git.sesse.net Git - vlc/blob - src/input/decoder_synchro.c

   1 /*****************************************************************************
   2  * decoder_synchro.c : frame dropping routines
   3  *****************************************************************************
   4  * Copyright (C) 1999-2005 the VideoLAN team
   5  * $Id$
   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., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, 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 #ifdef HAVE_CONFIG_H
  98 # include "config.h"
  99 #endif
 100
 101 #include <vlc_common.h>
 102 #include <vlc_input.h>
 103 #include <vlc_codec.h>
 104 #include <vlc_codec_synchro.h>
 105
 106 /*
 107  * Local prototypes
 108  */
 109
 110 #define MAX_PIC_AVERAGE         8
 111
 112 struct decoder_synchro_t
 113 {
 114     /* */
 115     decoder_t       *p_dec;
 116
 117     /* */
 118     int             i_frame_rate;
 119     int             i_current_rate;
 120     bool      b_no_skip;
 121     bool      b_quiet;
 122
 123     /* date of the beginning of the decoding of the current picture */
 124     mtime_t         decoding_start;
 125
 126     /* stream properties */
 127     unsigned int    i_n_p, i_n_b;
 128
 129     /* decoding values */
 130     mtime_t         p_tau[4];                  /* average decoding durations */
 131     unsigned int    pi_meaningful[4];            /* number of durations read */
 132
 133     /* render_time filled by SynchroChoose() */
 134     int i_render_time;
 135
 136     /* stream context */
 137     int             i_nb_ref;                /* Number of reference pictures */
 138     int             i_dec_nb_ref;      /* Number of reference pictures we'll *
 139                                         * have if we decode the current pic  */
 140     int             i_trash_nb_ref;    /* Number of reference pictures we'll *
 141                                         * have if we trash the current pic   */
 142     unsigned int    i_eta_p, i_eta_b;
 143     mtime_t         backward_pts, current_pts;
 144     int             i_current_period;   /* period to add to the next picture */
 145     int             i_backward_period;  /* period to add after the next
 146                                          * reference picture
 147                                          * (backward_period * period / 2) */
 148
 149     /* statistics */
 150     unsigned int    i_trashed_pic, i_not_chosen_pic, i_pic;
 151 };
 152
 153 /* Error margins */
 154 #define DELTA                   (int)(0.075*CLOCK_FREQ)
 155 #define MAX_VALID_TAU           (int)(0.3*CLOCK_FREQ)
 156
 157 #define DEFAULT_NB_P            5
 158 #define DEFAULT_NB_B            1
 159
 160 /*****************************************************************************
 161  * decoder_SynchroInit : You know what ?
 162  *****************************************************************************/
 163 decoder_synchro_t * decoder_SynchroInit( decoder_t *p_dec, int i_frame_rate )
 164 {
 165     decoder_synchro_t * p_synchro = malloc( sizeof(*p_synchro) );
 166     if ( p_synchro == NULL )
 167         return NULL;
 168     memset( p_synchro, 0, sizeof(*p_synchro) );
 169
 170     p_synchro->p_dec = p_dec;
 171     p_synchro->b_no_skip = !config_GetInt( p_dec, "skip-frames" );
 172     p_synchro->b_quiet = config_GetInt( p_dec, "quiet-synchro" );
 173
 174     /* We use a fake stream pattern, which is often right. */
 175     p_synchro->i_n_p = p_synchro->i_eta_p = DEFAULT_NB_P;
 176     p_synchro->i_n_b = p_synchro->i_eta_b = DEFAULT_NB_B;
 177     memset( p_synchro->p_tau, 0, 4 * sizeof(mtime_t) );
 178     memset( p_synchro->pi_meaningful, 0, 4 * sizeof(unsigned int) );
 179     p_synchro->i_nb_ref = 0;
 180     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 181     p_synchro->current_pts = mdate() + DEFAULT_PTS_DELAY;
 182     p_synchro->backward_pts = 0;
 183     p_synchro->i_current_period = p_synchro->i_backward_period = 0;
 184     p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic =
 185         p_synchro->i_pic = 0;
 186
 187     p_synchro->i_frame_rate = i_frame_rate;
 188
 189     return p_synchro;
 190 }
 191
 192 /*****************************************************************************
 193  * decoder_SynchroRelease : You know what ?
