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

   1 /*****************************************************************************
   2  * vpar_synchro.c : frame dropping routines
   3  *****************************************************************************
   4  * Copyright (C) 1999, 2000 VideoLAN
   5  * $Id: vpar_synchro.c,v 1.4 2001/07/24 12:03:00 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  * 2. Definitions
  45  *    ===========
  46  * t[0..12]     : Presentation timestamps of pictures 0..12.
  47  * t            : Current timestamp, at the moment of the decoding.
  48  * T            : Picture period, T = 1/frame_rate.
  49  * tau[I,P,B]   : Mean time to decode an [I,P,B] picture.
  50  * tauYUV       : Mean time to render a picture (given by the video_output).
  51  * tau´[I,P,B] = 2 * tau[I,P,B] + tauYUV
  52  *              : Mean time + typical difference (estimated to tau/2, that
  53  *                needs to be confirmed) + render time.
  54  * DELTA        : A given error margin.
  55  *
  56  * 3. General considerations
  57  *    ======================
  58  * We define three types of machines :
  59  *      14T > tauI : machines capable of decoding all I pictures
  60  *      2T > tauP  : machines capable of decoding all P pictures
  61  *      T > tauB   : machines capable of decoding all B pictures
  62  *
  63  * 4. Decoding of an I picture
  64  *    ========================
  65  * On fast machines, we decode all I's.
  66  * Otherwise :
  67  * We can decode an I picture if we simply have enough time to decode it
  68  * before displaying :
  69  *      t0 - t > tau´I + DELTA
  70  *
  71  * 5. Decoding of a P picture
  72  *    =======================
  73  * On fast machines, we decode all P's.
  74  * Otherwise :
  75  * First criterion : have time to decode it.
  76  *      t2 - t > tau´P + DELTA
  77  *
  78  * Second criterion : it shouldn't prevent us from displaying the forthcoming
  79  * I picture, which is more important.
  80  *      t12 - t > tau´P + tau´I + DELTA
  81  *
  82  * 6. Decoding of a B picture
  83  *    =======================
  84  * On fast machines, we decode all B's. Otherwise :
  85  *      t1 - t > tau´B + DELTA
  86  * Since the next displayed I or P is already decoded, we don't have to
  87  * worry about it.
  88  *
  89  * I hope you will have a pleasant flight and do not forget your life
  90  * jacket.
  91  *                                                  --Meuuh (2000-12-29)
  92  */
  93
  94 /*****************************************************************************
  95  * Preamble
  96  *****************************************************************************/
  97 #include "defs.h"
  98
  99 #include <string.h>                                    /* memcpy(), memset() */
 100
 101 #include "config.h"
 102 #include "common.h"
 103 #include "threads.h"
 104 #include "mtime.h"
 105
 106 #include "intf_msg.h"
 107
 108 #include "stream_control.h"
 109 #include "input_ext-dec.h"
 110
 111 #include "video.h"
 112 #include "video_output.h"
 113
 114 #include "vdec_ext-plugins.h"
 115 #include "vpar_pool.h"
 116 #include "video_parser.h"
 117
 118 #include "main.h"
 119
 120 /*
 121  * Local prototypes
 122  */
 123 static int  SynchroType( void );
 124
 125 /* Error margins */
 126 #define DELTA                   (int)(0.075*CLOCK_FREQ)
 127
 128 #define DEFAULT_NB_P            5
 129 #define DEFAULT_NB_B            1
 130
 131 /*****************************************************************************
 132  * vpar_SynchroInit : You know what ?
