git.sesse.net Git - vlc/blob - src/video_output/vout_synchro.c

   1 /*****************************************************************************
   2  * vout_synchro.c : frame dropping routines
   3  *****************************************************************************
   4  * Copyright (C) 1999-2004 VideoLAN
   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., 59 Temple Place - Suite 330, Boston, MA  02111, 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 #include <stdlib.h>                                                /* free() */
  98 #include <string.h>                                    /* memcpy(), memset() */
  99
 100 #include <vlc/vlc.h>
 101 #include <vlc/vout.h>
 102 #include <vlc/input.h>
 103
 104 #include "vout_synchro.h"
 105
 106 /*
 107  * Local prototypes
 108  */
 109
 110 /* Error margins */
 111 #define DELTA                   (int)(0.075*CLOCK_FREQ)
 112 #define MAX_VALID_TAU           (int)(0.3*CLOCK_FREQ)
 113
 114 #define DEFAULT_NB_P            5
 115 #define DEFAULT_NB_B            1
 116
 117 /*****************************************************************************
 118  * vout_SynchroInit : You know what ?
 119  *****************************************************************************/
 120 vout_synchro_t * __vout_SynchroInit( vlc_object_t * p_object,
 121                                      int i_frame_rate )
 122 {
 123     vout_synchro_t * p_synchro = vlc_object_create( p_object,
 124                                                   sizeof(vout_synchro_t) );
 125     if ( p_synchro == NULL )
 126     {
 127         msg_Err( p_object, "out of memory" );
 128         return NULL;
 129     }
 130     vlc_object_attach( p_synchro, p_object );
 131
 132     p_synchro->b_no_skip = !config_GetInt( p_object, "skip-frames" );
 133
 134     /* We use a fake stream pattern, which is often right. */
 135     p_synchro->i_n_p = p_synchro->i_eta_p = DEFAULT_NB_P;
 136     p_synchro->i_n_b = p_synchro->i_eta_b = DEFAULT_NB_B;
 137     memset( p_synchro->p_tau, 0, 4 * sizeof(mtime_t) );
 138     memset( p_synchro->pi_meaningful, 0, 4 * sizeof(unsigned int) );
 139     p_synchro->i_nb_ref = 0;
 140     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 141     p_synchro->current_pts = mdate() + DEFAULT_PTS_DELAY;
 142     p_synchro->backward_pts = 0;
 143     p_synchro->i_current_period = p_synchro->i_backward_period = 0;
 144     p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic =
 145         p_synchro->i_pic = 0;
 146
 147     p_synchro->i_frame_rate = i_frame_rate;
 148
 149     return p_synchro;
 150 }
 151
 152 /*****************************************************************************
 153  * vout_SynchroRelease : You know what ?
 154  *****************************************************************************/
 155 void vout_SynchroRelease( vout_synchro_t * p_synchro )
 156 {
 157     vlc_object_detach( p_synchro );
 158     vlc_object_destroy( p_synchro );
 159 }
 160
 161 /*****************************************************************************
 162  * vout_SynchroReset : Reset the reference picture counter
 163  *****************************************************************************/
 164 void vout_SynchroReset( vout_synchro_t * p_synchro )
 165 {
 166     p_synchro->i_nb_ref = 0;
 167     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 168 }
 169
 170 /*****************************************************************************
 171  * vout_SynchroChoose : Decide whether we will decode a picture or not
 172  *****************************************************************************/
 173 vlc_bool_t vout_SynchroChoose( vout_synchro_t * p_synchro, int i_coding_type,
 174                                int i_render_time )
 175 {
 176 #define TAU_PRIME( coding_type )    (p_synchro->p_tau[(coding_type)] \
 177                                     + (p_synchro->p_tau[(coding_type)] >> 1) \
 178                                     + p_synchro->i_render_time)
 179 #define S (*p_synchro)
 180     mtime_t         now, period;
 181     mtime_t         pts = 0;
 182     vlc_bool_t      b_decode = 0;
 183
 184     if ( p_synchro->b_no_skip )
 185         return 1;
 186
 187     now = mdate();
 188     period = 1000000 * 1001 / p_synchro->i_frame_rate
 189                      * p_synchro->i_current_rate / INPUT_RATE_DEFAULT;
