sys->p_context->channel_layout;
    }
#endif

    int i_channels_src = 0;
#if API_CHANNEL_LAYOUT_STRUCT
    uint64_t channel_layout_mask = p_sys->p_context->ch_layout.u.mask;
    int channel_count = p_sys->p_context->ch_layout.nb_channels;
#else
    uint64_t channel_layout_mask =
        p_sys->p_context->channel_layout ? p_sys->p_context->channel_layout :
        (uint64_t)av_get_default_channel_layout( p_sys->p_context->channels );
    int channel_count = p_sys->p_context->channels;
#endif

    if( channel_layout_mask )
    {
        uint32_t* pi_order_src = calloc(channel_count,sizeof(uint32_t));

        if( unlikely(pi_order_src == NULL) )
        {
            p_dec->fmt_out.audio.i_physical_channels = 0;
            p_dec->fmt_out.audio.i_channels = channel_count;

            aout_FormatPrepare(&p_dec->fmt_out.audio);
            p_sys->b_extract = false;
            return;
        }

        assert(stdc_count_ones(channel_layout_mask) == (unsigned)channel_count);

        for( unsigned i = 0; pi_channels_map[i][0]
         && i_channels_src < channel_count; i++ )
        {
            if( channel_layout_mask & pi_channels_map[i][0] )
                pi_order_src[i_channels_src++] = pi_channels_map[i][1];
        }

        if( i_channels_src != channel_count && b_trust )
            msg_Err( p_dec, "Channel layout not understood" );

        /* Detect special dual mono case */
        if( i_channels_src == 2 && pi_order_src[0] == AOUT_CHAN_CENTER
         && pi_order_src[1] == AOUT_CHAN_CENTER )
        {
            p_dec->fmt_out.audio.i_chan_mode |= AOUT_CHANMODE_DUALMONO;
            pi_order_src[0] = AOUT_CHAN_LEFT;
            pi_order_src[1] = AOUT_CHAN_RIGHT;
        }

        uint32_t i_layout_dst;
        int      i_channels_dst;
        p_sys->b_extract = aout_CheckChannelExtraction( p_sys->pi_extraction,
                                                        &i_layout_dst, &i_channels_dst,
                                                        NULL, pi_order_src, i_channels_src );
        if( i_channels_dst != i_channels_src && b_trust )
            msg_Warn( p_dec, "%d channels are dropped", i_channels_src - i_channels_dst );

        /* No reordering for Ambisonic order 1 channels encoded in AAC... */
        if (p_dec->fmt_out.audio.channel_type == AUDIO_CHANNEL_TYPE_AMBISONICS
            && p_dec->fmt_in->i_codec == VLC_CODEC_MP4A
            && i_channels_src == 4)
            p_sys->b_extract = false;

        p_dec->fmt_out.audio.i_physical_channels = i_layout_dst;
        free(pi_order_src);
    }
    else
    {
        msg_Warn( p_dec, "no channel layout found");
        p_dec->fmt_out.audio.i_physical_channels = 0;
        p_dec->fmt_out.audio.i_channels = channel_count;
    }

    aout_FormatPrepare( &p_dec->fmt_out.audio );
}