git.sesse.net Git - vlc/blob - modules/packetizer/flac.c

   1 /*****************************************************************************
   2  * flac.c: flac packetizer module.
   3  *****************************************************************************
   4  * Copyright (C) 1999-2001 the VideoLAN team
   5  * $Id$
   6  *
   7  * Authors: Gildas Bazin <gbazin@videolan.org>
   8  *          Sigmund Augdal Helberg <dnumgis@videolan.org>
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License as published by
  12  * the Free Software Foundation; either version 2 of the License, or
  13  * (at your option) any later version.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU General Public License
  21  * along with this program; if not, write to the Free Software
  22  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  23  *****************************************************************************/
  24
  25 /*****************************************************************************
  26  * Preamble
  27  *****************************************************************************/
  28
  29 #ifdef HAVE_CONFIG_H
  30 # include "config.h"
  31 #endif
  32
  33 #include <vlc_common.h>
  34 #include <vlc_plugin.h>
  35 #include <vlc_codec.h>
  36
  37 #include <vlc_block_helper.h>
  38 #include <vlc_bits.h>
  39
  40 /*****************************************************************************
  41  * Module descriptor
  42  *****************************************************************************/
  43 static int  Open ( vlc_object_t * );
  44 static void Close( vlc_object_t * );
  45
  46 vlc_module_begin()
  47     set_category( CAT_SOUT )
  48     set_subcategory( SUBCAT_SOUT_PACKETIZER )
  49     set_description( N_("Flac audio packetizer") )
  50     set_capability( "packetizer", 50 )
  51     set_callbacks( Open, Close )
  52 vlc_module_end()
  53
  54 /*****************************************************************************
  55  * decoder_sys_t : FLAC decoder descriptor
  56  *****************************************************************************/
  57 #define MAX_FLAC_HEADER_SIZE 16
  58 struct decoder_sys_t
  59 {
  60     /*
  61      * Input properties
  62      */
  63     int i_state;
  64
  65     block_bytestream_t bytestream;
  66
  67     /*
  68      * FLAC properties
  69      */
  70     struct
  71     {
  72         unsigned min_blocksize, max_blocksize;
  73         unsigned min_framesize, max_framesize;
  74         unsigned sample_rate;
  75         unsigned channels;
  76         unsigned bits_per_sample;
  77
  78     } stream_info;
  79     bool b_stream_info;
  80
  81     /*
  82      * Common properties
  83      */
  84     date_t  end_date;
  85     mtime_t i_pts;
  86
  87     int i_frame_length;
  88     size_t i_frame_size;
  89     unsigned int i_rate, i_channels, i_bits_per_sample;
  90 };
  91
  92 enum
  93 {
  94     STATE_NOSYNC,
  95     STATE_SYNC,
  96     STATE_HEADER,
  97     STATE_NEXT_SYNC,
  98     STATE_GET_DATA,
  99     STATE_SEND_DATA
 100 };
 101
 102 /*****************************************************************************
 103  * Local prototypes
 104  *****************************************************************************/
 105 static block_t *Packetize( decoder_t *, block_t ** );
 106
 107 static int SyncInfo( decoder_t *, uint8_t *, unsigned int *,
 108                      unsigned int *, unsigned int * );
 109
 110 static uint64_t read_utf8( const uint8_t *p_buf, int *pi_read );
 111 static uint8_t flac_crc8( const uint8_t *data, unsigned len );
 112
 113 static int Open( vlc_object_t *p_this )
 114 {
 115     decoder_t *p_dec = (decoder_t*)p_this;
 116     decoder_sys_t *p_sys;
 117
 118     if( p_dec->fmt_in.i_codec != VLC_CODEC_FLAC )
 119         return VLC_EGENERIC;
 120
 121     /* */
 122     p_dec->p_sys = p_sys = malloc(sizeof(*p_sys));
 123     if( !p_sys )
 124         return VLC_ENOMEM;
 125
 126     date_Set( &p_sys->end_date, 0 );
 127     p_sys->i_state       = STATE_NOSYNC;
 128     p_sys->b_stream_info = false;
 129     p_sys->i_pts         = VLC_TS_INVALID;
 130     p_sys->bytestream    = block_BytestreamInit();
 131
 132     /* */
 133     es_format_Copy( &p_dec->fmt_out, &p_dec->fmt_in );
 134     p_dec->fmt_out.i_cat   = AUDIO_ES;
 135     p_dec->fmt_out.i_codec = VLC_CODEC_FLAC;
 136
 137     /* */
 138     p_dec->pf_decode_audio = NULL;
 139     p_dec->pf_packetize    = Packetize;
 140
 141     return VLC_SUCCESS;
 142 }
 143
 144 static void Close( vlc_object_t *p_this )
 145 {
 146     decoder_t *p_dec = (decoder_t *)p_this;
 147     decoder_sys_t *p_sys = p_dec->p_sys;
 148
 149     block_BytestreamRelease( &p_sys->bytestream );
 150     free( p_sys );
 151 }
 152
 153 /*****************************************************************************
 154  * ProcessHeader: process Flac header.
