1 /*****************************************************************************
2 * input_clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999-2008 the VideoLAN team
7 * Authors: Christophe Massiot <massiot@via.ecp.fr>
8 * Laurent Aimar < fenrir _AT_ videolan _DOT_ org >
10 * This program is free software; you can redistribute it and/or modify
11 * it under the terms of the GNU General Public License as published by
12 * the Free Software Foundation; either version 2 of the License, or
13 * (at your option) any later version.
15 * This program is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 * GNU General Public License for more details.
20 * You should have received a copy of the GNU General Public License
21 * along with this program; if not, write to the Free Software
22 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
23 *****************************************************************************/
25 /*****************************************************************************
27 *****************************************************************************/
32 #include <vlc_common.h>
33 #include <vlc_input.h>
34 #include "input_clock.h"
37 * DISCUSSION : SYNCHRONIZATION METHOD
39 * In some cases we can impose the pace of reading (when reading from a
40 * file or a pipe), and for the synchronization we simply sleep() until
41 * it is time to deliver the packet to the decoders. When reading from
42 * the network, we must be read at the same pace as the server writes,
43 * otherwise the kernel's buffer will trash packets. The risk is now to
44 * overflow the input buffers in case the server goes too fast, that is
45 * why we do these calculations :
47 * We compute a mean for the pcr because we want to eliminate the
48 * network jitter and keep the low frequency variations. The mean is
49 * in fact a low pass filter and the jitter is a high frequency signal
50 * that is why it is eliminated by the filter/average.
52 * The low frequency variations enable us to synchronize the client clock
53 * with the server clock because they represent the time variation between
54 * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
55 * the presentation dates for the audio and video frames. With those dates
56 * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
57 * as it is sent by the server and so we keep the synchronization between
58 * the server and the client.
60 * It is a very important matter if you want to avoid underflow or overflow
61 * in all the FIFOs, but it may be not enough.
64 /* p_input->p->i_cr_average : Maximum number of samples used to compute the
65 * dynamic average value.
66 * We use the following formula :
67 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
70 /*****************************************************************************
72 *****************************************************************************/
74 /* Maximum gap allowed between two CRs. */
75 #define CR_MAX_GAP (INT64_C(2000000)*100/9)
77 /* Latency introduced on DVDs with CR == 0 on chapter change - this is from
79 #define CR_MEAN_PTS_GAP (300000)
81 /*****************************************************************************
83 *****************************************************************************/
95 * It is used to detect unexpected stream discontinuities */
102 /* Maixmal timestamp returned by input_clock_GetTS (in system unit) */
106 mtime_t i_delta_update; /* System time to wait for drift update */
110 /* Current modifiers */
114 /* Static configuration */
118 static mtime_t ClockStreamToSystem( input_clock_t *, mtime_t i_clock );
119 static mtime_t ClockSystemToStream( input_clock_t *, mtime_t i_system );
120 static void ClockSetReference( input_clock_t *, mtime_t i_clock, mtime_t i_system );
122 /*****************************************************************************
123 * input_clock_New: create a new clock
124 *****************************************************************************/
125 input_clock_t *input_clock_New( bool b_master, int i_cr_average, int i_rate )
127 input_clock_t *cl = malloc( sizeof(*cl) );
131 cl->b_has_reference = false;
133 cl->ref.i_system = 0;
135 cl->last.i_clock = 0;
136 cl->last.i_system = 0;
141 cl->i_delta_residue = 0;
143 cl->b_master = b_master;
146 cl->i_cr_average = i_cr_average;
151 /*****************************************************************************
152 * input_clock_Delete: destroy a new clock
153 *****************************************************************************/
154 void input_clock_Delete( input_clock_t *cl )
159 /*****************************************************************************
160 * input_clock_SetPCR: manages a clock reference
162 * i_ck_stream: date in stream clock
163 * i_ck_system: date in system clock
164 *****************************************************************************/
165 void input_clock_SetPCR( input_clock_t *cl,
