git.sesse.net Git - vlc/blob - modules/codec/mpeg_audio.c

   1 /*****************************************************************************
   2  * mpeg_audio.c: parse MPEG audio sync info and packetize the stream
   3  *****************************************************************************
   4  * Copyright (C) 2001-2003 VideoLAN (Centrale Réseaux) and its contributors
   5  * $Id$
   6  *
   7  * Authors: Laurent Aimar <fenrir@via.ecp.fr>
   8  *          Eric Petit <titer@videolan.org>
   9  *          Christophe Massiot <massiot@via.ecp.fr>
  10  *          Gildas Bazin <gbazin@videolan.org>
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; if not, write to the Free Software
  24  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
  25  *****************************************************************************/
  26
  27 /*****************************************************************************
  28  * Preamble
  29  *****************************************************************************/
  30 #include <vlc/vlc.h>
  31 #include <vlc/decoder.h>
  32 #include <vlc/aout.h>
  33
  34 #include "vlc_block_helper.h"
  35
  36 /*****************************************************************************
  37  * decoder_sys_t : decoder descriptor
  38  *****************************************************************************/
  39 struct decoder_sys_t
  40 {
  41     /* Module mode */
  42     vlc_bool_t b_packetizer;
  43
  44     /*
  45      * Input properties
  46      */
  47     int        i_state;
  48
  49     block_bytestream_t bytestream;
  50
  51     /*
  52      * Common properties
  53      */
  54     audio_date_t          end_date;
  55     unsigned int          i_current_layer;
  56
  57     mtime_t i_pts;
  58
  59     int i_frame_size, i_free_frame_size;
  60     unsigned int i_channels_conf, i_channels;
  61     unsigned int i_rate, i_max_frame_size, i_frame_length;
  62     unsigned int i_layer, i_bit_rate;
  63 };
  64
  65 enum {
  66
  67     STATE_NOSYNC,
  68     STATE_SYNC,
  69     STATE_HEADER,
  70     STATE_NEXT_SYNC,
  71     STATE_GET_DATA,
  72     STATE_SEND_DATA
  73 };
  74
  75 /* This isn't the place to put mad-specific stuff. However, it makes the
  76  * mad plug-in's life much easier if we put 8 extra bytes at the end of the
  77  * buffer, because that way it doesn't have to copy the aout_buffer_t to a
  78  * bigger buffer. This has no implication on other plug-ins, and we only
  79  * lose 8 bytes per frame. --Meuuh */
  80 #define MAD_BUFFER_GUARD 8
  81 #define MPGA_HEADER_SIZE 4
  82
  83 /****************************************************************************
  84  * Local prototypes
  85  ****************************************************************************/
  86 static int  OpenDecoder   ( vlc_object_t * );
  87 static int  OpenPacketizer( vlc_object_t * );
  88 static void CloseDecoder  ( vlc_object_t * );
  89 static void *DecodeBlock  ( decoder_t *, block_t ** );
  90
  91 static uint8_t       *GetOutBuffer ( decoder_t *, void ** );
  92 static aout_buffer_t *GetAoutBuffer( decoder_t * );
  93 static block_t       *GetSoutBuffer( decoder_t * );
  94
  95 static int SyncInfo( uint32_t i_header, unsigned int * pi_channels,
  96                      unsigned int * pi_channels_conf,
  97                      unsigned int * pi_sample_rate, unsigned int * pi_bit_rate,