 155  *****************************************************************************/
 156 static void ProcessHeader( decoder_t *p_dec )
 157 {
 158     decoder_sys_t *p_sys = p_dec->p_sys;
 159
 160     bs_t bs;
 161
 162     if( p_dec->fmt_in.i_extra < 8 + 14 )
 163         return;
 164
 165     bs_init( &bs, (uint8_t*)p_dec->fmt_in.p_extra + 8, p_dec->fmt_in.i_extra - 8 );
 166
 167     p_sys->stream_info.min_blocksize = bs_read( &bs, 16 );
 168     p_sys->stream_info.max_blocksize = bs_read( &bs, 16 );
 169
 170     p_sys->stream_info.min_framesize = bs_read( &bs, 24 );
 171     p_sys->stream_info.max_framesize = bs_read( &bs, 24 );
 172
 173     p_sys->stream_info.sample_rate = bs_read( &bs, 20 );
 174     p_sys->stream_info.channels = bs_read( &bs, 3 ) + 1;
 175     p_sys->stream_info.bits_per_sample = bs_read( &bs, 5 ) + 1;
 176
 177     p_sys->b_stream_info = true;
 178
 179     p_dec->fmt_out.i_extra = p_dec->fmt_in.i_extra;
 180     p_dec->fmt_out.p_extra = xrealloc( p_dec->fmt_out.p_extra,
 181                                        p_dec->fmt_out.i_extra );
 182     memcpy( p_dec->fmt_out.p_extra,
 183             p_dec->fmt_in.p_extra, p_dec->fmt_out.i_extra );
 184 }
 185
 186 /* */
 187 static block_t *Packetize( decoder_t *p_dec, block_t **pp_block )
 188 {
 189     decoder_sys_t *p_sys = p_dec->p_sys;
 190     uint8_t p_header[MAX_FLAC_HEADER_SIZE];
 191     block_t *p_sout_block;
 192
 193     if( !pp_block || !*pp_block ) return NULL;
 194
 195     if( (*pp_block)->i_flags&(BLOCK_FLAG_DISCONTINUITY|BLOCK_FLAG_CORRUPTED) )
 196     {
 197         if( (*pp_block)->i_flags&BLOCK_FLAG_CORRUPTED )
 198         {
 199             p_sys->i_state = STATE_NOSYNC;
 200             block_BytestreamEmpty( &p_sys->bytestream );
 201         }
 202         date_Set( &p_sys->end_date, 0 );
 203         block_Release( *pp_block );
 204         return NULL;
 205     }
 206
 207     if( !p_sys->b_stream_info )
 208         ProcessHeader( p_dec );
 209
 210     if( p_sys->stream_info.channels > 8 )
 211     {
 212         msg_Err( p_dec, "This stream uses too many audio channels" );
 213         return NULL;
 214     }
 215
 216     if( !date_Get( &p_sys->end_date ) && (*pp_block)->i_pts <= VLC_TS_INVALID )
 217     {
 218         /* We've just started the stream, wait for the first PTS. */
 219         block_Release( *pp_block );
 220         return NULL;
 221     }
 222     else if( !date_Get( &p_sys->end_date ) )
 223     {
 224         /* The first PTS is as good as anything else. */
 225         p_sys->i_rate = p_dec->fmt_out.audio.i_rate;
 226         date_Init( &p_sys->end_date, p_sys->i_rate, 1 );
 227         date_Set( &p_sys->end_date, (*pp_block)->i_pts );
 228     }
 229
 230     block_BytestreamPush( &p_sys->bytestream, *pp_block );
