git.sesse.net Git - vlc/blob - modules/packetizer/mpeg4video.c

   1 /*****************************************************************************
   2  * mpeg4video.c: mpeg 4 video packetizer
   3  *****************************************************************************
   4  * Copyright (C) 2001-2006 the VideoLAN team
   5  * $Id$
   6  *
   7  * Authors: Gildas Bazin <gbazin@videolan.org>
   8  *          Laurent Aimar <fenrir@via.ecp.fr>
   9  *          Eric Petit <titer@videolan.org>
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License as published by
  13  * the Free Software Foundation; either version 2 of the License, or
  14  * (at your option) any later version.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  24  *****************************************************************************/
  25
  26 /*****************************************************************************
  27  * Preamble
  28  *****************************************************************************/
  29 #include <stdlib.h>                                      /* malloc(), free() */
  30
  31 #include <vlc/vlc.h>
  32 #include <vlc/decoder.h>
  33 #include <vlc/sout.h>
  34 #include <vlc/input.h>                  /* hmmm, just for INPUT_RATE_DEFAULT */
  35
  36 #include "vlc_bits.h"
  37 #include "vlc_block_helper.h"
  38
  39 /*****************************************************************************
  40  * Module descriptor
  41  *****************************************************************************/
  42 static int  Open ( vlc_object_t * );
  43 static void Close( vlc_object_t * );
  44
  45 vlc_module_begin();
  46     set_category( CAT_SOUT );
  47     set_subcategory( SUBCAT_SOUT_PACKETIZER );
  48     set_description( _("MPEG4 video packetizer") );
  49     set_capability( "packetizer", 50 );
  50     set_callbacks( Open, Close );
  51 vlc_module_end();
  52
  53 /****************************************************************************
  54  * Local prototypes
  55  ****************************************************************************/
  56 static block_t *Packetize( decoder_t *, block_t ** );
  57
  58 struct decoder_sys_t
  59 {
  60     /*
  61      * Input properties
  62      */
  63     block_bytestream_t bytestream;
  64     int i_state;
  65     int i_offset;
  66     uint8_t p_startcode[3];
  67
  68     /*
  69      * Common properties
  70      */
  71     mtime_t i_interpolated_pts;
  72     mtime_t i_interpolated_dts;
  73     mtime_t i_last_ref_pts;
  74     mtime_t i_last_time_ref;
  75     mtime_t i_time_ref;
  76     mtime_t i_last_time;
  77     mtime_t i_last_timeincr;
  78
  79     unsigned int i_flags;
  80
  81     int         i_fps_num;
  82     int         i_fps_den;
  83     int         i_last_incr;
  84     int         i_last_incr_diff;
  85
  86     vlc_bool_t  b_frame;
  87
  88     /* Current frame being built */
  89     block_t    *p_frame;
  90     block_t    **pp_last;
  91 };
  92
  93 enum {
  94     STATE_NOSYNC,
  95     STATE_NEXT_SYNC
  96 };
  97
  98 static block_t *ParseMPEGBlock( decoder_t *, block_t * );
  99 static int ParseVOL( decoder_t *, es_format_t *, uint8_t *, int );
 100 static int ParseVOP( decoder_t *, block_t * );
 101 static int vlc_log2( unsigned int );
 102
 103 #define VIDEO_OBJECT_MASK                       0x01f
 104 #define VIDEO_OBJECT_LAYER_MASK                 0x00f
 105
 106 #define VIDEO_OBJECT_START_CODE                 0x100
 107 #define VIDEO_OBJECT_LAYER_START_CODE           0x120
 108 #define VISUAL_OBJECT_SEQUENCE_START_CODE       0x1b0
 109 #define VISUAL_OBJECT_SEQUENCE_END_CODE         0x1b1
 110 #define USER_DATA_START_CODE                    0x1b2
 111 #define GROUP_OF_VOP_START_CODE                 0x1b3
 112 #define VIDEO_SESSION_ERROR_CODE                0x1b4