 133  *****************************************************************************/
 134 void vpar_SynchroInit( vpar_thread_t * p_vpar )
 135 {
 136     p_vpar->synchro.i_type = SynchroType();
 137
 138     /* We use a fake stream pattern, which is often right. */
 139     p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p = DEFAULT_NB_P;
 140     p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b = DEFAULT_NB_B;
 141     memset( p_vpar->synchro.p_tau, 0, 4 * sizeof(mtime_t) );
 142     memset( p_vpar->synchro.pi_meaningful, 0, 4 * sizeof(unsigned int) );
 143     p_vpar->synchro.b_dropped_last = 0;
 144     p_vpar->synchro.current_pts = mdate() + DEFAULT_PTS_DELAY;
 145     p_vpar->synchro.backward_pts = 0;
 146     p_vpar->synchro.i_current_period = p_vpar->synchro.i_backward_period = 0;
 147 #ifdef STATS
 148     p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic =
 149         p_vpar->synchro.i_pic = 0;
 150 #endif
 151 }
 152
 153 /*****************************************************************************
 154  * vpar_SynchroChoose : Decide whether we will decode a picture or not
 155  *****************************************************************************/
 156 boolean_t vpar_SynchroChoose( vpar_thread_t * p_vpar, int i_coding_type,
 157                               int i_structure )
 158 {
 159     /* For clarity reasons, we separated the special synchros code from the
 160      * mathematical synchro */
 161
 162     if( p_vpar->synchro.i_type != VPAR_SYNCHRO_DEFAULT )
 163     {
 164         switch( i_coding_type )
 165         {
 166         case I_CODING_TYPE:
 167             /* I, IP, IP+, IPB */
 168             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus )
 169             {
 170                 p_vpar->synchro.b_dropped_last = 1;
 171             }
 172             return( 1 );
 173
 174         case P_CODING_TYPE:
 175             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_I ) /* I */
 176             {
 177                 return( 0 );
 178             }
 179
 180             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus ) /* I+ */
 181             {
 182                 if( p_vpar->synchro.b_dropped_last )
 183                 {
 184                     p_vpar->synchro.b_dropped_last = 0;
 185                     return( 1 );
 186                 }
 187                 else
 188                 {
 189                     return( 0 );
 190                 }
 191             }
 192
 193             return( 1 ); /* IP, IP+, IPB */
 194
 195         case B_CODING_TYPE:
 196             if( p_vpar->synchro.i_type <= VPAR_SYNCHRO_IP ) /* I, IP */
 197             {
 198                 return( 0 );
 199             }
 200             else if( p_vpar->synchro.i_type == VPAR_SYNCHRO_IPB ) /* IPB */
 201             {
 202                 return( 1 );
 203             }
 204
 205             p_vpar->synchro.b_dropped_last ^= 1; /* IP+ */
 206             return( !p_vpar->synchro.b_dropped_last );
 207         }
 208         return( 0 ); /* never reached but gcc yells at me */
 209     }
 210     else
 211     {
 212 #define TAU_PRIME( coding_type )    (p_vpar->synchro.p_tau[(coding_type)] \
 213                                  + (p_vpar->synchro.p_tau[(coding_type)] >> 1) \
 214                                             + tau_yuv)
 215 #define S                           p_vpar->synchro
 216         /* VPAR_SYNCHRO_DEFAULT */
 217         mtime_t         now, period, tau_yuv;
 218         mtime_t         pts = 0;
 219         boolean_t       b_decode = 0;
 220 #ifdef TRACE_VPAR
 221         char            p_date[MSTRTIME_MAX_SIZE];
 222 #endif
 223
 224         now = mdate();
 225         period = 1000000 * 1001 / p_vpar->sequence.i_frame_rate
 226                     * p_vpar->sequence.i_current_rate / DEFAULT_RATE;
 227
 228         vlc_mutex_lock( &p_vpar->p_vout->change_lock );
 229         tau_yuv = p_vpar->p_vout->render_time;
 230         vlc_mutex_unlock( &p_vpar->p_vout->change_lock );
 231
 232         switch( i_coding_type )
 233         {
 234         case I_CODING_TYPE:
 235             if( S.backward_pts )
 236             {
 237                 pts = S.backward_pts;
 238             }
 239             else
 240             {
 241                 /* displaying order : B B P B B I
 242                  *                      ^       ^
 243                  *                      |       +- current picture
 244                  *                      +- current PTS
 245                  */
 246                 pts = S.current_pts + period * (S.i_n_b + 2);
 247             }
 248
 249             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 250                     S.p_tau[I_CODING_TYPE] )
 251             {
 252                 b_decode = 1;
 253             }
 254             else
 255             {