 231
 232     while( 1 )
 233     {
 234         switch( p_sys->i_state )
 235         {
 236         case STATE_NOSYNC:
 237             while( block_PeekBytes( &p_sys->bytestream, p_header, 2 )
 238                    == VLC_SUCCESS )
 239             {
 240                 if( p_header[0] == 0xFF && (p_header[1] & 0xFE) == 0xF8 )
 241                 {
 242                     p_sys->i_state = STATE_SYNC;
 243                     break;
 244                 }
 245                 block_SkipByte( &p_sys->bytestream );
 246             }
 247             if( p_sys->i_state != STATE_SYNC )
 248             {
 249                 block_BytestreamFlush( &p_sys->bytestream );
 250
 251                 /* Need more data */
 252                 return NULL;
 253             }
 254
 255         case STATE_SYNC:
 256             /* New frame, set the Presentation Time Stamp */
 257             p_sys->i_pts = p_sys->bytestream.p_block->i_pts;
 258             if( p_sys->i_pts > VLC_TS_INVALID &&
 259                 p_sys->i_pts != date_Get( &p_sys->end_date ) )
 260             {
 261                 date_Set( &p_sys->end_date, p_sys->i_pts );
 262             }
 263             p_sys->i_state = STATE_HEADER;
 264
 265         case STATE_HEADER:
 266             /* Get FLAC frame header (MAX_FLAC_HEADER_SIZE bytes) */
 267             if( block_PeekBytes( &p_sys->bytestream, p_header,
 268                                  MAX_FLAC_HEADER_SIZE ) != VLC_SUCCESS )
 269             {
 270                 /* Need more data */
 271                 return NULL;
 272             }
 273
 274             /* Check if frame is valid and get frame info */
 275             p_sys->i_frame_length = SyncInfo( p_dec, p_header,
 276                                               &p_sys->i_channels,
 277                                               &p_sys->i_rate,
 278                                               &p_sys->i_bits_per_sample );
 279             if( !p_sys->i_frame_length )
 280             {
 281                 msg_Dbg( p_dec, "emulated sync word" );
 282                 block_SkipByte( &p_sys->bytestream );
 283                 p_sys->i_state = STATE_NOSYNC;
 284                 break;
 285             }
 286             if( p_sys->i_rate != p_dec->fmt_out.audio.i_rate )
 287             {
 288                 p_dec->fmt_out.audio.i_rate = p_sys->i_rate;
 289                 const mtime_t i_end_date = date_Get( &p_sys->end_date );
 290                 date_Init( &p_sys->end_date, p_sys->i_rate, 1 );
 291                 date_Set( &p_sys->end_date, i_end_date );
 292             }
 293             p_sys->i_state = STATE_NEXT_SYNC;
 294             p_sys->i_frame_size = p_sys->b_stream_info && p_sys->stream_info.min_framesize > 0 ?