 113 #define VISUAL_OBJECT_START_CODE                0x1b5
 114 #define VOP_START_CODE                          0x1b6
 115 #define FACE_OBJECT_START_CODE                  0x1ba
 116 #define FACE_OBJECT_PLANE_START_CODE            0x1bb
 117 #define MESH_OBJECT_START_CODE                  0x1bc
 118 #define MESH_OBJECT_PLANE_START_CODE            0x1bd
 119 #define STILL_TEXTURE_OBJECT_START_CODE         0x1be
 120 #define TEXTURE_SPATIAL_LAYER_START_CODE        0x1bf
 121 #define TEXTURE_SNR_LAYER_START_CODE            0x1c0
 122
 123 /*****************************************************************************
 124  * Open: probe the packetizer and return score
 125  *****************************************************************************/
 126 static int Open( vlc_object_t *p_this )
 127 {
 128     decoder_t     *p_dec = (decoder_t*)p_this;
 129     decoder_sys_t *p_sys;
 130
 131     switch( p_dec->fmt_in.i_codec )
 132     {
 133         case VLC_FOURCC( 'm', '4', 's', '2'):
 134         case VLC_FOURCC( 'M', '4', 'S', '2'):
 135         case VLC_FOURCC( 'm', 'p', '4', 's'):
 136         case VLC_FOURCC( 'M', 'P', '4', 'S'):
 137         case VLC_FOURCC( 'm', 'p', '4', 'v'):
 138         case VLC_FOURCC( 'M', 'P', '4', 'V'):
 139         case VLC_FOURCC( 'D', 'I', 'V', 'X'):
 140         case VLC_FOURCC( 'd', 'i', 'v', 'x'):
 141         case VLC_FOURCC( 'X', 'V', 'I', 'D'):
 142         case VLC_FOURCC( 'X', 'v', 'i', 'D'):
 143         case VLC_FOURCC( 'x', 'v', 'i', 'd'):
 144         case VLC_FOURCC( 'D', 'X', '5', '0'):
 145         case VLC_FOURCC( 'd', 'x', '5', '0'):
 146         case VLC_FOURCC( 0x04, 0,   0,   0):
 147         case VLC_FOURCC( '3', 'I', 'V', '2'):
 148         case VLC_FOURCC( 'm', '4', 'c', 'c'):
 149         case VLC_FOURCC( 'M', '4', 'C', 'C'):
 150             break;
 151
 152         default:
 153             return VLC_EGENERIC;
 154     }
 155
 156     /* Allocate the memory needed to store the decoder's structure */
 157     if( ( p_dec->p_sys = p_sys = malloc( sizeof(decoder_sys_t) ) ) == NULL )
 158     {
 159         msg_Err( p_dec, "out of memory" );
 160         return VLC_EGENERIC;
 161     }
 162     memset( p_sys, 0, sizeof(decoder_sys_t) );
 163
 164     /* Misc init */
 165     p_sys->i_state = STATE_NOSYNC;
 166     p_sys->bytestream = block_BytestreamInit( p_dec );
 167     p_sys->p_startcode[0] = 0;
 168     p_sys->p_startcode[1] = 0;
 169     p_sys->p_startcode[2] = 1;
 170     p_sys->i_offset = 0;
 171     p_sys->p_frame = NULL;
 172     p_sys->pp_last = &p_sys->p_frame;
 173
 174     /* Setup properties */
 175     es_format_Copy( &p_dec->fmt_out, &p_dec->fmt_in );
 176     p_dec->fmt_out.i_codec = VLC_FOURCC( 'm', 'p', '4', 'v' );
 177
 178     if( p_dec->fmt_in.i_extra )
 179     {
 180         /* We have a vol */
 181         p_dec->fmt_out.i_extra = p_dec->fmt_in.i_extra;
 182         p_dec->fmt_out.p_extra = malloc( p_dec->fmt_in.i_extra );
 183         memcpy( p_dec->fmt_out.p_extra, p_dec->fmt_in.p_extra,
 184                 p_dec->fmt_in.i_extra );
 185
 186         msg_Dbg( p_dec, "opening with vol size: %d", p_dec->fmt_in.i_extra );
 187         ParseVOL( p_dec, &p_dec->fmt_out,
 188                   p_dec->fmt_out.p_extra, p_dec->fmt_out.i_extra );
 189     }
 190     else
 191     {
 192         /* No vol, we'll have to look for one later on */
 193         p_dec->fmt_out.i_extra = 0;
 194         p_dec->fmt_out.p_extra = 0;
 195     }
 196
 197     /* Set callback */
 198     p_dec->pf_packetize = Packetize;
 199
 200     return VLC_SUCCESS;
 201 }
 202
 203 /*****************************************************************************
 204  * Close: clean up the packetizer
 205  *****************************************************************************/
