git.sesse.net Git - vlc/blob - src/video_parser/vpar_synchro.c

   1 /*****************************************************************************
   2  * vpar_synchro.c : frame dropping routines
   3  *****************************************************************************
   4  * Copyright (C) 1999, 2000 VideoLAN
   5  * $Id: vpar_synchro.c,v 1.77 2001/01/16 18:06:01 massiot Exp $
   6  *
   7  * Authors: Christophe Massiot <massiot@via.ecp.fr>
   8  *          Samuel Hocevar <sam@via.ecp.fr>
   9  *          Jean-Marc Dressler <polux@via.ecp.fr>
  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., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
  24  *****************************************************************************/
  25
  26 /*
  27  * DISCUSSION : How to Write an efficient Frame-Dropping Algorithm
  28  * ==========
  29  *
  30  * This implementation is based on mathematical and statistical
  31  * developments. Older implementations used an enslavement, considering
  32  * that if we're late when reading an I picture, we will decode one frame
  33  * less. It had a tendancy to derive, and wasn't responsive enough, which
  34  * would have caused trouble with the stream control stuff.
  35  *
  36  * 1. Structure of a picture stream
  37  *    =============================
  38  * Between 2 I's, we have for instance :
  39  *    I   B   P   B   P   B   P   B   P   B   P   B   I
  40  *    t0  t1  t2  t3  t4  t5  t6  t7  t8  t9  t10 t11 t12
  41  * Please bear in mind that B's and IP's will be inverted when displaying
  42  * (decoding order != presentation order). Thus, t1 < t0.
  43  *
  44  * FIXME: write a few words about stream structure changes.
  45  *
  46  * 2. Definitions
  47  *    ===========
  48  * t[0..12]     : Presentation timestamps of pictures 0..12.
  49  * t            : Current timestamp, at the moment of the decoding.
  50  * T            : Picture period, T = 1/frame_rate.
  51  * tau[I,P,B]   : Mean time to decode an [I,P,B] picture.
  52  * tauYUV       : Mean time to render a picture (given by the video_output).
  53  * tau´[I,P,B] = 2 * tau[I,P,B] + tauYUV
  54  *              : Mean time + typical difference (estimated to tau/2, that
  55  *                needs to be confirmed) + render time.
  56  * DELTA        : A given error margin.
  57  *
  58  * 3. General considerations
  59  *    ======================
  60  * We define three types of machines :
  61  *      14T > tauI : machines capable of decoding all I pictures
  62  *      2T > tauP  : machines capable of decoding all P pictures
  63  *      T > tauB   : machines capable of decoding all B pictures
  64  *
  65  * 4. Decoding of an I picture
  66  *    ========================
  67  * On fast machines, we decode all I's.
  68  * Otherwise :
  69  * We can decode an I picture if we simply have enough time to decode it
  70  * before displaying :
  71  *      t0 - t > tau´I + DELTA
  72  *
  73  * 5. Decoding of a P picture
  74  *    =======================
  75  * On fast machines, we decode all P's.
  76  * Otherwise :
  77  * First criterion : have time to decode it.
  78  *      t2 - t > tau´P + DELTA
  79  *
  80  * Second criterion : it shouldn't prevent us from displaying the forthcoming
  81  * I picture, which is more important.
  82  *      t12 - t > tau´P + tau´I + DELTA
  83  *
  84  * 6. Decoding of a B picture
  85  *    =======================
  86  * On fast machines, we decode all B's. Otherwise :
  87  *      t1 - t > tau´B + DELTA
  88  * Since the next displayed I or P is already decoded, we don't have to
  89  * worry about it.
  90  *
  91  * I hope you will have a pleasant flight and do not forget your life
  92  * jacket.
