1 /*****************************************************************************
2 * clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999-2008 the VideoLAN team
5 * Copyright (C) 2008 Laurent Aimar
8 * Authors: Christophe Massiot <massiot@via.ecp.fr>
9 * Laurent Aimar < fenrir _AT_ videolan _DOT_ org >
11 * This program is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU General Public License as published by
13 * the Free Software Foundation; either version 2 of the License, or
14 * (at your option) any later version.
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
24 *****************************************************************************/
26 /*****************************************************************************
28 *****************************************************************************/
33 #include <vlc_common.h>
34 #include <vlc_input.h>
39 * - clean up locking once clock code is stable
44 * DISCUSSION : SYNCHRONIZATION METHOD
46 * In some cases we can impose the pace of reading (when reading from a
47 * file or a pipe), and for the synchronization we simply sleep() until
48 * it is time to deliver the packet to the decoders. When reading from
49 * the network, we must be read at the same pace as the server writes,
50 * otherwise the kernel's buffer will trash packets. The risk is now to
51 * overflow the input buffers in case the server goes too fast, that is
52 * why we do these calculations :
54 * We compute a mean for the pcr because we want to eliminate the
55 * network jitter and keep the low frequency variations. The mean is
56 * in fact a low pass filter and the jitter is a high frequency signal
57 * that is why it is eliminated by the filter/average.
59 * The low frequency variations enable us to synchronize the client clock
60 * with the server clock because they represent the time variation between
61 * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
62 * the presentation dates for the audio and video frames. With those dates
63 * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
64 * as it is sent by the server and so we keep the synchronization between
65 * the server and the client.
67 * It is a very important matter if you want to avoid underflow or overflow
68 * in all the FIFOs, but it may be not enough.
71 /* i_cr_average : Maximum number of samples used to compute the
72 * dynamic average value.
73 * We use the following formula :
74 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
78 /*****************************************************************************
80 *****************************************************************************/
82 /* Maximum gap allowed between two CRs. */
83 #define CR_MAX_GAP (INT64_C(2000000)*100/9)
85 /* Latency introduced on DVDs with CR == 0 on chapter change - this is from
87 #define CR_MEAN_PTS_GAP (300000)
89 /*****************************************************************************
91 *****************************************************************************/
94 * This structure holds long term average
104 static void AvgInit( average_t *, int i_divider );
105 static void AvgClean( average_t * );
107 static void AvgReset( average_t * );
108 static void AvgUpdate( average_t *, mtime_t i_value );
109 static mtime_t AvgGet( average_t * );
118 static inline clock_point_t clock_point_Create( mtime_t i_stream, mtime_t i_system )
120 clock_point_t p = { .i_stream = i_stream, .i_system = i_system };
130 /* Reference point */
131 bool b_has_reference;
135 * It is used to detect unexpected stream discontinuities */
138 /* Maximal timestamp returned by input_clock_GetTS (in system unit) */
142 mtime_t i_next_drift_update;
145 /* Current modifiers */
148 mtime_t i_pause_date;
151 static mtime_t ClockStreamToSystem( input_clock_t *, mtime_t i_stream );
152 static mtime_t ClockSystemToStream( input_clock_t *, mtime_t i_system );
154 /*****************************************************************************
155 * input_clock_New: create a new clock
156 *****************************************************************************/
157 input_clock_t *input_clock_New( int i_cr_average, int i_rate )
159 input_clock_t *cl = malloc( sizeof(*cl) );
163 vlc_mutex_init( &cl->lock );
164 cl->b_has_reference = false;
165 cl->ref = clock_point_Create( 0, 0 );
167 cl->last = clock_point_Create( 0, 0 );
171 cl->i_next_drift_update = 0;
172 AvgInit( &cl->drift, i_cr_average );
175 cl->b_paused = false;
176 cl->i_pause_date = 0;
181 /*****************************************************************************
182 * input_clock_Delete: destroy a new clock
183 *****************************************************************************/
184 void input_clock_Delete( input_clock_t *cl )
186 AvgClean( &cl->drift );
187 vlc_mutex_destroy( &cl->lock );
191 /*****************************************************************************
192 * input_clock_Update: manages a clock reference
194 * i_ck_stream: date in stream clock
195 * i_ck_system: date in system clock
196 *****************************************************************************/
197 void input_clock_Update( input_clock_t *cl,
198 vlc_object_t *p_log, bool b_can_pace_control,
199 mtime_t i_ck_stream, mtime_t i_ck_system )
201 bool b_reset_reference = false;
203 vlc_mutex_lock( &cl->lock );
205 if( ( !cl->b_has_reference ) ||
206 ( i_ck_stream == 0 && cl->last.i_stream != 0 ) )
209 b_reset_reference= true;
211 else if( cl->last.i_stream != 0 &&
212 ( (cl->last.i_stream - i_ck_stream) > CR_MAX_GAP ||
213 (cl->last.i_stream - i_ck_stream) < -CR_MAX_GAP ) )
215 /* Stream discontinuity, for which we haven't received a
