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     bool            b_no_skip;
 120     bool            b_quiet;
 121
 122     /* date of the beginning of the decoding of the current picture */
 123     mtime_t         decoding_start;
 124
 125     /* stream properties */
 126     unsigned int    i_n_p, i_n_b;
 127
 128     /* decoding values */
 129     mtime_t         p_tau[4];                  /* average decoding durations */
 130     unsigned int    pi_meaningful[4];            /* number of durations read */
 131
 132     /* render_time filled by SynchroChoose() */
 133     int             i_render_time;
 134
 135     /* stream context */
 136     int             i_nb_ref;                /* Number of reference pictures */
 137     int             i_dec_nb_ref;      /* Number of reference pictures we'll *
 138                                         * have if we decode the current pic  */
 139     int             i_trash_nb_ref;    /* Number of reference pictures we'll *
 140                                         * have if we trash the current pic   */
 141     unsigned int    i_eta_p, i_eta_b;
 142     mtime_t         backward_pts, current_pts;
 143     int             i_current_period;   /* period to add to the next picture */
 144     int             i_backward_period;  /* period to add after the next
 145                                          * reference picture
 146                                          * (backward_period * period / 2) */
 147
 148     /* statistics */
 149     unsigned int    i_trashed_pic, i_not_chosen_pic, i_pic;
 150 };
 151
 152 /* Error margins */
 153 #define DELTA                   (int)(0.075*CLOCK_FREQ)
 154 #define MAX_VALID_TAU           (int)(0.3*CLOCK_FREQ)
 155
 156 #define DEFAULT_NB_P            5
 157 #define DEFAULT_NB_B            1
 158
 159 /*****************************************************************************
 160  * decoder_SynchroInit : You know what ?
 161  *****************************************************************************/
 162 decoder_synchro_t * decoder_SynchroInit( decoder_t *p_dec, int i_frame_rate )
 163 {
 164     decoder_synchro_t * p_synchro = calloc( 1, sizeof(*p_synchro) );
 165     if( !p_synchro )
 166         return NULL;
 167
 168     p_synchro->p_dec = p_dec;
 169     p_synchro->b_no_skip = !var_InheritBool( p_dec, "skip-frames" );
 170     p_synchro->b_quiet = var_InheritBool( p_dec, "quiet-synchro" );
 171
 172     /* We use a fake stream pattern, which is often right. */
 173     p_synchro->i_n_p = p_synchro->i_eta_p = DEFAULT_NB_P;
 174     p_synchro->i_n_b = p_synchro->i_eta_b = DEFAULT_NB_B;
 175     memset( p_synchro->p_tau, 0, 4 * sizeof(mtime_t) );
 176     memset( p_synchro->pi_meaningful, 0, 4 * sizeof(unsigned int) );
 177     p_synchro->i_nb_ref = 0;
 178     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 179     p_synchro->current_pts = 1,
 180     p_synchro->backward_pts = 0;
 181     p_synchro->i_current_period = p_synchro->i_backward_period = 0;
 182     p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic =
 183         p_synchro->i_pic = 0;
 184
 185     p_synchro->i_frame_rate = i_frame_rate;
 186
 187     return p_synchro;
 188 }
 189
 190 /*****************************************************************************
 191  * decoder_SynchroRelease : You know what ?