  98                      unsigned int * pi_frame_length,
  99                      unsigned int * pi_max_frame_size,
 100                      unsigned int * pi_layer );
 101
 102 /*****************************************************************************
 103  * Module descriptor
 104  *****************************************************************************/
 105 vlc_module_begin();
 106     set_description( _("MPEG audio layer I/II/III parser") );
 107     set_category( CAT_INPUT );
 108     set_subcategory( SUBCAT_INPUT_ACODEC );
 109 #if defined(SYS_DARWIN) || defined(UNDER_CE)
 110    set_capability( "decoder", 5 );
 111 #else
 112     set_capability( "decoder", 100 );
 113 #endif
 114     set_callbacks( OpenDecoder, CloseDecoder );
 115
 116     add_submodule();
 117     set_description( _("MPEG audio layer I/II/III packetizer") );
 118     set_capability( "packetizer", 10 );
 119     set_callbacks( OpenPacketizer, CloseDecoder );
 120 vlc_module_end();
 121
 122 /*****************************************************************************
 123  * OpenDecoder: probe the decoder and return score
 124  *****************************************************************************/
 125 static int OpenDecoder( vlc_object_t *p_this )
 126 {
 127     decoder_t *p_dec = (decoder_t*)p_this;
 128     decoder_sys_t *p_sys;
 129
 130     if( p_dec->fmt_in.i_codec != VLC_FOURCC('m','p','g','a') )
 131     {
 132         return VLC_EGENERIC;
 133     }
 134
 135     /* HACK: Don't use this codec if we don't have an mpga audio filter */
 136     if( p_dec->i_object_type == VLC_OBJECT_DECODER &&
 137         !config_FindModule( p_this, "mpgatofixed32" ) )
 138     {
 139         return VLC_EGENERIC;
 140     }
 141
 142     /* Allocate the memory needed to store the decoder's structure */
 143     if( ( p_dec->p_sys = p_sys =
 144           (decoder_sys_t *)malloc(sizeof(decoder_sys_t)) ) == NULL )
 145     {
 146         msg_Err( p_dec, "out of memory" );
 147         return VLC_EGENERIC;
 148     }
 149
 150     /* Misc init */
 151     p_sys->b_packetizer = VLC_FALSE;
 152     p_sys->i_state = STATE_NOSYNC;
 153     aout_DateSet( &p_sys->end_date, 0 );
 154     p_sys->bytestream = block_BytestreamInit( p_dec );
 155
 156     /* Set output properties */
 157     p_dec->fmt_out.i_cat = AUDIO_ES;
 158     p_dec->fmt_out.i_codec = VLC_FOURCC('m','p','g','a');
 159     p_dec->fmt_out.audio.i_rate = 0; /* So end_date gets initialized */
 160
 161     /* Set callback */
 162     p_dec->pf_decode_audio = (aout_buffer_t *(*)(decoder_t *, block_t **))
 163         DecodeBlock;
 164     p_dec->pf_packetize    = (block_t *(*)(decoder_t *, block_t **))
 165         DecodeBlock;
 166
 167     /* Start with the minimum size for a free bitrate frame */
 168     p_sys->i_free_frame_size = MPGA_HEADER_SIZE;
 169
 170     return VLC_SUCCESS;
 171 }
 172
 173 static int OpenPacketizer( vlc_object_t *p_this )
 174 {
 175     decoder_t *p_dec = (decoder_t*)p_this;
 176
 177     int i_ret = OpenDecoder( p_this );
 178
 179     if( i_ret == VLC_SUCCESS ) p_dec->p_sys->b_packetizer = VLC_TRUE;
 180
 181     return i_ret;
 182 }
 183
 184 /****************************************************************************
 185  * DecodeBlock: the whole thing
 186  ****************************************************************************
 187  * This function is called just after the thread is launched.
