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)
69 /*****************************************************************************
71 *****************************************************************************/
73 /* Maximum gap allowed between two CRs. */
74 #define CR_MAX_GAP (INT64_C(2000000)*100/9)
76 /* Latency introduced on DVDs with CR == 0 on chapter change - this is from
78 #define CR_MEAN_PTS_GAP 300000
80 /*****************************************************************************
81 * ClockToSysdate: converts a movie clock to system date
82 *****************************************************************************/
83 static mtime_t ClockToSysdate( input_clock_t *cl, mtime_t i_clock )
85 if( !cl->b_has_reference )
88 return (i_clock - cl->cr_ref) * cl->i_rate / INPUT_RATE_DEFAULT +
92 /*****************************************************************************
93 * ClockFromSysdate: converts a system date to movie clock
94 *****************************************************************************
95 * Caution : a valid reference point is needed for this to operate.
96 *****************************************************************************/
97 static mtime_t ClockFromSysdate( input_clock_t *cl, mtime_t i_ck_system )
99 assert( cl->b_has_reference );
100 return ( i_ck_system - cl->sysdate_ref ) * INPUT_RATE_DEFAULT / cl->i_rate +
104 /*****************************************************************************
105 * ClockNewRef: writes a new clock reference
106 *****************************************************************************/
107 static void ClockNewRef( input_clock_t *cl,
108 mtime_t i_clock, mtime_t i_sysdate )
110 cl->b_has_reference = true;
111 cl->cr_ref = i_clock;
112 cl->sysdate_ref = i_sysdate ;
115 /*****************************************************************************
116 * input_ClockInit: reinitializes the clock reference after a stream
118 *****************************************************************************/
119 void input_ClockInit( input_clock_t *cl, bool b_master, int i_cr_average, int i_rate )
121 cl->b_has_reference = false;
125 cl->last_sysdate = 0;
129 cl->i_delta_cr_residue = 0;
132 cl->i_cr_average = i_cr_average;
134 cl->b_master = b_master;
137 /*****************************************************************************
138 * input_ClockSetPCR: manages a clock reference
140 * i_ck_stream: date in stream clock
141 * i_ck_system: date in system clock
142 *****************************************************************************/
143 void input_ClockSetPCR( input_thread_t *p_input,
145 mtime_t i_ck_stream, mtime_t i_ck_system )
147 const bool b_synchronize = p_input->b_can_pace_control && cl->b_master;
148 bool b_reset_reference = false;
150 if( ( !cl->b_has_reference ) ||
151 ( i_ck_stream == 0 && cl->last_cr != 0 ) )
156 b_reset_reference= true;
158 else if ( cl->last_cr != 0 &&
159 ( (cl->last_cr - i_ck_stream) > CR_MAX_GAP ||
160 (cl->last_cr - i_ck_stream) < - CR_MAX_GAP ) )
162 /* Stream discontinuity, for which we haven't received a
163 * warning from the stream control facilities (dd-edited
165 msg_Warn( p_input, "clock gap, unexpected stream discontinuity" );
169 msg_Warn( p_input, "feeding synchro with a new reference point trying to recover from clock gap" );
170 b_reset_reference= true;
172 if( b_reset_reference )
175 cl->i_delta_cr_residue = 0;
177 /* Feed synchro with a new reference point. */
178 ClockNewRef( cl, i_ck_stream,
179 __MAX( cl->last_pts + CR_MEAN_PTS_GAP, i_ck_system ) );
182 cl->last_cr = i_ck_stream;
183 cl->last_sysdate = i_ck_system;
185 if( !b_synchronize && i_ck_system - cl->last_update > 200000 )
187 /* Smooth clock reference variations. */
188 const mtime_t i_extrapoled_clock = ClockFromSysdate( cl, i_ck_system );
189 /* Bresenham algorithm to smooth variations. */
190 const mtime_t i_tmp = cl->delta_cr * (cl->i_cr_average - 1) +
191 ( i_extrapoled_clock - i_ck_stream ) * 1 +
192 cl->i_delta_cr_residue;
194 cl->i_delta_cr_residue = i_tmp % cl->i_cr_average;
195 cl->delta_cr = i_tmp / cl->i_cr_average;
197 cl->last_update = i_ck_system;
201 /*****************************************************************************
202 * input_ClockResetPCR:
203 *****************************************************************************/
204 void input_ClockResetPCR( input_clock_t *cl )
206 cl->b_has_reference = false;
210 /*****************************************************************************
211 * input_ClockGetTS: manages a PTS or DTS
212 *****************************************************************************/
213 mtime_t input_ClockGetTS( input_thread_t * p_input,
214 input_clock_t *cl, mtime_t i_ts )
216 if( !cl->b_has_reference )
219 cl->last_pts = ClockToSysdate( cl, i_ts + cl->delta_cr );
220 return cl->last_pts + p_input->i_pts_delay;
223 /*****************************************************************************
224 * input_ClockSetRate:
225 *****************************************************************************/
226 void input_ClockSetRate( input_clock_t *cl, int i_rate )
228 /* Move the reference point */
229 if( cl->b_has_reference )
230 ClockNewRef( cl, cl->last_cr, cl->last_sysdate );
235 /*****************************************************************************
236 * input_ClockGetWakeup
237 *****************************************************************************/
238 mtime_t input_ClockGetWakeup( input_thread_t *p_input, input_clock_t *cl )
240 /* Not synchronized, we cannot wait */
241 if( !cl->b_has_reference )
244 /* We must not wait if not pace controled, or we are not the
246 if( !p_input->b_can_pace_control || !cl->b_master ||
247 p_input->p->b_out_pace_control )
251 return ClockToSysdate( cl, cl->last_cr );