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 1.9 2001/04/06 09:15:47 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
  31 #include "config.h"
  32 #include "common.h"
  33 #include "threads.h"
  34 #include "mtime.h"
  35 #include "intf_msg.h"
  36
  37 #include "stream_control.h"
  38 #include "input_ext-intf.h"
  39 #include "input_ext-dec.h"
  40
  41 #include "input.h"
  42
  43 /*
  44  * DISCUSSION : SYNCHRONIZATION METHOD
  45  *
  46  * In some cases we can impose the pace of reading (when reading from a
  47  * file or a pipe), and for the synchronization we simply sleep() until
  48  * it is time to deliver the packet to the decoders. When reading from
  49  * the network, we must be read at the same pace as the server writes,
  50  * otherwise the kernel's buffer will trash packets. The risk is now to
  51  * overflow the input buffers in case the server goes too fast, that is
  52  * why we do these calculations :
  53  *
  54  * We compute a mean for the pcr because we want to eliminate the
  55  * network jitter and keep the low frequency variations. The mean is
  56  * in fact a low pass filter and the jitter is a high frequency signal
  57  * that is why it is eliminated by the filter/average.
  58  *
  59  * The low frequency variations enable us to synchronize the client clock
  60  * with the server clock because they represent the time variation between
  61  * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
  62  * the presentation dates for the audio and video frames. With those dates
  63  * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
  64  * as it is sent by the server and so we keep the synchronization between
  65  * the server and the client.
  66  *
  67  * It is a very important matter if you want to avoid underflow or overflow
  68  * in all the FIFOs, but it may be not enough.
  69  */
  70
  71 /*****************************************************************************
  72  * Constants
  73  *****************************************************************************/
  74
  75 /* Maximum number of samples used to compute the dynamic average value.
  76  * We use the following formula :
  77  * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
  78  */
  79 #define CR_MAX_AVERAGE_COUNTER 40
  80
  81 /* Maximum gap allowed between two CRs. */
  82 #define CR_MAX_GAP 1000000
  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                         / (mtime_t)27
  98                         / (mtime_t)DEFAULT_RATE
  99                         + (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( input_thread_t * p_input, 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->cr_ref = 0;
 136     p_pgrm->sysdate_ref = 0;
 137     p_pgrm->delta_cr = 0;
 138     p_pgrm->c_average_count = 0;
 139 }
 140
 141 /*****************************************************************************
 142  * input_ClockManageRef: manages a clock reference
 143  *****************************************************************************/
 144 void input_ClockManageRef( input_thread_t * p_input,
 145                            pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
 146 {
 147     if( p_pgrm->i_synchro_state != SYNCHRO_OK )
 148     {
 149         /* Feed synchro with a new reference point. */
 150         ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
 151         p_pgrm->i_synchro_state = SYNCHRO_OK;
 152     }
 153     else
 154     {
 155         if ( p_pgrm->last_cr != 0 &&
 156                (    (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
 157                  || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
 158         {
 159             /* Stream discontinuity, for which we haven't received a
 160              * warning from the stream control facilities (dd-edited
 161              * stream ?). */
 162             intf_WarnMsg( 3, "Clock gap, unexpected stream discontinuity" );
 163             input_ClockInit( p_pgrm );
 164             p_pgrm->i_synchro_state = SYNCHRO_START;
 165             input_EscapeDiscontinuity( p_input, p_pgrm );
 166         }
 167
 168         p_pgrm->last_cr = i_clock;
 169
 170         if( p_input->stream.b_pace_control
 171              && p_input->stream.pp_programs[0] == p_pgrm )
 172         {
 173             /* Wait a while before delivering the packets to the decoder.
 174              * In case of multiple programs, we arbitrarily follow the
 175              * clock of the first program. */
 176             mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
 177
 178             /* Now take into account interface changes. */
 179             vlc_mutex_lock( &p_input->stream.stream_lock );
 180             if( p_input->stream.i_new_status != UNDEF_S )
 181             {
 182                 if( p_input->stream.i_new_status == PAUSE_S )
 183                 {
 184                     vlc_cond_wait( &p_input->stream.stream_wait,
 185                                    &p_input->stream.stream_lock );
 186                     ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
 187                 }
 188                 else
 189                 {
 190                     ClockNewRef( p_input, p_pgrm, i_clock,
 191                                ClockToSysdate( p_input, p_pgrm, i_clock ) );
 192                 }
 193
 194                 vlc_mutex_lock( &p_input->stream.control.control_lock );
 195                 p_input->stream.control.i_status = p_input->stream.i_new_status;
 196
 197                 if( p_input->stream.control.i_status != PLAYING_S
 198                      && p_input->stream.control.i_status != PAUSE_S )
 199                 {
 200                     p_input->stream.control.i_rate = p_input->stream.i_new_rate;
 201                     p_input->stream.control.b_mute = 1;
 202
 203                     /* Feed the audio decoders with a NULL packet to avoid
 204                      * discontinuities. */
 205                     input_EscapeAudioDiscontinuity( p_input, p_pgrm );
 206                 }
 207                 else
 208                 {
 209                     p_input->stream.control.i_rate = DEFAULT_RATE;
 210                     p_input->stream.control.b_mute = 0;
 211                 }
 212                 vlc_mutex_unlock( &p_input->stream.control.control_lock );
 213
 214                 p_input->stream.i_new_status = UNDEF_S;
 215                 p_input->stream.i_new_rate = UNDEF_S;
 216             }
 217             vlc_mutex_unlock( &p_input->stream.stream_lock );
 218         }
 219         else
 220         {
 221             /* Smooth clock reference variations. */
 222             mtime_t     i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
 223
 224             /* Bresenham algorithm to smooth variations. */
 225             if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
 226             {
 227                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 228                                         * (CR_MAX_AVERAGE_COUNTER - 1)
 229                                       + i_extrapoled_clock )
 230                                     / CR_MAX_AVERAGE_COUNTER;
 231             }
 232             else
 233             {
 234                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 235                                         * p_pgrm->c_average_count
 236                                       + i_extrapoled_clock )
 237                                     / (p_pgrm->c_average_count + 1);
 238                 p_pgrm->c_average_count++;
 239             }
 240         }
 241     }
 242 }
 243
 244 /*****************************************************************************
 245  * input_ClockGetTS: manages a PTS or DTS
 246  *****************************************************************************/
 247 mtime_t input_ClockGetTS( input_thread_t * p_input,
 248                           pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
 249 {
 250     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
 251     {
 252         return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
 253                  + DEFAULT_PTS_DELAY );
 254     }
 255     else
 256     {
 257         return 0;
 258     }
 259 }
 260