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

   1 /*****************************************************************************
   2  * vpar_synchro.c : frame dropping routines
   3  *****************************************************************************
   4  * Copyright (C) 1999-2001 VideoLAN
   5  * $Id: synchro.c,v 1.3 2002/10/20 12:23:47 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 <stdlib.h>                                                /* free() */
  98 #include <string.h>                                    /* memcpy(), memset() */
  99
 100 #include <vlc/vlc.h>
 101 #include <vlc/vout.h>
 102 #include <vlc/decoder.h>
 103
 104 #include "plugins.h"
 105 #include "decoder.h"
 106 #include "pool.h"
 107 #include "parser.h"
 108
 109 /*
 110  * Local prototypes
 111  */
 112 static int  SynchroType( decoder_fifo_t * );
 113
 114 /* Error margins */
 115 #define DELTA                   (int)(0.075*CLOCK_FREQ)
 116
 117 #define DEFAULT_NB_P            5
 118 #define DEFAULT_NB_B            1
 119
 120 /*****************************************************************************
 121  * vpar_SynchroInit : You know what ?
 122  *****************************************************************************/
 123 void vpar_SynchroInit( vpar_thread_t * p_vpar )
 124 {
 125     p_vpar->synchro.i_type = SynchroType( p_vpar->p_fifo );
 126
 127     /* We use a fake stream pattern, which is often right. */
 128     p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p = DEFAULT_NB_P;
 129     p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b = DEFAULT_NB_B;
 130     memset( p_vpar->synchro.p_tau, 0, 4 * sizeof(mtime_t) );
 131     memset( p_vpar->synchro.pi_meaningful, 0, 4 * sizeof(unsigned int) );
 132     p_vpar->synchro.b_dropped_last = 0;
 133     p_vpar->synchro.current_pts = mdate() + DEFAULT_PTS_DELAY;
 134     p_vpar->synchro.backward_pts = 0;
 135     p_vpar->synchro.i_current_period = p_vpar->synchro.i_backward_period = 0;
 136     p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic =
 137         p_vpar->synchro.i_pic = 0;
 138 }
 139
 140 /*****************************************************************************
 141  * vpar_SynchroChoose : Decide whether we will decode a picture or not
 142  *****************************************************************************/
 143 vlc_bool_t vpar_SynchroChoose( vpar_thread_t * p_vpar, int i_coding_type,
 144                                int i_structure )
 145 {
 146     /* For clarity reasons, we separated the special synchros code from the
 147      * mathematical synchro */
 148
 149     if( p_vpar->synchro.i_type != VPAR_SYNCHRO_DEFAULT )
 150     {
 151         switch( i_coding_type )
 152         {
 153         case I_CODING_TYPE:
 154             /* I, IP, IP+, IPB */
 155             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus )
 156             {
 157                 p_vpar->synchro.b_dropped_last = 1;
 158             }
 159             return( 1 );
 160
 161         case P_CODING_TYPE:
 162             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_I ) /* I */
 163             {
 164                 return( 0 );
 165             }
 166
 167             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus ) /* I+ */
 168             {
 169                 if( p_vpar->synchro.b_dropped_last )
 170                 {
 171                     p_vpar->synchro.b_dropped_last = 0;
 172                     return( 1 );
 173                 }
 174                 else
 175                 {
 176                     return( 0 );
 177                 }
 178             }
 179
 180             return( 1 ); /* IP, IP+, IPB */
 181
 182         case B_CODING_TYPE:
 183             if( p_vpar->synchro.i_type <= VPAR_SYNCHRO_IP ) /* I, IP */
 184             {
 185                 return( 0 );
 186             }
 187             else if( p_vpar->synchro.i_type == VPAR_SYNCHRO_IPB ) /* IPB */
 188             {
 189                 return( 1 );
 190             }
 191
 192             p_vpar->synchro.b_dropped_last ^= 1; /* IP+ */
 193             return( !p_vpar->synchro.b_dropped_last );
 194         }
 195         return( 0 ); /* never reached but gcc yells at me */
 196     }
 197     else
 198     {
 199 #define TAU_PRIME( coding_type )    (p_vpar->synchro.p_tau[(coding_type)] \
 200                                  + (p_vpar->synchro.p_tau[(coding_type)] >> 1) \
 201                                             + tau_yuv)
 202 #define S                           p_vpar->synchro
 203         /* VPAR_SYNCHRO_DEFAULT */
 204         mtime_t         now, period, tau_yuv;
 205         mtime_t         pts = 0;
 206         vlc_bool_t      b_decode = 0;
 207
 208         now = mdate();
 209         period = 1000000 * 1001 / p_vpar->sequence.i_frame_rate
 210                     * p_vpar->sequence.i_current_rate / DEFAULT_RATE;
 211