 206 static void Close( vlc_object_t *p_this )
 207 {
 208     decoder_t *p_dec = (decoder_t*)p_this;
 209
 210     block_BytestreamRelease( &p_dec->p_sys->bytestream );
 211     if( p_dec->p_sys->p_frame ) block_ChainRelease( p_dec->p_sys->p_frame );
 212     free( p_dec->p_sys );
 213 }
 214
 215 /****************************************************************************
 216  * Packetize: the whole thing
 217  ****************************************************************************/
 218 static block_t *Packetize( decoder_t *p_dec, block_t **pp_block )
 219 {
 220     decoder_sys_t *p_sys = p_dec->p_sys;
 221     block_t       *p_pic;
 222     mtime_t       i_pts, i_dts;
 223
 224     if( pp_block == NULL || *pp_block == NULL ) return NULL;
 225
 226     if( (*pp_block)->i_flags & BLOCK_FLAG_DISCONTINUITY )
 227     {
 228         p_sys->i_state = STATE_NOSYNC;
 229         if( p_sys->p_frame ) block_ChainRelease( p_sys->p_frame );
 230         p_sys->p_frame = NULL;
 231         p_sys->pp_last = &p_sys->p_frame;
 232         block_Release( *pp_block );
 233         return NULL;
 234     }
 235
 236     block_BytestreamPush( &p_sys->bytestream, *pp_block );
 237
 238     while( 1 )
 239     {
 240         switch( p_sys->i_state )
 241         {
 242
 243         case STATE_NOSYNC:
 244             if( block_FindStartcodeFromOffset( &p_sys->bytestream,
 245                     &p_sys->i_offset, p_sys->p_startcode, 3 ) == VLC_SUCCESS )
 246             {
 247                 p_sys->i_state = STATE_NEXT_SYNC;
 248             }
 249
 250             if( p_sys->i_offset )
 251             {
 252                 block_SkipBytes( &p_sys->bytestream, p_sys->i_offset );
 253                 p_sys->i_offset = 0;
 254                 block_BytestreamFlush( &p_sys->bytestream );
 255             }
 256
 257             if( p_sys->i_state != STATE_NEXT_SYNC )
 258             {
 259                 /* Need more data */
 260                 return NULL;
 261             }
 262
 263             p_sys->i_offset = 1; /* To find next startcode */
 264
 265         case STATE_NEXT_SYNC:
 266             /* TODO: If p_block == NULL, flush the buffer without checking the
 267              * next sync word */
 268
 269             /* Find the next startcode */
 270             if( block_FindStartcodeFromOffset( &p_sys->bytestream,
 271                     &p_sys->i_offset, p_sys->p_startcode, 3 ) != VLC_SUCCESS )
 272             {
 273                 /* Need more data */
 274                 return NULL;
 275             }
 276
 277             /* Get the new fragment and set the pts/dts */
 278             p_pic = block_New( p_dec, p_sys->i_offset );
 279             block_BytestreamFlush( &p_sys->bytestream );
 280             p_pic->i_pts = i_pts = p_sys->bytestream.p_block->i_pts;
 281             p_pic->i_dts = i_dts = p_sys->bytestream.p_block->i_dts;
 282             p_pic->i_rate = p_sys->bytestream.p_block->i_rate;
 283
 284             block_GetBytes( &p_sys->bytestream, p_pic->p_buffer,
 285                             p_pic->i_buffer );
 286
 287             p_sys->i_offset = 0;
 288
 289             /* Get picture if any */
 290             if( !( p_pic = ParseMPEGBlock( p_dec, p_pic ) ) )
 291             {
 292                 p_sys->i_state = STATE_NOSYNC;
 293                 break;
 294             }
 295
 296             /* don't reuse the same timestamps several times */
 297             if( i_pts == p_sys->bytestream.p_block->i_pts &&
 298                 i_dts == p_sys->bytestream.p_block->i_dts )
 299             {
 300                 p_sys->bytestream.p_block->i_pts = 0;
 301                 p_sys->bytestream.p_block->i_dts = 0;
 302             }
 303
 304             /* We've just started the stream, wait for the first PTS.