 194  *****************************************************************************/
 195 void decoder_SynchroRelease( decoder_synchro_t * p_synchro )
 196 {
 197     free( p_synchro );
 198 }
 199
 200 /*****************************************************************************
 201  * decoder_SynchroReset : Reset the reference picture counter
 202  *****************************************************************************/
 203 void decoder_SynchroReset( decoder_synchro_t * p_synchro )
 204 {
 205     p_synchro->i_nb_ref = 0;
 206     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 207 }
 208
 209 /*****************************************************************************
 210  * decoder_SynchroChoose : Decide whether we will decode a picture or not
 211  *****************************************************************************/
 212 bool decoder_SynchroChoose( decoder_synchro_t * p_synchro, int i_coding_type,
 213                                int i_render_time, bool b_low_delay )
 214 {
 215 #define TAU_PRIME( coding_type )    (p_synchro->p_tau[(coding_type)] \
 216                                     + (p_synchro->p_tau[(coding_type)] >> 1) \
 217                                     + p_synchro->i_render_time)
 218 #define S (*p_synchro)
 219     mtime_t         now, period;
 220     mtime_t         pts = 0;
 221     bool      b_decode = 0;
 222
 223     if ( p_synchro->b_no_skip )
 224         return 1;
 225
 226     now = mdate();
 227     period = 1000000 * 1001 / p_synchro->i_frame_rate
 228                      * p_synchro->i_current_rate / INPUT_RATE_DEFAULT;
 229
 230     p_synchro->i_render_time = i_render_time;
 231
 232     switch( i_coding_type )
 233     {
 234     case I_CODING_TYPE:
 235         if( b_low_delay )
 236         {
 237             pts = S.current_pts;
 238         }
 239         else if( S.backward_pts )
 240         {
 241             pts = S.backward_pts;
 242         }
 243         else
 244         {
 245             /* displaying order : B B P B B I
 246              *                      ^       ^
 247              *                      |       +- current picture
 248              *                      +- current PTS
 249              */
 250             pts = S.current_pts + period * (S.i_n_b + 2);
 251         }
 252
 253         if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 254                 S.p_tau[I_CODING_TYPE] )
 255         {
 256             b_decode = 1;
 257         }
 258         else
 259         {
 260             b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 261         }
 262         if( !b_decode && !p_synchro->b_quiet )
 263         {
 264             msg_Warn( p_synchro->p_dec,
 265                       "synchro trashing I (%"PRId64")", pts - now );
 266         }
 267         break;
 268
 269     case P_CODING_TYPE:
 270         if( b_low_delay )
 271         {
 272             pts = S.current_pts;
 273         }
 274         else if( S.backward_pts )
 275         {
 276             pts = S.backward_pts;
 277         }
 278         else
 279         {
 280             pts = S.current_pts + period * (S.i_n_b + 1);
 281         }
 282
 283         if( p_synchro->i_nb_ref < 1 )
 284         {
 285             b_decode = 0;
 286         }
 287         else if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 288                 S.p_tau[I_CODING_TYPE] )
 289         {
 290             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 291             {
 292                 /* Security in case we're _really_ late */
 293                 b_decode = (pts - now > 0);
 294             }
 295             else
 296             {
 297                 b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 298                 /* next I */
 299                 b_decode &= (pts - now
 300                               + period
 301                           * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 302                             > (TAU_PRIME(P_CODING_TYPE)
 303                                 + TAU_PRIME(I_CODING_TYPE) + DELTA);
 304             }
 305         }
 306         else
 307         {
 308             b_decode = 0;
 309         }
 310         break;
 311
 312     case B_CODING_TYPE:
 313         pts = S.current_pts;
 314
 315         if( p_synchro->i_nb_ref < 2 )
 316         {
 317             b_decode = 0;
 318         }
 319         else if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 320         {
 321             b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 322         }
 323         else
 324         {
 325             b_decode = 0;
 326         }
 327     }
 328
 329     if( !b_decode )
 330     {
 331         S.i_not_chosen_pic++;
 332     }
 333     return( b_decode );
 334 #undef S
 335 #undef TAU_PRIME
 336 }
 337
 338 /*****************************************************************************
 339  * decoder_SynchroTrash : Update counters when we trash a picture
 340  *****************************************************************************/
 341 void decoder_SynchroTrash( decoder_synchro_t * p_synchro )
 342 {
 343     p_synchro->i_trashed_pic++;
