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: vout_synchro.c,v 1.6 2004/01/06 12:02:06 zorglub Exp $
   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
 103 #include "vout_synchro.h"
 104 #include "stream_control.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     /* We use a fake stream pattern, which is often right. */
 133     p_synchro->i_n_p = p_synchro->i_eta_p = DEFAULT_NB_P;
 134     p_synchro->i_n_b = p_synchro->i_eta_b = DEFAULT_NB_B;
 135     memset( p_synchro->p_tau, 0, 4 * sizeof(mtime_t) );
 136     memset( p_synchro->pi_meaningful, 0, 4 * sizeof(unsigned int) );
 137     p_synchro->i_nb_ref = 0;
 138     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 139     p_synchro->current_pts = mdate() + DEFAULT_PTS_DELAY;
 140     p_synchro->backward_pts = 0;
 141     p_synchro->i_current_period = p_synchro->i_backward_period = 0;
 142     p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic =
 143         p_synchro->i_pic = 0;
 144
 145     p_synchro->i_frame_rate = i_frame_rate;
 146
 147     return p_synchro;
 148 }
 149
 150 /*****************************************************************************
 151  * vout_SynchroRelease : You know what ?
 152  *****************************************************************************/
 153 void vout_SynchroRelease( vout_synchro_t * p_synchro )
 154 {
 155     vlc_object_detach( p_synchro );
 156     vlc_object_destroy( p_synchro );
 157 }
 158
 159 /*****************************************************************************
 160  * vout_SynchroReset : Reset the reference picture counter
 161  *****************************************************************************/
 162 void vout_SynchroReset( vout_synchro_t * p_synchro )
 163 {
 164     p_synchro->i_nb_ref = 0;
 165     p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
 166 }
 167
 168 /*****************************************************************************
 169  * vout_SynchroChoose : Decide whether we will decode a picture or not
 170  *****************************************************************************/
 171 vlc_bool_t vout_SynchroChoose( vout_synchro_t * p_synchro, int i_coding_type,
 172                                int i_render_time )
 173 {
 174 #define TAU_PRIME( coding_type )    (p_synchro->p_tau[(coding_type)] \
 175                                     + (p_synchro->p_tau[(coding_type)] >> 1) \
 176                                     + p_synchro->i_render_time)
 177 #define S (*p_synchro)
 178     /* VPAR_SYNCHRO_DEFAULT */
 179     mtime_t         now, period;
 180     mtime_t         pts = 0;
 181     vlc_bool_t      b_decode = 0;
 182
 183     now = mdate();
 184     period = 1000000 * 1001 / p_synchro->i_frame_rate
 185                      * p_synchro->i_current_rate / DEFAULT_RATE;
 186
 187     p_synchro->i_render_time = i_render_time;
 188
 189     switch( i_coding_type )
 190     {
 191     case I_CODING_TYPE:
 192         if( S.backward_pts )
 193         {
 194             pts = S.backward_pts;
 195         }
 196         else
 197         {
 198             /* displaying order : B B P B B I
 199              *                      ^       ^
 200              *                      |       +- current picture
 201              *                      +- current PTS
 202              */
 203             pts = S.current_pts + period * (S.i_n_b + 2);
 204         }
 205
 206         if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 207                 S.p_tau[I_CODING_TYPE] )
 208         {
 209             b_decode = 1;
 210         }
 211         else
 212         {
 213             b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 214         }
 215         if( !b_decode )
 216         {
 217             msg_Warn( p_synchro,
 218                       "synchro trashing I ("I64Fd")", pts - now );
 219         }
 220         break;
 221
 222     case P_CODING_TYPE:
 223         if( S.backward_pts )
 224         {
 225             pts = S.backward_pts;
 226         }
 227         else
 228         {
 229             pts = S.current_pts + period * (S.i_n_b + 1);
 230         }
 231
 232         if( p_synchro->i_nb_ref < 1 )
 233         {
 234             b_decode = 0;
 235         }
 236         else if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 237                 S.p_tau[I_CODING_TYPE] )
 238         {
 239             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 240             {
 241                 /* Security in case we're _really_ late */
 242                 b_decode = (pts - now > 0);
 243             }
 244             else
 245             {
 246                 b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 247                 /* next I */
 248                 b_decode &= (pts - now
 249                               + period
 250                           * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 251                             > (TAU_PRIME(P_CODING_TYPE)
 252                                 + TAU_PRIME(I_CODING_TYPE) + DELTA);
 253             }
 254         }
 255         else
 256         {
 257             b_decode = 0;
 258         }
 259         break;
 260
 261     case B_CODING_TYPE:
 262         pts = S.current_pts;
 263