 305              * We discard here so we can still get the sequence header. */
 306             if( p_sys->i_interpolated_pts <= 0 &&
 307                 p_sys->i_interpolated_dts <= 0 )
 308             {
 309                 msg_Dbg( p_dec, "need a starting pts/dts" );
 310                 p_sys->i_state = STATE_NOSYNC;
 311                 block_Release( p_pic );
 312                 break;
 313             }
 314
 315             /* When starting the stream we can have the first frame with
 316              * a null DTS (i_interpolated_pts is initialized to 0) */
 317             if( !p_pic->i_dts ) p_pic->i_dts = p_pic->i_pts;
 318
 319             /* So p_block doesn't get re-added several times */
 320             *pp_block = block_BytestreamPop( &p_sys->bytestream );
 321
 322             p_sys->i_state = STATE_NOSYNC;
 323
 324             return p_pic;
 325         }
 326     }
 327 }
 328
 329 /*****************************************************************************
 330  * ParseMPEGBlock: Re-assemble fragments into a block containing a picture
 331  *****************************************************************************/
 332 static block_t *ParseMPEGBlock( decoder_t *p_dec, block_t *p_frag )
 333 {
 334     decoder_sys_t *p_sys = p_dec->p_sys;
 335     block_t *p_pic = NULL;
 336
 337     if( p_frag->p_buffer[3] == 0xB0 || p_frag->p_buffer[3] == 0xB1 )
 338     {
 339         /* Remove VOS start/end code from the original stream */
 340         block_Release( p_frag );
 341         return NULL;
 342     }
 343     if( p_frag->p_buffer[3] >= 0x20 && p_frag->p_buffer[3] <= 0x2f )
 344     {
 345         /* Copy the complete VOL */
 346         p_dec->fmt_out.i_extra = p_frag->i_buffer;
 347         p_dec->fmt_out.p_extra =
 348             realloc( p_dec->fmt_out.p_extra, p_dec->fmt_out.i_extra );
 349         memcpy( p_dec->fmt_out.p_extra, p_frag->p_buffer, p_frag->i_buffer );
 350         ParseVOL( p_dec, &p_dec->fmt_out,
 351                   p_dec->fmt_out.p_extra, p_dec->fmt_out.i_extra );
 352
 353         /* Remove from the original stream */
 354         block_Release( p_frag );
 355         return NULL;
 356     }
 357     else
 358     {
 359         if( !p_dec->fmt_out.i_extra )
 360         {
 361             msg_Warn( p_dec, "waiting for VOL" );
 362             block_Release( p_frag );
 363             return NULL;
 364         }
 365
 366         /* Append the block */
 367         block_ChainLastAppend( &p_sys->pp_last, p_frag );
 368     }
 369
 370     if( p_frag->p_buffer[3] == 0xb6 &&
 371         ParseVOP( p_dec, p_frag ) == VLC_SUCCESS )
 372     {
 373         /* We are dealing with a VOP */
 374         p_pic = block_ChainGather( p_sys->p_frame );
 375         p_pic->i_pts = p_sys->i_interpolated_pts;
 376         p_pic->i_dts = p_sys->i_interpolated_dts;
 377
 378         /* Reset context */
 379         p_sys->p_frame = NULL;
 380         p_sys->pp_last = &p_sys->p_frame;
 381     }
 382
 383     return p_pic;
 384 }
 385
 386 /* ParseVOL:
 387  *  TODO:
 388  *      - support aspect ratio
 389  */
 390 static int ParseVOL( decoder_t *p_dec, es_format_t *fmt,
 391                      uint8_t *p_vol, int i_vol )
 392 {
 393     decoder_sys_t *p_sys = p_dec->p_sys;
 394     int i_vo_type, i_vo_ver_id, i_ar, i_shape;
 395     bs_t s;
 396