  93  *                                                  --Meuuh (2000-12-29)
  94  */
  95
  96 /*****************************************************************************
  97  * Preamble
  98  *****************************************************************************/
  99 #include "defs.h"
 100
 101 #include "config.h"
 102 #include "common.h"
 103 #include "threads.h"
 104 #include "mtime.h"
 105 #include "plugins.h"
 106
 107 #include "intf_msg.h"
 108
 109 #include "stream_control.h"
 110 #include "input_ext-dec.h"
 111
 112 #include "video.h"
 113 #include "video_output.h"
 114
 115 #include "video_decoder.h"
 116 #include "../video_decoder/vdec_idct.h"
 117 #include "../video_decoder/vdec_motion.h"
 118
 119 #include "../video_decoder/vpar_blocks.h"
 120 #include "../video_decoder/vpar_headers.h"
 121 #include "../video_decoder/vpar_synchro.h"
 122 #include "../video_decoder/video_parser.h"
 123
 124 #include "main.h"
 125
 126 /*
 127  * Local prototypes
 128  */
 129 static int  SynchroType( void );
 130
 131 /* Error margins */
 132 #define DELTA                   (int)(0.040*CLOCK_FREQ)
 133
 134 #define DEFAULT_NB_P            5
 135 #define DEFAULT_NB_B            1
 136
 137 /*****************************************************************************
 138  * vpar_SynchroInit : You know what ?
 139  *****************************************************************************/
 140 void vpar_SynchroInit( vpar_thread_t * p_vpar )
 141 {
 142     p_vpar->synchro.i_type = SynchroType();
 143     p_vpar->synchro.i_start = p_vpar->synchro.i_end = 0;
 144     vlc_mutex_init( &p_vpar->synchro.fifo_lock );
 145
 146     /* We use a fake stream pattern, which is often right. */
 147     p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p = DEFAULT_NB_P;
 148     p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b = DEFAULT_NB_B;
 149     memset( p_vpar->synchro.p_tau, 0, 4 * sizeof(mtime_t) );
 150     memset( p_vpar->synchro.pi_meaningful, 0, 4 * sizeof(unsigned int) );
 151     p_vpar->synchro.b_dropped_last = 0;
 152     p_vpar->synchro.current_pts = mdate() + DEFAULT_PTS_DELAY;
 153     p_vpar->synchro.backward_pts = 0;
 154     p_vpar->synchro.i_current_period = p_vpar->synchro.i_backward_period = 0;
 155 #ifdef STATS
 156     p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic =
 157         p_vpar->synchro.i_pic = 0;
 158 #endif
 159 }
 160
 161 /*****************************************************************************
 162  * vpar_SynchroChoose : Decide whether we will decode a picture or not
 163  *****************************************************************************/
 164 boolean_t vpar_SynchroChoose( vpar_thread_t * p_vpar, int i_coding_type,
 165                               int i_structure )
 166 {
 167     /* For clarity reasons, we separated the special synchros code from the
 168      * mathematical synchro */
 169
 170     if( p_vpar->synchro.i_type != VPAR_SYNCHRO_DEFAULT )
 171     {
 172         switch( i_coding_type )
 173         {
 174         case I_CODING_TYPE:
 175             /* I, IP, IP+, IPB */
 176             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus )
 177             {
 178                 p_vpar->synchro.b_dropped_last = 1;
 179             }
 180             return( 1 );
 181
 182         case P_CODING_TYPE:
 183             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_I ) /* I */
 184             {
 185                 return( 0 );
 186             }
 187
 188             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus ) /* I+ */
 189             {
 190                 if( p_vpar->synchro.b_dropped_last )
 191                 {
 192                     p_vpar->synchro.b_dropped_last = 0;
 193                     return( 1 );
 194                 }
 195                 else
 196                 {
 197                     return( 0 );
 198                 }
 199             }
 200
 201             return( 1 ); /* IP, IP+, IPB */
 202
 203         case B_CODING_TYPE:
