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