 264         if( p_synchro->i_nb_ref < 2 )
 265         {
 266             b_decode = 0;
 267         }
 268         else if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 269         {
 270             b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 271         }
 272         else
 273         {
 274             b_decode = 0;
 275         }
 276     }
 277
 278     if( !b_decode )
 279     {
 280         S.i_not_chosen_pic++;
 281     }
 282     return( b_decode );
 283 #undef S
 284 #undef TAU_PRIME
 285 }
 286
 287 /*****************************************************************************
 288  * vout_SynchroTrash : Update counters when we trash a picture
 289  *****************************************************************************/
 290 void vout_SynchroTrash( vout_synchro_t * p_synchro )
 291 {
 292     p_synchro->i_trashed_pic++;
 293     p_synchro->i_nb_ref = p_synchro->i_trash_nb_ref;
 294 }
 295
 296 /*****************************************************************************
 297  * vout_SynchroDecode : Update timers when we decide to decode a picture
 298  *****************************************************************************/
 299 void vout_SynchroDecode( vout_synchro_t * p_synchro )
 300 {
 301     p_synchro->decoding_start = mdate();
 302     p_synchro->i_nb_ref = p_synchro->i_dec_nb_ref;
 303 }
 304
 305 /*****************************************************************************
 306  * vout_SynchroEnd : Called when the image is totally decoded
 307  *****************************************************************************/
 308 void vout_SynchroEnd( vout_synchro_t * p_synchro, int i_coding_type,
 309                       vlc_bool_t b_garbage )
 310 {
 311     mtime_t     tau;
 312
 313     if( !b_garbage )
 314     {
 315         tau = mdate() - p_synchro->decoding_start;
 316
 317         /* If duration too high, something happened (pause ?), so don't
 318          * take it into account. */
 319         if( tau < 3 * p_synchro->p_tau[i_coding_type]
 320              || ( !p_synchro->pi_meaningful[i_coding_type]
 321                    && tau < MAX_VALID_TAU ) )
 322         {
 323             /* Mean with average tau, to ensure stability. */
 324             p_synchro->p_tau[i_coding_type] =
 325                 (p_synchro->pi_meaningful[i_coding_type]
 326                  * p_synchro->p_tau[i_coding_type] + tau)
 327                 / (p_synchro->pi_meaningful[i_coding_type] + 1);
 328             if( p_synchro->pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 329             {
 330                 p_synchro->pi_meaningful[i_coding_type]++;
 331             }
 332         }
 333     }
 334 }
 335
 336 /*****************************************************************************
 337  * vout_SynchroDate : When an image has been decoded, ask for its date
 338  *****************************************************************************/
 339 mtime_t vout_SynchroDate( vout_synchro_t * p_synchro )
 340 {
 341     /* No need to lock, since PTS are only used by the video parser. */
 342     return p_synchro->current_pts;
 343 }
 344
 345 /*****************************************************************************
 346  * vout_SynchroNewPicture: Update stream structure and PTS
 347  *****************************************************************************/
 348 void vout_SynchroNewPicture( vout_synchro_t * p_synchro, int i_coding_type,
 349                              int i_repeat_field, mtime_t next_pts,
 350                              mtime_t next_dts, int i_current_rate )
 351 {
 352     mtime_t         period = 1000000 * 1001 / p_synchro->i_frame_rate
 353                               * i_current_rate / DEFAULT_RATE;
 354 #if 0
 355     mtime_t         now = mdate();
 356 #endif
 357     p_synchro->i_current_rate = i_current_rate;
 358
 359     switch( i_coding_type )
 360     {
 361     case I_CODING_TYPE:
 362         if( p_synchro->i_eta_p
 363              && p_synchro->i_eta_p != p_synchro->i_n_p )
 364         {
 365             msg_Dbg( p_synchro,
 366                      "stream periodicity changed from P[%d] to P[%d]",
 367                      p_synchro->i_n_p, p_synchro->i_eta_p );
 368             p_synchro->i_n_p = p_synchro->i_eta_p;
 369         }
 370         p_synchro->i_eta_p = p_synchro->i_eta_b = 0;
 371         p_synchro->i_trash_nb_ref = 0;
 372         if( p_synchro->i_nb_ref < 2 )
 373             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref + 1;
 374         else
 375             p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref;
 376
 377 #if 0
 378         msg_Dbg( p_synchro, "I("I64Fd") P("I64Fd")[%d] B("I64Fd")"
 379               "[%d] YUV("I64Fd") : trashed %d:%d/%d",
 380               p_synchro->p_tau[I_CODING_TYPE],
 381               p_synchro->p_tau[P_CODING_TYPE],
 382               p_synchro->i_n_p,
 383               p_synchro->p_tau[B_CODING_TYPE],
 384               p_synchro->i_n_b,
 385               p_synchro->i_render_time,
 386               p_synchro->i_not_chosen_pic,
 387               p_synchro->i_trashed_pic -
 388               p_synchro->i_not_chosen_pic,
 389               p_synchro->i_pic );
