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 1.11 2001/04/28 03:36:25 sam 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 <string.h>                                    /* memcpy(), memset() */
  30 #include <sys/types.h>                                              /* off_t */
  31
  32 #include "config.h"
  33 #include "common.h"
  34 #include "threads.h"
  35 #include "mtime.h"
  36 #include "intf_msg.h"
  37
  38 #include "stream_control.h"
  39 #include "input_ext-intf.h"
  40 #include "input_ext-dec.h"
  41
  42 #include "input.h"
  43
  44 /*
  45  * DISCUSSION : SYNCHRONIZATION METHOD
  46  *
  47  * In some cases we can impose the pace of reading (when reading from a
  48  * file or a pipe), and for the synchronization we simply sleep() until
  49  * it is time to deliver the packet to the decoders. When reading from
  50  * the network, we must be read at the same pace as the server writes,
  51  * otherwise the kernel's buffer will trash packets. The risk is now to
  52  * overflow the input buffers in case the server goes too fast, that is
  53  * why we do these calculations :
  54  *
  55  * We compute a mean for the pcr because we want to eliminate the
  56  * network jitter and keep the low frequency variations. The mean is
  57  * in fact a low pass filter and the jitter is a high frequency signal
  58  * that is why it is eliminated by the filter/average.
  59  *
  60  * The low frequency variations enable us to synchronize the client clock
  61  * with the server clock because they represent the time variation between
  62  * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
  63  * the presentation dates for the audio and video frames. With those dates
  64  * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
  65  * as it is sent by the server and so we keep the synchronization between
  66  * the server and the client.
  67  *
  68  * It is a very important matter if you want to avoid underflow or overflow
  69  * in all the FIFOs, but it may be not enough.
  70  */
  71
  72 /*****************************************************************************
  73  * Constants
  74  *****************************************************************************/
  75
  76 /* Maximum number of samples used to compute the dynamic average value.
  77  * We use the following formula :
  78  * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
  79  */
  80 #define CR_MAX_AVERAGE_COUNTER 40
  81
  82 /* Maximum gap allowed between two CRs. */
  83 #define CR_MAX_GAP 1000000
  84
  85 /*****************************************************************************
  86  * ClockToSysdate: converts a movie clock to system date
  87  *****************************************************************************/
  88 static mtime_t ClockToSysdate( input_thread_t * p_input,
  89                                pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
  90 {
  91     mtime_t     i_sysdate = 0;
  92
  93     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
  94     {
  95         i_sysdate = (mtime_t)(i_clock - p_pgrm->cr_ref)
  96                         * (mtime_t)p_input->stream.control.i_rate
  97                         * (mtime_t)300
  98                         / (mtime_t)27
  99                         / (mtime_t)DEFAULT_RATE
 100                         + (mtime_t)p_pgrm->sysdate_ref;
 101     }
 102
 103     return( i_sysdate );
 104 }
 105
 106 /*****************************************************************************
 107  * ClockCurrent: converts current system date to clock units
 108  *****************************************************************************
 109  * Caution : the synchro state must be SYNCHRO_OK for this to operate.
 110  *****************************************************************************/
 111 static mtime_t ClockCurrent( input_thread_t * p_input,
 112                              pgrm_descriptor_t * p_pgrm )
 113 {
 114     return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
 115              / p_input->stream.control.i_rate / 300
 116              + p_pgrm->cr_ref );
 117 }
 118
 119 /*****************************************************************************
 120  * ClockNewRef: writes a new clock reference
 121  *****************************************************************************/
 122 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
 123                          mtime_t i_clock, mtime_t i_sysdate )
 124 {
 125     p_pgrm->cr_ref = i_clock;
 126     p_pgrm->sysdate_ref = i_sysdate;
 127 }
 128
 129 /*****************************************************************************
 130  * input_ClockInit: reinitializes the clock reference after a stream
 131  *                  discontinuity
 132  *****************************************************************************/
 133 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
 134 {
 135     p_pgrm->last_cr = 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_ClockManageRef: manages a clock reference
 144  *****************************************************************************/
 145 void input_ClockManageRef( input_thread_t * p_input,
 146                            pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
 147 {
 148     if( p_pgrm->i_synchro_state != SYNCHRO_OK )
 149     {
 150         /* Feed synchro with a new reference point. */
 151         ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
 152         p_pgrm->i_synchro_state = SYNCHRO_OK;
 153     }
 154     else
 155     {
 156         if ( p_pgrm->last_cr != 0 &&
 157                (    (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
 158                  || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
 159         {
 160             /* Stream discontinuity, for which we haven't received a
 161              * warning from the stream control facilities (dd-edited
 162              * stream ?). */
 163             intf_WarnMsg( 3, "Clock gap, unexpected stream discontinuity" );
 164             input_ClockInit( p_pgrm );
 165             p_pgrm->i_synchro_state = SYNCHRO_START;
 166             input_EscapeDiscontinuity( p_input, p_pgrm );
 167         }
 168
 169         p_pgrm->last_cr = i_clock;
 170
 171         if( p_input->stream.b_pace_control
 172              && p_input->stream.pp_programs[0] == p_pgrm )
 173         {
 174             /* Wait a while before delivering the packets to the decoder.