 212         vlc_mutex_lock( &p_vpar->p_vout->change_lock );
 213         tau_yuv = p_vpar->p_vout->render_time;
 214         vlc_mutex_unlock( &p_vpar->p_vout->change_lock );
 215
 216         switch( i_coding_type )
 217         {
 218         case I_CODING_TYPE:
 219             if( S.backward_pts )
 220             {
 221                 pts = S.backward_pts;
 222             }
 223             else
 224             {
 225                 /* displaying order : B B P B B I
 226                  *                      ^       ^
 227                  *                      |       +- current picture
 228                  *                      +- current PTS
 229                  */
 230                 pts = S.current_pts + period * (S.i_n_b + 2);
 231             }
 232
 233             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 234                     S.p_tau[I_CODING_TYPE] )
 235             {
 236                 b_decode = 1;
 237             }
 238             else
 239             {
 240                 b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 241             }
 242             if( !b_decode )
 243                 msg_Warn( p_vpar->p_fifo,
 244                           "synchro trashing I (%lld)", pts - now );
 245             break;
 246
 247         case P_CODING_TYPE:
 248             if( S.backward_pts )
 249             {
 250                 pts = S.backward_pts;
 251             }
 252             else
 253             {
 254                 pts = S.current_pts + period * (S.i_n_b + 1);
 255             }
 256
 257             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 258                     S.p_tau[I_CODING_TYPE] )
 259             {
 260                 if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 261                 {
 262                     /* Security in case we're _really_ late */
 263                     b_decode = (pts - now > 0);
 264                 }
 265                 else
 266                 {
 267                     b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 268                     /* next I */
 269                     b_decode &= (pts - now
 270                                   + period
 271                               * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 272                                 > (TAU_PRIME(P_CODING_TYPE)
 273                                     + TAU_PRIME(I_CODING_TYPE) + DELTA);
 274                 }
 275             }
 276             else
 277             {
 278                 b_decode = 0;
 279             }
 280             break;
 281
 282         case B_CODING_TYPE:
 283             pts = S.current_pts;
 284
 285             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 286             {
 287                 b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 288             }
 289             else
 290             {
 291                 b_decode = 0;
 292             }
 293         }
 294
 295         if( !b_decode )
 296         {
 297             S.i_not_chosen_pic++;
 298         }
 299         return( b_decode );
 300 #undef S
 301 #undef TAU_PRIME
 302     }
 303 }
 304
 305 /*****************************************************************************
 306  * vpar_SynchroTrash : Update counters when we trash a picture
 307  *****************************************************************************/
 308 void vpar_SynchroTrash( vpar_thread_t * p_vpar, int i_coding_type,
 309                         int i_structure )
 310 {
 311     p_vpar->synchro.i_trashed_pic++;
 312 }
 313
 314 /*****************************************************************************
 315  * vpar_SynchroDecode : Update timers when we decide to decode a picture
 316  *****************************************************************************/
 317 void vpar_SynchroDecode( vpar_thread_t * p_vpar, int i_coding_type,
 318                          int i_structure )
 319 {
 320     p_vpar->synchro.decoding_start = mdate();
 321 }
 322
 323 /*****************************************************************************
 324  * vpar_SynchroEnd : Called when the image is totally decoded
 325  *****************************************************************************/
 326 void vpar_SynchroEnd( vpar_thread_t * p_vpar, int i_coding_type,
 327                       int i_structure, int i_garbage )
 328 {
 329     mtime_t     tau;
 330
 331     if( !i_garbage )
 332     {
 333         tau = mdate() - p_vpar->synchro.decoding_start;
 334
 335         /* If duration too high, something happened (pause ?), so don't
 336          * take it into account. */
 337         if( tau < 3 * p_vpar->synchro.p_tau[i_coding_type]
 338              || !p_vpar->synchro.pi_meaningful[i_coding_type] )
 339         {
 340             /* Mean with average tau, to ensure stability. */
 341             p_vpar->synchro.p_tau[i_coding_type] =
 342                 (p_vpar->synchro.pi_meaningful[i_coding_type]
