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/vlc.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     {
 168         msg_Err( p_dec, "out of memory" );
 169         return NULL;
 170     }
 171     memset( p_synchro, 0, sizeof(*p_synchro) );
 172
 173     p_synchro->p_dec = p_dec;
 174     p_synchro->b_no_skip = !config_GetInt( p_dec, "skip-frames" );
 175     p_synchro->b_quiet = config_GetInt( p_dec, "quiet-synchro" );
 176
 177     /* We use a fake stream pattern, which is often right. */
 178     p_synchro->i_n_p = p_synchro->i_eta_p = DEFAULT_NB_P;
 179     p_synchro->i_n_b = p_synchro->i_eta_b = DEFAULT_NB_B;
 180     memset( p_synchro->p_tau, 0, 4 * sizeof(mtime_t) );
 181     memset( p_synchro->pi_meaningful, 0, 4 * sizeof(unsigned int) );
 182     p_synchro->i_nb_ref = 0;
 183     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 184     p_synchro->current_pts = mdate() + DEFAULT_PTS_DELAY;
 185     p_synchro->backward_pts = 0;
 186     p_synchro->i_current_period = p_synchro->i_backward_period = 0;
 187     p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic =
 188         p_synchro->i_pic = 0;
 189
 190     p_synchro->i_frame_rate = i_frame_rate;
 191
 192     return p_synchro;
 193 }
 194
 195 /*****************************************************************************
 196  * decoder_SynchroRelease : You know what ?
 197  *****************************************************************************/
 198 void decoder_SynchroRelease( decoder_synchro_t * p_synchro )
 199 {
 200     free( p_synchro );
 201 }
 202
 203 /*****************************************************************************
 204  * decoder_SynchroReset : Reset the reference picture counter
 205  *****************************************************************************/
 206 void decoder_SynchroReset( decoder_synchro_t * p_synchro )
 207 {
 208     p_synchro->i_nb_ref = 0;
 209     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 210 }
 211
 212 /*****************************************************************************
 213  * decoder_SynchroChoose : Decide whether we will decode a picture or not
 214  *****************************************************************************/
 215 bool decoder_SynchroChoose( decoder_synchro_t * p_synchro, int i_coding_type,
 216                                int i_render_time, bool b_low_delay )
 217 {
 218 #define TAU_PRIME( coding_type )    (p_synchro->p_tau[(coding_type)] \
 219                                     + (p_synchro->p_tau[(coding_type)] >> 1) \
 220                                     + p_synchro->i_render_time)
 221 #define S (*p_synchro)
 222     mtime_t         now, period;
 223     mtime_t         pts = 0;
 224     bool      b_decode = 0;
 225
 226     if ( p_synchro->b_no_skip )
 227         return 1;
 228
 229     now = mdate();
 230     period = 1000000 * 1001 / p_synchro->i_frame_rate
 231                      * p_synchro->i_current_rate / INPUT_RATE_DEFAULT;
 232
 233     p_synchro->i_render_time = i_render_time;
 234
 235     switch( i_coding_type )
 236     {
 237     case I_CODING_TYPE:
 238         if( b_low_delay )
 239         {
 240             pts = S.current_pts;
 241         }
 242         else if( S.backward_pts )
 243         {
 244             pts = S.backward_pts;
 245         }
 246         else
 247         {
 248             /* displaying order : B B P B B I
 249              *                      ^       ^
 250              *                      |       +- current picture
 251              *                      +- current PTS
 252              */
 253             pts = S.current_pts + period * (S.i_n_b + 2);
 254         }
 255
 256         if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 257                 S.p_tau[I_CODING_TYPE] )
 258         {
 259             b_decode = 1;
 260         }
 261         else
 262         {
 263             b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 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 = S.current_pts;
 276         }
 277         else if( S.backward_pts )
 278         {
 279             pts = S.backward_pts;
 280         }
 281         else
 282         {
 283             pts = 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         break;
 314
 315     case B_CODING_TYPE:
 316         pts = S.current_pts;
 317
 318         if( p_synchro->i_nb_ref < 2 )
 319         {
 320             b_decode = 0;
 321         }
 322         else if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 323         {
 324             b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 325         }
 326         else
 327         {
 328             b_decode = 0;
 329         }
 330     }
 331
 332     if( !b_decode )
 333     {
 334         S.i_not_chosen_pic++;
 335     }
 336     return( b_decode );
 337 #undef S
 338 #undef TAU_PRIME
 339 }
 340
 341 /*****************************************************************************
 342  * decoder_SynchroTrash : Update counters when we trash a picture
 343  *****************************************************************************/
 344 void decoder_SynchroTrash( decoder_synchro_t * p_synchro )