 295                                                             p_sys->stream_info.min_framesize : 1;
 296
 297         case STATE_NEXT_SYNC:
 298             /* TODO: If pp_block == NULL, flush the buffer without checking the
 299              * next sync word */
 300
 301             /* Check if next expected frame contains the sync word */
 302             while( block_PeekOffsetBytes( &p_sys->bytestream,
 303                                           p_sys->i_frame_size, p_header,
 304                                           MAX_FLAC_HEADER_SIZE )
 305                    == VLC_SUCCESS )
 306             {
 307                 if( p_header[0] == 0xFF && (p_header[1] & 0xFE) == 0xF8 )
 308                 {
 309                     /* Check if frame is valid and get frame info */
 310                     int i_frame_length =
 311                         SyncInfo( p_dec, p_header,
 312                                   &p_sys->i_channels,
 313                                   &p_sys->i_rate,
 314                                   &p_sys->i_bits_per_sample );
 315
 316                     if( i_frame_length )
 317                     {
 318                         p_sys->i_state = STATE_SEND_DATA;
 319                         break;
 320                     }
 321                 }
 322                 p_sys->i_frame_size++;
 323             }
 324
 325             if( p_sys->i_state != STATE_SEND_DATA )
 326             {
 327                 if( p_sys->b_stream_info && p_sys->stream_info.max_framesize > 0 &&
 328                     p_sys->i_frame_size > p_sys->stream_info.max_framesize )
 329                 {
 330                     block_SkipByte( &p_sys->bytestream );
 331                     p_sys->i_state = STATE_NOSYNC;
 332                     return NULL;
 333                 }
 334                 /* Need more data */
 335                 return NULL;
 336             }
 337
 338         case STATE_SEND_DATA:
 339             p_sout_block = block_New( p_dec, p_sys->i_frame_size );
 340
 341             /* Copy the whole frame into the buffer. When we reach this point
 342              * we already know we have enough data available. */
 343             block_GetBytes( &p_sys->bytestream, p_sout_block->p_buffer,
 344                             p_sys->i_frame_size );
 345
 346             /* Make sure we don't reuse the same pts twice */
 347             if( p_sys->i_pts == p_sys->bytestream.p_block->i_pts )
 348                 p_sys->i_pts = p_sys->bytestream.p_block->i_pts = VLC_TS_INVALID;
 349
 350             /* So p_block doesn't get re-added several times */
 351             *pp_block = block_BytestreamPop( &p_sys->bytestream );
 352
 353             p_sys->i_state = STATE_NOSYNC;
 354
 355             /* Date management */
 356             p_sout_block->i_pts =
 357                 p_sout_block->i_dts = date_Get( &p_sys->end_date );
 358             date_Increment( &p_sys->end_date, p_sys->i_frame_length );
 359             p_sout_block->i_length =
 360                 date_Get( &p_sys->end_date ) - p_sout_block->i_pts;
 361
 362             return p_sout_block;
 363         }
 364     }
 365
 366     return NULL;
 367 }
 368
 369 /*****************************************************************************
 370  * SyncInfo: parse FLAC sync info
 371  *****************************************************************************/