 390         p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 391             = p_synchro->i_pic = 0;
 392 #else
 393         if ( p_synchro->i_pic >= 100 )
 394         {
 395             msg_Dbg( p_synchro, "decoded %d/%d pictures",
 396                      p_synchro->i_pic
 397                        - p_synchro->i_trashed_pic,
 398                      p_synchro->i_pic );
 399             p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
 400                 = p_synchro->i_pic = 0;
 401         }
 402 #endif
 403         break;
 404
 405     case P_CODING_TYPE:
 406         p_synchro->i_eta_p++;
 407         if( p_synchro->i_eta_b
 408              && p_synchro->i_eta_b != p_synchro->i_n_b )
 409         {
 410             msg_Dbg( p_synchro,
 411                      "stream periodicity changed from B[%d] to B[%d]",
 412                      p_synchro->i_n_b, p_synchro->i_eta_b );
 413             p_synchro->i_n_b = p_synchro->i_eta_b;
 414         }
 415         p_synchro->i_eta_b = 0;
 416         p_synchro->i_dec_nb_ref = 2;
 417         p_synchro->i_trash_nb_ref = 0;
 418         break;
 419
 420     case B_CODING_TYPE:
 421         p_synchro->i_eta_b++;
 422         p_synchro->i_dec_nb_ref = p_synchro->i_trash_nb_ref
 423             = p_synchro->i_nb_ref;
 424         break;
 425     }
 426
 427     p_synchro->current_pts += p_synchro->i_current_period
 428                                         * (period >> 1);
 429
 430 #define PTS_THRESHOLD   (period >> 2)
 431     if( i_coding_type == B_CODING_TYPE )
 432     {
 433         /* A video frame can be displayed 1, 2 or 3 times, according to
 434          * repeat_first_field, top_field_first, progressive_sequence and
 435          * progressive_frame. */
 436         p_synchro->i_current_period = i_repeat_field;
 437
 438         if( next_pts )
 439         {
 440             if( next_pts - p_synchro->current_pts
 441                     > PTS_THRESHOLD
 442                  || p_synchro->current_pts - next_pts
 443                     > PTS_THRESHOLD )
 444             {
 445                 msg_Warn( p_synchro, "vout synchro warning: pts != "
 446                           "current_date ("I64Fd")",
 447                           p_synchro->current_pts
 448                               - next_pts );
 449             }
 450             p_synchro->current_pts = next_pts;
 451         }
 452     }
 453     else
 454     {
 455         p_synchro->i_current_period = p_synchro->i_backward_period;
 456         p_synchro->i_backward_period = i_repeat_field;
 457
 458         if( p_synchro->backward_pts )
 459         {
 460             if( next_dts &&
 461                 (next_dts - p_synchro->backward_pts
 462                     > PTS_THRESHOLD
 463               || p_synchro->backward_pts - next_dts
 464                     > PTS_THRESHOLD) )
 465             {
 466                 msg_Warn( p_synchro, "backward_pts != dts ("I64Fd")",
 467                            next_dts
 468                                - p_synchro->backward_pts );
 469             }
 470             if( p_synchro->backward_pts - p_synchro->current_pts
 471                     > PTS_THRESHOLD
 472                  || p_synchro->current_pts - p_synchro->backward_pts
 473                     > PTS_THRESHOLD )
 474             {
 475                 msg_Warn( p_synchro,
 476                           "backward_pts != current_pts ("I64Fd")",
 477                           p_synchro->current_pts
 478                               - p_synchro->backward_pts );
 479             }
 480             p_synchro->current_pts = p_synchro->backward_pts;
 481             p_synchro->backward_pts = 0;
 482         }
 483         else if( next_dts )
 484         {
 485             if( next_dts - p_synchro->current_pts
 486                     > PTS_THRESHOLD
 487                  || p_synchro->current_pts - next_dts
 488                     > PTS_THRESHOLD )
 489             {
 490                 msg_Warn( p_synchro, "dts != current_pts ("I64Fd")",
 491                           p_synchro->current_pts
 492                               - next_dts );
 493             }
 494             /* By definition of a DTS. */
 495             p_synchro->current_pts = next_dts;
 496             next_dts = 0;
 497         }
 498
 499         if( next_pts )
 500         {
 501             /* Store the PTS for the next time we have to date an I picture. */
 502             p_synchro->backward_pts = next_pts;
 503             next_pts = 0;
 504         }
 505     }
 506 #undef PTS_THRESHOLD
 507
 508 #if 0
 509     /* Removed for incompatibility with slow motion */
 510     if( p_synchro->current_pts + DEFAULT_PTS_DELAY < now )
 511     {
 512         /* We cannot be _that_ late, something must have happened, reinit
 513          * the dates. */
 514         msg_Warn( p_synchro, "PTS << now ("I64Fd"), resetting",
 515                    now - p_synchro->current_pts - DEFAULT_PTS_DELAY );
 516         p_synchro->current_pts = now + DEFAULT_PTS_DELAY;
 517     }
 518     if( p_synchro->backward_pts
 519          && p_synchro->backward_pts + DEFAULT_PTS_DELAY < now )
 520     {
 521         /* The same. */
 522         p_synchro->backward_pts = 0;
 523     }
 524 #endif
 525
 526     p_synchro->i_pic++;
 527 }