 345 {
 346     p_synchro->i_trashed_pic++;
 347     p_synchro->i_nb_ref = p_synchro->i_trash_nb_ref;
 348 }
 349
 350 /*****************************************************************************
 351  * decoder_SynchroDecode : Update timers when we decide to decode a picture
 352  *****************************************************************************/
 353 void decoder_SynchroDecode( decoder_synchro_t * p_synchro )
 354 {
 355     p_synchro->decoding_start = mdate();
 356     p_synchro->i_nb_ref = p_synchro->i_dec_nb_ref;
 357 }
 358
 359 /*****************************************************************************
 360  * decoder_SynchroEnd : Called when the image is totally decoded
 361  *****************************************************************************/
 362 void decoder_SynchroEnd( decoder_synchro_t * p_synchro, int i_coding_type,
 363                       bool b_garbage )
 364 {
 365     mtime_t     tau;
 366
 367     if( !b_garbage )
 368     {
 369         tau = mdate() - p_synchro->decoding_start;
 370
 371         /* If duration too high, something happened (pause ?), so don't
 372          * take it into account. */
 373         if( tau < 3 * p_synchro->p_tau[i_coding_type]
 374              || ( !p_synchro->pi_meaningful[i_coding_type]
 375                    && tau < MAX_VALID_TAU ) )
 376         {
 377             /* Mean with average tau, to ensure stability. */
 378             p_synchro->p_tau[i_coding_type] =
 379                 (p_synchro->pi_meaningful[i_coding_type]
 380                  * p_synchro->p_tau[i_coding_type] + tau)
 381                 / (p_synchro->pi_meaningful[i_coding_type] + 1);
 382             if( p_synchro->pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 383             {
 384                 p_synchro->pi_meaningful[i_coding_type]++;
 385             }
 386         }
 387     }
 388 }
 389
 390 /*****************************************************************************
 391  * decoder_SynchroDate : When an image has been decoded, ask for its date
 392  *****************************************************************************/
 393 mtime_t decoder_SynchroDate( decoder_synchro_t * p_synchro )
 394 {
 395     /* No need to lock, since PTS are only used by the video parser. */
 396     return p_synchro->current_pts;
 397 }
 398
 399 /*****************************************************************************
 400  * decoder_SynchroNewPicture: Update stream structure and PTS
 401  *****************************************************************************/
 402 void decoder_SynchroNewPicture( decoder_synchro_t * p_synchro, int i_coding_type,
 403                              int i_repeat_field, mtime_t next_pts,
 404                              mtime_t next_dts, int i_current_rate,
 405                              bool b_low_delay )
 406 {
 407     mtime_t         period = 1000000 * 1001 / p_synchro->i_frame_rate
 408                               * i_current_rate / INPUT_RATE_DEFAULT;
 409 #if 0
 410     mtime_t         now = mdate();
 411 #endif
 412     p_synchro->i_current_rate = i_current_rate;
 413
 414     switch( i_coding_type )
 415     {
 416     case I_CODING_TYPE:
 417         if( p_synchro->i_eta_p
 418              && p_synchro->i_eta_p != p_synchro->i_n_p )
 419         {
 420 #if 0
 421             if( !p_synchro->b_quiet )
 422                 msg_Dbg( p_synchro->p_dec,
 423                          "stream periodicity changed from P[%d] to P[%d]",
 424                          p_synchro->i_n_p, p_synchro->i_eta_p );
 425 #endif
 426             p_synchro->i_n_p = p_synchro->i_eta_p;
 427         }
 428         p_synchro->i_eta_p = p_synchro->i_eta_b = 0;
 429         p_synchro->i_trash_nb_ref = 0;
 430         if( p_synchro->i_nb_ref < 2 )
 431             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref + 1;
 432         else
 433             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref;
 434
 435 #if 0
 436         if( !p_synchro->b_quiet )
 437             msg_Dbg( p_synchro->p_dec, "I(%"PRId64") P(%"PRId64")[%d] B(%"PRId64")"
 438                   "[%d] YUV(%"PRId64") : trashed %d:%d/%d",
 439                   p_synchro->p_tau[I_CODING_TYPE],
 440                   p_synchro->p_tau[P_CODING_TYPE],
 441                   p_synchro->i_n_p,
 442                   p_synchro->p_tau[B_CODING_TYPE],
 443                   p_synchro->i_n_b,
 444                   p_synchro->i_render_time,
 445                   p_synchro->i_not_chosen_pic,
 446                   p_synchro->i_trashed_pic -
 447                   p_synchro->i_not_chosen_pic,
 448                   p_synchro->i_pic );
 449         p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 450             = p_synchro->i_pic = 0;
 451 #else
 452         if( p_synchro->i_pic >= 100 )
 453         {
 454             if( !p_synchro->b_quiet && p_synchro->i_trashed_pic != 0 )
 455                 msg_Dbg( p_synchro->p_dec, "decoded %d/%d pictures",
 456                          p_synchro->i_pic
 457                            - p_synchro->i_trashed_pic,
 458                          p_synchro->i_pic );