 372 static int SyncInfo( decoder_t *p_dec, uint8_t *p_buf,
 373                      unsigned int * pi_channels,
 374                      unsigned int * pi_sample_rate,
 375                      unsigned int * pi_bits_per_sample )
 376 {
 377     decoder_sys_t *p_sys = p_dec->p_sys;
 378     int i_header, i_temp, i_read;
 379     unsigned i_blocksize = 0;
 380     int i_blocksize_hint = 0, i_sample_rate_hint = 0;
 381
 382     /* Check syncword */
 383     if( p_buf[0] != 0xFF || (p_buf[1] & 0xFE) != 0xF8 ) return 0;
 384
 385     /* Check there is no emulated sync code in the rest of the header */
 386     if( p_buf[2] == 0xff || p_buf[3] == 0xFF ) return 0;
 387
 388     /* Find blocksize (framelength) */
 389     switch( i_temp = p_buf[2] >> 4 )
 390     {
 391     case 0:
 392         if( p_sys->b_stream_info &&
 393             p_sys->stream_info.min_blocksize == p_sys->stream_info.max_blocksize )
 394             i_blocksize = p_sys->stream_info.min_blocksize;
 395         else return 0; /* We can't do anything with this */
 396         break;
 397
 398     case 1:
 399         i_blocksize = 192;
 400         break;
 401
 402     case 2:
 403     case 3:
 404     case 4:
 405     case 5:
 406         i_blocksize = 576 << (i_temp - 2);
 407         break;
 408
 409     case 6:
 410     case 7:
 411         i_blocksize_hint = i_temp;
 412         break;
 413
 414     case 8:
 415     case 9:
 416     case 10:
 417     case 11:
 418     case 12:
 419     case 13:
 420     case 14:
 421     case 15:
 422         i_blocksize = 256 << (i_temp - 8);
 423         break;
 424     }
 425     if( p_sys->b_stream_info &&
 426         ( i_blocksize < p_sys->stream_info.min_blocksize ||
 427           i_blocksize > p_sys->stream_info.max_blocksize ) )
 428         return 0;
 429
 430     /* Find samplerate */
 431     switch( i_temp = p_buf[2] & 0x0f )
 432     {
 433     case 0:
 434         if( p_sys->b_stream_info )
 435             *pi_sample_rate = p_sys->stream_info.sample_rate;
 436         else return 0; /* We can't do anything with this */
 437         break;
 438
 439     case 1:
 440         *pi_sample_rate = 88200;
 441         break;
 442
 443     case 2:
 444         *pi_sample_rate = 176400;
 445         break;
 446
 447     case 3:
 448         *pi_sample_rate = 192000;
 449         break;
 450
 451     case 4:
 452         *pi_sample_rate = 8000;
 453         break;
 454
 455     case 5:
 456         *pi_sample_rate = 16000;
 457         break;
 458
 459     case 6:
 460         *pi_sample_rate = 22050;
 461         break;
 462
 463     case 7:
 464         *pi_sample_rate = 24000;
 465         break;
 466
 467     case 8:
 468         *pi_sample_rate = 32000;
 469         break;
 470
 471     case 9:
 472         *pi_sample_rate = 44100;
 473         break;
 474
 475     case 10:
 476         *pi_sample_rate = 48000;
 477         break;
 478
 479     case 11:
 480         *pi_sample_rate = 96000;
 481         break;
 482
 483     case 12:
 484     case 13:
 485     case 14:
 486         i_sample_rate_hint = i_temp;
 487         break;
 488
 489     case 15:
 490         return 0;
 491     }
 492
 493     /* Find channels */
 494     i_temp = (unsigned)(p_buf[3] >> 4);
 495     if( i_temp & 8 )
 496     {
 497         if( ( i_temp & 7 ) >= 3 )
 498             return 0;
 499         *pi_channels = 2;
 500     }
 501     else