 188  ****************************************************************************/
 189 static void *DecodeBlock( decoder_t *p_dec, block_t **pp_block )
 190 {
 191     decoder_sys_t *p_sys = p_dec->p_sys;
 192     uint8_t p_header[MAD_BUFFER_GUARD];
 193     uint32_t i_header;
 194     uint8_t *p_buf;
 195     void *p_out_buffer;
 196
 197     if( !pp_block || !*pp_block ) return NULL;
 198
 199     if( !aout_DateGet( &p_sys->end_date ) && !(*pp_block)->i_pts )
 200     {
 201         /* We've just started the stream, wait for the first PTS. */
 202         block_Release( *pp_block );
 203         return NULL;
 204     }
 205
 206     if( (*pp_block)->i_flags&(BLOCK_FLAG_DISCONTINUITY|BLOCK_FLAG_CORRUPTED) )
 207     {
 208         p_sys->i_state = STATE_NOSYNC;
 209     }
 210
 211     block_BytestreamPush( &p_sys->bytestream, *pp_block );
 212
 213     while( 1 )
 214     {
 215         switch( p_sys->i_state )
 216         {
 217
 218         case STATE_NOSYNC:
 219             while( block_PeekBytes( &p_sys->bytestream, p_header, 2 )
 220                    == VLC_SUCCESS )
 221             {
 222                 /* Look for sync word - should be 0xffe */
 223                 if( p_header[0] == 0xff && (p_header[1] & 0xe0) == 0xe0 )
 224                 {
 225                     p_sys->i_state = STATE_SYNC;
 226                     break;
 227                 }
 228                 block_SkipByte( &p_sys->bytestream );
 229             }
 230             if( p_sys->i_state != STATE_SYNC )
 231             {
 232                 block_BytestreamFlush( &p_sys->bytestream );
 233
 234                 /* Need more data */
 235                 return NULL;
 236             }
 237
 238         case STATE_SYNC:
 239             /* New frame, set the Presentation Time Stamp */
 240             p_sys->i_pts = p_sys->bytestream.p_block->i_pts;
 241             if( p_sys->i_pts != 0 &&
 242                 p_sys->i_pts != aout_DateGet( &p_sys->end_date ) )
 243             {
 244                 aout_DateSet( &p_sys->end_date, p_sys->i_pts );
 245             }
 246             p_sys->i_state = STATE_HEADER;
 247
 248         case STATE_HEADER:
 249             /* Get MPGA frame header (MPGA_HEADER_SIZE bytes) */
 250             if( block_PeekBytes( &p_sys->bytestream, p_header,
 251                                  MPGA_HEADER_SIZE ) != VLC_SUCCESS )
 252             {
 253                 /* Need more data */
 254                 return NULL;
 255             }
 256
 257             /* Build frame header */
 258             i_header = (p_header[0]<<24)|(p_header[1]<<16)|(p_header[2]<<8)
 259                        |p_header[3];
 260
 261             /* Check if frame is valid and get frame info */
 262             p_sys->i_frame_size = SyncInfo( i_header,
 263                                             &p_sys->i_channels,
 264                                             &p_sys->i_channels_conf,
 265                                             &p_sys->i_rate,
 266                                             &p_sys->i_bit_rate,
 267                                             &p_sys->i_frame_length,
 268                                             &p_sys->i_max_frame_size,
 269                                             &p_sys->i_layer );
 270
 271             if( p_sys->i_frame_size == -1 )
 272             {
 273                 msg_Dbg( p_dec, "emulated startcode" );
 274                 block_SkipByte( &p_sys->bytestream );
 275                 p_sys->i_state = STATE_NOSYNC;
 276                 break;
 277             }
 278
 279             if( p_sys->i_bit_rate == 0 )
 280             {
 281                 /* Free birate, but 99% emulated startcode :( */
 282                 if( p_dec->p_sys->i_free_frame_size == MPGA_HEADER_SIZE )
 283                 {
 284                     msg_Dbg( p_dec, "free bitrate mode");
 285                 }
 286                 p_sys->i_frame_size = p_sys->i_free_frame_size;
 287             }
 288
 289             p_sys->i_state = STATE_NEXT_SYNC;
 290
 291         case STATE_NEXT_SYNC:
 292             /* TODO: If p_block == NULL, flush the buffer without checking the
 293              * next sync word */
 294
 295             /* Check if next expected frame contains the sync word */
 296             if( block_PeekOffsetBytes( &p_sys->bytestream,
 297                                        p_sys->i_frame_size, p_header,
 298                                        MAD_BUFFER_GUARD ) != VLC_SUCCESS )
 299             {
 300                 /* Need more data */
 301                 return NULL;
 302             }
 303
 304             if( p_header[0] == 0xff && (p_header[1] & 0xe0) == 0xe0 )
 305             {
 306                 /* Startcode is fine, let's try the header as an extra check */
 307                 int i_next_frame_size;