 190
 191     p_synchro->i_render_time = i_render_time;
 192
 193     switch( i_coding_type )
 194     {
 195     case I_CODING_TYPE:
 196         if( S.backward_pts )
 197         {
 198             pts = S.backward_pts;
 199         }
 200         else
 201         {
 202             /* displaying order : B B P B B I
 203              *                      ^       ^
 204              *                      |       +- current picture
 205              *                      +- current PTS
 206              */
 207             pts = S.current_pts + period * (S.i_n_b + 2);
 208         }
 209
 210         if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 211                 S.p_tau[I_CODING_TYPE] )
 212         {
 213             b_decode = 1;
 214         }
 215         else
 216         {
 217             b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 218         }
 219         if( !b_decode )
 220         {
 221             msg_Warn( p_synchro,
 222                       "synchro trashing I ("I64Fd")", pts - now );
 223         }
 224         break;
 225
 226     case P_CODING_TYPE:
 227         if( S.backward_pts )
 228         {
 229             pts = S.backward_pts;
 230         }
 231         else
 232         {
 233             pts = S.current_pts + period * (S.i_n_b + 1);
 234         }
 235
 236         if( p_synchro->i_nb_ref < 1 )
 237         {
 238             b_decode = 0;
 239         }
 240         else if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 241                 S.p_tau[I_CODING_TYPE] )
 242         {
 243             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 244             {
 245                 /* Security in case we're _really_ late */
 246                 b_decode = (pts - now > 0);
 247             }
 248             else
 249             {
 250                 b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 251                 /* next I */
 252                 b_decode &= (pts - now
 253                               + period
 254                           * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 255                             > (TAU_PRIME(P_CODING_TYPE)
 256                                 + TAU_PRIME(I_CODING_TYPE) + DELTA);
 257             }
 258         }
 259         else
 260         {
 261             b_decode = 0;
 262         }
 263         break;
 264
 265     case B_CODING_TYPE:
 266         pts = S.current_pts;
 267
 268         if( p_synchro->i_nb_ref < 2 )
 269         {
 270             b_decode = 0;
 271         }
 272         else if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 273         {
 274             b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 275         }
 276         else
 277         {
 278             b_decode = 0;
 279         }
 280     }
 281
 282     if( !b_decode )
 283     {
 284         S.i_not_chosen_pic++;
 285     }
 286     return( b_decode );
 287 #undef S
 288 #undef TAU_PRIME
 289 }
 290
 291 /*****************************************************************************
 292  * vout_SynchroTrash : Update counters when we trash a picture
 293  *****************************************************************************/
 294 void vout_SynchroTrash( vout_synchro_t * p_synchro )
 295 {
 296     p_synchro->i_trashed_pic++;
 297     p_synchro->i_nb_ref = p_synchro->i_trash_nb_ref;
 298 }
 299
 300 /*****************************************************************************
 301  * vout_SynchroDecode : Update timers when we decide to decode a picture
 302  *****************************************************************************/
 303 void vout_SynchroDecode( vout_synchro_t * p_synchro )
 304 {
 305     p_synchro->decoding_start = mdate();
 306     p_synchro->i_nb_ref = p_synchro->i_dec_nb_ref;
 307 }
 308
 309 /*****************************************************************************
 310  * vout_SynchroEnd : Called when the image is totally decoded
 311  *****************************************************************************/
 312 void vout_SynchroEnd( vout_synchro_t * p_synchro, int i_coding_type,
 313                       vlc_bool_t b_garbage )
 314 {
 315     mtime_t     tau;
 316
 317     if( !b_garbage )
 318     {
 319         tau = mdate() - p_synchro->decoding_start;