 344     p_synchro->i_nb_ref = p_synchro->i_trash_nb_ref;
 345 }
 346
 347 /*****************************************************************************
 348  * decoder_SynchroDecode : Update timers when we decide to decode a picture
 349  *****************************************************************************/
 350 void decoder_SynchroDecode( decoder_synchro_t * p_synchro )
 351 {
 352     p_synchro->decoding_start = mdate();
 353     p_synchro->i_nb_ref = p_synchro->i_dec_nb_ref;
 354 }
 355
 356 /*****************************************************************************
 357  * decoder_SynchroEnd : Called when the image is totally decoded
 358  *****************************************************************************/
 359 void decoder_SynchroEnd( decoder_synchro_t * p_synchro, int i_coding_type,
 360                       bool b_garbage )
 361 {
 362     mtime_t     tau;
 363
 364     if( !b_garbage )
 365     {
 366         tau = mdate() - p_synchro->decoding_start;
 367
 368         /* If duration too high, something happened (pause ?), so don't
 369          * take it into account. */
 370         if( tau < 3 * p_synchro->p_tau[i_coding_type]
 371              || ( !p_synchro->pi_meaningful[i_coding_type]
 372                    && tau < MAX_VALID_TAU ) )
 373         {
 374             /* Mean with average tau, to ensure stability. */
 375             p_synchro->p_tau[i_coding_type] =
 376                 (p_synchro->pi_meaningful[i_coding_type]
 377                  * p_synchro->p_tau[i_coding_type] + tau)
 378                 / (p_synchro->pi_meaningful[i_coding_type] + 1);
 379             if( p_synchro->pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 380             {
 381                 p_synchro->pi_meaningful[i_coding_type]++;
 382             }
 383         }
 384     }
 385 }
 386
 387 /*****************************************************************************
 388  * decoder_SynchroDate : When an image has been decoded, ask for its date
 389  *****************************************************************************/
 390 mtime_t decoder_SynchroDate( decoder_synchro_t * p_synchro )
 391 {
 392     /* No need to lock, since PTS are only used by the video parser. */
 393     return p_synchro->current_pts;
 394 }
 395
 396 /*****************************************************************************
 397  * decoder_SynchroNewPicture: Update stream structure and PTS
 398  *****************************************************************************/
 399 void decoder_SynchroNewPicture( decoder_synchro_t * p_synchro, int i_coding_type,
 400                              int i_repeat_field, mtime_t next_pts,
 401                              mtime_t next_dts, int i_current_rate,
 402                              bool b_low_delay )
 403 {
 404     mtime_t         period = 1000000 * 1001 / p_synchro->i_frame_rate
 405                               * i_current_rate / INPUT_RATE_DEFAULT;
 406 #if 0
 407     mtime_t         now = mdate();
 408 #endif
 409     p_synchro->i_current_rate = i_current_rate;
 410
 411     switch( i_coding_type )
 412     {
 413     case I_CODING_TYPE:
 414         if( p_synchro->i_eta_p
 415              && p_synchro->i_eta_p != p_synchro->i_n_p )
 416         {
 417 #if 0
 418             if( !p_synchro->b_quiet )
 419                 msg_Dbg( p_synchro->p_dec,
 420                          "stream periodicity changed from P[%d] to P[%d]",
 421                          p_synchro->i_n_p, p_synchro->i_eta_p );
 422 #endif
 423             p_synchro->i_n_p = p_synchro->i_eta_p;
 424         }
 425         p_synchro->i_eta_p = p_synchro->i_eta_b = 0;
 426         p_synchro->i_trash_nb_ref = 0;
 427         if( p_synchro->i_nb_ref < 2 )
 428             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref + 1;
 429         else
 430             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref;
 431
 432 #if 0
 433         if( !p_synchro->b_quiet )
 434             msg_Dbg( p_synchro->p_dec, "I(%"PRId64") P(%"PRId64")[%d] B(%"PRId64")"
 435                   "[%d] YUV(%"PRId64") : trashed %d:%d/%d",
 436                   p_synchro->p_tau[I_CODING_TYPE],
 437                   p_synchro->p_tau[P_CODING_TYPE],
 438                   p_synchro->i_n_p,
 439                   p_synchro->p_tau[B_CODING_TYPE],
 440                   p_synchro->i_n_b,
 441                   p_synchro->i_render_time,
 442                   p_synchro->i_not_chosen_pic,
 443                   p_synchro->i_trashed_pic -
 444                   p_synchro->i_not_chosen_pic,
 445                   p_synchro->i_pic );
 446         p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 447             = p_synchro->i_pic = 0;
 448 #else
 449         if( p_synchro->i_pic >= 100 )
 450         {
 451             if( !p_synchro->b_quiet && p_synchro->i_trashed_pic != 0 )
 452                 msg_Dbg( p_synchro->p_dec, "decoded %d/%d pictures",
 453                          p_synchro->i_pic
 454                            - p_synchro->i_trashed_pic,
 455                          p_synchro->i_pic );
 456             p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 457                 = p_synchro->i_pic = 0;