 397     for( ;; )
 398     {
 399         if( p_vol[0] == 0x00 && p_vol[1] == 0x00 && p_vol[2] == 0x01 &&
 400             p_vol[3] >= 0x20 && p_vol[3] <= 0x2f ) break;
 401
 402         p_vol++; i_vol--;
 403         if( i_vol <= 4 ) return VLC_EGENERIC;
 404     }
 405
 406     bs_init( &s, &p_vol[4], i_vol - 4 );
 407
 408     bs_skip( &s, 1 );   /* random access */
 409     i_vo_type = bs_read( &s, 8 );
 410     if( bs_read1( &s ) )
 411     {
 412         i_vo_ver_id = bs_read( &s, 4 );
 413         bs_skip( &s, 3 );
 414     }
 415     else
 416     {
 417         i_vo_ver_id = 1;
 418     }
 419     i_ar = bs_read( &s, 4 );
 420     if( i_ar == 0xf )
 421     {
 422         int i_ar_width, i_ar_height;
 423
 424         i_ar_width = bs_read( &s, 8 );
 425         i_ar_height= bs_read( &s, 8 );
 426     }
 427     if( bs_read1( &s ) )
 428     {
 429         int i_chroma_format;
 430         int i_low_delay;
 431
 432         /* vol control parameter */
 433         i_chroma_format = bs_read( &s, 2 );
 434         i_low_delay = bs_read1( &s );
 435
 436         if( bs_read1( &s ) )
 437         {
 438             bs_skip( &s, 16 );
 439             bs_skip( &s, 16 );
 440             bs_skip( &s, 16 );
 441             bs_skip( &s, 3 );
 442             bs_skip( &s, 11 );
 443             bs_skip( &s, 1 );
 444             bs_skip( &s, 16 );
 445         }
 446     }
 447     /* shape 0->RECT, 1->BIN, 2->BIN_ONLY, 3->GRAY */
 448     i_shape = bs_read( &s, 2 );
 449     if( i_shape == 3 && i_vo_ver_id != 1 )
 450     {
 451         bs_skip( &s, 4 );
 452     }
 453
 454     if( !bs_read1( &s ) ) return VLC_EGENERIC; /* Marker */
 455
 456     p_sys->i_fps_num = bs_read( &s, 16 ); /* Time increment resolution*/
 457     if( !p_sys->i_fps_num ) p_sys->i_fps_num = 1;
 458
 459     if( !bs_read1( &s ) ) return VLC_EGENERIC; /* Marker */
 460
 461     if( bs_read1( &s ) )
 462     {
 463         int i_time_increment_bits = vlc_log2( p_sys->i_fps_num - 1 ) + 1;
 464
 465         if( i_time_increment_bits < 1 ) i_time_increment_bits = 1;
 466
 467         p_sys->i_fps_den = bs_read( &s, i_time_increment_bits );
 468     }
 469     if( i_shape == 0 )
 470     {
 471         bs_skip( &s, 1 );
 472         fmt->video.i_width = bs_read( &s, 13 );
 473         bs_skip( &s, 1 );
 474         fmt->video.i_height= bs_read( &s, 13 );
 475         bs_skip( &s, 1 );
 476     }
 477
 478     return VLC_SUCCESS;
 479 }
 480
 481 static int ParseVOP( decoder_t *p_dec, block_t *p_vop )
 482 {
 483     decoder_sys_t *p_sys = p_dec->p_sys;
 484     int64_t i_time_increment, i_time_ref;
 485     int i_modulo_time_base = 0, i_time_increment_bits;
 486     bs_t s;
 487
 488     bs_init( &s, &p_vop->p_buffer[4], p_vop->i_buffer - 4 );
 489
 490     switch( bs_read( &s, 2 ) )
 491     {
 492     case 0:
 493         p_sys->i_flags = BLOCK_FLAG_TYPE_I;
 494         break;
 495     case 1:
 496         p_sys->i_flags = BLOCK_FLAG_TYPE_P;
 497         break;
 498     case 2:
 499         p_sys->i_flags = BLOCK_FLAG_TYPE_B;
 500         p_sys->b_frame = VLC_TRUE;
 501         break;
 502     case 3: /* gni ? */
 503         p_sys->i_flags = BLOCK_FLAG_TYPE_PB;
 504         break;
 505     }
 506
 507     while( bs_read( &s, 1 ) ) i_modulo_time_base++;
 508     if( !bs_read1( &s ) ) return VLC_EGENERIC; /* Marker */