 320
 321         /* If duration too high, something happened (pause ?), so don't
 322          * take it into account. */
 323         if( tau < 3 * p_synchro->p_tau[i_coding_type]
 324              || ( !p_synchro->pi_meaningful[i_coding_type]
 325                    && tau < MAX_VALID_TAU ) )
 326         {
 327             /* Mean with average tau, to ensure stability. */
 328             p_synchro->p_tau[i_coding_type] =
 329                 (p_synchro->pi_meaningful[i_coding_type]
 330                  * p_synchro->p_tau[i_coding_type] + tau)
 331                 / (p_synchro->pi_meaningful[i_coding_type] + 1);
 332             if( p_synchro->pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 333             {
 334                 p_synchro->pi_meaningful[i_coding_type]++;
 335             }
 336         }
 337     }
 338 }
 339
 340 /*****************************************************************************
 341  * vout_SynchroDate : When an image has been decoded, ask for its date
 342  *****************************************************************************/
 343 mtime_t vout_SynchroDate( vout_synchro_t * p_synchro )
 344 {
 345     /* No need to lock, since PTS are only used by the video parser. */
 346     return p_synchro->current_pts;
 347 }
 348
 349 /*****************************************************************************
 350  * vout_SynchroNewPicture: Update stream structure and PTS
 351  *****************************************************************************/
 352 void vout_SynchroNewPicture( vout_synchro_t * p_synchro, int i_coding_type,
 353                              int i_repeat_field, mtime_t next_pts,
 354                              mtime_t next_dts, int i_current_rate )
 355 {
 356     mtime_t         period = 1000000 * 1001 / p_synchro->i_frame_rate
 357                               * i_current_rate / INPUT_RATE_DEFAULT;
 358 #if 0
 359     mtime_t         now = mdate();
 360 #endif
 361     p_synchro->i_current_rate = i_current_rate;
 362
 363     switch( i_coding_type )
 364     {
 365     case I_CODING_TYPE:
 366         if( p_synchro->i_eta_p
 367              && p_synchro->i_eta_p != p_synchro->i_n_p )
 368         {
 369             msg_Dbg( p_synchro,
 370                      "stream periodicity changed from P[%d] to P[%d]",
 371                      p_synchro->i_n_p, p_synchro->i_eta_p );
 372             p_synchro->i_n_p = p_synchro->i_eta_p;
 373         }
 374         p_synchro->i_eta_p = p_synchro->i_eta_b = 0;
 375         p_synchro->i_trash_nb_ref = 0;
 376         if( p_synchro->i_nb_ref < 2 )
 377             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref + 1;
 378         else
 379             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref;
 380
 381 #if 0
 382         msg_Dbg( p_synchro, "I("I64Fd") P("I64Fd")[%d] B("I64Fd")"
 383               "[%d] YUV("I64Fd") : trashed %d:%d/%d",
 384               p_synchro->p_tau[I_CODING_TYPE],
 385               p_synchro->p_tau[P_CODING_TYPE],
 386               p_synchro->i_n_p,
 387               p_synchro->p_tau[B_CODING_TYPE],
 388               p_synchro->i_n_b,
 389               p_synchro->i_render_time,
 390               p_synchro->i_not_chosen_pic,
 391               p_synchro->i_trashed_pic -
 392               p_synchro->i_not_chosen_pic,
 393               p_synchro->i_pic );
 394         p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 395             = p_synchro->i_pic = 0;
 396 #else
 397         if ( p_synchro->i_pic >= 100 )
 398         {
 399             msg_Dbg( p_synchro, "decoded %d/%d pictures",
 400                      p_synchro->i_pic
 401                        - p_synchro->i_trashed_pic,
 402                      p_synchro->i_pic );
 403             p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 404                 = p_synchro->i_pic = 0;
 405         }
 406 #endif
 407         break;
 408
 409     case P_CODING_TYPE:
 410         p_synchro->i_eta_p++;
 411         if( p_synchro->i_eta_b
 412              && p_synchro->i_eta_b != p_synchro->i_n_b )
 413         {
 414             msg_Dbg( p_synchro,
 415                      "stream periodicity changed from B[%d] to B[%d]",
 416                      p_synchro->i_n_b, p_synchro->i_eta_b );
 417             p_synchro->i_n_b = p_synchro->i_eta_b;