 256                 b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 257             }
 258             if( !b_decode )
 259                 intf_WarnMsg( 1, "vpar synchro warning: trashing I (%lld)",
 260                              pts - now);
 261             break;
 262
 263         case P_CODING_TYPE:
 264             if( S.backward_pts )
 265             {
 266                 pts = S.backward_pts;
 267             }
 268             else
 269             {
 270                 pts = S.current_pts + period * (S.i_n_b + 1);
 271             }
 272
 273             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 274                     S.p_tau[I_CODING_TYPE] )
 275             {
 276                 if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 277                 {
 278                     /* Security in case we're _really_ late */
 279                     b_decode = (pts - now > 0);
 280                 }
 281                 else
 282                 {
 283                     b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 284                     /* next I */
 285                     b_decode &= (pts - now
 286                                   + period
 287                               * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 288                                 > (TAU_PRIME(P_CODING_TYPE)
 289                                     + TAU_PRIME(I_CODING_TYPE) + DELTA);
 290                 }
 291             }
 292             else
 293             {
 294                 b_decode = 0;
 295             }
 296             break;
 297
 298         case B_CODING_TYPE:
 299             pts = S.current_pts;
 300
 301             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 302             {
 303                 b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 304             }
 305             else
 306             {
 307                 b_decode = 0;
 308             }
 309         }
 310
 311 #ifdef TRACE_VPAR
 312         intf_DbgMsg("vpar synchro debug: %s picture scheduled for %s, %s (%lld)",
 313                     i_coding_type == B_CODING_TYPE ? "B" :
 314                     (i_coding_type == P_CODING_TYPE ? "P" : "I"),
 315                     mstrtime(p_date, pts), b_decode ? "decoding" : "trashed",
 316                     S.p_tau[i_coding_type]);
 317 #endif
 318 #ifdef STATS
 319         if( !b_decode )
 320         {
 321             S.i_not_chosen_pic++;
 322         }
 323 #endif
 324         return( b_decode );
 325 #undef S
 326 #undef TAU_PRIME
 327     }
 328 }
 329
 330 /*****************************************************************************
 331  * vpar_SynchroTrash : Update counters when we trash a picture
 332  *****************************************************************************/
 333 void vpar_SynchroTrash( vpar_thread_t * p_vpar, int i_coding_type,
 334                         int i_structure )
 335 {
 336 #ifdef STATS
 337     p_vpar->synchro.i_trashed_pic++;
 338 #endif
 339 }
 340
 341 /*****************************************************************************
 342  * vpar_SynchroDecode : Update timers when we decide to decode a picture
 343  *****************************************************************************/
 344 void vpar_SynchroDecode( vpar_thread_t * p_vpar, int i_coding_type,
 345                          int i_structure )
 346 {
 347     p_vpar->synchro.decoding_start = mdate();
 348 }
 349
 350 /*****************************************************************************
 351  * vpar_SynchroEnd : Called when the image is totally decoded
 352  *****************************************************************************/
 353 void vpar_SynchroEnd( vpar_thread_t * p_vpar, int i_coding_type,
 354                       int i_structure, int i_garbage )
 355 {
 356     mtime_t     tau;
 357
 358     if( !i_garbage )
 359     {
 360         tau = mdate() - p_vpar->synchro.decoding_start;
 361
 362         /* If duration too high, something happened (pause ?), so don't
 363          * take it into account. */
 364         if( tau < 3 * p_vpar->synchro.p_tau[i_coding_type]
 365              || !p_vpar->synchro.pi_meaningful[i_coding_type] )
 366         {
 367             /* Mean with average tau, to ensure stability. */
 368             p_vpar->synchro.p_tau[i_coding_type] =
 369                 (p_vpar->synchro.pi_meaningful[i_coding_type]
 370                  * p_vpar->synchro.p_tau[i_coding_type] + tau)
 371                 / (p_vpar->synchro.pi_meaningful[i_coding_type] + 1);
 372             if( p_vpar->synchro.pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 373             {
 374                 p_vpar->synchro.pi_meaningful[i_coding_type]++;
 375             }
 376         }
 377
 378 #ifdef TRACE_VPAR
 379         intf_DbgMsg("vpar synchro debug: finished decoding %s (%lld)",