 204             if( p_vpar->synchro.i_type <= VPAR_SYNCHRO_IP ) /* I, IP */
 205             {
 206                 return( 0 );
 207             }
 208             else if( p_vpar->synchro.i_type == VPAR_SYNCHRO_IPB ) /* IPB */
 209             {
 210                 return( 1 );
 211             }
 212
 213             p_vpar->synchro.b_dropped_last ^= 1; /* IP+ */
 214             return( !p_vpar->synchro.b_dropped_last );
 215         }
 216         return( 0 ); /* never reached but gcc yells at me */
 217     }
 218     else
 219     {
 220 #define TAU_PRIME( coding_type )    (p_vpar->synchro.p_tau[(coding_type)] \
 221                                  + (p_vpar->synchro.p_tau[(coding_type)] >> 1) \
 222                                             + tau_yuv)
 223 #define S                           p_vpar->synchro
 224         /* VPAR_SYNCHRO_DEFAULT */
 225         mtime_t         now, pts, period, tau_yuv;
 226         boolean_t       b_decode = 0;
 227 #ifdef DEBUG_VPAR
 228         char            p_date[MSTRTIME_MAX_SIZE];
 229 #endif
 230
 231         now = mdate();
 232         period = 1000000 * 1001 / p_vpar->sequence.i_frame_rate;
 233
 234         vlc_mutex_lock( &p_vpar->p_vout->change_lock );
 235         tau_yuv = p_vpar->p_vout->render_time;
 236         vlc_mutex_unlock( &p_vpar->p_vout->change_lock );
 237
 238         vlc_mutex_lock( &p_vpar->synchro.fifo_lock );
 239
 240         switch( i_coding_type )
 241         {
 242         case I_CODING_TYPE:
 243             if( S.backward_pts )
 244             {
 245                 pts = S.backward_pts;
 246             }
 247             else
 248             {
 249                 /* displaying order : B B P B B I
 250                  *                      ^       ^
 251                  *                      |       +- current picture
 252                  *                      +- current PTS
 253                  */
 254                 pts = S.current_pts + period * (S.i_n_b + 2);
 255             }
 256
 257             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 258                     S.p_tau[I_CODING_TYPE] )
 259             {
 260                 b_decode = 1;
 261             }
 262             else
 263             {
 264                 b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 265             }
 266             if( !b_decode )
 267                 intf_WarnMsg( 3, "vpar synchro warning: trashing I" );
 268             break;
 269
 270         case P_CODING_TYPE:
 271             if( S.backward_pts )
 272             {
 273                 pts = S.backward_pts;
 274             }
 275             else
 276             {
 277                 pts = S.current_pts + period * (S.i_n_b + 1);
 278             }
 279
 280             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 281                     S.p_tau[I_CODING_TYPE] )
 282             {
 283                 if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 284                 {
 285                     /* Security in case we're _really_ late */
 286                     b_decode = (pts - now > 0);
 287                 }
 288                 else
 289                 {
 290                     b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 291                     /* next I */
 292                     b_decode &= (pts - now
 293                                   + period
 294                               * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 295                                 > (TAU_PRIME(P_CODING_TYPE)
 296                                     + TAU_PRIME(I_CODING_TYPE) + DELTA);
 297                 }
 298             }
 299             else
 300             {
 301                 b_decode = 0;
 302             }
 303             break;
 304
 305         case B_CODING_TYPE:
 306             pts = S.current_pts;
 307
 308             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 309             {
 310                 b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 311             }
 312             else
