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 = !config_GetInt( p_dec, "skip-frames" );
 170     p_synchro->b_quiet = config_GetInt( 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 = 0;
 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 >
 255                 S.p_tau[I_CODING_TYPE] )
 256         {
 257             b_decode = 1;
 258         }
 259         else
 260         {
 261             b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 262         }
 263         if( !b_decode && !p_synchro->b_quiet )
 264         {
 265             msg_Warn( p_synchro->p_dec,
 266                       "synchro trashing I (%"PRId64")", pts - now );
 267         }
 268         break;
 269
 270     case P_CODING_TYPE:
 271         if( b_low_delay )
 272         {
 273             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts );
 274         }
 275         else if( S.backward_pts )
 276         {
 277             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.backward_pts );
 278         }
 279         else
 280         {
 281             pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts + period * (S.i_n_b + 1) );
 282         }
 283
 284         if( p_synchro->i_nb_ref < 1 )
 285         {
 286             b_decode = 0;
 287         }
 288         else if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 289                 S.p_tau[I_CODING_TYPE] )
 290         {
 291             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 292             {
 293                 /* Security in case we're _really_ late */
 294                 b_decode = (pts - now > 0);
 295             }
 296             else
 297             {
 298                 b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 299                 /* next I */
 300                 b_decode &= (pts - now
 301                               + period
 302                           * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 303                             > (TAU_PRIME(P_CODING_TYPE)
 304                                 + TAU_PRIME(I_CODING_TYPE) + DELTA);
 305             }
 306         }
 307         else
 308         {
 309             b_decode = 0;
 310         }
 311         break;
 312
 313     case B_CODING_TYPE:
 314         pts = decoder_GetDisplayDate( p_synchro->p_dec, S.current_pts );
 315
 316         if( p_synchro->i_nb_ref < 2 )
 317         {
 318             b_decode = 0;
 319         }
 320         else if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 321         {
 322             b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 323         }
 324         else
 325         {
 326             b_decode = 0;
 327         }
 328     }
 329
 330     if( !b_decode )
 331     {
 332         S.i_not_chosen_pic++;
 333     }
 334     return( b_decode );
 335 #undef S
 336 #undef TAU_PRIME
 337 }
 338
 339 /*****************************************************************************
 340  * decoder_SynchroTrash : Update counters when we trash a picture
 341  *****************************************************************************/
 342 void decoder_SynchroTrash( decoder_synchro_t * p_synchro )
 343 {
 344     p_synchro->i_trashed_pic++;
 345     p_synchro->i_nb_ref = p_synchro->i_trash_nb_ref;
 346 }
 347
 348 /*****************************************************************************
 349  * decoder_SynchroDecode : Update timers when we decide to decode a picture
 350  *****************************************************************************/
 351 void decoder_SynchroDecode( decoder_synchro_t * p_synchro )
 352 {
 353     p_synchro->decoding_start = mdate();
 354     p_synchro->i_nb_ref = p_synchro->i_dec_nb_ref;
 355 }
 356
 357 /*****************************************************************************
 358  * decoder_SynchroEnd : Called when the image is totally decoded
 359  *****************************************************************************/
 360 void decoder_SynchroEnd( decoder_synchro_t * p_synchro, int i_coding_type,
 361                       bool b_garbage )
 362 {
 363     mtime_t     tau;
 364
 365     if( !b_garbage )
 366     {
 367         tau = mdate() - p_synchro->decoding_start;
 368
 369         /* If duration too high, something happened (pause ?), so don't
 370          * take it into account. */
 371         if( tau < 3 * p_synchro->p_tau[i_coding_type]
 372              || ( !p_synchro->pi_meaningful[i_coding_type]