 343                  * p_vpar->synchro.p_tau[i_coding_type] + tau)
 344                 / (p_vpar->synchro.pi_meaningful[i_coding_type] + 1);
 345             if( p_vpar->synchro.pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 346             {
 347                 p_vpar->synchro.pi_meaningful[i_coding_type]++;
 348             }
 349         }
 350     }
 351 }
 352
 353 /*****************************************************************************
 354  * vpar_SynchroDate : When an image has been decoded, ask for its date
 355  *****************************************************************************/
 356 mtime_t vpar_SynchroDate( vpar_thread_t * p_vpar )
 357 {
 358     /* No need to lock, since PTS are only used by the video parser. */
 359     return( p_vpar->synchro.current_pts );
 360 }
 361
 362 /*****************************************************************************
 363  * vpar_SynchroNewPicture: Update stream structure and PTS
 364  *****************************************************************************/
 365 void vpar_SynchroNewPicture( vpar_thread_t * p_vpar, int i_coding_type,
 366                              int i_repeat_field )
 367 {
 368     mtime_t         period = 1000000 * 1001 / p_vpar->sequence.i_frame_rate
 369                               * p_vpar->sequence.i_current_rate / DEFAULT_RATE;
 370 #if 0
 371     mtime_t         now = mdate();
 372 #endif
 373
 374     switch( i_coding_type )
 375     {
 376     case I_CODING_TYPE:
 377         if( p_vpar->synchro.i_eta_p
 378              && p_vpar->synchro.i_eta_p != p_vpar->synchro.i_n_p )
 379         {
 380             msg_Dbg( p_vpar->p_fifo,
 381                      "stream periodicity changed from P[%d] to P[%d]",
 382                      p_vpar->synchro.i_n_p, p_vpar->synchro.i_eta_p );
 383             p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p;
 384         }
 385         p_vpar->synchro.i_eta_p = p_vpar->synchro.i_eta_b = 0;
 386
 387         if( p_vpar->synchro.i_type == VPAR_SYNCHRO_DEFAULT )
 388         {
 389             msg_Dbg( p_vpar->p_fifo, "I(%lld) P(%lld)[%d] B(%lld)[%d] YUV(%lld) : trashed %d:%d/%d",
 390                   p_vpar->synchro.p_tau[I_CODING_TYPE],
 391                   p_vpar->synchro.p_tau[P_CODING_TYPE],
 392                   p_vpar->synchro.i_n_p,
 393                   p_vpar->synchro.p_tau[B_CODING_TYPE],
 394                   p_vpar->synchro.i_n_b,
 395                   p_vpar->p_vout->render_time,
 396                   p_vpar->synchro.i_not_chosen_pic,
 397                   p_vpar->synchro.i_trashed_pic -
 398                   p_vpar->synchro.i_not_chosen_pic,
 399                   p_vpar->synchro.i_pic );
 400             p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic
 401                 = p_vpar->synchro.i_pic = 0;
 402         }
 403         break;
 404
 405     case P_CODING_TYPE:
 406         p_vpar->synchro.i_eta_p++;
 407         if( p_vpar->synchro.i_eta_b
 408              && p_vpar->synchro.i_eta_b != p_vpar->synchro.i_n_b )
 409         {
 410             msg_Warn( p_vpar->p_fifo,
 411                       "stream periodicity changed from B[%d] to B[%d]",
 412                       p_vpar->synchro.i_n_b, p_vpar->synchro.i_eta_b );
 413             p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b;
 414         }
 415         p_vpar->synchro.i_eta_b = 0;
 416         break;
 417     case B_CODING_TYPE:
 418         p_vpar->synchro.i_eta_b++;
 419         break;
 420     }
 421
 422     p_vpar->synchro.current_pts += p_vpar->synchro.i_current_period
 423                                         * (period >> 1);
 424
 425 #define PTS_THRESHOLD   (period >> 2)
 426     if( i_coding_type == B_CODING_TYPE )
 427     {
 428         /* A video frame can be displayed 1, 2 or 3 times, according to
 429          * repeat_first_field, top_field_first, progressive_sequence and
 430          * progressive_frame. */
 431         p_vpar->synchro.i_current_period = i_repeat_field;
 432
 433         if( p_vpar->sequence.next_pts )
 434         {
 435             if( p_vpar->sequence.next_pts - p_vpar->synchro.current_pts
 436                     > PTS_THRESHOLD
 437                  || p_vpar->synchro.current_pts - p_vpar->sequence.next_pts
 438                     > PTS_THRESHOLD )
 439             {
 440                 msg_Warn( p_vpar->p_fifo,
 441                           "vpar synchro warning: pts != current_date (%lld)",
 442                           p_vpar->synchro.current_pts
 443                               - p_vpar->sequence.next_pts );
 444             }
 445             p_vpar->synchro.current_pts = p_vpar->sequence.next_pts;
 446             p_vpar->sequence.next_pts = 0;
 447         }
 448     }
 449     else
 450     {
 451         p_vpar->synchro.i_current_period = p_vpar->synchro.i_backward_period;
 452         p_vpar->synchro.i_backward_period = i_repeat_field;