 313             {
 314                 b_decode = 0;
 315             }
 316         }
 317
 318         vlc_mutex_unlock( &p_vpar->synchro.fifo_lock );
 319 #ifdef DEBUG_VPAR
 320         intf_DbgMsg("vpar synchro debug: %s picture scheduled for %s, %s (%lld)",
 321                     i_coding_type == B_CODING_TYPE ? "B" :
 322                     (i_coding_type == P_CODING_TYPE ? "P" : "I"),
 323                     mstrtime(p_date, pts), b_decode ? "decoding" : "trashed",
 324                     S.p_tau[i_coding_type]);
 325 #endif
 326 #ifdef STATS
 327         if( !b_decode )
 328         {
 329             S.i_not_chosen_pic++;
 330         }
 331 #endif
 332         return( b_decode );
 333 #undef S
 334 #undef TAU_PRIME
 335     }
 336 }
 337
 338 /*****************************************************************************
 339  * vpar_SynchroTrash : Update counters when we trash a picture
 340  *****************************************************************************/
 341 void vpar_SynchroTrash( vpar_thread_t * p_vpar, int i_coding_type,
 342                         int i_structure )
 343 {
 344 #ifdef STATS
 345     p_vpar->synchro.i_trashed_pic++;
 346 #endif
 347 }
 348
 349 /*****************************************************************************
 350  * vpar_SynchroDecode : Update timers when we decide to decode a picture
 351  *****************************************************************************/
 352 void vpar_SynchroDecode( vpar_thread_t * p_vpar, int i_coding_type,
 353                          int i_structure )
 354 {
 355     vlc_mutex_lock( &p_vpar->synchro.fifo_lock );
 356
 357     if( ((p_vpar->synchro.i_end + 1 - p_vpar->synchro.i_start)
 358             % MAX_DECODING_PIC) )
 359     {
 360         p_vpar->synchro.p_date_fifo[p_vpar->synchro.i_end] = mdate();
 361         p_vpar->synchro.pi_coding_types[p_vpar->synchro.i_end] = i_coding_type;
 362
 363         FIFO_INCREMENT( i_end );
 364     }
 365     else
 366     {
 367         /* FIFO full, panic() */
 368         intf_ErrMsg("vpar error: synchro fifo full, estimations will be biased");
 369     }
 370     vlc_mutex_unlock( &p_vpar->synchro.fifo_lock );
 371 }
 372
 373 /*****************************************************************************
 374  * vpar_SynchroEnd : Called when the image is totally decoded
 375  *****************************************************************************/
 376 void vpar_SynchroEnd( vpar_thread_t * p_vpar, int i_garbage )
 377 {
 378     mtime_t     tau;
 379     int         i_coding_type;
 380
 381     vlc_mutex_lock( &p_vpar->synchro.fifo_lock );
 382
 383     if (!i_garbage)
 384     {
 385         tau = mdate() - p_vpar->synchro.p_date_fifo[p_vpar->synchro.i_start];
 386         i_coding_type = p_vpar->synchro.pi_coding_types[p_vpar->synchro.i_start];
 387
 388         /* Mean with average tau, to ensure stability. */
 389         p_vpar->synchro.p_tau[i_coding_type] =
 390             (p_vpar->synchro.pi_meaningful[i_coding_type]
 391              * p_vpar->synchro.p_tau[i_coding_type] + tau)
 392             / (p_vpar->synchro.pi_meaningful[i_coding_type] + 1);
 393         if( p_vpar->synchro.pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 394         {
 395             p_vpar->synchro.pi_meaningful[i_coding_type]++;
 396         }
 397 #ifdef DEBUG_VPAR
 398         intf_DbgMsg("vpar synchro debug: finished decoding %s (%lld)",
 399                     i_coding_type == B_CODING_TYPE ? "B" :
 400                     (i_coding_type == P_CODING_TYPE ? "P" : "I"), tau);
 401 #endif
 402     }
 403
 404     FIFO_INCREMENT( i_start );
 405
 406     vlc_mutex_unlock( &p_vpar->synchro.fifo_lock );
 407 }
 408
 409 /*****************************************************************************
 410  * vpar_SynchroDate : When an image has been decoded, ask for its date
 411  *****************************************************************************/
 412 mtime_t vpar_SynchroDate( vpar_thread_t * p_vpar )
 413 {
