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, 2000 VideoLAN
   5  * $Id: input_clock.c,v 1.3 2001/02/07 17:44:52 massiot Exp $
   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 "defs.h"
  28
  29 #include "config.h"
  30 #include "common.h"
  31 #include "threads.h"
  32 #include "mtime.h"
  33 #include "intf_msg.h"
  34
  35 #include "stream_control.h"
  36 #include "input_ext-intf.h"
  37 #include "input_ext-dec.h"
  38
  39 #include "input.h"
  40
  41 /*
  42  * DISCUSSION : SYNCHRONIZATION METHOD
  43  *
  44  * In some cases we can impose the pace of reading (when reading from a
  45  * file or a pipe), and for the synchronization we simply sleep() until
  46  * it is time to deliver the packet to the decoders. When reading from
  47  * the network, we must be read at the same pace as the server writes,
  48  * otherwise the kernel's buffer will trash packets. The risk is now to
  49  * overflow the input buffers in case the server goes too fast, that is
  50  * why we do these calculations :
  51  *
  52  * We compute a mean for the pcr because we want to eliminate the
  53  * network jitter and keep the low frequency variations. The mean is
  54  * in fact a low pass filter and the jitter is a high frequency signal
  55  * that is why it is eliminated by the filter/average.
  56  *
  57  * The low frequency variations enable us to synchronize the client clock
  58  * with the server clock because they represent the time variation between
  59  * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
  60  * the presentation dates for the audio and video frames. With those dates
  61  * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
  62  * as it is sent by the server and so we keep the synchronization between
  63  * the server and the client.
  64  *
  65  * It is a very important matter if you want to avoid underflow or overflow
  66  * in all the FIFOs, but it may be not enough.
  67  */
  68
  69 /*****************************************************************************
  70  * Constants
  71  *****************************************************************************/
  72
  73 /* Maximum number of samples used to compute the dynamic average value.
  74  * We use the following formula :
  75  * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
  76  */
  77 #define CR_MAX_AVERAGE_COUNTER 40
  78
  79 /* Maximum gap allowed between two CRs. */
  80 #define CR_MAX_GAP 1000000
  81
  82 /*****************************************************************************
  83  * ClockToSysdate: converts a movie clock to system date
  84  *****************************************************************************/
  85 static mtime_t ClockToSysdate( input_thread_t * p_input,
  86                                pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
  87 {
  88     mtime_t     i_sysdate = 0;
  89
  90     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
  91     {
  92         i_sysdate = (i_clock - p_pgrm->cr_ref)
  93                         * p_input->stream.control.i_rate
  94                         * 300
  95                         / 27
  96                         / DEFAULT_RATE
  97                         + p_pgrm->sysdate_ref;
  98     }
  99
 100     return( i_sysdate );
 101 }
 102
 103 /*****************************************************************************
 104  * ClockCurrent: converts current system date to clock units
 105  *****************************************************************************
 106  * Caution : the synchro state must be SYNCHRO_OK for this to operate.
 107  *****************************************************************************/
 108 static mtime_t ClockCurrent( input_thread_t * p_input,
 109                              pgrm_descriptor_t * p_pgrm )
 110 {
 111     return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
 112              / p_input->stream.control.i_rate / 300
 113              + p_pgrm->cr_ref );
 114 }
 115
 116 /*****************************************************************************
 117  * input_ClockNewRef: writes a new clock reference
 118  *****************************************************************************/
 119 void input_ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
 120                         mtime_t i_clock, mtime_t i_sysdate )
 121 {
 122     intf_WarnMsg( 1, "Old ref: %lld/%lld, New ref: %lld/%lld", p_pgrm->cr_ref,
 123               p_pgrm->sysdate_ref, i_clock, i_sysdate );
 124     p_pgrm->cr_ref = i_clock;
 125     p_pgrm->sysdate_ref = i_sysdate;
 126 }
 127
 128 /*****************************************************************************
 129  * EscapeDiscontinuity: send a NULL packet to the decoders
 130  *****************************************************************************/
 131 static void EscapeDiscontinuity( input_thread_t * p_input,
 132                                  pgrm_descriptor_t * p_pgrm )
 133 {
 134     int     i_es;
 135
 136     for( i_es = 0; i_es < p_pgrm->i_es_number; i_es++ )
 137     {
 138         es_descriptor_t * p_es = p_pgrm->pp_es[i_es];
 139
 140         if( p_es->p_decoder_fifo != NULL )
 141         {
 142             input_NullPacket( p_input, p_es );
 143         }
 144     }
 145 }
 146
 147 /*****************************************************************************
 148  * EscapeAudioDiscontinuity: send a NULL packet to the audio decoders
 149  *****************************************************************************/
 150 static void EscapeAudioDiscontinuity( input_thread_t * p_input,
 151                                       pgrm_descriptor_t * p_pgrm )
 152 {
 153     int     i_es;
 154
 155     for( i_es = 0; i_es < p_pgrm->i_es_number; i_es++ )
 156     {
 157         es_descriptor_t * p_es = p_pgrm->pp_es[i_es];