 458         }
 459 #endif
 460         break;
 461
 462     case P_CODING_TYPE:
 463         p_synchro->i_eta_p++;
 464         if( p_synchro->i_eta_b
 465              && p_synchro->i_eta_b != p_synchro->i_n_b )
 466         {
 467 #if 0
 468             if( !p_synchro->b_quiet )
 469                 msg_Dbg( p_synchro->p_dec,
 470                          "stream periodicity changed from B[%d] to B[%d]",
 471                          p_synchro->i_n_b, p_synchro->i_eta_b );
 472 #endif
 473             p_synchro->i_n_b = p_synchro->i_eta_b;
 474         }
 475         p_synchro->i_eta_b = 0;
 476         p_synchro->i_dec_nb_ref = 2;
 477         p_synchro->i_trash_nb_ref = 0;
 478         break;
 479
 480     case B_CODING_TYPE:
 481         p_synchro->i_eta_b++;
 482         p_synchro->i_dec_nb_ref = p_synchro->i_trash_nb_ref
 483             = p_synchro->i_nb_ref;
 484         break;
 485     }
 486
 487     p_synchro->current_pts += p_synchro->i_current_period
 488                                         * (period >> 1);
 489
 490 #define PTS_THRESHOLD   (period >> 2)
 491     if( i_coding_type == B_CODING_TYPE || b_low_delay )
 492     {
 493         /* A video frame can be displayed 1, 2 or 3 times, according to
 494          * repeat_first_field, top_field_first, progressive_sequence and
 495          * progressive_frame. */
 496         p_synchro->i_current_period = i_repeat_field;
 497
 498         if( next_pts )
 499         {
 500             if( (next_pts - p_synchro->current_pts
 501                     > PTS_THRESHOLD
 502                   || p_synchro->current_pts - next_pts
 503                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 504             {
 505                 msg_Warn( p_synchro->p_dec, "decoder synchro warning: pts != "
 506                           "current_date (%"PRId64")",
 507                           p_synchro->current_pts
 508                               - next_pts );
 509             }
 510             p_synchro->current_pts = next_pts;
 511         }
 512     }
 513     else
 514     {
 515         p_synchro->i_current_period = p_synchro->i_backward_period;
 516         p_synchro->i_backward_period = i_repeat_field;
 517
 518         if( p_synchro->backward_pts )
 519         {
 520             if( next_dts &&
 521                 (next_dts - p_synchro->backward_pts
 522                     > PTS_THRESHOLD
 523                   || p_synchro->backward_pts - next_dts
 524                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 525             {
 526                 msg_Warn( p_synchro->p_dec, "backward_pts != dts (%"PRId64")",
 527                            next_dts
 528                                - p_synchro->backward_pts );
 529             }
 530             if( (p_synchro->backward_pts - p_synchro->current_pts
 531                     > PTS_THRESHOLD
 532                   || p_synchro->current_pts - p_synchro->backward_pts
 533                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 534             {
 535                 msg_Warn( p_synchro->p_dec,
 536                           "backward_pts != current_pts (%"PRId64")",
 537                           p_synchro->current_pts
 538                               - p_synchro->backward_pts );
 539             }
 540             p_synchro->current_pts = p_synchro->backward_pts;
 541             p_synchro->backward_pts = 0;
 542         }
 543         else if( next_dts )
 544         {
 545             if( (next_dts - p_synchro->current_pts
 546                     > PTS_THRESHOLD
 547                   || p_synchro->current_pts - next_dts
 548                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 549             {
 550                 msg_Warn( p_synchro->p_dec, "dts != current_pts (%"PRId64")",
 551                           p_synchro->current_pts
 552                               - next_dts );
 553             }
 554             /* By definition of a DTS. */
 555             p_synchro->current_pts = next_dts;
 556             next_dts = 0;
 557         }
 558
 559         if( next_pts )
 560         {
 561             /* Store the PTS for the next time we have to date an I picture. */
 562             p_synchro->backward_pts = next_pts;
 563             next_pts = 0;
 564         }
 565     }
 566 #undef PTS_THRESHOLD
 567
 568 #if 0
 569     /* Removed for incompatibility with slow motion */
 570     if( p_synchro->current_pts + DEFAULT_PTS_DELAY < now )
 571     {
 572         /* We cannot be _that_ late, something must have happened, reinit
 573          * the dates. */
 574         if( !p_synchro->b_quiet )
 575             msg_Warn( p_synchro->p_dec, "PTS << now (%"PRId64"), resetting",
 576                       now - p_synchro->current_pts - DEFAULT_PTS_DELAY );
 577         p_synchro->current_pts = now + DEFAULT_PTS_DELAY;
 578     }
 579     if( p_synchro->backward_pts
 580          && p_synchro->backward_pts + DEFAULT_PTS_DELAY < now )
 581     {
 582         /* The same. */
 583         p_synchro->backward_pts = 0;
 584     }
 585 #endif
 586
 587     p_synchro->i_pic++;
 588 }