 414     /* No need to lock, since PTS are only used by the video parser. */
 415     return( p_vpar->synchro.current_pts );
 416 }
 417
 418 /*****************************************************************************
 419  * vpar_SynchroNewPicture: Update stream structure and PTS
 420  *****************************************************************************/
 421 void vpar_SynchroNewPicture( vpar_thread_t * p_vpar, int i_coding_type,
 422                              int i_repeat_field )
 423 {
 424     mtime_t         period = 1000000 * 1001 / p_vpar->sequence.i_frame_rate;
 425
 426     switch( i_coding_type )
 427     {
 428     case I_CODING_TYPE:
 429         if( p_vpar->synchro.i_eta_p
 430                 && p_vpar->synchro.i_eta_p != p_vpar->synchro.i_n_p )
 431         {
 432             intf_WarnMsg( 1, "Stream periodicity changed from P[%d] to P[%d]",
 433                           p_vpar->synchro.i_n_p, p_vpar->synchro.i_eta_p );
 434             p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p;
 435         }
 436         p_vpar->synchro.i_eta_p = p_vpar->synchro.i_eta_b = 0;
 437 #ifdef STATS
 438         if( p_vpar->synchro.i_type == VPAR_SYNCHRO_DEFAULT )
 439         {
 440             intf_Msg( "vpar synchro stats: I(%lld) P(%lld)[%d] B(%lld)[%d] YUV(%lld) : trashed %d:%d/%d",
 441                   p_vpar->synchro.p_tau[I_CODING_TYPE],
 442                   p_vpar->synchro.p_tau[P_CODING_TYPE],
 443                   p_vpar->synchro.i_n_p,
 444                   p_vpar->synchro.p_tau[B_CODING_TYPE],
 445                   p_vpar->synchro.i_n_b,
 446                   p_vpar->p_vout->render_time,
 447                   p_vpar->synchro.i_not_chosen_pic,
 448                   p_vpar->synchro.i_trashed_pic -
 449                   p_vpar->synchro.i_not_chosen_pic,
 450                   p_vpar->synchro.i_pic );
 451             p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic
 452                 = p_vpar->synchro.i_pic = 0;
 453         }
 454 #endif
 455         break;
 456     case P_CODING_TYPE:
 457         p_vpar->synchro.i_eta_p++;
 458         if( p_vpar->synchro.i_eta_b
 459                 && p_vpar->synchro.i_eta_b != p_vpar->synchro.i_n_b )
 460         {
 461             intf_WarnMsg( 1, "Stream periodicity changed from B[%d] to B[%d]",
 462                           p_vpar->synchro.i_n_b, p_vpar->synchro.i_eta_b );
 463             p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b;
 464         }
 465         p_vpar->synchro.i_eta_b = 0;
 466         break;
 467     case B_CODING_TYPE:
 468         p_vpar->synchro.i_eta_b++;
 469         break;
 470     }
 471
 472     p_vpar->synchro.current_pts += p_vpar->synchro.i_current_period
 473                                         * (period >> 1);
 474
 475 #define PTS_THRESHOLD   (period >> 2)
 476     if( i_coding_type == B_CODING_TYPE )
 477     {
 478         /* A video frame can be displayed 1, 2 or 3 times, according to
 479          * repeat_first_field, top_field_first, progressive_sequence and
 480          * progressive_frame. */
 481         p_vpar->synchro.i_current_period = i_repeat_field;
 482
 483         if( p_vpar->sequence.next_pts )
 484         {
 485             if( p_vpar->sequence.next_pts - p_vpar->synchro.current_pts
 486                     > PTS_THRESHOLD
 487                  || p_vpar->synchro.current_pts - p_vpar->sequence.next_pts
 488                     > PTS_THRESHOLD )
 489             {
 490                 intf_WarnMsg( 2,
 491                         "vpar synchro warning: pts != current_date (%lld)",
 492                         p_vpar->synchro.current_pts
 493                             - p_vpar->sequence.next_pts );
 494             }
 495             p_vpar->synchro.current_pts = p_vpar->sequence.next_pts;
 496             p_vpar->sequence.next_pts = 0;
 497         }
 498     }
 499     else
 500     {
 501         p_vpar->synchro.i_current_period = p_vpar->synchro.i_backward_period;
 502         p_vpar->synchro.i_backward_period = i_repeat_field;
 503
 504         if( p_vpar->synchro.backward_pts )