 308                 unsigned int i_next_channels, i_next_channels_conf;
 309                 unsigned int i_next_rate, i_next_bit_rate;
 310                 unsigned int i_next_frame_length, i_next_max_frame_size;
 311                 unsigned int i_next_layer;
 312
 313                 /* Build frame header */
 314                 i_header = (p_header[0]<<24)|(p_header[1]<<16)|(p_header[2]<<8)
 315                            |p_header[3];
 316
 317                 i_next_frame_size = SyncInfo( i_header,
 318                                               &i_next_channels,
 319                                               &i_next_channels_conf,
 320                                               &i_next_rate,
 321                                               &i_next_bit_rate,
 322                                               &i_next_frame_length,
 323                                               &i_next_max_frame_size,
 324                                               &i_next_layer );
 325
 326                 /* Free bitrate only */
 327                 if( p_sys->i_bit_rate == 0 && i_next_frame_size == -1 )
 328                 {
 329                     if( (unsigned int)p_sys->i_frame_size >
 330                         p_sys->i_max_frame_size )
 331                     {
 332                         msg_Dbg( p_dec, "frame too big %d > %d "
 333                                  "(emulated startcode ?)", p_sys->i_frame_size,
 334                                  p_sys->i_max_frame_size );
 335                         block_SkipByte( &p_sys->bytestream );
 336                         p_sys->i_state = STATE_NOSYNC;
 337                         p_sys->i_free_frame_size = MPGA_HEADER_SIZE;
 338                         break;
 339                     }
 340
 341                     p_sys->i_frame_size++;
 342                     break;
 343                 }
 344
 345                 if( i_next_frame_size == -1 )
 346                 {
 347                     msg_Dbg( p_dec, "emulated startcode on next frame" );
 348                     block_SkipByte( &p_sys->bytestream );
 349                     p_sys->i_state = STATE_NOSYNC;
 350                     break;
 351                 }
 352
 353                 /* Check info is in sync with previous one */
 354                 if( i_next_channels_conf != p_sys->i_channels_conf ||
 355                     i_next_rate != p_sys->i_rate ||
 356                     i_next_layer != p_sys->i_layer ||
 357                     i_next_frame_length != p_sys->i_frame_length )
 358                 {
 359                     /* Free bitrate only */
 360                     if( p_sys->i_bit_rate == 0 )
 361                     {
 362                         p_sys->i_frame_size++;
 363                         break;
 364                     }
 365
 366                     msg_Dbg( p_dec, "parameters changed unexpectedly "
 367                              "(emulated startcode ?)" );
 368                     block_SkipByte( &p_sys->bytestream );
 369                     p_sys->i_state = STATE_NOSYNC;
 370                     break;
 371                 }
 372
 373                 /* Free bitrate only */
 374                 if( p_sys->i_bit_rate == 0 )
 375                 {
 376                     if( i_next_bit_rate != 0 )
 377                     {
 378                         p_sys->i_frame_size++;
 379                         break;
 380                     }
 381                 }
 382
 383             }
 384             else
 385             {
 386                 /* Free bitrate only */
 387                 if( p_sys->i_bit_rate == 0 )
 388                 {
 389                     if( (unsigned int)p_sys->i_frame_size >
 390                         p_sys->i_max_frame_size )
 391                     {
 392                         msg_Dbg( p_dec, "frame too big %d > %d "
 393                                  "(emulated startcode ?)", p_sys->i_frame_size,
 394                                  p_sys->i_max_frame_size );
 395                         block_SkipByte( &p_sys->bytestream );
 396                         p_sys->i_state = STATE_NOSYNC;
 397                         p_sys->i_free_frame_size = MPGA_HEADER_SIZE;
 398                         break;
 399                     }
 400
 401                     p_sys->i_frame_size++;
 402                     break;
 403                 }
 404
 405                 msg_Dbg( p_dec, "emulated startcode "
 406                          "(no startcode on following frame)" );
 407                 p_sys->i_state = STATE_NOSYNC;
 408                 block_SkipByte( &p_sys->bytestream );
 409                 break;
 410             }
 411
 412             p_sys->i_state = STATE_SEND_DATA;
 413             break;
 414
 415         case STATE_GET_DATA:
 416             /* Make sure we have enough data.