 502     {
 503         *pi_channels = i_temp + 1;
 504     }
 505
 506     /* Find bits per sample */
 507     switch( i_temp = (unsigned)(p_buf[3] & 0x0e) >> 1 )
 508     {
 509     case 0:
 510         if( p_sys->b_stream_info )
 511             *pi_bits_per_sample = p_sys->stream_info.bits_per_sample;
 512         else
 513             return 0;
 514         break;
 515
 516     case 1:
 517         *pi_bits_per_sample = 8;
 518         break;
 519
 520     case 2:
 521         *pi_bits_per_sample = 12;
 522         break;
 523
 524     case 4:
 525         *pi_bits_per_sample = 16;
 526         break;
 527
 528     case 5:
 529         *pi_bits_per_sample = 20;
 530         break;
 531
 532     case 6:
 533         *pi_bits_per_sample = 24;
 534         break;
 535
 536     case 3:
 537     case 7:
 538         return 0;
 539         break;
 540     }
 541
 542     /* Zero padding bit */
 543     if( p_buf[3] & 0x01 ) return 0;
 544
 545     /* End of fixed size header */
 546     i_header = 4;
 547
 548     /* Check Sample/Frame number */
 549     if( read_utf8( &p_buf[i_header++], &i_read ) == INT64_C(0xffffffffffffffff) )
 550         return 0;
 551
 552     i_header += i_read;
 553
 554     /* Read blocksize */
 555     if( i_blocksize_hint )
 556     {
 557         int i_val1 = p_buf[i_header++];
 558         if( i_blocksize_hint == 7 )
 559         {
 560             int i_val2 = p_buf[i_header++];
 561             i_val1 = (i_val1 << 8) | i_val2;
 562         }
 563         i_blocksize = i_val1 + 1;
 564     }
 565
 566     /* Read sample rate */
 567     if( i_sample_rate_hint )
 568     {
 569         int i_val1 = p_buf[i_header++];
 570         if( i_sample_rate_hint != 12 )
 571         {
 572             int i_val2 = p_buf[i_header++];
 573             i_val1 = (i_val1 << 8) | i_val2;
 574         }
 575         if( i_sample_rate_hint == 12 ) *pi_sample_rate = i_val1 * 1000;
 576         else if( i_sample_rate_hint == 13 ) *pi_sample_rate = i_val1;
 577         else *pi_sample_rate = i_val1 * 10;
 578     }
 579
 580     /* Check the CRC-8 byte */
 581     if( flac_crc8( p_buf, i_header ) != p_buf[i_header] )
 582     {
 583         return 0;
 584     }
 585
 586     /* Sanity check using stream info header when possible */
 587     if( p_sys->b_stream_info )
 588     {
 589         if( i_blocksize < p_sys->stream_info.min_blocksize ||
 590             i_blocksize > p_sys->stream_info.max_blocksize )
 591             return 0;
 592         if( *pi_bits_per_sample != p_sys->stream_info.bits_per_sample )
 593             return 0;
 594         if( *pi_sample_rate != p_sys->stream_info.sample_rate )
 595             return 0;
 596     }
 597     return i_blocksize;
 598 }
 599
 600 /* Will return 0xffffffffffffffff for an invalid utf-8 sequence */
 601 static uint64_t read_utf8( const uint8_t *p_buf, int *pi_read )
 602 {
 603     uint64_t i_result = 0;
 604     unsigned i, j;
 605
 606     if( !(p_buf[0] & 0x80) ) /* 0xxxxxxx */
 607     {
 608         i_result = p_buf[0];
 609         i = 0;
 610     }
 611     else if( p_buf[0] & 0xC0 && !(p_buf[0] & 0x20) ) /* 110xxxxx */
 612     {
 613         i_result = p_buf[0] & 0x1F;
 614         i = 1;
 615     }
 616     else if( p_buf[0] & 0xE0 && !(p_buf[0] & 0x10) ) /* 1110xxxx */
 617     {
 618         i_result = p_buf[0] & 0x0F;
 619         i = 2;
 620     }
