path: root/libhb/reader.c

/* reader.c

   Copyright (c) 2003-2015 HandBrake Team
   This file is part of the HandBrake source code
   Homepage: <http://handbrake.fr/>.
   It may be used under the terms of the GNU General Public License v2.
   For full terms see the file COPYING file or visit http://www.gnu.org/licenses/gpl-2.0.html
 */
#include "hb.h"

static int  hb_reader_init( hb_work_object_t * w, hb_job_t * job );
static void hb_reader_close( hb_work_object_t * w );

hb_work_object_t hb_reader =
{
    WORK_READER,
    "Reader",
    hb_reader_init,
    NULL,
    hb_reader_close,
    NULL,
    NULL
};

typedef struct
{
    int    startup;
    double average; // average time between packets
    double filtered_average; // average time between packets
    int64_t last;   // last timestamp seen on this stream
    int id;         // stream id
    int is_audio;   // != 0 if this is an audio stream
    int valid;      // Stream timing is not valid until next scr.
} stream_timing_t;

struct hb_work_private_s
{
    hb_handle_t  * h;
    hb_job_t     * job;
    hb_title_t   * title;
    volatile int * die;

    hb_bd_t      * bd;
    hb_dvd_t     * dvd;
    hb_stream_t  * stream;

    stream_timing_t *stream_timing;
    int64_t        scr_offset;
    hb_psdemux_t   demux;
    int            scr_changes;
    uint32_t       sequence;
    uint8_t        st_slots;        // size (in slots) of stream_timing array
    uint8_t        saw_video;       // != 0 if we've seen video
    uint8_t        saw_audio;       // != 0 if we've seen audio

    int            start_found;     // found pts_to_start point
    int64_t        pts_to_start;
    uint64_t       st_first;
    uint64_t       duration;
    hb_fifo_t    * fifos[100];
};

/***********************************************************************
 * Local prototypes
 **********************************************************************/
static hb_fifo_t ** GetFifoForId( hb_work_private_t * r, int id );
static void UpdateState( hb_work_private_t  * r, int64_t start);

/***********************************************************************
 * hb_reader_init
 ***********************************************************************
 *
 **********************************************************************/
static int hb_reader_open( hb_work_private_t * r )
{
    if ( r->title->type == HB_BD_TYPE )
    {
        if ( !( r->bd = hb_bd_init( r->h, r->title->path ) ) )
            return 1;
    }
    else if ( r->title->type == HB_DVD_TYPE )
    {
        if ( !( r->dvd = hb_dvd_init( r->title->path ) ) )
            return 1;
    }
    else if ( r->title->type == HB_STREAM_TYPE ||
              r->title->type == HB_FF_STREAM_TYPE )
    {
        if (!(r->stream = hb_stream_open(r->h, r->title->path, r->title, 0)))
            return 1;
    }
    else
    {
        // Unknown type, should never happen
        return 1;
    }
    return 0;
}

static int hb_reader_init( hb_work_object_t * w, hb_job_t * job )
{
    hb_work_private_t * r;

    r = calloc( sizeof( hb_work_private_t ), 1 );
    w->private_data = r;

    r->h     = job->h;
    r->job   = job;
    r->title = job->title;
    r->die   = job->die;
    r->sequence = 0;

    r->st_slots = 4;
    r->stream_timing = calloc( sizeof(stream_timing_t), r->st_slots );
    r->stream_timing[0].id = r->title->video_id;
    r->stream_timing[0].average = 90000. * (double)job->vrate.den /
                                           job->vrate.num;
    r->stream_timing[0].filtered_average = r->stream_timing[0].average;
    r->stream_timing[0].last = -r->stream_timing[0].average;
    r->stream_timing[0].valid = 1;
    r->stream_timing[0].startup = 10;
    r->stream_timing[1].id = -1;

    r->demux.last_scr = AV_NOPTS_VALUE;

    if ( !job->pts_to_start )
        r->start_found = 1;
    else
    {
        // The frame at the actual start time may not be an i-frame
        // so can't be decoded without starting a little early.
        // sync.c will drop early frames.
        // Starting a little over 10 seconds early
        r->pts_to_start = MAX(0, job->pts_to_start - 1000000);
    }

    if (job->pts_to_stop)
    {
        r->duration = job->pts_to_start + job->pts_to_stop;
    }
    else if (job->frame_to_stop)
    {
        int frames = job->frame_to_start + job->frame_to_stop;
        r->duration = (int64_t)frames * job->title->vrate.den * 90000 /
                               job->title->vrate.num;
    }
    else
    {
        hb_chapter_t *chapter;
        int ii;

        r->duration = 0;
        for (ii = job->chapter_start; ii < job->chapter_end; ii++)
        {
            chapter = hb_list_item( job->title->list_chapter, ii - 1);
            r->duration += chapter->duration;
        }
    }

