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 *****************************************************************************/
86 * This structure holds long term average
96 static void AvgInit( average_t *, int i_divider );
97 static void AvgClean( average_t * );
99 static void AvgReset( average_t * );
100 static void AvgUpdate( average_t *, mtime_t i_value );
101 static mtime_t AvgGet( average_t * );
106 /* Reference point */
107 bool b_has_reference;
115 * It is used to detect unexpected stream discontinuities */
122 /* Maximal timestamp returned by input_clock_GetTS (in system unit) */
126 mtime_t i_next_drift_update;
129 /* Current modifiers */
134 static mtime_t ClockStreamToSystem( input_clock_t *, mtime_t i_clock );
135 static mtime_t ClockSystemToStream( input_clock_t *, mtime_t i_system );
136 static void ClockSetReference( input_clock_t *, mtime_t i_clock, mtime_t i_system );
138 /*****************************************************************************
139 * input_clock_New: create a new clock
140 *****************************************************************************/
141 input_clock_t *input_clock_New( bool b_master, int i_cr_average, int i_rate )
143 input_clock_t *cl = malloc( sizeof(*cl) );
147 cl->b_has_reference = false;
149 cl->ref.i_system = 0;
151 cl->last.i_clock = 0;
152 cl->last.i_system = 0;
156 cl->i_next_drift_update = 0;
157 AvgInit( &cl->drift, i_cr_average );
159 cl->b_master = b_master;
165 /*****************************************************************************
166 * input_clock_Delete: destroy a new clock
167 *****************************************************************************/
168 void input_clock_Delete( input_clock_t *cl )
170 AvgClean( &cl->drift );
174 /*****************************************************************************
175 * input_clock_Update: manages a clock reference
177 * i_ck_stream: date in stream clock
178 * i_ck_system: date in system clock
179 *****************************************************************************/
180 void input_clock_Update( input_clock_t *cl,
181 vlc_object_t *p_log, bool b_can_pace_control,
182 mtime_t i_ck_stream, mtime_t i_ck_system )
184 const bool b_synchronize = b_can_pace_control && cl->b_master;
185 bool b_reset_reference = false;
187 if( ( !cl->b_has_reference ) ||
188 ( i_ck_stream == 0 && cl->last.i_clock != 0 ) )
191 b_reset_reference= true;
193 else if( cl->last.i_clock != 0 &&
194 ( (cl->last.i_clock - i_ck_stream) > CR_MAX_GAP ||
195 (cl->last.i_clock - i_ck_stream) < -CR_MAX_GAP ) )
197 /* Stream discontinuity, for which we haven't received a
198 * warning from the stream control facilities (dd-edited
200 msg_Warn( p_log, "clock gap, unexpected stream discontinuity" );
204 msg_Warn( p_log, "feeding synchro with a new reference point trying to recover from clock gap" );
205 b_reset_reference= true;
207 if( b_reset_reference )
209 cl->i_next_drift_update = 0;
210 AvgReset( &cl->drift );
212 /* Feed synchro with a new reference point. */
213 ClockSetReference( cl, i_ck_stream,
214 __MAX( cl->i_ts_max + CR_MEAN_PTS_GAP, i_ck_system ) );
217 if( !b_synchronize && cl->i_next_drift_update < i_ck_system )
219 const mtime_t i_converted = ClockSystemToStream( cl, i_ck_system );
221 AvgUpdate( &cl->drift, i_converted - i_ck_stream );
223 cl->i_next_drift_update = i_ck_system + CLOCK_FREQ/5; /* FIXME why that */
225 cl->last.i_clock = i_ck_stream;
226 cl->last.i_system = i_ck_system;
229 /*****************************************************************************
230 * input_clock_ResetPCR:
231 *****************************************************************************/
232 void input_clock_ResetPCR( input_clock_t *cl )
234 cl->b_has_reference = false;
238 /*****************************************************************************
239 * input_clock_GetTS: manages a PTS or DTS
240 *****************************************************************************/
241 mtime_t input_clock_GetTS( input_clock_t *cl,
242 mtime_t i_pts_delay, mtime_t i_ts )
244 mtime_t i_converted_ts;
246 if( !cl->b_has_reference )
250 i_converted_ts = ClockStreamToSystem( cl, i_ts + AvgGet( &cl->drift ) );
251 if( i_converted_ts > cl->i_ts_max )
252 cl->i_ts_max = i_converted_ts;
254 return i_converted_ts + i_pts_delay;
257 /*****************************************************************************
258 * input_clock_ChangeRate:
259 *****************************************************************************/
260 void input_clock_ChangeRate( input_clock_t *cl, int i_rate )
262 /* Move the reference point */
263 if( cl->b_has_reference )
264 ClockSetReference( cl, cl->last.i_clock, cl->last.i_system );
269 /*****************************************************************************
270 * input_clock_ChangeMaster:
271 *****************************************************************************/
272 void input_clock_ChangeMaster( input_clock_t *cl, bool b_master )
274 cl->b_master = b_master;
277 /*****************************************************************************
278 * input_clock_GetWakeup
279 *****************************************************************************/
280 mtime_t input_clock_GetWakeup( input_clock_t *cl )
282 /* Not synchronized, we cannot wait */
283 if( !cl->b_has_reference )
286 /* We must not wait if we are not the master clock */
291 return ClockStreamToSystem( cl, cl->last.i_clock );
294 /*****************************************************************************
295 * ClockStreamToSystem: converts a movie clock to system date
296 *****************************************************************************/
297 static mtime_t ClockStreamToSystem( input_clock_t *cl, mtime_t i_clock )
299 if( !cl->b_has_reference )
302 return ( i_clock - cl->ref.i_clock ) * cl->i_rate / INPUT_RATE_DEFAULT +
306 /*****************************************************************************
307 * ClockSystemToStream: converts a system date to movie clock
308 *****************************************************************************
309 * Caution : a valid reference point is needed for this to operate.
310 *****************************************************************************/
311 static mtime_t ClockSystemToStream( input_clock_t *cl, mtime_t i_system )
313 assert( cl->b_has_reference );
314 return ( i_system - cl->ref.i_system ) * INPUT_RATE_DEFAULT / cl->i_rate +
318 /*****************************************************************************
319 * ClockSetReference: writes a new clock reference
320 *****************************************************************************/
321 static void ClockSetReference( input_clock_t *cl,
322 mtime_t i_clock, mtime_t i_system )
324 cl->b_has_reference = true;
325 cl->ref.i_clock = i_clock;
326 cl->ref.i_system = i_system;
329 /*****************************************************************************
330 * Long term average helpers
331 *****************************************************************************/
332 static void AvgInit( average_t *p_avg, int i_divider )
334 p_avg->i_divider = i_divider;
337 static void AvgClean( average_t *p_avg )
341 static void AvgReset( average_t *p_avg )
344 p_avg->i_residue = 0;
347 static void AvgUpdate( average_t *p_avg, mtime_t i_value )
349 const int i_f0 = __MIN( p_avg->i_divider - 1, p_avg->i_count );
350 const int i_f1 = p_avg->i_divider - i_f0;
352 const mtime_t i_tmp = i_f0 * p_avg->i_value + i_f1 * i_value + p_avg->i_residue;
354 p_avg->i_value = i_tmp / p_avg->i_divider;
355 p_avg->i_residue = i_tmp % p_avg->i_divider;
359 static mtime_t AvgGet( average_t *p_avg )
361 return p_avg->i_value;