 373                    && tau < MAX_VALID_TAU ) )
 374         {
 375             /* Mean with average tau, to ensure stability. */
 376             p_synchro->p_tau[i_coding_type] =
 377                 (p_synchro->pi_meaningful[i_coding_type]
 378                  * p_synchro->p_tau[i_coding_type] + tau)
 379                 / (p_synchro->pi_meaningful[i_coding_type] + 1);
 380             if( p_synchro->pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 381             {
 382                 p_synchro->pi_meaningful[i_coding_type]++;
 383             }
 384         }
 385     }
 386 }
 387
 388 /*****************************************************************************
 389  * decoder_SynchroDate : When an image has been decoded, ask for its date
 390  *****************************************************************************/
 391 mtime_t decoder_SynchroDate( decoder_synchro_t * p_synchro )
 392 {
 393     /* No need to lock, since PTS are only used by the video parser. */
 394     return p_synchro->current_pts;
 395 }
 396
 397 /*****************************************************************************
 398  * decoder_SynchroNewPicture: Update stream structure and PTS
 399  *****************************************************************************/
 400 void decoder_SynchroNewPicture( decoder_synchro_t * p_synchro, int i_coding_type,
 401                                 int i_repeat_field, mtime_t next_pts,
 402                                 mtime_t next_dts, bool b_low_delay )
 403 {
 404     mtime_t         period = 1000000 * 1001 / p_synchro->i_frame_rate;
 405 #if 0
 406     mtime_t         now = mdate();
 407 #endif
 408
 409     switch( i_coding_type )
 410     {
 411     case I_CODING_TYPE:
 412         if( p_synchro->i_eta_p
 413              && p_synchro->i_eta_p != p_synchro->i_n_p )
 414         {
 415 #if 0
 416             if( !p_synchro->b_quiet )
 417                 msg_Dbg( p_synchro->p_dec,
 418                          "stream periodicity changed from P[%d] to P[%d]",
 419                          p_synchro->i_n_p, p_synchro->i_eta_p );
 420 #endif
 421             p_synchro->i_n_p = p_synchro->i_eta_p;
 422         }
 423         p_synchro->i_eta_p = p_synchro->i_eta_b = 0;
 424         p_synchro->i_trash_nb_ref = 0;
 425         if( p_synchro->i_nb_ref < 2 )
 426             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref + 1;
 427         else
 428             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref;
 429
 430 #if 0
 431         if( !p_synchro->b_quiet )
 432             msg_Dbg( p_synchro->p_dec, "I(%"PRId64") P(%"PRId64")[%d] B(%"PRId64")"
 433                   "[%d] YUV(%"PRId64") : trashed %d:%d/%d",
 434                   p_synchro->p_tau[I_CODING_TYPE],
 435                   p_synchro->p_tau[P_CODING_TYPE],
 436                   p_synchro->i_n_p,
 437                   p_synchro->p_tau[B_CODING_TYPE],
 438                   p_synchro->i_n_b,
 439                   p_synchro->i_render_time,
 440                   p_synchro->i_not_chosen_pic,
 441                   p_synchro->i_trashed_pic -
 442                   p_synchro->i_not_chosen_pic,
 443                   p_synchro->i_pic );
 444         p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 445             = p_synchro->i_pic = 0;
 446 #else
 447         if( p_synchro->i_pic >= 100 )
 448         {
 449             if( !p_synchro->b_quiet && p_synchro->i_trashed_pic != 0 )
 450                 msg_Dbg( p_synchro->p_dec, "decoded %d/%d pictures",
 451                          p_synchro->i_pic
 452                            - p_synchro->i_trashed_pic,
 453                          p_synchro->i_pic );
 454             p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 455                 = p_synchro->i_pic = 0;
 456         }
 457 #endif
 458         break;
 459
 460     case P_CODING_TYPE:
 461         p_synchro->i_eta_p++;
 462         if( p_synchro->i_eta_b
 463              && p_synchro->i_eta_b != p_synchro->i_n_b )
 464         {
 465 #if 0
 466             if( !p_synchro->b_quiet )
 467                 msg_Dbg( p_synchro->p_dec,
 468                          "stream periodicity changed from B[%d] to B[%d]",
 469                          p_synchro->i_n_b, p_synchro->i_eta_b );
 470 #endif
 471             p_synchro->i_n_b = p_synchro->i_eta_b;
 472         }
 473         p_synchro->i_eta_b = 0;
 474         p_synchro->i_dec_nb_ref = 2;