 418         }
 419         p_synchro->i_eta_b = 0;
 420         p_synchro->i_dec_nb_ref = 2;
 421         p_synchro->i_trash_nb_ref = 0;
 422         break;
 423
 424     case B_CODING_TYPE:
 425         p_synchro->i_eta_b++;
 426         p_synchro->i_dec_nb_ref = p_synchro->i_trash_nb_ref
 427             = p_synchro->i_nb_ref;
 428         break;
 429     }
 430
 431     p_synchro->current_pts += p_synchro->i_current_period
 432                                         * (period >> 1);
 433
 434 #define PTS_THRESHOLD   (period >> 2)
 435     if( i_coding_type == B_CODING_TYPE )
 436     {
 437         /* A video frame can be displayed 1, 2 or 3 times, according to
 438          * repeat_first_field, top_field_first, progressive_sequence and
 439          * progressive_frame. */
 440         p_synchro->i_current_period = i_repeat_field;
 441
 442         if( next_pts )
 443         {
 444             if( next_pts - p_synchro->current_pts
 445                     > PTS_THRESHOLD
 446                  || p_synchro->current_pts - next_pts
 447                     > PTS_THRESHOLD )
 448             {
 449                 msg_Warn( p_synchro, "vout synchro warning: pts != "
 450                           "current_date ("I64Fd")",
 451                           p_synchro->current_pts
 452                               - next_pts );
 453             }
 454             p_synchro->current_pts = next_pts;
 455         }
 456     }
 457     else
 458     {
 459         p_synchro->i_current_period = p_synchro->i_backward_period;
 460         p_synchro->i_backward_period = i_repeat_field;
 461
 462         if( p_synchro->backward_pts )
 463         {
 464             if( next_dts &&
 465                 (next_dts - p_synchro->backward_pts
 466                     > PTS_THRESHOLD
 467               || p_synchro->backward_pts - next_dts
 468                     > PTS_THRESHOLD) )
 469             {
 470                 msg_Warn( p_synchro, "backward_pts != dts ("I64Fd")",
 471                            next_dts
 472                                - p_synchro->backward_pts );
 473             }
 474             if( p_synchro->backward_pts - p_synchro->current_pts
 475                     > PTS_THRESHOLD
 476                  || p_synchro->current_pts - p_synchro->backward_pts
 477                     > PTS_THRESHOLD )
 478             {
 479                 msg_Warn( p_synchro,
 480                           "backward_pts != current_pts ("I64Fd")",
 481                           p_synchro->current_pts
 482                               - p_synchro->backward_pts );
 483             }
 484             p_synchro->current_pts = p_synchro->backward_pts;
 485             p_synchro->backward_pts = 0;
 486         }
 487         else if( next_dts )
 488         {
 489             if( next_dts - p_synchro->current_pts
 490                     > PTS_THRESHOLD
 491                  || p_synchro->current_pts - next_dts
 492                     > PTS_THRESHOLD )
 493             {
 494                 msg_Warn( p_synchro, "dts != current_pts ("I64Fd")",
 495                           p_synchro->current_pts
 496                               - next_dts );
 497             }
 498             /* By definition of a DTS. */
 499             p_synchro->current_pts = next_dts;
 500             next_dts = 0;
 501         }
 502
 503         if( next_pts )
 504         {
 505             /* Store the PTS for the next time we have to date an I picture. */
 506             p_synchro->backward_pts = next_pts;
 507             next_pts = 0;
 508         }
 509     }
 510 #undef PTS_THRESHOLD
 511
 512 #if 0
 513     /* Removed for incompatibility with slow motion */
 514     if( p_synchro->current_pts + DEFAULT_PTS_DELAY < now )
 515     {
 516         /* We cannot be _that_ late, something must have happened, reinit
 517          * the dates. */
 518         msg_Warn( p_synchro, "PTS << now ("I64Fd"), resetting",
 519                    now - p_synchro->current_pts - DEFAULT_PTS_DELAY );
 520         p_synchro->current_pts = now + DEFAULT_PTS_DELAY;
 521     }
 522     if( p_synchro->backward_pts
 523          && p_synchro->backward_pts + DEFAULT_PTS_DELAY < now )
 524     {
 525         /* The same. */
 526         p_synchro->backward_pts = 0;
 527     }
 528 #endif
 529
 530     p_synchro->i_pic++;
 531 }