 509
 510     /* VOP time increment */
 511     i_time_increment_bits = vlc_log2(p_dec->p_sys->i_fps_num - 1) + 1;
 512     if( i_time_increment_bits < 1 ) i_time_increment_bits = 1;
 513     i_time_increment = bs_read( &s, i_time_increment_bits );
 514
 515     /* Interpolate PTS/DTS */
 516     if( !(p_sys->i_flags & BLOCK_FLAG_TYPE_B) )
 517     {
 518         p_sys->i_last_time_ref = p_sys->i_time_ref;
 519         p_sys->i_time_ref +=
 520             (i_modulo_time_base * p_dec->p_sys->i_fps_num);
 521         i_time_ref = p_sys->i_time_ref;
 522     }
 523     else
 524     {
 525         i_time_ref = p_sys->i_last_time_ref +
 526             (i_modulo_time_base * p_dec->p_sys->i_fps_num);
 527     }
 528
 529 #if 0
 530     msg_Err( p_dec, "interp pts/dts (%lli,%lli), pts/dts (%lli,%lli)",
 531              p_sys->i_interpolated_pts, p_sys->i_interpolated_dts,
 532              p_vop->i_pts, p_vop->i_dts );
 533 #endif
 534
 535     if( p_dec->p_sys->i_fps_num < 5 && /* Work-around buggy streams */
 536         p_dec->fmt_in.video.i_frame_rate > 0 &&
 537         p_dec->fmt_in.video.i_frame_rate_base > 0 )
 538     {
 539         p_sys->i_interpolated_pts += I64C(1000000) *
 540         p_dec->fmt_in.video.i_frame_rate_base *
 541         p_vop->i_rate / INPUT_RATE_DEFAULT /
 542         p_dec->fmt_in.video.i_frame_rate;
 543     }
 544     else if( p_dec->p_sys->i_fps_num )
 545         p_sys->i_interpolated_pts +=
 546             ( I64C(1000000) * (i_time_ref + i_time_increment -
 547               p_sys->i_last_time - p_sys->i_last_timeincr) *
 548               p_vop->i_rate / INPUT_RATE_DEFAULT /
 549               p_dec->p_sys->i_fps_num );
 550
 551     p_sys->i_last_time = i_time_ref;
 552     p_sys->i_last_timeincr = i_time_increment;
 553
 554     /* Correct interpolated dts when we receive a new pts/dts */
 555     if( p_vop->i_pts > 0 )
 556         p_sys->i_interpolated_pts = p_vop->i_pts;
 557     if( p_vop->i_dts > 0 )
 558         p_sys->i_interpolated_dts = p_vop->i_dts;
 559
 560     if( (p_sys->i_flags & BLOCK_FLAG_TYPE_B) || !p_sys->b_frame )
 561     {
 562         /* Trivial case (DTS == PTS) */
 563
 564         p_sys->i_interpolated_dts = p_sys->i_interpolated_pts;
 565
 566         if( p_vop->i_pts > 0 )
 567             p_sys->i_interpolated_dts = p_vop->i_pts;
 568         if( p_vop->i_dts > 0 )
 569             p_sys->i_interpolated_dts = p_vop->i_dts;
 570
 571         p_sys->i_interpolated_pts = p_sys->i_interpolated_dts;
 572     }
 573     else
 574     {
 575         if( p_sys->i_last_ref_pts > 0 )
 576             p_sys->i_interpolated_dts = p_sys->i_last_ref_pts;
 577
 578         p_sys->i_last_ref_pts = p_sys->i_interpolated_pts;
 579     }
 580
 581     return VLC_SUCCESS;
 582 }
 583
 584 /* look at ffmpeg av_log2 ;) */
 585 static int vlc_log2( unsigned int v )
 586 {
 587     int n = 0;
 588     static const int vlc_log2_table[16] =
 589     {
 590         0,0,1,1,2,2,2,2, 3,3,3,3,3,3,3,3
 591     };
 592
 593     if( v&0xffff0000 )
 594     {
 595         v >>= 16;
 596         n += 16;
 597     }
 598     if( v&0xff00 )
 599     {
 600         v >>= 8;
 601         n += 8;
 602     }
 603     if( v&0xf0 )
 604     {
 605         v >>= 4;
 606         n += 4;
 607     }
 608     n += vlc_log2_table[v];
 609
 610     return n;
 611 }