git.sesse.net Git - vlc/blob - src/input/input_clock.c

   1 /*****************************************************************************
   2  * input_clock.c: Clock/System date convertions, stream management
   3  *****************************************************************************
   4  * Copyright (C) 1999-2004 VideoLAN
   5  * $Id$
   6  *
   7  * Authors: Christophe Massiot <massiot@via.ecp.fr>
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License as published by
  11  * the Free Software Foundation; either version 2 of the License, or
  12  * (at your option) any later version.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this program; if not, write to the Free Software
  21  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
  22  *****************************************************************************/
  23
  24 /*****************************************************************************
  25  * Preamble
  26  *****************************************************************************/
  27 #include <string.h>                                    /* memcpy(), memset() */
  28
  29 #include <vlc/vlc.h>
  30
  31 #include "stream_control.h"
  32 #include "input_ext-intf.h"
  33 #include "input_ext-dec.h"
  34 #include "input_ext-plugins.h"
  35
  36 /*
  37  * DISCUSSION : SYNCHRONIZATION METHOD
  38  *
  39  * In some cases we can impose the pace of reading (when reading from a
  40  * file or a pipe), and for the synchronization we simply sleep() until
  41  * it is time to deliver the packet to the decoders. When reading from
  42  * the network, we must be read at the same pace as the server writes,
  43  * otherwise the kernel's buffer will trash packets. The risk is now to
  44  * overflow the input buffers in case the server goes too fast, that is
  45  * why we do these calculations :
  46  *
  47  * We compute a mean for the pcr because we want to eliminate the
  48  * network jitter and keep the low frequency variations. The mean is
  49  * in fact a low pass filter and the jitter is a high frequency signal
  50  * that is why it is eliminated by the filter/average.
  51  *
  52  * The low frequency variations enable us to synchronize the client clock
  53  * with the server clock because they represent the time variation between
  54  * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
  55  * the presentation dates for the audio and video frames. With those dates
  56  * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
  57  * as it is sent by the server and so we keep the synchronization between
  58  * the server and the client.
  59  *
  60  * It is a very important matter if you want to avoid underflow or overflow
  61  * in all the FIFOs, but it may be not enough.
  62  */
  63
  64 /* p_input->i_cr_average : Maximum number of samples used to compute the
  65  * dynamic average value.
  66  * We use the following formula :
  67  * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
  68  */
  69
  70 static void ClockNewRef( pgrm_descriptor_t * p_pgrm,
  71                          mtime_t i_clock, mtime_t i_sysdate );
  72
  73 /*****************************************************************************
  74  * Constants
  75  *****************************************************************************/
  76
  77 /* Maximum gap allowed between two CRs. */
  78 #define CR_MAX_GAP 2000000
  79
  80 /* Latency introduced on DVDs with CR == 0 on chapter change - this is from
  81  * my dice --Meuuh */
  82 #define CR_MEAN_PTS_GAP 300000
  83
  84 /*****************************************************************************
  85  * ClockToSysdate: converts a movie clock to system date
  86  *****************************************************************************/
  87 static mtime_t ClockToSysdate( input_thread_t * p_input,
  88                                pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
  89 {
  90     mtime_t     i_sysdate = 0;
  91
  92     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
  93     {
  94         i_sysdate = (mtime_t)(i_clock - p_pgrm->cr_ref)
  95                         * (mtime_t)p_input->stream.control.i_rate
  96                         * (mtime_t)300;
  97         i_sysdate /= 27;
  98         i_sysdate /= 1000;
  99         i_sysdate += (mtime_t)p_pgrm->sysdate_ref;
 100     }
 101
 102     return( i_sysdate );
 103 }
 104
 105 /*****************************************************************************
 106  * ClockCurrent: converts current system date to clock units
 107  *****************************************************************************
 108  * Caution : the synchro state must be SYNCHRO_OK for this to operate.