    // The stream needs to be open before starting the reader thead
    // to prevent a race with decoders that may share information
    // with the reader. Specifically avcodec needs this.
    if ( hb_reader_open( r ) )
    {
        free( r->stream_timing );
        free( r );
        return 1;
    }
    return 0;
}


static void hb_reader_close( hb_work_object_t * w )
{
    hb_work_private_t * r = w->private_data;

    if (r->bd)
    {
        hb_bd_stop( r->bd );
        hb_bd_close( &r->bd );
    }
    else if (r->dvd)
    {
        hb_dvd_stop( r->dvd );
        hb_dvd_close( &r->dvd );
    }
    else if (r->stream)
    {
        hb_stream_close(&r->stream);
    }

    if ( r->stream_timing )
    {
        free( r->stream_timing );
    }

    free( r );
}

static void push_buf( const hb_work_private_t *r, hb_fifo_t *fifo, hb_buffer_t *buf )
{
    while ( !*r->die && !r->job->done )
    {
        if ( hb_fifo_full_wait( fifo ) )
        {
            hb_fifo_push( fifo, buf );
            buf = NULL;
            break;
        }
    }
    if ( buf )
    {
        hb_buffer_close( &buf );
    }
}

static int is_audio( hb_work_private_t *r, int id )
{
    int i;
    hb_audio_t *audio;

    for( i = 0; ( audio = hb_list_item( r->title->list_audio, i ) ); ++i )
    {
        if ( audio->id == id )
        {
            return 1;
        }
    }
    return 0;
}

// The MPEG STD (Standard Target Decoder) essentially requires that we keep
// per-stream timing so that when there's a timing discontinuity we can
// seemlessly join packets on either side of the discontinuity. This join
// requires that we know the timestamp of the previous packet and the
// average inter-packet time (since we position the new packet at the end
// of the previous packet). The next four routines keep track of this
// per-stream timing.

// find or create the per-stream timing state for 'buf'

static stream_timing_t *id_to_st( hb_work_private_t *r, const hb_buffer_t *buf, int valid )
{
    stream_timing_t *st = r->stream_timing;
    while ( st->id != buf->s.id && st->id != -1)
    {
        ++st;
    }
    // if we haven't seen this stream add it.
    if ( st->id == -1 )
    {
        // we keep the steam timing info in an array with some power-of-two
        // number of slots. If we don't have two slots left (one for our new
        // entry plus one for the "-1" eol) we need to expand the array.
        int slot = st - r->stream_timing;
        if ( slot + 1 >= r->st_slots )
        {
            r->st_slots *= 2;
            r->stream_timing = realloc( r->stream_timing, r->st_slots *
                                        sizeof(*r->stream_timing) );
            st = r->stream_timing + slot;
        }
        st->id = buf->s.id;
        st->average = 30.*90.;
        st->filtered_average = st->average;
        st->startup = 10;
        st->last = -st->average;
        if ( ( st->is_audio = is_audio( r, buf->s.id ) ) != 0 )
        {
            r->saw_audio = 1;
        }
        st[1].id = -1;
        st->valid = valid;
    }
    return st;
}

// update the average inter-packet time of the stream associated with 'buf'
// using a recursive low-pass filter with a 16 packet time constant.

static void update_ipt( hb_work_private_t *r, const hb_buffer_t *buf )
{
    stream_timing_t *st = id_to_st( r, buf, 1 );

    if (buf->s.renderOffset == AV_NOPTS_VALUE)
    {
        st->last += st->filtered_average;
        return;
    }

    double dt = buf->s.renderOffset - st->last;