 380                     i_coding_type == B_CODING_TYPE ? "B" :
 381                     (i_coding_type == P_CODING_TYPE ? "P" : "I"), tau);
 382 #endif
 383     }
 384     else
 385     {
 386         intf_DbgMsg("vpar synchro debug: aborting %s",
 387                     i_coding_type == B_CODING_TYPE ? "B" :
 388                     (i_coding_type == P_CODING_TYPE ? "P" : "I"));
 389     }
 390 }
 391
 392 /*****************************************************************************
 393  * vpar_SynchroDate : When an image has been decoded, ask for its date
 394  *****************************************************************************/
 395 mtime_t vpar_SynchroDate( vpar_thread_t * p_vpar )
 396 {
 397     /* No need to lock, since PTS are only used by the video parser. */
 398     return( p_vpar->synchro.current_pts );
 399 }
 400
 401 /*****************************************************************************
 402  * vpar_SynchroNewPicture: Update stream structure and PTS
 403  *****************************************************************************/
 404 void vpar_SynchroNewPicture( vpar_thread_t * p_vpar, int i_coding_type,
 405                              int i_repeat_field )
 406 {
 407     mtime_t         period = 1000000 * 1001 / p_vpar->sequence.i_frame_rate
 408                               * p_vpar->sequence.i_current_rate / DEFAULT_RATE;
 409 #if 0
 410     mtime_t         now = mdate();
 411 #endif
 412
 413     switch( i_coding_type )
 414     {
 415     case I_CODING_TYPE:
 416         if( p_vpar->synchro.i_eta_p
 417              && p_vpar->synchro.i_eta_p != p_vpar->synchro.i_n_p )
 418         {
 419             intf_WarnMsg( 3, "vpar info: stream periodicity changed "
 420                           "from P[%d] to P[%d]",
 421                           p_vpar->synchro.i_n_p, p_vpar->synchro.i_eta_p );
 422             p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p;
 423         }
 424         p_vpar->synchro.i_eta_p = p_vpar->synchro.i_eta_b = 0;
 425 #ifdef STATS
 426         if( p_vpar->synchro.i_type == VPAR_SYNCHRO_DEFAULT )
 427         {
 428             intf_Msg( "vpar synchro stats: I(%lld) P(%lld)[%d] B(%lld)[%d] YUV(%lld) : trashed %d:%d/%d",
 429                   p_vpar->synchro.p_tau[I_CODING_TYPE],
 430                   p_vpar->synchro.p_tau[P_CODING_TYPE],
 431                   p_vpar->synchro.i_n_p,
 432                   p_vpar->synchro.p_tau[B_CODING_TYPE],
 433                   p_vpar->synchro.i_n_b,
 434                   p_vpar->p_vout->render_time,
 435                   p_vpar->synchro.i_not_chosen_pic,
 436                   p_vpar->synchro.i_trashed_pic -
 437                   p_vpar->synchro.i_not_chosen_pic,
 438                   p_vpar->synchro.i_pic );
 439             p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic
 440                 = p_vpar->synchro.i_pic = 0;
 441         }
 442 #endif
 443         break;
 444     case P_CODING_TYPE:
 445         p_vpar->synchro.i_eta_p++;
 446         if( p_vpar->synchro.i_eta_b
 447              && p_vpar->synchro.i_eta_b != p_vpar->synchro.i_n_b )
 448         {
 449             intf_WarnMsg( 3, "vpar info: stream periodicity changed "
 450                           "from B[%d] to B[%d]",
 451                           p_vpar->synchro.i_n_b, p_vpar->synchro.i_eta_b );
 452             p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b;
 453         }
 454         p_vpar->synchro.i_eta_b = 0;
 455         break;
 456     case B_CODING_TYPE:
 457         p_vpar->synchro.i_eta_b++;
 458         break;
 459     }
 460
 461     p_vpar->synchro.current_pts += p_vpar->synchro.i_current_period
 462                                         * (period >> 1);
 463
 464 #define PTS_THRESHOLD   (period >> 2)
 465     if( i_coding_type == B_CODING_TYPE )
 466     {
 467         /* A video frame can be displayed 1, 2 or 3 times, according to
 468          * repeat_first_field, top_field_first, progressive_sequence and
 469          * progressive_frame. */
 470         p_vpar->synchro.i_current_period = i_repeat_field;
 471
 472         if( p_vpar->sequence.next_pts )
 473         {
 474             if( p_vpar->sequence.next_pts - p_vpar->synchro.current_pts
 475                     > PTS_THRESHOLD
 476                  || p_vpar->synchro.current_pts - p_vpar->sequence.next_pts
 477                     > PTS_THRESHOLD )
 478             {
 479                 intf_WarnMsg( 2,
 480                         "vpar synchro warning: pts != current_date (%lld)",
 481                         p_vpar->synchro.current_pts
 482                             - p_vpar->sequence.next_pts );
 483             }
 484             p_vpar->synchro.current_pts = p_vpar->sequence.next_pts;
 485             p_vpar->sequence.next_pts = 0;
 486         }
 487     }
 488     else
 489     {
 490         p_vpar->synchro.i_current_period = p_vpar->synchro.i_backward_period;