 192  *****************************************************************************/
 193 void decoder_SynchroRelease( decoder_synchro_t * p_synchro )
 194 {
 195     free( p_synchro );
 196 }
 197
 198 /*****************************************************************************
 199  * decoder_SynchroReset : Reset the reference picture counter
 200  *****************************************************************************/
 201 void decoder_SynchroReset( decoder_synchro_t * p_synchro )
 202 {
 203     p_synchro->i_nb_ref = 0;
 204     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 205 }
 206
 207 /*****************************************************************************
 208  * decoder_SynchroChoose : Decide whether we will decode a picture or not
 209  *****************************************************************************/
 210 bool decoder_SynchroChoose( decoder_synchro_t * p_synchro, int i_coding_type,
 211                                int i_render_time, bool b_low_delay )
 212 {
 213 #define TAU_PRIME( coding_type )    (p_synchro->p_tau[(coding_type)] \
 214                                     + (p_synchro->p_tau[(coding_type)] >> 1) \
 215                                     + p_synchro->i_render_time)
 216 #define S (*p_synchro)
 217     mtime_t         now, period;
 218     mtime_t         pts;
 219     bool      b_decode = 0;
 220     int       i_current_rate;
 221
 222     if ( p_synchro->b_no_skip )
 223         return 1;
 224
 225     i_current_rate = decoder_GetDisplayRate( p_synchro->p_dec );
 226
 227     now = mdate();
 228     period = 1000000 * 1001 / p_synchro->i_frame_rate
 229                      * i_current_rate / INPUT_RATE_DEFAULT;
 230
 231     p_synchro->i_render_time = i_render_time;
 232
 233     switch( i_coding_type )
 234     {
 235     case I_CODING_TYPE:
 236         if( b_low_delay )
 237         {
 238             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts );
 239         }
 240         else if( S.backward_pts )
 241         {
 242             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.backward_pts );
 243         }
 244         else
 245         {
 246             /* displaying order : B B P B B I
 247              *                      ^       ^
 248              *                      |       +- current picture
 249              *                      +- current PTS
 250              */
 251             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts ) + period * (S.i_n_b + 2);
 252         }
 253
 254         if( (1 + S.i_n_p * (S.i_n_b + 1)) * period > 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( pts <= VLC_TS_INVALID )
 263             b_decode = 1;
 264
 265         if( !b_decode && !p_synchro->b_quiet )
 266         {
 267             msg_Warn( p_synchro->p_dec,
 268                       "synchro trashing I (%"PRId64")", pts - now );
 269         }
 270         break;
 271
 272     case P_CODING_TYPE:
 273         if( b_low_delay )
 274         {
 275             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts );
 276         }
 277         else if( S.backward_pts )
 278         {
 279             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.backward_pts );
 280         }
 281         else
 282         {
 283             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts + period * (S.i_n_b + 1) );
 284         }
 285
 286         if( p_synchro->i_nb_ref < 1 )
 287         {
 288             b_decode = 0;
 289         }
 290         else if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 291                 S.p_tau[I_CODING_TYPE] )
 292         {
 293             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 294             {
 295                 /* Security in case we're _really_ late */
 296                 b_decode = (pts - now > 0);
 297             }
 298             else
 299             {
 300                 b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 301                 /* next I */
 302                 b_decode &= (pts - now
 303                               + period
 304                           * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 305                             > (TAU_PRIME(P_CODING_TYPE)
 306                                 + TAU_PRIME(I_CODING_TYPE) + DELTA);
 307             }
 308         }
 309         else
 310         {
 311             b_decode = 0;
 312         }
 313         if( p_synchro->i_nb_ref >= 1 && pts <= VLC_TS_INVALID )
 314             b_decode = 1;
 315         break;
 316
 317     case B_CODING_TYPE:
 318         pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts );
 319
 320         if( p_synchro->i_nb_ref < 2 )
 321         {
 322             b_decode = 0;
 323         }
 324         else if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 325         {
 326             b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 327         }
 328         else
 329         {
 330             b_decode = 0;
 331         }
 332         if( p_synchro->i_nb_ref >= 2 && pts <= VLC_TS_INVALID )
 333             b_decode = 1;
 334         break;
 335     }
 336
 337     if( !b_decode )
 338     {
 339         S.i_not_chosen_pic++;
 340     }
 341     return( b_decode );
 342 #undef S
