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 1.8 2001/03/14 00:40:24 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 = (mtime_t)(i_clock - p_pgrm->cr_ref)
  93                         * (mtime_t)p_input->stream.control.i_rate
  94                         * (mtime_t)300
  95                         / (mtime_t)27
  96                         / (mtime_t)DEFAULT_RATE
  97                         + (mtime_t)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  * ClockNewRef: writes a new clock reference
 118  *****************************************************************************/
 119 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
 120                          mtime_t i_clock, mtime_t i_sysdate )
 121 {
 122     p_pgrm->cr_ref = i_clock;
 123     p_pgrm->sysdate_ref = i_sysdate;
 124 }
 125
 126 /*****************************************************************************
 127  * input_ClockInit: reinitializes the clock reference after a stream
 128  *                  discontinuity
 129  *****************************************************************************/
 130 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
 131 {
 132     p_pgrm->last_cr = 0;
 133     p_pgrm->cr_ref = 0;
 134     p_pgrm->sysdate_ref = 0;
 135     p_pgrm->delta_cr = 0;
 136     p_pgrm->c_average_count = 0;
 137 }
 138
 139 /*****************************************************************************
 140  * input_ClockManageRef: manages a clock reference
 141  *****************************************************************************/
 142 void input_ClockManageRef( input_thread_t * p_input,
 143                            pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
 144 {
 145     if( p_pgrm->i_synchro_state != SYNCHRO_OK )
 146     {
 147         /* Feed synchro with a new reference point. */
 148         ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
 149         p_pgrm->i_synchro_state = SYNCHRO_OK;
 150     }
 151     else
 152     {
 153         if ( p_pgrm->last_cr != 0 &&
 154                (    (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
 155                  || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
 156         {
 157             /* Stream discontinuity, for which we haven't received a
 158              * warning from the stream control facilities (dd-edited
 159              * stream ?). */
 160             intf_WarnMsg( 3, "Clock gap, unexpected stream discontinuity" );
 161             input_ClockInit( p_pgrm );
 162             p_pgrm->i_synchro_state = SYNCHRO_START;
 163             input_EscapeDiscontinuity( p_input, p_pgrm );
 164         }
 165
 166         p_pgrm->last_cr = i_clock;
 167
 168         if( p_input->stream.b_pace_control
 169              && p_input->stream.pp_programs[0] == p_pgrm )
 170         {
 171             /* Wait a while before delivering the packets to the decoder.
 172              * In case of multiple programs, we arbitrarily follow the
 173              * clock of the first program. */
 174             mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
 175
 176             /* Now take into account interface changes. */
 177             vlc_mutex_lock( &p_input->stream.stream_lock );
 178             if( p_input->stream.i_new_status != UNDEF_S )
 179             {
 180                 if( p_input->stream.i_new_status == PAUSE_S )
 181                 {
 182                     vlc_cond_wait( &p_input->stream.stream_wait,
 183                                    &p_input->stream.stream_lock );
 184                     ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
 185                 }
 186                 else
 187                 {
 188                     ClockNewRef( p_input, p_pgrm, i_clock,
 189                                ClockToSysdate( p_input, p_pgrm, i_clock ) );
 190                 }
 191
 192                 vlc_mutex_lock( &p_input->stream.control.control_lock );
 193                 p_input->stream.control.i_status = p_input->stream.i_new_status;
 194
 195                 if( p_input->stream.control.i_status != PLAYING_S
 196                      && p_input->stream.control.i_status != PAUSE_S )
 197                 {
 198                     p_input->stream.control.i_rate = p_input->stream.i_new_rate;
 199                     p_input->stream.control.b_mute = 1;
 200
 201                     /* Feed the audio decoders with a NULL packet to avoid
 202                      * discontinuities. */
 203                     input_EscapeAudioDiscontinuity( p_input, p_pgrm );
 204                 }
 205                 else
 206                 {
 207                     p_input->stream.control.i_rate = DEFAULT_RATE;
 208                     p_input->stream.control.b_mute = 0;
 209                 }
 210                 vlc_mutex_unlock( &p_input->stream.control.control_lock );
 211
 212                 p_input->stream.i_new_status = UNDEF_S;
 213                 p_input->stream.i_new_rate = UNDEF_S;
 214             }
 215             vlc_mutex_unlock( &p_input->stream.stream_lock );
 216         }
 217         else
 218         {
 219             /* Smooth clock reference variations. */
 220             mtime_t     i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
 221
 222             /* Bresenham algorithm to smooth variations. */
 223             if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
 224             {
 225                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 226                                         * (CR_MAX_AVERAGE_COUNTER - 1)
 227                                       + i_extrapoled_clock )
 228                                     / CR_MAX_AVERAGE_COUNTER;
 229             }
 230             else
 231             {
 232                 p_pgrm->delta_cr = ( p_pgrm->delta_cr
 233                                         * p_pgrm->c_average_count
 234                                       + i_extrapoled_clock )
 235                                     / (p_pgrm->c_average_count + 1);
 236                 p_pgrm->c_average_count++;
 237             }
 238         }
 239     }
 240 }
 241
 242 /*****************************************************************************
 243  * input_ClockGetTS: manages a PTS or DTS
 244  *****************************************************************************/
 245 mtime_t input_ClockGetTS( input_thread_t * p_input,
 246                           pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
 247 {
 248     if( p_pgrm->i_synchro_state == SYNCHRO_OK )
 249     {
 250         return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
 251                  + DEFAULT_PTS_DELAY );
 252     }
 253     else
 254     {
 255         return 0;
 256     }
 257 }
 258