 491         p_vpar->synchro.i_backward_period = i_repeat_field;
 492
 493         if( p_vpar->synchro.backward_pts )
 494         {
 495             if( p_vpar->sequence.next_dts &&
 496                 (p_vpar->sequence.next_dts - p_vpar->synchro.backward_pts
 497                     > PTS_THRESHOLD
 498               || p_vpar->synchro.backward_pts - p_vpar->sequence.next_dts
 499                     > PTS_THRESHOLD) )
 500             {
 501                 intf_WarnMsg( 2,
 502                         "vpar synchro warning: backward_pts != dts (%lld)",
 503                         p_vpar->sequence.next_dts
 504                             - p_vpar->synchro.backward_pts );
 505             }
 506             if( p_vpar->synchro.backward_pts - p_vpar->synchro.current_pts
 507                     > PTS_THRESHOLD
 508                  || p_vpar->synchro.current_pts - p_vpar->synchro.backward_pts
 509                     > PTS_THRESHOLD )
 510             {
 511                 intf_WarnMsg( 2,
 512                    "vpar synchro warning: backward_pts != current_pts (%lld)",
 513                    p_vpar->synchro.current_pts - p_vpar->synchro.backward_pts );
 514             }
 515             p_vpar->synchro.current_pts = p_vpar->synchro.backward_pts;
 516             p_vpar->synchro.backward_pts = 0;
 517         }
 518         else if( p_vpar->sequence.next_dts )
 519         {
 520             if( p_vpar->sequence.next_dts - p_vpar->synchro.current_pts
 521                     > PTS_THRESHOLD
 522                  || p_vpar->synchro.current_pts - p_vpar->sequence.next_dts
 523                     > PTS_THRESHOLD )
 524             {
 525                 intf_WarnMsg( 2,
 526                         "vpar synchro warning: dts != current_pts (%lld)",
 527                         p_vpar->synchro.current_pts
 528                             - p_vpar->sequence.next_dts );
 529             }
 530             /* By definition of a DTS. */
 531             p_vpar->synchro.current_pts = p_vpar->sequence.next_dts;
 532             p_vpar->sequence.next_dts = 0;
 533         }
 534
 535         if( p_vpar->sequence.next_pts )
 536         {
 537             /* Store the PTS for the next time we have to date an I picture. */
 538             p_vpar->synchro.backward_pts = p_vpar->sequence.next_pts;
 539             p_vpar->sequence.next_pts = 0;
 540         }
 541     }
 542 #undef PTS_THRESHOLD
 543
 544 #if 0
 545     /* Removed for incompatibility with slow motion */
 546     if( p_vpar->synchro.current_pts + DEFAULT_PTS_DELAY < now )
 547     {
 548         /* We cannot be _that_ late, something must have happened, reinit
 549          * the dates. */
 550         intf_WarnMsg( 2, "PTS << now (%lld), resetting",
 551                       now - p_vpar->synchro.current_pts - DEFAULT_PTS_DELAY );
 552         p_vpar->synchro.current_pts = now + DEFAULT_PTS_DELAY;
 553     }
 554     if( p_vpar->synchro.backward_pts
 555          && p_vpar->synchro.backward_pts + DEFAULT_PTS_DELAY < now )
 556     {
 557         /* The same. */
 558         p_vpar->synchro.backward_pts = 0;
 559     }
 560 #endif
 561
 562 #ifdef STATS
 563     p_vpar->synchro.i_pic++;
 564 #endif
 565 }
 566
 567 /*****************************************************************************
 568  * SynchroType: Get the user's synchro type
 569  *****************************************************************************
 570  * This function is called at initialization.
 571  *****************************************************************************/
 572 static int SynchroType( void )
 573 {
 574     char * psz_synchro = main_GetPszVariable( VPAR_SYNCHRO_VAR, NULL );
 575
 576     if( psz_synchro == NULL )
 577     {
 578         return VPAR_SYNCHRO_DEFAULT;
 579     }
 580
 581     switch( *psz_synchro++ )
 582     {
 583       case 'i':
 584       case 'I':
 585         switch( *psz_synchro++ )
 586         {
 587           case '\0':
 588             return VPAR_SYNCHRO_I;
 589
 590           case '+':
 591             if( *psz_synchro ) return 0;
 592             return VPAR_SYNCHRO_Iplus;
 593
 594           case 'p':
 595           case 'P':
 596             switch( *psz_synchro++ )
 597             {
 598               case '\0':
 599                 return VPAR_SYNCHRO_IP;
 600
 601               case '+':
 602                 if( *psz_synchro ) return 0;
 603                 return VPAR_SYNCHRO_IPplus;
 604
 605               case 'b':
 606               case 'B':
 607                 if( *psz_synchro ) return 0;
 608                 return VPAR_SYNCHRO_IPB;
 609
 610               default:
 611                 return VPAR_SYNCHRO_DEFAULT;
 612
 613             }
 614
 615           default:
 616             return VPAR_SYNCHRO_DEFAULT;
 617         }
 618     }
 619
 620     return VPAR_SYNCHRO_DEFAULT;
 621 }
 622