166 vlc_object_t *p_log, bool b_can_pace_control,
167 mtime_t i_ck_stream, mtime_t i_ck_system )
169 const bool b_synchronize = b_can_pace_control && cl->b_master;
170 bool b_reset_reference = false;
172 if( ( !cl->b_has_reference ) ||
173 ( i_ck_stream == 0 && cl->last.i_clock != 0 ) )
175 cl->i_delta_update = 0;
178 b_reset_reference= true;
180 else if( cl->last.i_clock != 0 &&
181 ( (cl->last.i_clock - i_ck_stream) > CR_MAX_GAP ||
182 (cl->last.i_clock - i_ck_stream) < -CR_MAX_GAP ) )
184 /* Stream discontinuity, for which we haven't received a
185 * warning from the stream control facilities (dd-edited
187 msg_Warn( p_log, "clock gap, unexpected stream discontinuity" );
191 msg_Warn( p_log, "feeding synchro with a new reference point trying to recover from clock gap" );
192 b_reset_reference= true;
194 if( b_reset_reference )
197 cl->i_delta_residue = 0;
199 /* Feed synchro with a new reference point. */
200 ClockSetReference( cl, i_ck_stream,
201 __MAX( cl->i_ts_max + CR_MEAN_PTS_GAP, i_ck_system ) );
204 cl->last.i_clock = i_ck_stream;
205 cl->last.i_system = i_ck_system;
207 if( !b_synchronize && i_ck_system - cl->i_delta_update > 200000 )
209 /* Smooth clock reference variations. */
210 const mtime_t i_extrapoled_clock = ClockSystemToStream( cl, i_ck_system );
211 /* Bresenham algorithm to smooth variations. */
212 const mtime_t i_tmp = cl->i_delta * (cl->i_cr_average - 1) +
213 ( i_extrapoled_clock - i_ck_stream ) * 1 +
216 cl->i_delta_residue = i_tmp % cl->i_cr_average;
217 cl->i_delta = i_tmp / cl->i_cr_average;
219 cl->i_delta_update = i_ck_system;
223 /*****************************************************************************
224 * input_clock_ResetPCR:
225 *****************************************************************************/
226 void input_clock_ResetPCR( input_clock_t *cl )
228 cl->b_has_reference = false;
232 /*****************************************************************************
233 * input_clock_GetTS: manages a PTS or DTS
234 *****************************************************************************/
235 mtime_t input_clock_GetTS( input_clock_t *cl,
236 mtime_t i_pts_delay, mtime_t i_ts )
238 mtime_t i_converted_ts;
240 if( !cl->b_has_reference )
244 i_converted_ts = ClockStreamToSystem( cl, i_ts + cl->i_delta );
245 if( i_converted_ts > cl->i_ts_max )
246 cl->i_ts_max = i_converted_ts;
248 return i_converted_ts + i_pts_delay;
251 /*****************************************************************************
252 * input_clock_SetRate:
253 *****************************************************************************/
254 void input_clock_SetRate( input_clock_t *cl, int i_rate )
256 /* Move the reference point */
257 if( cl->b_has_reference )
258 ClockSetReference( cl, cl->last.i_clock, cl->last.i_system );
263 /*****************************************************************************
264 * input_clock_SetMaster:
265 *****************************************************************************/
266 void input_clock_SetMaster( input_clock_t *cl, bool b_master )
268 cl->b_master = b_master;
271 /*****************************************************************************
272 * input_clock_GetWakeup
273 *****************************************************************************/
274 mtime_t input_clock_GetWakeup( input_clock_t *cl )
276 /* Not synchronized, we cannot wait */
277 if( !cl->b_has_reference )
280 /* We must not wait if we are not the master clock */
285 return ClockStreamToSystem( cl, cl->last.i_clock );
288 /*****************************************************************************
289 * ClockStreamToSystem: converts a movie clock to system date
290 *****************************************************************************/
291 static mtime_t ClockStreamToSystem( input_clock_t *cl, mtime_t i_clock )
293 if( !cl->b_has_reference )
296 return ( i_clock - cl->ref.i_clock ) * cl->i_rate / INPUT_RATE_DEFAULT +
300 /*****************************************************************************
301 * ClockSystemToStream: converts a system date to movie clock
302 *****************************************************************************
303 * Caution : a valid reference point is needed for this to operate.
304 *****************************************************************************/
305 static mtime_t ClockSystemToStream( input_clock_t *cl, mtime_t i_system )
307 assert( cl->b_has_reference );
308 return ( i_system - cl->ref.i_system ) * INPUT_RATE_DEFAULT / cl->i_rate +
312 /*****************************************************************************
313 * ClockSetReference: writes a new clock reference
314 *****************************************************************************/
315 static void ClockSetReference( input_clock_t *cl,
316 mtime_t i_clock, mtime_t i_system )
318 cl->b_has_reference = true;
319 cl->ref.i_clock = i_clock;
320 cl->ref.i_system = i_system;