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mpga.c：源码内容
							/*****************************************************************************
 * mpga.c : MPEG-I/II Audio input module for vlc
 *****************************************************************************
 * Copyright (C) 2001-2004 VideoLAN
 * $Id: mpga.c 9061 2004-10-26 13:03:03Z gbazin $
 *
 * 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 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., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
 *****************************************************************************/
/*****************************************************************************
 * Preamble
 *****************************************************************************/
#include <stdlib.h>                                      /* malloc(), free() */
#include <vlc/vlc.h>
#include <vlc/input.h>
#include "vlc_codec.h"
#include "vlc_meta.h"
#define MPGA_PACKET_SIZE 4096
/*****************************************************************************
 * Module descriptor
 *****************************************************************************/
static int  Open ( vlc_object_t * );
static void Close( vlc_object_t * );
vlc_module_begin();
    set_description( _("MPEG-I/II audio demuxer" ) );
    set_capability( "demux2", 100 );
    set_callbacks( Open, Close );
    add_shortcut( "mpga" );
    add_shortcut( "mp3" );
vlc_module_end();
/*****************************************************************************
 * Local prototypes
 *****************************************************************************/
static int Demux  ( demux_t * );
static int Control( demux_t *, int, va_list );
struct demux_sys_t
{
    es_out_id_t *p_es;
    vlc_meta_t  *meta;
    vlc_bool_t  b_start;
    decoder_t   *p_packetizer;
    mtime_t     i_pts;
    mtime_t     i_time_offset;
    int         i_bitrate_avg;  /* extracted from Xing header */
    int i_xing_frames;
    int i_xing_bytes;
    int i_xing_bitrate_avg;
    int i_xing_frame_samples;
};
static int HeaderCheck( uint32_t h )
{
    if( ((( h >> 21 )&0x07FF) != 0x07FF )   /* header sync */
        || (((h >> 17)&0x03) == 0 )         /* valid layer ?*/
        || (((h >> 12)&0x0F) == 0x0F )
        || (((h >> 12)&0x0F) == 0x00 )      /* valid bitrate ? */
        || (((h >> 10) & 0x03) == 0x03 )    /* valide sampling freq ? */
        || ((h & 0x03) == 0x02 ))           /* valid emphasis ? */
    {
        return VLC_FALSE;
    }
    return VLC_TRUE;
}
#define MPGA_VERSION( h )   ( 1 - (((h)>>19)&0x01) )
#define MPGA_LAYER( h )     ( 3 - (((h)>>17)&0x03) )
#define MPGA_MODE(h)        (((h)>> 6)&0x03)
static int mpga_frame_samples( uint32_t h )
{
    switch( MPGA_LAYER(h) )
    {
        case 0:
            return 384;
        case 1:
            return 1152;
        case 2:
            return MPGA_VERSION(h) ? 576 : 1152;
        default:
            return 0;
    }
}
/*****************************************************************************
 * Open: initializes demux structures
 *****************************************************************************/
static int Open( vlc_object_t * p_this )
{
    demux_t     *p_demux = (demux_t*)p_this;
    demux_sys_t *p_sys;
    vlc_bool_t  b_forced = VLC_FALSE;
    uint32_t     header;
    uint8_t     *p_peek;
    module_t    *p_id3;
    vlc_meta_t  *p_meta = NULL;
    if( p_demux->psz_path )
    {
        int  i_len = strlen( p_demux->psz_path );
        if( i_len > 4 && !strcasecmp( &p_demux->psz_path[i_len - 4], ".mp3" ) )
        {
            b_forced = VLC_TRUE;
        }
    }
    /* Skip/parse possible id3 header */
    if( ( p_id3 = module_Need( p_demux, "id3", NULL, 0 ) ) )
    {
        p_meta = (vlc_meta_t *)p_demux->p_private;
        p_demux->p_private = NULL;
        module_Unneed( p_demux, p_id3 );
    }
    if( stream_Peek( p_demux->s, &p_peek, 4 ) < 4 )
    {
        msg_Err( p_demux, "cannot peek" );
        if( p_meta ) vlc_meta_Delete( p_meta );