 175              * In case of multiple programs, we arbitrarily follow the
 176              * clock of the first program. */
 177             mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
 178
 179             /* Now take into account interface changes. */
 180             vlc_mutex_lock( &p_input->stream.stream_lock );
 181
 182             if( p_input->stream.i_new_status == PAUSE_S )
 183             {
 184                 int i_old_status;
 185                 vlc_mutex_lock( &p_input->stream.control.control_lock );
 186                 i_old_status = p_input->stream.control.i_status;
 187
 188                 p_input->stream.control.i_status = PAUSE_S;
 189                 vlc_cond_wait( &p_input->stream.stream_wait,
 190                                &p_input->stream.stream_lock );
 191                 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
 192
 193                 if( p_input->stream.i_new_status == PAUSE_S )
 194                 {
 195                     /* PAUSE_S undoes the pause state: Return to old state. */
 196                     p_input->stream.control.i_status = i_old_status;
 197                     p_input->stream.i_new_status = UNDEF_S;
 198                     p_input->stream.i_new_rate = UNDEF_S;
 199                 }
 200
 201                 /*  We handle i_new_status != PAUSE_S below... */
 202                 vlc_mutex_unlock( &p_input->stream.control.control_lock );
 203             }
 204
 205             if( p_input->stream.i_new_status != UNDEF_S )
 206             {
 207                 vlc_mutex_lock( &p_input->stream.control.control_lock );
 208
 209                 p_input->stream.control.i_status = p_input->stream.i_new_status;
 210
 211                 ClockNewRef( p_input, p_pgrm, i_clock,
 212                            ClockToSysdate( p_input, p_pgrm, i_clock ) );
 213
 214                 if( p_input->stream.control.i_status == PLAYING_S )
 215                 {
 216                     p_input->stream.control.i_rate = DEFAULT_RATE;
 217                     p_input->stream.control.b_mute = 0;
 218                 }
 219                 else
 220                 {
 221                     p_input->stream.control.i_rate = p_input->stream.i_new_rate;
 222                     p_input->stream.control.b_mute = 1;
 223
 224                     /* Feed the audio decoders with a NULL packet to avoid
 225                      * discontinuities. */
 226                     input_EscapeAudioDiscontinuity( p_input, p_pgrm );
 227                 }
 228
 229                 p_input->stream.i_new_status = UNDEF_S;
 230                 p_input->stream.i_new_rate = UNDEF_S;
 231
 232                 vlc_mutex_unlock( &p_input->stream.control.control_lock );
 233             }
 234
 235             vlc_mutex_unlock( &p_input->stream.stream_lock );
 236         }
 237         else
 238         {
 239             /* Smooth clock reference variations. */
 240             mtime_t     i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
 241
 242             /* Bresenham algorithm to smooth variations. */
 243             if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
 244             {
 245                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 246                                         * (CR_MAX_AVERAGE_COUNTER - 1)
 247                                       + i_extrapoled_clock )
 248                                     / CR_MAX_AVERAGE_COUNTER;
 249             }
 250             else
 251             {
 252                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 253                                         * p_pgrm->c_average_count
 254                                       + i_extrapoled_clock )
 255                                     / (p_pgrm->c_average_count + 1);
 256                 p_pgrm->c_average_count++;
 257             }
 258         }
 259     }
 260 }
 261
 262 /*****************************************************************************
 263  * input_ClockGetTS: manages a PTS or DTS
 264  *****************************************************************************/
 265 mtime_t input_ClockGetTS( input_thread_t * p_input,
 266                           pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
 267 {
 268     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
 269     {
 270         return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
 271                  + DEFAULT_PTS_DELAY );
 272     }
 273     else
 274     {
 275         return 0;
 276     }
 277 }
 278