 505         {
 506             if( p_vpar->sequence.next_dts &&
 507                 (p_vpar->sequence.next_dts - p_vpar->synchro.backward_pts
 508                     > PTS_THRESHOLD
 509               || p_vpar->synchro.backward_pts - p_vpar->sequence.next_dts
 510                     > PTS_THRESHOLD) )
 511             {
 512                 intf_WarnMsg( 2,
 513                         "vpar synchro warning: backward_pts != dts (%lld)",
 514                         p_vpar->sequence.next_dts
 515                             - p_vpar->synchro.backward_pts );
 516             }
 517             if( p_vpar->synchro.backward_pts - p_vpar->synchro.current_pts
 518                     > PTS_THRESHOLD
 519                  || p_vpar->synchro.current_pts - p_vpar->synchro.backward_pts
 520                     > PTS_THRESHOLD )
 521             {
 522                 intf_WarnMsg( 2,
 523                    "vpar synchro warning: backward_pts != current_pts (%lld)",
 524                    p_vpar->synchro.current_pts - p_vpar->synchro.backward_pts );
 525             }
 526             p_vpar->synchro.current_pts = p_vpar->synchro.backward_pts;
 527             p_vpar->synchro.backward_pts = 0;
 528         }
 529         else if( p_vpar->sequence.next_dts )
 530         {
 531             if( p_vpar->sequence.next_dts - p_vpar->synchro.current_pts
 532                     > PTS_THRESHOLD
 533                  || p_vpar->synchro.current_pts - p_vpar->sequence.next_dts
 534                     > PTS_THRESHOLD )
 535             {
 536                 intf_WarnMsg( 2,
 537                         "vpar synchro warning: dts != current_pts (%lld)",
 538                         p_vpar->synchro.current_pts
 539                             - p_vpar->sequence.next_dts );
 540             }
 541             /* By definition of a DTS. */
 542             p_vpar->synchro.current_pts = p_vpar->sequence.next_dts;
 543             p_vpar->sequence.next_dts = 0;
 544         }
 545
 546         if( p_vpar->sequence.next_pts )
 547         {
 548             /* Store the PTS for the next time we have to date an I picture. */
 549             p_vpar->synchro.backward_pts = p_vpar->sequence.next_pts;
 550             p_vpar->sequence.next_pts = 0;
 551         }
 552     }
 553 #undef PTS_THRESHOLD
 554
 555 #ifdef STATS
 556     p_vpar->synchro.i_pic++;
 557 #endif
 558 }
 559
 560 /*****************************************************************************
 561  * SynchroType: Get the user's synchro type
 562  *****************************************************************************
 563  * This function is called at initialization.
 564  *****************************************************************************/
 565 static int SynchroType( void )
 566 {
 567     char * psz_synchro = main_GetPszVariable( VPAR_SYNCHRO_VAR, NULL );
 568
 569     if( psz_synchro == NULL )
 570     {
 571         return VPAR_SYNCHRO_DEFAULT;
 572     }
 573
 574     switch( *psz_synchro++ )
 575     {
 576       case 'i':
 577       case 'I':
 578         switch( *psz_synchro++ )
 579         {
 580           case '\0':
 581             return VPAR_SYNCHRO_I;
 582
 583           case '+':
 584             if( *psz_synchro ) return 0;
 585             return VPAR_SYNCHRO_Iplus;
 586
 587           case 'p':
 588           case 'P':
 589             switch( *psz_synchro++ )
 590             {
 591               case '\0':
 592                 return VPAR_SYNCHRO_IP;
 593
 594               case '+':
 595                 if( *psz_synchro ) return 0;
 596                 return VPAR_SYNCHRO_IPplus;
 597
 598               case 'b':
 599               case 'B':
 600                 if( *psz_synchro ) return 0;
 601                 return VPAR_SYNCHRO_IPB;
 602
 603               default:
 604                 return VPAR_SYNCHRO_DEFAULT;
 605
 606             }
 607
 608           default:
 609             return VPAR_SYNCHRO_DEFAULT;
 610         }
 611     }
 612
 613     return VPAR_SYNCHRO_DEFAULT;
 614 }
 615