1 /*****************************************************************************
2 * input_clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999-2004 the VideoLAN team
7 * Authors: Christophe Massiot <massiot@via.ecp.fr>
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.
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.
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., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
22 *****************************************************************************/
24 /*****************************************************************************
26 *****************************************************************************/
31 #include <vlc_common.h>
33 #include "input_internal.h"
36 * DISCUSSION : SYNCHRONIZATION METHOD
38 * In some cases we can impose the pace of reading (when reading from a
39 * file or a pipe), and for the synchronization we simply sleep() until
40 * it is time to deliver the packet to the decoders. When reading from
41 * the network, we must be read at the same pace as the server writes,
42 * otherwise the kernel's buffer will trash packets. The risk is now to
43 * overflow the input buffers in case the server goes too fast, that is
44 * why we do these calculations :
46 * We compute a mean for the pcr because we want to eliminate the
47 * network jitter and keep the low frequency variations. The mean is
48 * in fact a low pass filter and the jitter is a high frequency signal
49 * that is why it is eliminated by the filter/average.
51 * The low frequency variations enable us to synchronize the client clock
52 * with the server clock because they represent the time variation between
53 * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
54 * the presentation dates for the audio and video frames. With those dates
55 * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
56 * as it is sent by the server and so we keep the synchronization between
57 * the server and the client.
59 * It is a very important matter if you want to avoid underflow or overflow
60 * in all the FIFOs, but it may be not enough.
63 /* p_input->p->i_cr_average : Maximum number of samples used to compute the
64 * dynamic average value.
65 * We use the following formula :
66 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
70 static void ClockNewRef( input_clock_t * p_pgrm,
71 mtime_t i_clock, mtime_t i_sysdate );
73 /*****************************************************************************
75 *****************************************************************************/
77 /* Maximum gap allowed between two CRs. */
78 #define CR_MAX_GAP (INT64_C(2000000)*100/9)
80 /* Latency introduced on DVDs with CR == 0 on chapter change - this is from
82 #define CR_MEAN_PTS_GAP 300000
84 /*****************************************************************************
85 * ClockToSysdate: converts a movie clock to system date
86 *****************************************************************************/
87 static mtime_t ClockToSysdate( input_clock_t *cl, mtime_t i_clock )
89 if( cl->i_synchro_state != SYNCHRO_OK )
92 return (i_clock - cl->cr_ref) * cl->i_rate / INPUT_RATE_DEFAULT +
96 /*****************************************************************************
97 * ClockCurrent: converts current system date to clock units
98 *****************************************************************************
99 * Caution : the synchro state must be SYNCHRO_OK for this to operate.
100 *****************************************************************************/
101 static mtime_t ClockCurrent( input_clock_t *cl )
103 return (mdate() - cl->sysdate_ref) * INPUT_RATE_DEFAULT / cl->i_rate +
107 /*****************************************************************************
108 * ClockNewRef: writes a new clock reference
109 *****************************************************************************/
110 static void ClockNewRef( input_clock_t *cl,
111 mtime_t i_clock, mtime_t i_sysdate )
113 cl->cr_ref = i_clock;
114 cl->sysdate_ref = i_sysdate ;
117 /*****************************************************************************
118 * input_ClockInit: reinitializes the clock reference after a stream
120 *****************************************************************************/
121 void input_ClockInit( input_clock_t *cl, bool b_master, int i_cr_average, int i_rate )
123 cl->i_synchro_state = SYNCHRO_START;
127 cl->last_sysdate = 0;
131 cl->i_delta_cr_residue = 0;
134 cl->i_cr_average = i_cr_average;
136 cl->b_master = b_master;
139 /*****************************************************************************
140 * input_ClockSetPCR: manages a clock reference
141 *****************************************************************************/
142 void input_ClockSetPCR( input_thread_t *p_input,
143 input_clock_t *cl, mtime_t i_clock )
145 const bool b_synchronize = p_input->b_can_pace_control && cl->b_master;
146 const mtime_t i_mdate = mdate();
148 if( ( cl->i_synchro_state != SYNCHRO_OK ) ||
149 ( i_clock == 0 && cl->last_cr != 0 ) )
151 /* Feed synchro with a new reference point. */
152 ClockNewRef( cl, i_clock,
153 __MAX( cl->last_pts + CR_MEAN_PTS_GAP, i_mdate ) );
154 cl->i_synchro_state = SYNCHRO_OK;
159 cl->i_delta_cr_residue = 0;
163 else if ( cl->last_cr != 0 &&
164 ( (cl->last_cr - i_clock) > CR_MAX_GAP ||
165 (cl->last_cr - i_clock) < - CR_MAX_GAP ) )
167 /* Stream discontinuity, for which we haven't received a
168 * warning from the stream control facilities (dd-edited
170 msg_Warn( p_input, "clock gap, unexpected stream discontinuity" );
171 input_ClockInit( cl, cl->b_master, cl->i_cr_average, cl->i_rate );
172 /* Feed synchro with a new reference point. */
173 msg_Warn( p_input, "feeding synchro with a new reference point trying to recover from clock gap" );
174 ClockNewRef( cl, i_clock,
175 __MAX( cl->last_pts + CR_MEAN_PTS_GAP, i_mdate ) );
176 cl->i_synchro_state = SYNCHRO_OK;
179 cl->last_cr = i_clock;
180 cl->last_sysdate = i_mdate;
184 /* Wait a while before delivering the packets to the decoder.
185 * In case of multiple programs, we arbitrarily follow the
186 * clock of the selected program. */
187 if( !p_input->p->b_out_pace_control )
189 mtime_t i_wakeup = ClockToSysdate( cl, i_clock );
190 while( (i_wakeup - mdate()) / CLOCK_FREQ > 1 )
192 msleep( CLOCK_FREQ );
193 if( p_input->b_die ) i_wakeup = mdate();
198 else if ( i_mdate - cl->last_update > 200000 )
200 /* Smooth clock reference variations. */
201 const mtime_t i_extrapoled_clock = ClockCurrent( cl );
202 /* Bresenham algorithm to smooth variations. */
203 const mtime_t i_tmp = cl->delta_cr * (cl->i_cr_average - 1) +
204 ( i_extrapoled_clock - i_clock ) * 1 +
205 cl->i_delta_cr_residue;
207 cl->i_delta_cr_residue = i_tmp % cl->i_cr_average;
208 cl->delta_cr = i_tmp / cl->i_cr_average;
210 cl->last_update = i_mdate;
214 /*****************************************************************************
215 * input_ClockResetPCR:
216 *****************************************************************************/
217 void input_ClockResetPCR( input_clock_t *cl )
219 cl->i_synchro_state = SYNCHRO_REINIT;
223 /*****************************************************************************
224 * input_ClockGetTS: manages a PTS or DTS
225 *****************************************************************************/
226 mtime_t input_ClockGetTS( input_thread_t * p_input,
227 input_clock_t *cl, mtime_t i_ts )
229 if( cl->i_synchro_state != SYNCHRO_OK )
232 cl->last_pts = ClockToSysdate( cl, i_ts + cl->delta_cr );
233 return cl->last_pts + p_input->i_pts_delay;
236 /*****************************************************************************
237 * input_ClockSetRate:
238 *****************************************************************************/
239 void input_ClockSetRate( input_clock_t *cl, int i_rate )
241 /* Move the reference point */
242 if( cl->i_synchro_state == SYNCHRO_OK )
243 ClockNewRef( cl, cl->last_cr, cl->last_sysdate );