 621     else if( p_buf[0] & 0xF0 && !(p_buf[0] & 0x08) ) /* 11110xxx */
 622     {
 623         i_result = p_buf[0] & 0x07;
 624         i = 3;
 625     }
 626     else if( p_buf[0] & 0xF8 && !(p_buf[0] & 0x04) ) /* 111110xx */
 627     {
 628         i_result = p_buf[0] & 0x03;
 629         i = 4;
 630     }
 631     else if( p_buf[0] & 0xFC && !(p_buf[0] & 0x02) ) /* 1111110x */
 632     {
 633         i_result = p_buf[0] & 0x01;
 634         i = 5;
 635     }
 636     else if( p_buf[0] & 0xFE && !(p_buf[0] & 0x01) ) /* 11111110 */
 637     {
 638         i_result = 0;
 639         i = 6;
 640     }
 641     else {
 642         return INT64_C(0xffffffffffffffff);
 643     }
 644
 645     for( j = 1; j <= i; j++ )
 646     {
 647         if( !(p_buf[j] & 0x80) || (p_buf[j] & 0x40) ) /* 10xxxxxx */
 648         {
 649             return INT64_C(0xffffffffffffffff);
 650         }
 651         i_result <<= 6;
 652         i_result |= (p_buf[j] & 0x3F);
 653     }
 654
 655     *pi_read = i;
 656     return i_result;
 657 }
 658
 659 /* CRC-8, poly = x^8 + x^2 + x^1 + x^0, init = 0 */
 660 static const uint8_t flac_crc8_table[256] = {
 661         0x00, 0x07, 0x0E, 0x09, 0x1C, 0x1B, 0x12, 0x15,
 662         0x38, 0x3F, 0x36, 0x31, 0x24, 0x23, 0x2A, 0x2D,
 663         0x70, 0x77, 0x7E, 0x79, 0x6C, 0x6B, 0x62, 0x65,
 664         0x48, 0x4F, 0x46, 0x41, 0x54, 0x53, 0x5A, 0x5D,
 665         0xE0, 0xE7, 0xEE, 0xE9, 0xFC, 0xFB, 0xF2, 0xF5,
 666         0xD8, 0xDF, 0xD6, 0xD1, 0xC4, 0xC3, 0xCA, 0xCD,
 667         0x90, 0x97, 0x9E, 0x99, 0x8C, 0x8B, 0x82, 0x85,
 668         0xA8, 0xAF, 0xA6, 0xA1, 0xB4, 0xB3, 0xBA, 0xBD,
 669         0xC7, 0xC0, 0xC9, 0xCE, 0xDB, 0xDC, 0xD5, 0xD2,
 670         0xFF, 0xF8, 0xF1, 0xF6, 0xE3, 0xE4, 0xED, 0xEA,
 671         0xB7, 0xB0, 0xB9, 0xBE, 0xAB, 0xAC, 0xA5, 0xA2,
 672         0x8F, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9D, 0x9A,
 673         0x27, 0x20, 0x29, 0x2E, 0x3B, 0x3C, 0x35, 0x32,
 674         0x1F, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0D, 0x0A,
 675         0x57, 0x50, 0x59, 0x5E, 0x4B, 0x4C, 0x45, 0x42,
 676         0x6F, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7D, 0x7A,
 677         0x89, 0x8E, 0x87, 0x80, 0x95, 0x92, 0x9B, 0x9C,
 678         0xB1, 0xB6, 0xBF, 0xB8, 0xAD, 0xAA, 0xA3, 0xA4,
 679         0xF9, 0xFE, 0xF7, 0xF0, 0xE5, 0xE2, 0xEB, 0xEC,
 680         0xC1, 0xC6, 0xCF, 0xC8, 0xDD, 0xDA, 0xD3, 0xD4,
 681         0x69, 0x6E, 0x67, 0x60, 0x75, 0x72, 0x7B, 0x7C,
 682         0x51, 0x56, 0x5F, 0x58, 0x4D, 0x4A, 0x43, 0x44,
 683         0x19, 0x1E, 0x17, 0x10, 0x05, 0x02, 0x0B, 0x0C,
 684         0x21, 0x26, 0x2F, 0x28, 0x3D, 0x3A, 0x33, 0x34,
 685         0x4E, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5C, 0x5B,
 686         0x76, 0x71, 0x78, 0x7F, 0x6A, 0x6D, 0x64, 0x63,
 687         0x3E, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2C, 0x2B,
 688         0x06, 0x01, 0x08, 0x0F, 0x1A, 0x1D, 0x14, 0x13,
 689         0xAE, 0xA9, 0xA0, 0xA7, 0xB2, 0xB5, 0xBC, 0xBB,
 690         0x96, 0x91, 0x98, 0x9F, 0x8A, 0x8D, 0x84, 0x83,
 691         0xDE, 0xD9, 0xD0, 0xD7, 0xC2, 0xC5, 0xCC, 0xCB,
 692         0xE6, 0xE1, 0xE8, 0xEF, 0xFA, 0xFD, 0xF4, 0xF3
 693 };
 694
 695 static uint8_t flac_crc8( const uint8_t *data, unsigned len )
 696 {
 697     uint8_t crc = 0;
 698
 699     while(len--)
 700         crc = flac_crc8_table[crc ^ *data++];
 701
 702     return crc;
 703 }
 704