 109  *****************************************************************************/
 110 static mtime_t ClockCurrent( input_thread_t * p_input,
 111                              pgrm_descriptor_t * p_pgrm )
 112 {
 113     return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
 114              / p_input->stream.control.i_rate / 300
 115              + p_pgrm->cr_ref );
 116 }
 117
 118 /*****************************************************************************
 119  * ClockNewRef: writes a new clock reference
 120  *****************************************************************************/
 121 static void ClockNewRef( pgrm_descriptor_t * p_pgrm,
 122                          mtime_t i_clock, mtime_t i_sysdate )
 123 {
 124     p_pgrm->cr_ref = i_clock;
 125     p_pgrm->sysdate_ref = i_sysdate ;
 126 }
 127
 128 /*****************************************************************************
 129  * input_ClockInit: reinitializes the clock reference after a stream
 130  *                  discontinuity
 131  *****************************************************************************/
 132 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
 133 {
 134     p_pgrm->last_cr = 0;
 135     p_pgrm->last_pts = 0;
 136     p_pgrm->cr_ref = 0;
 137     p_pgrm->sysdate_ref = 0;
 138     p_pgrm->delta_cr = 0;
 139     p_pgrm->c_average_count = 0;
 140 }
 141
 142 /*****************************************************************************
 143  * input_ClockManageControl: handles the messages from the interface
 144  *****************************************************************************
 145  * Returns UNDEF_S if nothing happened, PAUSE_S if the stream was paused
 146  *****************************************************************************/
 147 int input_ClockManageControl( input_thread_t * p_input,
 148                                pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
 149 {
 150     vlc_value_t val;
 151     int i_return_value = UNDEF_S;
 152
 153     vlc_mutex_lock( &p_input->stream.stream_lock );
 154
 155     if( p_input->stream.i_new_status == PAUSE_S )
 156     {
 157         int i_old_status;
 158
 159         vlc_mutex_lock( &p_input->stream.control.control_lock );
 160         i_old_status = p_input->stream.control.i_status;
 161         p_input->stream.control.i_status = PAUSE_S;
 162         vlc_mutex_unlock( &p_input->stream.control.control_lock );
 163
 164         vlc_cond_wait( &p_input->stream.stream_wait,
 165                        &p_input->stream.stream_lock );
 166         ClockNewRef( p_pgrm, i_clock, p_pgrm->last_pts > mdate() ?
 167                                       p_pgrm->last_pts : mdate() );
 168
 169         if( p_input->stream.i_new_status == PAUSE_S )
 170         {
 171             /* PAUSE_S undoes the pause state: Return to old state. */
 172             vlc_mutex_lock( &p_input->stream.control.control_lock );
 173             p_input->stream.control.i_status = i_old_status;
 174             vlc_mutex_unlock( &p_input->stream.control.control_lock );
 175
 176             p_input->stream.i_new_status = UNDEF_S;
 177             p_input->stream.i_new_rate = UNDEF_S;
 178         }
 179
 180         /* We handle i_new_status != PAUSE_S below... */
 181
 182         i_return_value = PAUSE_S;
 183     }
 184
 185     if( p_input->stream.i_new_status != UNDEF_S )
 186     {
 187         vlc_mutex_lock( &p_input->stream.control.control_lock );
 188
 189         p_input->stream.control.i_status = p_input->stream.i_new_status;
 190
 191         ClockNewRef( p_pgrm, i_clock,
 192                      ClockToSysdate( p_input, p_pgrm, i_clock ) );
 193
 194         if( p_input->stream.control.i_status == PLAYING_S )
 195         {
 196             p_input->stream.control.i_rate = DEFAULT_RATE;
 197             p_input->stream.control.b_mute = 0;
 198         }
 199         else
 200         {
 201             p_input->stream.control.i_rate = p_input->stream.i_new_rate;
 202             p_input->stream.control.b_mute = 1;
 203
 204             /* Feed the audio decoders with a NULL packet to avoid
 205              * discontinuities. */
 206             input_EscapeAudioDiscontinuity( p_input );
 207         }
 208
 209         val.i_int = p_input->stream.control.i_rate;
 210         var_Change( p_input, "rate", VLC_VAR_SETVALUE, &val, NULL );
 211
 212         val.i_int = p_input->stream.control.i_status;
 213         var_Change( p_input, "state", VLC_VAR_SETVALUE, &val, NULL );
 214
 215         p_input->stream.i_new_status = UNDEF_S;
 216         p_input->stream.i_new_rate = UNDEF_S;
 217
 218         vlc_mutex_unlock( &p_input->stream.control.control_lock );
 219     }
 220
 221     vlc_mutex_unlock( &p_input->stream.stream_lock );
 222
 223     return( i_return_value );
 224 }
 225
 226 /*****************************************************************************
 227  * input_ClockManageRef: manages a clock reference
 228  *****************************************************************************/
 229 void input_ClockManageRef( input_thread_t * p_input,
 230                            pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
 231 {
 232     /* take selected program if none specified */
 233     if( !p_pgrm )
 234     {
 235         p_pgrm = p_input->stream.p_selected_program;
 236     }
 237
 238     if( ( p_pgrm->i_synchro_state != SYNCHRO_OK ) ||
 239         ( i_clock == 0 && p_pgrm->last_cr != 0 ) )
 240     {
 241         /* Feed synchro with a new reference point. */
 242         ClockNewRef( p_pgrm, i_clock,
 243                      p_pgrm->last_pts + CR_MEAN_PTS_GAP > mdate() ?