 475         p_synchro->i_trash_nb_ref = 0;
 476         break;
 477
 478     case B_CODING_TYPE:
 479         p_synchro->i_eta_b++;
 480         p_synchro->i_dec_nb_ref = p_synchro->i_trash_nb_ref
 481             = p_synchro->i_nb_ref;
 482         break;
 483     }
 484
 485     p_synchro->current_pts += p_synchro->i_current_period
 486                                         * (period >> 1);
 487
 488 #define PTS_THRESHOLD   (period >> 2)
 489     if( i_coding_type == B_CODING_TYPE || b_low_delay )
 490     {
 491         /* A video frame can be displayed 1, 2 or 3 times, according to
 492          * repeat_first_field, top_field_first, progressive_sequence and
 493          * progressive_frame. */
 494         p_synchro->i_current_period = i_repeat_field;
 495
 496         if( next_pts )
 497         {
 498             if( (next_pts - p_synchro->current_pts
 499                     > PTS_THRESHOLD
 500                   || p_synchro->current_pts - next_pts
 501                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 502             {
 503                 msg_Warn( p_synchro->p_dec, "decoder synchro warning: pts != "
 504                           "current_date (%"PRId64")",
 505                           p_synchro->current_pts
 506                               - next_pts );
 507             }
 508             p_synchro->current_pts = next_pts;
 509         }
 510     }
 511     else
 512     {
 513         p_synchro->i_current_period = p_synchro->i_backward_period;
 514         p_synchro->i_backward_period = i_repeat_field;
 515
 516         if( p_synchro->backward_pts )
 517         {
 518             if( next_dts &&
 519                 (next_dts - p_synchro->backward_pts
 520                     > PTS_THRESHOLD
 521                   || p_synchro->backward_pts - next_dts
 522                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 523             {
 524                 msg_Warn( p_synchro->p_dec, "backward_pts != dts (%"PRId64")",
 525                            next_dts
 526                                - p_synchro->backward_pts );
 527             }
 528             if( (p_synchro->backward_pts - p_synchro->current_pts
 529                     > PTS_THRESHOLD
 530                   || p_synchro->current_pts - p_synchro->backward_pts
 531                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 532             {
 533                 msg_Warn( p_synchro->p_dec,
 534                           "backward_pts != current_pts (%"PRId64")",
 535                           p_synchro->current_pts
 536                               - p_synchro->backward_pts );
 537             }
 538             p_synchro->current_pts = p_synchro->backward_pts;
 539             p_synchro->backward_pts = 0;
 540         }
 541         else if( next_dts )
 542         {
 543             if( (next_dts - p_synchro->current_pts
 544                     > PTS_THRESHOLD
 545                   || p_synchro->current_pts - next_dts
 546                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 547             {
 548                 msg_Warn( p_synchro->p_dec, "dts != current_pts (%"PRId64")",
 549                           p_synchro->current_pts
 550                               - next_dts );
 551             }
 552             /* By definition of a DTS. */
 553             p_synchro->current_pts = next_dts;
 554             next_dts = 0;
 555         }
 556
 557         if( next_pts )
 558         {
 559             /* Store the PTS for the next time we have to date an I picture. */
 560             p_synchro->backward_pts = next_pts;
 561             next_pts = 0;
 562         }
 563     }
 564 #undef PTS_THRESHOLD
 565
 566 #if 0
 567     /* Removed for incompatibility with slow motion */
 568     if( p_synchro->current_pts + DEFAULT_PTS_DELAY < now )
 569     {
 570         /* We cannot be _that_ late, something must have happened, reinit
 571          * the dates. */
 572         if( !p_synchro->b_quiet )
 573             msg_Warn( p_synchro->p_dec, "PTS << now (%"PRId64"), resetting",
 574                       now - p_synchro->current_pts - DEFAULT_PTS_DELAY );
 575         p_synchro->current_pts = now + DEFAULT_PTS_DELAY;
 576     }
 577     if( p_synchro->backward_pts
 578          && p_synchro->backward_pts + DEFAULT_PTS_DELAY < now )
 579     {
 580         /* The same. */
 581         p_synchro->backward_pts = 0;
 582     }
 583 #endif
 584
 585     p_synchro->i_pic++;
 586 }