    // Protect against spurious bad timestamps
    // timestamps should only move forward and by reasonable increments
    if ( dt > 0 && dt < 5 * 90000LL )
    {
        if( st->startup )
        {
            st->average += ( dt - st->average ) * (1./4.);
            st->startup--;
        }
        else
        {
            st->average += ( dt - st->average ) * (1./32.);
        }
        // Ignore outliers
        if (dt < 1.5 * st->average)
        {
            st->filtered_average += ( dt - st->filtered_average ) * (1./32.);
        }
    }
    st->last = buf->s.renderOffset;
    st->valid = 1;
}

// use the per-stream state associated with 'buf' to compute a new scr_offset
// such that 'buf' will follow the previous packet of this stream separated
// by the average packet time of the stream.

static void new_scr_offset( hb_work_private_t *r, hb_buffer_t *buf )
{
    stream_timing_t *st = id_to_st( r, buf, 1 );
    int64_t last;
    if ( !st->valid )
    {
        // !valid means we've not received any previous data
        // for this stream.  There is no 'last' packet time.
        // So approximate it with video's last time.
        last = r->stream_timing[0].last;
        st->valid = 1;
    }
    else
    {
        last = st->last;
    }
    int64_t nxt = last + st->filtered_average;
    r->scr_offset = buf->s.renderOffset - nxt;
    // This log is handy when you need to debug timing problems...
    //hb_log("id %x last %"PRId64" avg %g nxt %"PRId64" renderOffset %"PRId64
    //       " scr_offset %"PRId64"",
    //    buf->s.id, last, st->filtered_average, nxt,
    //    buf->s.renderOffset, r->scr_offset);
    r->scr_changes = r->demux.scr_changes;
}

/***********************************************************************
 * ReaderFunc
 ***********************************************************************
 *
 **********************************************************************/
void ReadLoop( void * _w )
{
    hb_work_object_t * w = _w;
    hb_work_private_t  * r = w->private_data;
    hb_fifo_t   ** fifos;
    hb_buffer_t  * buf = NULL;
    hb_list_t    * list;
    int            n;
    int            chapter = -1;
    int            chapter_end = r->job->chapter_end;
    uint8_t        done = 0;

    if (r->bd)
    {
        if( !hb_bd_start( r->bd, r->title ) )
        {
            hb_bd_close( &r->bd );
            return;
        }
        if ( r->job->start_at_preview )
        {
            // XXX code from DecodePreviews - should go into its own routine
            hb_bd_seek( r->bd, (float)r->job->start_at_preview /
                         ( r->job->seek_points ? ( r->job->seek_points + 1.0 ) : 11.0 ) );
        }
        else if ( r->job->pts_to_start )
        {
            // Note, bd seeks always put us to an i-frame.  no need
            // to start decoding early using r->pts_to_start
            hb_bd_seek_pts( r->bd, r->job->pts_to_start );
            r->duration -= r->job->pts_to_start;
            r->job->pts_to_start = 0;
            r->start_found = 1;
        }
        else
        {
            hb_bd_seek_chapter( r->bd, r->job->chapter_start );
        }
        if (r->job->angle > 1)
        {
            hb_bd_set_angle( r->bd, r->job->angle - 1 );
        }
    }
    else if (r->dvd)
    {
        /*
         * XXX this code is a temporary hack that should go away if/when
         *     chapter merging goes away in libhb/dvd.c
         * map the start and end chapter numbers to on-media chapter
         * numbers since chapter merging could cause the handbrake numbers
         * to diverge from the media numbers and, if our chapter_end is after
         * a media chapter that got merged, we'll stop ripping too early.
         */
        int start = r->job->chapter_start;
        hb_chapter_t *chap = hb_list_item( r->job->list_chapter, chapter_end - 1 );

        chapter_end = chap->index;
        if (start > 1)
        {
           chap = hb_list_item( r->job->list_chapter, start - 1 );
           start = chap->index;
        }
        /* end chapter mapping XXX */

        if( !hb_dvd_start( r->dvd, r->title, start ) )
        {
            hb_dvd_close( &r->dvd );
            return;
        }
        if (r->job->angle)
        {
            hb_dvd_set_angle( r->dvd, r->job->angle );
        }

        if ( r->job->start_at_preview )
        {
            // XXX code from DecodePreviews - should go into its own routine
            hb_dvd_seek( r->dvd, (float)r->job->start_at_preview /
                         ( r->job->seek_points ? ( r->job->seek_points + 1.0 ) : 11.0 ) );
        }
    }
    else if ( r->stream && r->job->start_at_preview )
    {
        