 343 #undef TAU_PRIME
 344 }
 345
 346 /*****************************************************************************
 347  * decoder_SynchroTrash : Update counters when we trash a picture
 348  *****************************************************************************/
 349 void decoder_SynchroTrash( decoder_synchro_t * p_synchro )
 350 {
 351     p_synchro->i_trashed_pic++;
 352     p_synchro->i_nb_ref = p_synchro->i_trash_nb_ref;
 353 }
 354
 355 /*****************************************************************************
 356  * decoder_SynchroDecode : Update timers when we decide to decode a picture
 357  *****************************************************************************/
 358 void decoder_SynchroDecode( decoder_synchro_t * p_synchro )
 359 {
 360     p_synchro->decoding_start = mdate();
 361     p_synchro->i_nb_ref = p_synchro->i_dec_nb_ref;
 362 }
 363
 364 /*****************************************************************************
 365  * decoder_SynchroEnd : Called when the image is totally decoded
 366  *****************************************************************************/
 367 void decoder_SynchroEnd( decoder_synchro_t * p_synchro, int i_coding_type,
 368                       bool b_garbage )
 369 {
 370     mtime_t     tau;
 371
 372     if( !b_garbage )
 373     {
 374         tau = mdate() - p_synchro->decoding_start;
 375
 376         /* If duration too high, something happened (pause ?), so don't
 377          * take it into account. */
 378         if( tau < 3 * p_synchro->p_tau[i_coding_type]
 379              || ( !p_synchro->pi_meaningful[i_coding_type]
 380                    && tau < MAX_VALID_TAU ) )
 381         {
 382             /* Mean with average tau, to ensure stability. */
 383             p_synchro->p_tau[i_coding_type] =
 384                 (p_synchro->pi_meaningful[i_coding_type]
 385                  * p_synchro->p_tau[i_coding_type] + tau)
 386                 / (p_synchro->pi_meaningful[i_coding_type] + 1);
 387             if( p_synchro->pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 388             {
 389                 p_synchro->pi_meaningful[i_coding_type]++;
 390             }
 391         }
 392     }
 393 }
 394
 395 /*****************************************************************************
 396  * decoder_SynchroDate : When an image has been decoded, ask for its date
 397  *****************************************************************************/
 398 mtime_t decoder_SynchroDate( decoder_synchro_t * p_synchro )
 399 {
 400     /* No need to lock, since PTS are only used by the video parser. */
 401     return p_synchro->current_pts;
 402 }
 403
 404 /*****************************************************************************
 405  * decoder_SynchroNewPicture: Update stream structure and PTS
 406  *****************************************************************************/
 407 void decoder_SynchroNewPicture( decoder_synchro_t * p_synchro, int i_coding_type,
 408                                 int i_repeat_field, mtime_t next_pts,
 409                                 mtime_t next_dts, bool b_low_delay )
 410 {
 411     mtime_t         period = 1000000 * 1001 / p_synchro->i_frame_rate;
 412 #if 0
 413     mtime_t         now = mdate();
 414 #endif
 415
 416     switch( i_coding_type )
 417     {
 418     case I_CODING_TYPE:
 419         if( p_synchro->i_eta_p
 420              && p_synchro->i_eta_p != p_synchro->i_n_p )
 421         {
 422 #if 0
 423             if( !p_synchro->b_quiet )
 424                 msg_Dbg( p_synchro->p_dec,
 425                          "stream periodicity changed from P[%d] to P[%d]",
 426                          p_synchro->i_n_p, p_synchro->i_eta_p );
 427 #endif
 428             p_synchro->i_n_p = p_synchro->i_eta_p;
 429         }
 430         p_synchro->i_eta_p = p_synchro->i_eta_b = 0;
 431         p_synchro->i_trash_nb_ref = 0;
 432         if( p_synchro->i_nb_ref < 2 )
 433             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref + 1;
 434         else
 435             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref;
 436
 437 #if 0
 438         if( !p_synchro->b_quiet )
 439             msg_Dbg( p_synchro->p_dec, "I(%"PRId64") P(%"PRId64")[%d] B(%"PRId64")"
 440                   "[%d] YUV(%"PRId64") : trashed %d:%d/%d",
 441                   p_synchro->p_tau[I_CODING_TYPE],
 442                   p_synchro->p_tau[P_CODING_TYPE],
 443                   p_synchro->i_n_p,
 444                   p_synchro->p_tau[B_CODING_TYPE],
 445                   p_synchro->i_n_b,
 446                   p_synchro->i_render_time,
 447                   p_synchro->i_not_chosen_pic,
 448                   p_synchro->i_trashed_pic -
 449                   p_synchro->i_not_chosen_pic,
 450                   p_synchro->i_pic );
 451         p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 452             = p_synchro->i_pic = 0;
 453 #else
 454         if( p_synchro->i_pic >= 100 )
 455         {
 456             if( !p_synchro->b_quiet && p_synchro->i_trashed_pic != 0 )
 457                 msg_Dbg( p_synchro->p_dec, "decoded %d/%d pictures",
 458                          p_synchro->i_pic
 459                            - p_synchro->i_trashed_pic,