 459             p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 460                 = p_synchro->i_pic = 0;
 461         }
 462 #endif
 463         break;
 464
 465     case P_CODING_TYPE:
 466         p_synchro->i_eta_p++;
 467         if( p_synchro->i_eta_b
 468              && p_synchro->i_eta_b != p_synchro->i_n_b )
 469         {
 470 #if 0
 471             if( !p_synchro->b_quiet )
 472                 msg_Dbg( p_synchro->p_dec,
 473                          "stream periodicity changed from B[%d] to B[%d]",
 474                          p_synchro->i_n_b, p_synchro->i_eta_b );
 475 #endif
 476             p_synchro->i_n_b = p_synchro->i_eta_b;
 477         }
 478         p_synchro->i_eta_b = 0;
 479         p_synchro->i_dec_nb_ref = 2;
 480         p_synchro->i_trash_nb_ref = 0;
 481         break;
 482
 483     case B_CODING_TYPE:
 484         p_synchro->i_eta_b++;
 485         p_synchro->i_dec_nb_ref = p_synchro->i_trash_nb_ref
 486             = p_synchro->i_nb_ref;
 487         break;
 488     }
 489
 490     p_synchro->current_pts += p_synchro->i_current_period
 491                                         * (period >> 1);
 492
 493 #define PTS_THRESHOLD   (period >> 2)
 494     if( i_coding_type == B_CODING_TYPE || b_low_delay )
 495     {
 496         /* A video frame can be displayed 1, 2 or 3 times, according to
 497          * repeat_first_field, top_field_first, progressive_sequence and
 498          * progressive_frame. */
 499         p_synchro->i_current_period = i_repeat_field;
 500
 501         if( next_pts )
 502         {
 503             if( (next_pts - p_synchro->current_pts
 504                     > PTS_THRESHOLD
 505                   || p_synchro->current_pts - next_pts
 506                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 507             {
 508                 msg_Warn( p_synchro->p_dec, "decoder synchro warning: pts != "
 509                           "current_date (%"PRId64")",
 510                           p_synchro->current_pts
 511                               - next_pts );
 512             }
 513             p_synchro->current_pts = next_pts;
 514         }
 515     }
 516     else
 517     {
 518         p_synchro->i_current_period = p_synchro->i_backward_period;
 519         p_synchro->i_backward_period = i_repeat_field;
 520
 521         if( p_synchro->backward_pts )
 522         {
 523             if( next_dts &&
 524                 (next_dts - p_synchro->backward_pts
 525                     > PTS_THRESHOLD
 526                   || p_synchro->backward_pts - next_dts
 527                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 528             {
 529                 msg_Warn( p_synchro->p_dec, "backward_pts != dts (%"PRId64")",
 530                            next_dts
 531                                - p_synchro->backward_pts );
 532             }
 533             if( (p_synchro->backward_pts - p_synchro->current_pts
 534                     > PTS_THRESHOLD
 535                   || p_synchro->current_pts - p_synchro->backward_pts
 536                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 537             {
 538                 msg_Warn( p_synchro->p_dec,
 539                           "backward_pts != current_pts (%"PRId64")",
 540                           p_synchro->current_pts
 541                               - p_synchro->backward_pts );
 542             }
 543             p_synchro->current_pts = p_synchro->backward_pts;
 544             p_synchro->backward_pts = 0;
 545         }
 546         else if( next_dts )
 547         {
 548             if( (next_dts - p_synchro->current_pts
 549                     > PTS_THRESHOLD
 550                   || p_synchro->current_pts - next_dts
 551                     > PTS_THRESHOLD) && !p_synchro->b_quiet )
 552             {
 553                 msg_Warn( p_synchro->p_dec, "dts != current_pts (%"PRId64")",
 554                           p_synchro->current_pts
 555                               - next_dts );
 556             }
 557             /* By definition of a DTS. */
 558             p_synchro->current_pts = next_dts;
 559             next_dts = 0;
 560         }
 561
 562         if( next_pts )
 563         {
 564             /* Store the PTS for the next time we have to date an I picture. */
 565             p_synchro->backward_pts = next_pts;
 566             next_pts = 0;
 567         }
 568     }
 569 #undef PTS_THRESHOLD
 570
 571 #if 0
 572     /* Removed for incompatibility with slow motion */
 573     if( p_synchro->current_pts + DEFAULT_PTS_DELAY < now )
 574     {
 575         /* We cannot be _that_ late, something must have happened, reinit
 576          * the dates. */
 577         if( !p_synchro->b_quiet )
 578             msg_Warn( p_synchro->p_dec, "PTS << now (%"PRId64"), resetting",
 579                       now - p_synchro->current_pts - DEFAULT_PTS_DELAY );
 580         p_synchro->current_pts = now + DEFAULT_PTS_DELAY;
 581     }
 582     if( p_synchro->backward_pts
 583          && p_synchro->backward_pts + DEFAULT_PTS_DELAY < now )
 584     {
 585         /* The same. */
 586         p_synchro->backward_pts = 0;
 587     }
 588 #endif
 589
 590     p_synchro->i_pic++;
 591 }