        // XXX code from DecodePreviews - should go into its own routine
        hb_stream_seek( r->stream, (float)( r->job->start_at_preview - 1 ) /
                        ( r->job->seek_points ? ( r->job->seek_points + 1.0 ) : 11.0 ) );

    } 
    else if ( r->stream && r->job->pts_to_start )
    {
        int64_t pts_to_start = r->job->pts_to_start;
        
        // Find out what the first timestamp of the stream is
        // and then seek to the appropriate offset from it
        if ( ( buf = hb_stream_read( r->stream ) ) )
        {
            if (buf->s.start != AV_NOPTS_VALUE)
            {
                pts_to_start += buf->s.start;
            }
        }
        
        if ( hb_stream_seek_ts( r->stream, pts_to_start ) >= 0 )
        {
            // Seek takes us to the nearest I-frame before the timestamp
            // that we want.  So we will retrieve the start time of the
            // first packet we get, subtract that from pts_to_start, and
            // inspect the reset of the frames in sync.
            r->start_found = 2;
            r->duration -= r->job->pts_to_start;
            r->job->pts_to_start = pts_to_start;
            hb_buffer_close(&buf);
        }
        // hb_stream_seek_ts does nothing for TS streams and will return
        // an error.  In this case, the current buf remains valid and
        // gets processed below.
    } 
    else if( r->stream )
    {
        /*
         * Standard stream, seek to the starting chapter, if set, and track the
         * end chapter so that we end at the right time.
         */
        int start = r->job->chapter_start;
        hb_chapter_t *chap = hb_list_item( r->job->list_chapter, chapter_end - 1 );
        
        chapter_end = chap->index;
        if (start > 1)
        {
            chap = hb_list_item( r->job->list_chapter, start - 1 );
            start = chap->index;
        }
        
        /*
         * Seek to the start chapter.
         */
        hb_stream_seek_chapter( r->stream, start );
    }

    list  = hb_list_init();

    while(!*r->die && !r->job->done && !done)
    {
        if (r->bd)
            chapter = hb_bd_chapter( r->bd );
        else if (r->dvd)
            chapter = hb_dvd_chapter( r->dvd );
        else if (r->stream)
            chapter = hb_stream_chapter( r->stream );

        if( chapter < 0 )
        {
            hb_log( "reader: end of the title reached" );
            break;
        }
        if( chapter > chapter_end )
        {
            hb_log( "reader: end of chapter %d (media %d) reached at media chapter %d",
                    r->job->chapter_end, chapter_end, chapter );
            break;
        }

        if (buf == NULL)
        {
            if (r->bd)
            {
                if( (buf = hb_bd_read( r->bd )) == NULL )
                {
                    break;
                }
            }
            else if (r->dvd)
            {
                if( (buf = hb_dvd_read( r->dvd )) == NULL )
                {
                    break;
                }
            }
            else if (r->stream)
            {
                if ( (buf = hb_stream_read( r->stream )) == NULL )
                {
                  break;
                }
            }
        }

        (hb_demux[r->title->demuxer])( buf, list, &r->demux );

        while( ( buf = hb_list_item( list, 0 ) ) )
        {
            hb_list_rem( list, buf );
            fifos = GetFifoForId( r, buf->s.id );

            if (fifos && r->stream && r->start_found == 2 )
            {
                // We will inspect the timestamps of each frame in sync
                // to skip from this seek point to the timestamp we
                // want to start at.
                if (buf->s.start != AV_NOPTS_VALUE &&
                    buf->s.start < r->job->pts_to_start)
                {
                    r->job->pts_to_start -= buf->s.start;
                }
                else if ( buf->s.start >= r->job->pts_to_start )
                {
                    r->job->pts_to_start = 0;
                }
                r->start_found = 1;
            }

            if ( fifos && ! r->saw_video && !r->job->indepth_scan )
            {
                // The first data packet with a PTS from an audio or video stream
                // that we're decoding defines 'time zero'. Discard packets until
                // we get one.
                if (buf->s.start != AV_NOPTS_VALUE &&
                    buf->s.renderOffset != AV_NOPTS_VALUE &&
                     (buf->s.id == r->title->video_id ||
                      is_audio( r, buf->s.id)))
                {
                    // force a new scr offset computation
                    r->scr_changes = r->demux.scr_changes - 1;
                    // create a stream state if we don't have one so the
                    // offset will get computed correctly.
                    id_to_st( r, buf, 1 );
                    r->saw_video = 1;
                    hb_log( "reader: first SCR %"PRId64" id 0x%x DTS %"PRId64,
                            r->demux.last_scr, buf->s.id, buf->s.renderOffset );
                }
                else
                {
                    fifos = NULL;
                }
            }