 460                          p_synchro->i_pic );
 461             p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 462                 = p_synchro->i_pic = 0;
 463         }
 464 #endif
 465         break;
 466
 467     case P_CODING_TYPE:
 468         p_synchro->i_eta_p++;
 469         if( p_synchro->i_eta_b
 470              && p_synchro->i_eta_b != p_synchro->i_n_b )
 471         {
 472 #if 0
 473             if( !p_synchro->b_quiet )
 474                 msg_Dbg( p_synchro->p_dec,
 475                          "stream periodicity changed from B[%d] to B[%d]",
 476                          p_synchro->i_n_b, p_synchro->i_eta_b );
 477 #endif
 478             p_synchro->i_n_b = p_synchro->i_eta_b;
 479         }
 480         p_synchro->i_eta_b = 0;
 481         p_synchro->i_dec_nb_ref = 2;
 482         p_synchro->i_trash_nb_ref = 0;
 483         break;
 484
 485     case B_CODING_TYPE:
 486         p_synchro->i_eta_b++;
 487         p_synchro->i_dec_nb_ref = p_synchro->i_trash_nb_ref
 488             = p_synchro->i_nb_ref;
 489         break;
 490     }
 491
 492     p_synchro->current_pts += p_synchro->i_current_period
 493                                         * (period >> 1);
 494
 495 #define PTS_THRESHOLD   (period >> 2)
 496     if( i_coding_type == B_CODING_TYPE || b_low_delay )
 497     {
 498         /* A video frame can be displayed 1, 2 or 3 times, according to
 499          * repeat_first_field, top_field_first, progressive_sequence and
 500          * progressive_frame. */
 501         p_synchro->i_current_period = i_repeat_field;
 502
 503         if( next_pts )
 504         {
 505             if( (next_pts - p_synchro->current_pts
 506                     > PTS_THRESHOLD
 507                   || p_synchro->current_pts - next_pts
 508                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 509             {
 510                 msg_Warn( p_synchro->p_dec, "decoder synchro warning: pts != "
 511                           "current_date (%"PRId64")",
 512                           p_synchro->current_pts
 513                               - next_pts );
 514             }
 515             p_synchro->current_pts = next_pts;
 516         }
 517     }
 518     else
 519     {
 520         p_synchro->i_current_period = p_synchro->i_backward_period;
 521         p_synchro->i_backward_period = i_repeat_field;
 522
 523         if( p_synchro->backward_pts )
 524         {
 525             if( next_dts &&
 526                 (next_dts - p_synchro->backward_pts
 527                     > PTS_THRESHOLD
 528                   || p_synchro->backward_pts - next_dts
 529                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 530             {
 531                 msg_Warn( p_synchro->p_dec, "backward_pts != dts (%"PRId64")",
 532                            next_dts
 533                                - p_synchro->backward_pts );
 534             }
 535             if( (p_synchro->backward_pts - p_synchro->current_pts
 536                     > PTS_THRESHOLD
 537                   || p_synchro->current_pts - p_synchro->backward_pts
 538                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 539             {
 540                 msg_Warn( p_synchro->p_dec,
 541                           "backward_pts != current_pts (%"PRId64")",
 542                           p_synchro->current_pts
 543                               - p_synchro->backward_pts );
 544             }
 545             p_synchro->current_pts = p_synchro->backward_pts;
 546             p_synchro->backward_pts = 0;
 547         }
 548         else if( next_dts )
 549         {
 550             if( (next_dts - p_synchro->current_pts
 551                     > PTS_THRESHOLD
 552                   || p_synchro->current_pts - next_dts
 553                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 554             {
 555                 msg_Warn( p_synchro->p_dec, "dts != current_pts (%"PRId64")",
 556                           p_synchro->current_pts
 557                               - next_dts );
 558             }
 559             /* By definition of a DTS. */
 560             p_synchro->current_pts = next_dts;
 561             next_dts = 0;
 562         }
 563
 564         if( next_pts )
 565         {
 566             /* Store the PTS for the next time we have to date an I picture. */
 567             p_synchro->backward_pts = next_pts;
 568             next_pts = 0;
 569         }
 570     }
 571 #undef PTS_THRESHOLD
 572
 573 #if 0
 574     /* Removed for incompatibility with slow motion */
 575     if( p_synchro->current_pts + DEFAULT_PTS_DELAY < now )
 576     {
 577         /* We cannot be _that_ late, something must have happened, reinit
 578          * the dates. */
 579         if( !p_synchro->b_quiet )
 580             msg_Warn( p_synchro->p_dec, "PTS << now (%"PRId64"), resetting",
 581                       now - p_synchro->current_pts - DEFAULT_PTS_DELAY );
 582         p_synchro->current_pts = now + DEFAULT_PTS_DELAY;
 583     }
 584     if( p_synchro->backward_pts
 585          && p_synchro->backward_pts + DEFAULT_PTS_DELAY < now )
 586     {
 587         /* The same. */
 588         p_synchro->backward_pts = 0;
 589     }
 590 #endif
 591
 592     p_synchro->i_pic++;
 593 }