midi

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trivial.c：源码内容
							/*****************************************************************************
 * trivial.c : trivial mixer plug-in (1 input, no downmixing)
 *****************************************************************************
 * Copyright (C) 2002 the VideoLAN team
 * $Id: 2512981ae52ce5f94e2b7452b5da8d9673c4bf74 $
 *
 * Authors: Christophe Massiot <massiot@via.ecp.fr>
 *
 * This program 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.
 *
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU 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 <stddef.h>
#include <vlc_common.h>
#include <vlc_plugin.h>
#include <vlc_aout.h>
/*****************************************************************************
 * Local prototypes
 *****************************************************************************/
static int  Create    ( vlc_object_t * );
static void DoWork    ( aout_instance_t *, aout_buffer_t * );
/*****************************************************************************
 * Module descriptor
 *****************************************************************************/
vlc_module_begin ()
    set_category( CAT_AUDIO )
    set_subcategory( SUBCAT_AUDIO_MISC )
    set_description( N_("Trivial audio mixer") )
    set_capability( "audio mixer", 1 )
    set_callbacks( Create, NULL )
vlc_module_end ()
/*****************************************************************************
 * Create: allocate trivial mixer
 *****************************************************************************/
static int Create( vlc_object_t *p_this )
{
    aout_instance_t * p_aout = (aout_instance_t *)p_this;
    if ( p_aout->mixer.mixer.i_format != VLC_FOURCC('f','l','3','2')
          && p_aout->mixer.mixer.i_format != VLC_FOURCC('f','i','3','2') )
    {
        return -1;
    }
    p_aout->mixer.pf_do_work = DoWork;
    return 0;
}
/*****************************************************************************
 * DoWork: mix a new output buffer
 *****************************************************************************/
static void DoWork( aout_instance_t * p_aout, aout_buffer_t * p_buffer )
{
    int i = 0;
    aout_input_t * p_input = p_aout->pp_inputs[i];
    int i_nb_channels = aout_FormatNbChannels( &p_aout->mixer.mixer );
    int i_nb_bytes = p_buffer->i_nb_samples * sizeof(int32_t)
                      * i_nb_channels;
    uint8_t * p_in;
    uint8_t * p_out;
    while ( p_input->b_error || p_input->b_paused )
    {
        p_input = p_aout->pp_inputs[++i];
        /* This can't crash because if no input has b_error == 0, the
         * audio mixer cannot run and we can't be here. */
    }
    p_in = p_input->p_first_byte_to_mix;
    p_out = p_buffer->p_buffer;
    for ( ; ; )
    {
        ptrdiff_t i_available_bytes = (p_input->fifo.p_first->p_buffer
                                        - p_in)
                                        + p_input->fifo.p_first->i_nb_samples
                                           * sizeof(int32_t)
                                           * i_nb_channels;
        if ( i_available_bytes < i_nb_bytes )
        {
            aout_buffer_t * p_old_buffer;
            vlc_memcpy( p_out, p_in, i_available_bytes );
            i_nb_bytes -= i_available_bytes;
            p_out += i_available_bytes;
            /* Next buffer */
            p_old_buffer = aout_FifoPop( p_aout, &p_input->fifo );
            aout_BufferFree( p_old_buffer );
            if ( p_input->fifo.p_first == NULL )
            {
                msg_Err( p_aout, "internal amix error" );
                return;
            }
            p_in = p_input->fifo.p_first->p_buffer;
        }
        else
        {
            vlc_memcpy( p_out, p_in, i_nb_bytes );
            p_input->p_first_byte_to_mix = p_in + i_nb_bytes;
            break;
        }
    }
    /* Empty other FIFOs to avoid a memory leak. */
    for ( i++; i < p_aout->i_nb_inputs; i++ )
    {
        aout_fifo_t * p_fifo;
        aout_buffer_t * p_deleted;
        p_input = p_aout->pp_inputs[i];
        if ( p_input->b_error || p_input->b_paused )
            continue;
        p_fifo = &p_input->fifo;
        p_deleted = p_fifo->p_first;
        while ( p_deleted != NULL )
        {
            aout_buffer_t * p_next = p_deleted->p_next;
            aout_BufferFree( p_deleted );
            p_deleted = p_next;
        }
        p_fifo->p_first = NULL;
        p_fifo->pp_last = &p_fifo->p_first;
    }
}

						