            if ( r->job->indepth_scan || fifos )
            {
                if ( buf->s.renderOffset != AV_NOPTS_VALUE )
                {
                    if ( r->scr_changes != r->demux.scr_changes )
                    {
                        // This is the first audio or video packet after an SCR
                        // change. Compute a new scr offset that would make this
                        // packet follow the last of this stream with the 
                        // correct average spacing.
                        stream_timing_t *st = id_to_st( r, buf, 0 );

                        // if this is the video stream and we don't have
                        // audio yet or this is an audio stream
                        // generate a new scr
                        if ( st->is_audio ||
                             ( st == r->stream_timing && !r->saw_audio ) )
                        {
                            new_scr_offset( r, buf );
                        }
                        else
                        {
                            // defer the scr change until we get some
                            // audio since audio has a timestamp per
                            // frame but video & subtitles don't. Clear
                            // the timestamps so the decoder will generate
                            // them from the frame durations.
                            buf->s.start = AV_NOPTS_VALUE;
                            buf->s.renderOffset = AV_NOPTS_VALUE;
                        }
                    }
                }
                if ( buf->s.start != AV_NOPTS_VALUE )
                {
                    int64_t start = buf->s.start - r->scr_offset;

                    if (!r->start_found || r->job->indepth_scan)
                    {
                        UpdateState( r, start );
                    }

                    if (r->job->indepth_scan && r->job->pts_to_stop &&
                        start >= r->pts_to_start + r->job->pts_to_stop)
                    {
                        // sync normally would terminate p-to-p
                        // but sync doesn't run during indepth scan
                        hb_log( "reader: reached pts %"PRId64", exiting early", start );
                        done = 1;
                        break;
                    }

                    if (!r->start_found && start >= r->pts_to_start)
                    {
                        // pts_to_start point found
                        r->start_found = 1;
                        if (r->stream)
                        {
                            // libav multi-threaded decoders can get into
                            // a bad state if the initial data is not
                            // decodable.  So try to improve the chances of
                            // a good start by waiting for an initial iframe
                            hb_stream_set_need_keyframe(r->stream, 1);
                            hb_buffer_close( &buf );
                            continue;
                        }
                    }
                    // This log is handy when you need to debug timing problems
                    //hb_log("id %x scr_offset %"PRId64
                    //       " start %"PRId64" --> %"PRId64"", 
                    //        buf->s.id, r->scr_offset, buf->s.start, 
                    //        buf->s.start - r->scr_offset);
                    buf->s.start -= r->scr_offset;
                    if ( buf->s.stop != AV_NOPTS_VALUE )
                    {
                        buf->s.stop -= r->scr_offset;
                    }
                }
                if ( buf->s.renderOffset != AV_NOPTS_VALUE )
                {
                    // This packet is referenced to the same SCR as the last.
                    // Adjust timestamp to remove the System Clock Reference
                    // offset then update the average inter-packet time
                    // for this stream.
                    buf->s.renderOffset -= r->scr_offset;
                    update_ipt( r, buf );
                }
#if 0
                // JAS: This was added to fix a rare "audio time went backward"
                // sync error I found in one sample.  But it has a bad side
                // effect on DVDs, causing frequent "adding silence" sync
                // errors. So I am disabling it.
                else
                {
                    update_ipt( r, buf );
                }
#endif
            }
            if( fifos )
            {
                if ( !r->start_found )
                {
                    hb_buffer_close( &buf );
                    continue;
                }

                buf->sequence = r->sequence++;
                /* if there are mutiple output fifos, send a copy of the
                 * buffer down all but the first (we have to not ship the
                 * original buffer or we'll race with the thread that's
                 * consuming the buffer & inject garbage into the data stream). */
                for( n = 1; fifos[n] != NULL; n++)
                {
                    hb_buffer_t *buf_copy = hb_buffer_init( buf->size );
                    buf_copy->s = buf->s;
                    memcpy( buf_copy->data, buf->data, buf->size );
                    push_buf( r, fifos[n], buf_copy );
                }
                push_buf( r, fifos[0], buf );
                buf = NULL;
            }
            else
            {
                hb_buffer_close( &buf );
            }
        }
    }