        return VLC_EGENERIC;
    }
    if( !HeaderCheck( header = GetDWBE( p_peek ) ) )
    {
        vlc_bool_t b_ok = VLC_FALSE;
        int i_peek;
        if( !p_demux->b_force && !b_forced )
        {
            if( p_meta ) vlc_meta_Delete( p_meta );
            return VLC_EGENERIC;
        }
        i_peek = stream_Peek( p_demux->s, &p_peek, 8096 );
        while( i_peek > 4 )
        {
            if( HeaderCheck( header = GetDWBE( p_peek ) ) )
            {
                b_ok = VLC_TRUE;
                break;
            }
            p_peek += 1;
            i_peek -= 1;
        }
        if( !b_ok && !p_demux->b_force )
        {
            msg_Warn( p_demux, "mpga module discarded" );
            if( p_meta ) vlc_meta_Delete( p_meta );
            return VLC_EGENERIC;
        }
    }
    p_demux->p_sys = p_sys = malloc( sizeof( demux_sys_t ) );
    memset( p_sys, 0, sizeof( demux_sys_t ) );
    p_sys->p_es = 0;
    p_sys->p_packetizer = 0;
    p_sys->b_start = VLC_TRUE;
    p_sys->meta = p_meta;
    p_demux->pf_demux   = Demux;
    p_demux->pf_control = Control;
    /*
     * Load the mpeg audio packetizer
     */
    p_sys->p_packetizer = vlc_object_create( p_demux, VLC_OBJECT_PACKETIZER );
    p_sys->p_packetizer->pf_decode_audio = NULL;
    p_sys->p_packetizer->pf_decode_video = NULL;
    p_sys->p_packetizer->pf_decode_sub = NULL;
    p_sys->p_packetizer->pf_packetize = NULL;
    es_format_Init( &p_sys->p_packetizer->fmt_in, AUDIO_ES,
                    VLC_FOURCC( 'm', 'p', 'g', 'a' ) );
    es_format_Init( &p_sys->p_packetizer->fmt_out, UNKNOWN_ES, 0 );
    p_sys->p_packetizer->p_module =
        module_Need( p_sys->p_packetizer, "packetizer", NULL, 0 );
    if( p_sys->p_packetizer->p_module == NULL )
    {
        msg_Err( p_demux, "cannot find mpga packetizer" );
        Close( VLC_OBJECT(p_demux ) );
        return VLC_EGENERIC;
    }
    /* Xing header */
    if( HeaderCheck( header ) )
    {
        int i_xing, i_skip;
        uint8_t *p_xing;
        if( ( i_xing = stream_Peek( p_demux->s, &p_xing, 1024 ) ) < 21 )
            return VLC_SUCCESS; /* No header */
        if( MPGA_VERSION( header ) == 0 )
        {
            i_skip = MPGA_MODE( header ) != 3 ? 36 : 21;
        }
        else
        {
            i_skip = MPGA_MODE( header ) != 3 ? 21 : 13;
        }
        if( i_skip + 8 < i_xing && !strncmp( &p_xing[i_skip], "Xing", 4 ) )
        {
            unsigned int i_flags = GetDWBE( &p_xing[i_skip+4] );
            p_xing += i_skip + 8;
            i_xing -= i_skip + 8;
            i_skip = 0;
            if( i_flags&0x01 && i_skip + 4 <= i_xing )   /* XING_FRAMES */
            {
                p_sys->i_xing_frames = GetDWBE( &p_xing[i_skip] );
                i_skip += 4;
            }
            if( i_flags&0x02 && i_skip + 4 <= i_xing )   /* XING_BYTES */
            {
                p_sys->i_xing_bytes = GetDWBE( &p_xing[i_skip] );
                i_skip += 4;
            }
            if( i_flags&0x04 )   /* XING_TOC */
            {
                i_skip += 100;
            }
            // FIXME: doesn't return the right bitrage average, at least
            // with some MP3's
            if( i_flags&0x08 && i_skip + 4 <= i_xing )   /* XING_VBR */
            {
                p_sys->i_xing_bitrate_avg = GetDWBE( &p_xing[i_skip] );
                msg_Dbg( p_demux, "xing vbr value present (%d)",
                         p_sys->i_xing_bitrate_avg );
            }
            if( p_sys->i_xing_frames > 0 && p_sys->i_xing_bytes > 0 )
            {
                p_sys->i_xing_frame_samples = mpga_frame_samples( header );
                msg_Dbg( p_demux, "xing frames&bytes value present "
                         "(%d bytes, %d frames, %d samples/frame)",
                         p_sys->i_xing_bytes, p_sys->i_xing_frames,
                         p_sys->i_xing_frame_samples );
            }
        }
    }
    return VLC_SUCCESS;
}
/*****************************************************************************