 417              * (Not useful if we went through NEXT_SYNC) */
 418             if( block_WaitBytes( &p_sys->bytestream,
 419                                  p_sys->i_frame_size ) != VLC_SUCCESS )
 420             {
 421                 /* Need more data */
 422                 return NULL;
 423             }
 424             p_sys->i_state = STATE_SEND_DATA;
 425
 426         case STATE_SEND_DATA:
 427             if( !(p_buf = GetOutBuffer( p_dec, &p_out_buffer )) )
 428             {
 429                 //p_dec->b_error = VLC_TRUE;
 430                 return NULL;
 431             }
 432
 433             /* Free bitrate only */
 434             if( p_sys->i_bit_rate == 0 )
 435             {
 436                 p_sys->i_free_frame_size = p_sys->i_frame_size;
 437             }
 438
 439             /* Copy the whole frame into the buffer. When we reach this point
 440              * we already know we have enough data available. */
 441             block_GetBytes( &p_sys->bytestream, p_buf, p_sys->i_frame_size );
 442
 443             /* Get beginning of next frame for libmad */
 444             if( !p_sys->b_packetizer )
 445             {
 446                 memcpy( p_buf + p_sys->i_frame_size,
 447                         p_header, MAD_BUFFER_GUARD );
 448             }
 449
 450             p_sys->i_state = STATE_NOSYNC;
 451
 452             /* Make sure we don't reuse the same pts twice */
 453             if( p_sys->i_pts == p_sys->bytestream.p_block->i_pts )
 454                 p_sys->i_pts = p_sys->bytestream.p_block->i_pts = 0;
 455
 456             /* So p_block doesn't get re-added several times */
 457             *pp_block = block_BytestreamPop( &p_sys->bytestream );
 458
 459             return p_out_buffer;
 460         }
 461     }
 462
 463     return NULL;
 464 }
 465
 466 /*****************************************************************************
 467  * GetOutBuffer:
 468  *****************************************************************************/
 469 static uint8_t *GetOutBuffer( decoder_t *p_dec, void **pp_out_buffer )
 470 {
 471     decoder_sys_t *p_sys = p_dec->p_sys;
 472     uint8_t *p_buf;
 473
 474     if( p_dec->fmt_out.audio.i_rate != p_sys->i_rate )
 475     {
 476         msg_Dbg( p_dec, "MPGA channels:%d samplerate:%d bitrate:%d",
 477                   p_sys->i_channels, p_sys->i_rate, p_sys->i_bit_rate );
 478
 479         aout_DateInit( &p_sys->end_date, p_sys->i_rate );
 480         aout_DateSet( &p_sys->end_date, p_sys->i_pts );
 481     }
 482
 483     p_dec->fmt_out.audio.i_rate     = p_sys->i_rate;
 484     p_dec->fmt_out.audio.i_channels = p_sys->i_channels;
 485     p_dec->fmt_out.audio.i_frame_length = p_sys->i_frame_length;
 486     p_dec->fmt_out.audio.i_bytes_per_frame =
 487         p_sys->i_max_frame_size + MAD_BUFFER_GUARD;
 488
 489     p_dec->fmt_out.audio.i_original_channels = p_sys->i_channels_conf;
 490     p_dec->fmt_out.audio.i_physical_channels =
 491         p_sys->i_channels_conf & AOUT_CHAN_PHYSMASK;
 492
 493     p_dec->fmt_out.i_bitrate = p_sys->i_bit_rate * 1000;
 494
 495     if( p_sys->b_packetizer )
 496     {
 497         block_t *p_sout_buffer = GetSoutBuffer( p_dec );
 498         p_buf = p_sout_buffer ? p_sout_buffer->p_buffer : NULL;
 499         *pp_out_buffer = p_sout_buffer;
 500     }
 501     else
 502     {
 503         aout_buffer_t *p_aout_buffer = GetAoutBuffer( p_dec );
 504         p_buf = p_aout_buffer ? p_aout_buffer->p_buffer : NULL;