    // send empty buffers downstream to video & audio decoders to signal we're done.
    if( !*r->die && !r->job->done )
    {
        push_buf( r, r->job->fifo_mpeg2, hb_buffer_init(0) );

        hb_audio_t *audio;
        for( n = 0; (audio = hb_list_item( r->job->list_audio, n)); ++n )
        {
            if ( audio->priv.fifo_in )
                push_buf( r, audio->priv.fifo_in, hb_buffer_init(0) );
        }

        hb_subtitle_t *subtitle;
        for( n = 0; (subtitle = hb_list_item( r->job->list_subtitle, n)); ++n )
        {
            if ( subtitle->fifo_in && subtitle->source == VOBSUB)
                push_buf( r, subtitle->fifo_in, hb_buffer_init(0) );
        }
    }

    hb_list_empty( &list );

    hb_log( "reader: done. %d scr changes", r->demux.scr_changes );
    if ( r->demux.dts_drops )
    {
        hb_log( "reader: %d drops because DTS out of range", r->demux.dts_drops );
    }
}

static void UpdateState( hb_work_private_t  * r, int64_t start)
{
    hb_state_t state;
    uint64_t now;
    double avg;

    now = hb_get_date();
    if( !r->st_first )
    {
        r->st_first = now;
    }

    hb_get_state2(r->job->h, &state);
#define p state.param.working
    if ( !r->job->indepth_scan )
    {
        state.state = HB_STATE_SEARCHING;
        p.progress  = (float) start / (float) r->job->pts_to_start;
    }
    else
    {
        state.state = HB_STATE_WORKING;
        p.progress  = (float) start / (float) r->duration;
    }
    if( p.progress > 1.0 )
    {
        p.progress = 1.0;
    }
    p.rate_cur = 0.0;
    p.rate_avg = 0.0;
    if (now > r->st_first)
    {
        int eta;

        avg = 1000.0 * (double)start / (now - r->st_first);
        if ( !r->job->indepth_scan )
            eta = ( r->job->pts_to_start - start ) / avg;
        else
            eta = ( r->duration - start ) / avg;
        p.hours   = eta / 3600;
        p.minutes = ( eta % 3600 ) / 60;
        p.seconds = eta % 60;
    }
    else
    {
        p.hours    = -1;
        p.minutes  = -1;
        p.seconds  = -1;
    }
#undef p

    hb_set_state( r->job->h, &state );
}
/***********************************************************************
 * GetFifoForId
 ***********************************************************************
 *
 **********************************************************************/
static hb_fifo_t ** GetFifoForId( hb_work_private_t * r, int id )
{
    hb_job_t      * job = r->job;
    hb_title_t    * title = job->title;
    hb_audio_t    * audio;
    hb_subtitle_t * subtitle;
    int             i, n, count;

    memset(r->fifos, 0, sizeof(r->fifos));

    if( id == title->video_id )
    {
        if (job->indepth_scan && !job->frame_to_stop)
        {
            /*
             * Ditch the video here during the indepth scan until
             * we can improve the MPEG2 decode performance.
             *
             * But if we specify a stop frame, we must decode the
             * frames in order to count them.
             */
            return NULL;
        }
        else
        {
            r->fifos[0] = job->fifo_mpeg2;
            return r->fifos;
        }
    }

    count = hb_list_count( job->list_subtitle );
    count = count > 99 ? 99 : count;
    for( i = n = 0; i < count; i++ )
    {
        subtitle =  hb_list_item( job->list_subtitle, i );
        if (id == subtitle->id)
        {
            /* pass the subtitles to be processed */
            r->fifos[n++] = subtitle->fifo_in;
        }
    }
    if ( n != 0 )
    {
        return r->fifos;
    }
    
    if( !job->indepth_scan )
    {
        for( i = n = 0; i < hb_list_count( job->list_audio ); i++ )
        {
            audio = hb_list_item( job->list_audio, i );
            if( id == audio->id )
            {
                r->fifos[n++] = audio->priv.fifo_in;
            }
        }

        if( n != 0 )
        {
            return r->fifos;
        }
    }

    return NULL;
}