 * Demux: reads and demuxes data packets
 *****************************************************************************
 * Returns -1 in case of error, 0 in case of EOF, 1 otherwise
 *****************************************************************************/
static int Demux( demux_t *p_demux )
{
    demux_sys_t *p_sys = p_demux->p_sys;
    block_t *p_block_in, *p_block_out;
    if( ( p_block_in = stream_Block( p_demux->s, MPGA_PACKET_SIZE ) ) == NULL )
    {
        return 0;
    }
    p_block_in->i_pts = p_block_in->i_dts = p_sys->b_start ? 1 : 0;
    p_sys->b_start = VLC_FALSE;
    while( (p_block_out = p_sys->p_packetizer->pf_packetize(
                                          p_sys->p_packetizer, &p_block_in )) )
    {
        while( p_block_out )
        {
            block_t *p_next = p_block_out->p_next;
            if( p_sys->p_es == NULL )
            {
                p_sys->p_packetizer->fmt_out.b_packetized = VLC_TRUE;
                p_sys->p_es = es_out_Add( p_demux->out,
                                          &p_sys->p_packetizer->fmt_out);
                p_sys->i_bitrate_avg = p_sys->p_packetizer->fmt_out.i_bitrate;
                if( p_sys->i_xing_bytes && p_sys->i_xing_frames &&
                    p_sys->i_xing_frame_samples )
                {
                    p_sys->i_bitrate_avg = p_sys->i_xing_bytes * I64C(8) *
                        p_sys->p_packetizer->fmt_out.audio.i_rate /
                        p_sys->i_xing_frames / p_sys->i_xing_frame_samples;
                }
            }
            es_out_Control( p_demux->out, ES_OUT_SET_PCR, p_block_out->i_dts );
            p_block_out->p_next = NULL;
            p_sys->i_pts = p_block_out->i_pts;
            es_out_Send( p_demux->out, p_sys->p_es, p_block_out );
            p_block_out = p_next;
        }
    }
    return 1;
}
/*****************************************************************************
 * Close: frees unused data
 *****************************************************************************/
static void Close( vlc_object_t * p_this )
{
    demux_t     *p_demux = (demux_t*)p_this;
    demux_sys_t *p_sys = p_demux->p_sys;
    if( p_sys->meta ) vlc_meta_Delete( p_sys->meta );
    if( p_sys->p_packetizer && p_sys->p_packetizer->p_module )
        module_Unneed( p_sys->p_packetizer, p_sys->p_packetizer->p_module );
    if( p_sys->p_packetizer )
        vlc_object_destroy( p_sys->p_packetizer );
    free( p_sys );
}
/*****************************************************************************
 * Control:
 *****************************************************************************/
static int Control( demux_t *p_demux, int i_query, va_list args )
{
    demux_sys_t *p_sys  = p_demux->p_sys;
    int64_t *pi64;
    vlc_meta_t **pp_meta;
    int i_ret;
    switch( i_query )
    {
        case DEMUX_GET_META:
            pp_meta = (vlc_meta_t **)va_arg( args, vlc_meta_t** );
            if( p_sys->meta ) *pp_meta = vlc_meta_Duplicate( p_sys->meta );
            else *pp_meta = NULL;
            return VLC_SUCCESS;
        case DEMUX_GET_TIME:
            pi64 = (int64_t*)va_arg( args, int64_t * );
            *pi64 = p_sys->i_pts + p_sys->i_time_offset;
            return VLC_SUCCESS;
        case DEMUX_SET_TIME:
            /* FIXME TODO: implement a high precision seek (with mp3 parsing)
             * needed for multi-input */
        default:
            i_ret = demux2_vaControlHelper( p_demux->s, 0, -1,
                                            p_sys->i_bitrate_avg, 1, i_query,
                                            args );
            if( !i_ret && p_sys->i_bitrate_avg > 0 &&
                (i_query == DEMUX_SET_POSITION || i_query == DEMUX_SET_TIME) )
            {
                int64_t i_time = I64C(8000000) * stream_Tell(p_demux->s) /
                    p_sys->i_bitrate_avg;
                /* Fix time_offset */
                if( i_time >= 0 ) p_sys->i_time_offset = i_time - p_sys->i_pts;
            }
            return i_ret;
    }
}

						