 453
 454         if( p_vpar->synchro.backward_pts )
 455         {
 456             if( p_vpar->sequence.next_dts &&
 457                 (p_vpar->sequence.next_dts - p_vpar->synchro.backward_pts
 458                     > PTS_THRESHOLD
 459               || p_vpar->synchro.backward_pts - p_vpar->sequence.next_dts
 460                     > PTS_THRESHOLD) )
 461             {
 462                 msg_Warn( p_vpar->p_fifo, "backward_pts != dts (%lld)",
 463                            p_vpar->sequence.next_dts
 464                                - p_vpar->synchro.backward_pts );
 465             }
 466             if( p_vpar->synchro.backward_pts - p_vpar->synchro.current_pts
 467                     > PTS_THRESHOLD
 468                  || p_vpar->synchro.current_pts - p_vpar->synchro.backward_pts
 469                     > PTS_THRESHOLD )
 470             {
 471                 msg_Warn( p_vpar->p_fifo,
 472                           "backward_pts != current_pts (%lld)",
 473                           p_vpar->synchro.current_pts
 474                               - p_vpar->synchro.backward_pts );
 475             }
 476             p_vpar->synchro.current_pts = p_vpar->synchro.backward_pts;
 477             p_vpar->synchro.backward_pts = 0;
 478         }
 479         else if( p_vpar->sequence.next_dts )
 480         {
 481             if( p_vpar->sequence.next_dts - p_vpar->synchro.current_pts
 482                     > PTS_THRESHOLD
 483                  || p_vpar->synchro.current_pts - p_vpar->sequence.next_dts
 484                     > PTS_THRESHOLD )
 485             {
 486                 msg_Warn( p_vpar->p_fifo, "dts != current_pts (%lld)",
 487                           p_vpar->synchro.current_pts
 488                               - p_vpar->sequence.next_dts );
 489             }
 490             /* By definition of a DTS. */
 491             p_vpar->synchro.current_pts = p_vpar->sequence.next_dts;
 492             p_vpar->sequence.next_dts = 0;
 493         }
 494
 495         if( p_vpar->sequence.next_pts )
 496         {
 497             /* Store the PTS for the next time we have to date an I picture. */
 498             p_vpar->synchro.backward_pts = p_vpar->sequence.next_pts;
 499             p_vpar->sequence.next_pts = 0;
 500         }
 501     }
 502 #undef PTS_THRESHOLD
 503
 504 #if 0
 505     /* Removed for incompatibility with slow motion */
 506     if( p_vpar->synchro.current_pts + DEFAULT_PTS_DELAY < now )
 507     {
 508         /* We cannot be _that_ late, something must have happened, reinit
 509          * the dates. */
 510         msg_Warn( p_vpar->p_fifo, "PTS << now (%lld), resetting",
 511                    now - p_vpar->synchro.current_pts - DEFAULT_PTS_DELAY );
 512         p_vpar->synchro.current_pts = now + DEFAULT_PTS_DELAY;
 513     }
 514     if( p_vpar->synchro.backward_pts
 515          && p_vpar->synchro.backward_pts + DEFAULT_PTS_DELAY < now )
 516     {
 517         /* The same. */
 518         p_vpar->synchro.backward_pts = 0;
 519     }
 520 #endif
 521
 522     p_vpar->synchro.i_pic++;
 523 }
 524
 525 /*****************************************************************************
 526  * SynchroType: Get the user's synchro type
 527  *****************************************************************************
 528  * This function is called at initialization.
 529  *****************************************************************************/
 530 static int SynchroType( decoder_fifo_t *p_this )
 531 {
 532     char psz_synchro_tmp[5];
 533     char * psz_synchro = config_GetPsz( p_this, "vpar-synchro" );
 534
 535     if( psz_synchro == NULL )
 536     {
 537         return VPAR_SYNCHRO_DEFAULT;
 538     }
 539
 540     strncpy( psz_synchro_tmp, psz_synchro, 5);
 541     free( psz_synchro );
 542     psz_synchro = psz_synchro_tmp;
 543
 544     switch( *psz_synchro++ )
 545     {
 546       case 'i':
 547       case 'I':
 548         switch( *psz_synchro++ )
 549         {
 550           case '\0':
 551             return VPAR_SYNCHRO_I;
 552
 553           case '+':
 554             if( *psz_synchro ) return 0;
 555             return VPAR_SYNCHRO_Iplus;
 556
 557           case 'p':
 558           case 'P':
 559             switch( *psz_synchro++ )
 560             {
 561               case '\0':
 562                 return VPAR_SYNCHRO_IP;
 563
 564               case '+':
 565                 if( *psz_synchro ) return 0;
 566                 return VPAR_SYNCHRO_IPplus;
 567
 568               case 'b':
 569               case 'B':
 570                 if( *psz_synchro ) return 0;
 571                 return VPAR_SYNCHRO_IPB;
 572
 573               default:
 574                 return VPAR_SYNCHRO_DEFAULT;
 575
 576             }
 577
 578           default:
 579             return VPAR_SYNCHRO_DEFAULT;
 580         }
 581     }
 582
 583     return VPAR_SYNCHRO_DEFAULT;
 584 }
 585