 244                      p_pgrm->last_pts + CR_MEAN_PTS_GAP : mdate() );
 245         p_pgrm->i_synchro_state = SYNCHRO_OK;
 246
 247         if( p_input->stream.b_pace_control
 248              && p_input->stream.p_selected_program == p_pgrm )
 249         {
 250             p_pgrm->last_cr = i_clock;
 251             if( !p_input->b_out_pace_control )
 252             {
 253                 mtime_t i_wakeup = ClockToSysdate( p_input, p_pgrm, i_clock );
 254                 while( (i_wakeup - mdate()) / CLOCK_FREQ > 1 )
 255                 {
 256                     msleep( CLOCK_FREQ );
 257                     if( p_input->b_die ) i_wakeup = mdate();
 258                 }
 259                 mwait( i_wakeup );
 260             }
 261         }
 262         else
 263         {
 264             p_pgrm->last_cr = 0;
 265             p_pgrm->delta_cr = 0;
 266             p_pgrm->c_average_count = 0;
 267         }
 268     }
 269     else
 270     {
 271         if ( p_pgrm->last_cr != 0 &&
 272                (    (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
 273                  || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
 274         {
 275             /* Stream discontinuity, for which we haven't received a
 276              * warning from the stream control facilities (dd-edited
 277              * stream ?). */
 278             msg_Warn( p_input, "clock gap, unexpected stream discontinuity" );
 279             input_ClockInit( p_pgrm );
 280             p_pgrm->i_synchro_state = SYNCHRO_START;
 281             input_EscapeDiscontinuity( p_input );
 282         }
 283
 284         p_pgrm->last_cr = i_clock;
 285
 286         if( p_input->stream.b_pace_control
 287              && p_input->stream.p_selected_program == p_pgrm )
 288         {
 289             /* Wait a while before delivering the packets to the decoder.
 290              * In case of multiple programs, we arbitrarily follow the
 291              * clock of the selected program. */
 292             if( !p_input->b_out_pace_control )
 293             {
 294                 mtime_t i_wakeup = ClockToSysdate( p_input, p_pgrm, i_clock );
 295                 while( (i_wakeup - mdate()) / CLOCK_FREQ > 1 )
 296                 {
 297                     msleep( CLOCK_FREQ );
 298                     if( p_input->b_die ) i_wakeup = mdate();
 299                 }
 300                 mwait( i_wakeup );
 301             }
 302
 303             /* Now take into account interface changes. */
 304             input_ClockManageControl( p_input, p_pgrm, i_clock );
 305         }
 306         else
 307         {
 308             /* Smooth clock reference variations. */
 309             mtime_t     i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
 310
 311             /* Bresenham algorithm to smooth variations. */
 312             if( p_pgrm->c_average_count == p_input->i_cr_average )
 313             {
 314                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 315                                         * (p_input->i_cr_average - 1)
 316                                       + ( i_extrapoled_clock - i_clock ) )
 317                                     / p_input->i_cr_average;
 318             }
 319             else
 320             {
 321                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 322                                         * p_pgrm->c_average_count
 323                                       + ( i_extrapoled_clock - i_clock ) )
 324                                     / (p_pgrm->c_average_count + 1);
 325                 p_pgrm->c_average_count++;
 326             }
 327         }
 328     }
 329 }
 330
 331 /*****************************************************************************
 332  * input_ClockGetTS: manages a PTS or DTS
 333  *****************************************************************************/
 334 mtime_t input_ClockGetTS( input_thread_t * p_input,
 335                           pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
 336 {
 337     /* take selected program if none specified */
 338     if( !p_pgrm )
 339     {
 340         p_pgrm = p_input->stream.p_selected_program;
 341     }
 342
 343     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
 344     {
 345         p_pgrm->last_pts = ClockToSysdate( p_input, p_pgrm,
 346                                            i_ts + p_pgrm->delta_cr );
 347         return( p_pgrm->last_pts + p_input->i_pts_delay );
 348     }
 349     else
 350     {
 351         return 0;
 352     }
 353 }
 354