 158
 159         if( p_es->p_decoder_fifo != NULL && p_es->b_audio )
 160         {
 161             input_NullPacket( p_input, p_es );
 162         }
 163     }
 164 }
 165
 166 /*****************************************************************************
 167  * input_ClockInit: reinitializes the clock reference after a stream
 168  *                  discontinuity
 169  *****************************************************************************/
 170 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
 171 {
 172     p_pgrm->last_cr = 0;
 173     p_pgrm->cr_ref = 0;
 174     p_pgrm->sysdate_ref = 0;
 175     p_pgrm->delta_cr = 0;
 176     p_pgrm->c_average_count = 0;
 177 }
 178
 179 /*****************************************************************************
 180  * input_ClockManageRef: manages a clock reference
 181  *****************************************************************************/
 182 void input_ClockManageRef( input_thread_t * p_input,
 183                            pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
 184 {
 185     if( p_pgrm->i_synchro_state != SYNCHRO_OK )
 186     {
 187         /* Feed synchro with a new reference point. */
 188         input_ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
 189         p_pgrm->i_synchro_state = SYNCHRO_OK;
 190     }
 191     else
 192     {
 193         if ( p_pgrm->last_cr != 0 &&
 194                (    (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
 195                  || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
 196         {
 197             /* Stream discontinuity, for which we haven't received a
 198              * warning from the stream control facilities (dd-edited
 199              * stream ?). */
 200             intf_WarnMsg( 3, "Clock gap, unexpected stream discontinuity" );
 201             input_ClockInit( p_pgrm );
 202             p_pgrm->i_synchro_state = SYNCHRO_START;
 203             input_EscapeDiscontinuity( p_input, p_pgrm );
 204         }
 205
 206         p_pgrm->last_cr = i_clock;
 207
 208         if( p_input->stream.b_pace_control
 209              && p_input->stream.pp_programs[0] == p_pgrm )
 210         {
 211             /* Wait a while before delivering the packets to the decoder.
 212              * In case of multiple programs, we arbitrarily follow the
 213              * clock of the first program. */
 214             mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
 215
 216             /* Now take into account interface changes. */
 217             vlc_mutex_lock( &p_input->stream.stream_lock );
 218             if( p_input->stream.i_new_status != UNDEF_S )
 219             {
 220                 /* For the moment, only PLAYING_S and FORWARD_S are
 221                  * supported. */
 222                 input_ClockNewRef( p_input, p_pgrm, i_clock,
 223                                    ClockToSysdate( p_input, p_pgrm, i_clock ) );
 224
 225                 vlc_mutex_lock( &p_input->stream.control.control_lock );
 226                 p_input->stream.control.i_status = p_input->stream.i_new_status;
 227
 228                 if( p_input->stream.control.i_status != PLAYING_S )
 229                 {
 230                     p_input->stream.control.i_rate = p_input->stream.i_new_rate;
 231                     p_input->stream.control.b_mute = 1;
 232
 233                     /* Feed the audio decoders with a NULL packet to avoid
 234                      * discontinuities. */
 235                     EscapeAudioDiscontinuity( p_input, p_pgrm );
 236                 }
 237                 else
 238                 {
 239                     p_input->stream.control.i_rate = DEFAULT_RATE;
 240                     p_input->stream.control.b_mute = 0;
 241                 }
 242                 vlc_mutex_unlock( &p_input->stream.control.control_lock );
 243
 244                 p_input->stream.i_new_status = UNDEF_S;
 245                 p_input->stream.i_new_rate = UNDEF_S;
 246             }
 247             vlc_mutex_unlock( &p_input->stream.stream_lock );
 248         }
 249         else
 250         {
 251             /* Smooth clock reference variations. */
 252             mtime_t     i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
 253
 254             /* Bresenham algorithm to smooth variations. */
 255             if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
 256             {
 257                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 258                                         * (CR_MAX_AVERAGE_COUNTER - 1)
 259                                       + i_extrapoled_clock )
 260                                     / CR_MAX_AVERAGE_COUNTER;
 261             }
 262             else
 263             {
 264                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 265                                         * p_pgrm->c_average_count
 266                                       + i_extrapoled_clock )
 267                                     / (p_pgrm->c_average_count + 1);
 268                 p_pgrm->c_average_count++;
 269             }
 270         }
 271     }
 272 }
 273
 274 /*****************************************************************************
 275  * input_ClockGetTS: manages a PTS or DTS
 276  *****************************************************************************/
 277 mtime_t input_ClockGetTS( input_thread_t * p_input,
 278                           pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
 279 {
 280     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
 281     {
 282         return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
 283                  + DEFAULT_PTS_DELAY );
 284     }
 285     else
 286     {
 287         return 0;
 288     }
 289 }
 290