 505         *pp_out_buffer = p_aout_buffer;
 506     }
 507
 508     return p_buf;
 509 }
 510
 511 /*****************************************************************************
 512  * GetAoutBuffer:
 513  *****************************************************************************/
 514 static aout_buffer_t *GetAoutBuffer( decoder_t *p_dec )
 515 {
 516     decoder_sys_t *p_sys = p_dec->p_sys;
 517     aout_buffer_t *p_buf;
 518
 519     p_buf = p_dec->pf_aout_buffer_new( p_dec, p_sys->i_frame_length );
 520     if( p_buf == NULL ) return NULL;
 521
 522     p_buf->start_date = aout_DateGet( &p_sys->end_date );
 523     p_buf->end_date =
 524         aout_DateIncrement( &p_sys->end_date, p_sys->i_frame_length );
 525
 526     /* Hack for libmad filter */
 527     p_buf->i_nb_bytes = p_sys->i_frame_size + MAD_BUFFER_GUARD;
 528
 529     return p_buf;
 530 }
 531
 532 /*****************************************************************************
 533  * GetSoutBuffer:
 534  *****************************************************************************/
 535 static block_t *GetSoutBuffer( decoder_t *p_dec )
 536 {
 537     decoder_sys_t *p_sys = p_dec->p_sys;
 538     block_t *p_block;
 539
 540     p_block = block_New( p_dec, p_sys->i_frame_size );
 541     if( p_block == NULL ) return NULL;
 542
 543     p_block->i_pts = p_block->i_dts = aout_DateGet( &p_sys->end_date );
 544
 545     p_block->i_length =
 546         aout_DateIncrement( &p_sys->end_date, p_sys->i_frame_length ) -
 547             p_block->i_pts;
 548
 549     return p_block;
 550 }
 551
 552 /*****************************************************************************
 553  * CloseDecoder: clean up the decoder
 554  *****************************************************************************/
 555 static void CloseDecoder( vlc_object_t *p_this )
 556 {
 557     decoder_t *p_dec = (decoder_t *)p_this;
 558     decoder_sys_t *p_sys = p_dec->p_sys;
 559
 560     block_BytestreamRelease( &p_sys->bytestream );
 561
 562     free( p_sys );
 563 }
 564
 565 /*****************************************************************************
 566  * SyncInfo: parse MPEG audio sync info
 567  *****************************************************************************/
 568 static int SyncInfo( uint32_t i_header, unsigned int * pi_channels,
 569                      unsigned int * pi_channels_conf,
 570                      unsigned int * pi_sample_rate, unsigned int * pi_bit_rate,
 571                      unsigned int * pi_frame_length,
 572                      unsigned int * pi_max_frame_size, unsigned int * pi_layer)
 573 {
 574     static const int ppi_bitrate[2][3][16] =
 575     {
 576         {
 577             /* v1 l1 */
 578             { 0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384,
 579               416, 448, 0},
 580             /* v1 l2 */
 581             { 0, 32, 48, 56,  64,  80,  96, 112, 128, 160, 192, 224, 256,
 582               320, 384, 0},
 583             /* v1 l3 */
 584             { 0, 32, 40, 48,  56,  64,  80,  96, 112, 128, 160, 192, 224,
 585               256, 320, 0}
 586         },
 587
 588         {
 589             /* v2 l1 */
 590             { 0, 32, 48, 56,  64,  80,  96, 112, 128, 144, 160, 176, 192,
 591               224, 256, 0},
 592             /* v2 l2 */
 593             { 0,  8, 16, 24,  32,  40,  48,  56,  64,  80,  96, 112, 128,
 594               144, 160, 0},
 595             /* v2 l3 */
 596             { 0,  8, 16, 24,  32,  40,  48,  56,  64,  80,  96, 112, 128,
 597               144, 160, 0}
 598         }
 599     };
 600
 601     static const int ppi_samplerate[2][4] = /* version 1 then 2 */
 602     {
 603         { 44100, 48000, 32000, 0 },
 604         { 22050, 24000, 16000, 0 }
 605     };
 606
 607     int i_version, i_mode, i_emphasis;
 608     vlc_bool_t b_padding, b_mpeg_2_5, b_crc;
 609     int i_frame_size = 0;
 610     int i_bitrate_index, i_samplerate_index;
 611     int i_max_bit_rate;
 612
 613     b_mpeg_2_5  = 1 - ((i_header & 0x100000) >> 20);
 614     i_version   = 1 - ((i_header & 0x80000) >> 19);
 615     *pi_layer   = 4 - ((i_header & 0x60000) >> 17);
 616     b_crc = !((i_header >> 16) & 0x01);
 617     i_bitrate_index = (i_header & 0xf000) >> 12;
 618     i_samplerate_index = (i_header & 0xc00) >> 10;
 619     b_padding   = (i_header & 0x200) >> 9;
 620     /* Extension */
 621     i_mode      = (i_header & 0xc0) >> 6;
 622     /* Modeext, copyright & original */
 623     i_emphasis  = i_header & 0x3;
 624
 625     if( *pi_layer != 4 &&
 626         i_bitrate_index < 0x0f &&
 627         i_samplerate_index != 0x03 &&
 628         i_emphasis != 0x02 )
 629     {
 630         switch ( i_mode )
 631         {
 632         case 0: /* stereo */
 633         case 1: /* joint stereo */
 634             *pi_channels = 2;
 635             *pi_channels_conf = AOUT_CHAN_LEFT | AOUT_CHAN_RIGHT;
 636             break;
 637         case 2: /* dual-mono */
 638             *pi_channels = 2;
 639             *pi_channels_conf = AOUT_CHAN_LEFT | AOUT_CHAN_RIGHT
 640                                 | AOUT_CHAN_DUALMONO;
 641             break;
 642         case 3: /* mono */
 643             *pi_channels = 1;
 644             *pi_channels_conf = AOUT_CHAN_CENTER;
 645             break;
 646         }
 647         *pi_bit_rate = ppi_bitrate[i_version][*pi_layer-1][i_bitrate_index];
 648         i_max_bit_rate = ppi_bitrate[i_version][*pi_layer-1][14];
 649         *pi_sample_rate = ppi_samplerate[i_version][i_samplerate_index];
 650
 651         if ( b_mpeg_2_5 )
 652         {
 653             *pi_sample_rate >>= 1;
 654         }
 655
 656         switch( *pi_layer )
 657         {
 658         case 1:
 659             i_frame_size = ( 12000 * *pi_bit_rate / *pi_sample_rate +
 660                            b_padding ) * 4;
 661             *pi_max_frame_size = ( 12000 * i_max_bit_rate /
 662                                  *pi_sample_rate + 1 ) * 4;
 663             *pi_frame_length = 384;
 664             break;
 665
 666         case 2:
 667             i_frame_size = 144000 * *pi_bit_rate / *pi_sample_rate + b_padding;
 668             *pi_max_frame_size = 144000 * i_max_bit_rate / *pi_sample_rate + 1;
 669             *pi_frame_length = 1152;
 670             break;
 671
 672         case 3:
 673             i_frame_size = ( i_version ? 72000 : 144000 ) *
 674                            *pi_bit_rate / *pi_sample_rate + b_padding;
 675             *pi_max_frame_size = ( i_version ? 72000 : 144000 ) *
 676                                  i_max_bit_rate / *pi_sample_rate + 1;
 677             *pi_frame_length = i_version ? 576 : 1152;
 678             break;
 679
 680         default:
 681             break;
 682         }
 683     }
 684     else
 685     {
 686         return -1;
 687     }
 688
 689     return i_frame_size;
 690 }