216 * warning from the stream control facilities (dd-edited
218 msg_Warn( p_log, "clock gap, unexpected stream discontinuity" );
222 msg_Warn( p_log, "feeding synchro with a new reference point trying to recover from clock gap" );
223 b_reset_reference= true;
225 if( b_reset_reference )
227 cl->i_next_drift_update = 0;
228 AvgReset( &cl->drift );
230 /* Feed synchro with a new reference point. */
231 cl->b_has_reference = true;
232 cl->ref = clock_point_Create( i_ck_stream,
233 __MAX( cl->i_ts_max + CR_MEAN_PTS_GAP, i_ck_system ) );
236 if( !b_can_pace_control && cl->i_next_drift_update < i_ck_system )
238 const mtime_t i_converted = ClockSystemToStream( cl, i_ck_system );
240 AvgUpdate( &cl->drift, i_converted - i_ck_stream );
242 cl->i_next_drift_update = i_ck_system + CLOCK_FREQ/5; /* FIXME why that */
244 cl->last = clock_point_Create( i_ck_stream, i_ck_system );
246 vlc_mutex_unlock( &cl->lock );
249 /*****************************************************************************
251 *****************************************************************************/
252 void input_clock_Reset( input_clock_t *cl )
254 vlc_mutex_lock( &cl->lock );
256 cl->b_has_reference = false;
257 cl->ref = clock_point_Create( 0, 0 );
260 vlc_mutex_unlock( &cl->lock );
263 /*****************************************************************************
264 * input_clock_ChangeRate:
265 *****************************************************************************/
266 void input_clock_ChangeRate( input_clock_t *cl, int i_rate )
268 vlc_mutex_lock( &cl->lock );
270 /* Move the reference point */
271 if( cl->b_has_reference )
273 cl->last.i_system = ClockStreamToSystem( cl, cl->last.i_stream );
279 vlc_mutex_unlock( &cl->lock );
282 /*****************************************************************************
283 * input_clock_ChangePause:
284 *****************************************************************************/
285 void input_clock_ChangePause( input_clock_t *cl, bool b_paused, mtime_t i_date )
287 vlc_mutex_lock( &cl->lock );
288 assert( (!cl->b_paused) != (!b_paused) );
292 const mtime_t i_duration = i_date - cl->i_pause_date;
294 if( cl->b_has_reference && i_duration > 0 )
296 cl->ref.i_system += i_duration;
297 cl->last.i_system += i_duration;
300 cl->i_pause_date = i_date;
301 cl->b_paused = b_paused;
303 vlc_mutex_unlock( &cl->lock );
306 /*****************************************************************************
307 * input_clock_GetWakeup
308 *****************************************************************************/
309 mtime_t input_clock_GetWakeup( input_clock_t *cl )
311 mtime_t i_wakeup = 0;
313 vlc_mutex_lock( &cl->lock );
315 /* Synchronized, we can wait */
316 if( cl->b_has_reference )
317 i_wakeup = ClockStreamToSystem( cl, cl->last.i_stream );
319 vlc_mutex_unlock( &cl->lock );
324 /*****************************************************************************
325 * input_clock_GetTS: manages a PTS or DTS
326 *****************************************************************************/
327 mtime_t input_clock_GetTS( input_clock_t *cl, int *pi_rate,
328 mtime_t i_pts_delay, mtime_t i_ts )
330 mtime_t i_converted_ts;
332 vlc_mutex_lock( &cl->lock );
335 *pi_rate = cl->i_rate;
337 if( !cl->b_has_reference )
339 vlc_mutex_unlock( &cl->lock );
344 i_converted_ts = ClockStreamToSystem( cl, i_ts + AvgGet( &cl->drift ) );
345 if( i_converted_ts > cl->i_ts_max )
346 cl->i_ts_max = i_converted_ts;
348 vlc_mutex_unlock( &cl->lock );
350 return i_converted_ts + i_pts_delay;
352 /*****************************************************************************
353 * input_clock_GetRate: Return current rate
354 *****************************************************************************/
355 int input_clock_GetRate( input_clock_t *cl )
359 vlc_mutex_lock( &cl->lock );
361 vlc_mutex_unlock( &cl->lock );
366 int input_clock_GetState( input_clock_t *cl,
367 mtime_t *pi_stream_start, mtime_t *pi_system_start,
368 mtime_t *pi_stream_duration, mtime_t *pi_system_duration )
370 vlc_mutex_lock( &cl->lock );
372 if( !cl->b_has_reference )
374 vlc_mutex_unlock( &cl->lock );
378 *pi_stream_start = cl->ref.i_stream;
379 *pi_system_start = cl->ref.i_system;
381 *pi_stream_duration = cl->last.i_stream - cl->ref.i_stream;
382 *pi_system_duration = cl->last.i_system - cl->ref.i_system;
384 vlc_mutex_unlock( &cl->lock );
389 void input_clock_ChangeSystemOrigin( input_clock_t *cl, mtime_t i_system )
391 vlc_mutex_lock( &cl->lock );
393 assert( cl->b_has_reference );
394 const mtime_t i_offset = i_system - cl->ref.i_system;
396 cl->ref.i_system += i_offset;
397 cl->last.i_system += i_offset;
399 vlc_mutex_unlock( &cl->lock );
402 /*****************************************************************************
403 * ClockStreamToSystem: converts a movie clock to system date
404 *****************************************************************************/
405 static mtime_t ClockStreamToSystem( input_clock_t *cl, mtime_t i_stream )
407 if( !cl->b_has_reference )
410 return ( i_stream - cl->ref.i_stream ) * cl->i_rate / INPUT_RATE_DEFAULT +
414 /*****************************************************************************
415 * ClockSystemToStream: converts a system date to movie clock
416 *****************************************************************************
417 * Caution : a valid reference point is needed for this to operate.
418 *****************************************************************************/
419 static mtime_t ClockSystemToStream( input_clock_t *cl, mtime_t i_system )
421 assert( cl->b_has_reference );
422 return ( i_system - cl->ref.i_system ) * INPUT_RATE_DEFAULT / cl->i_rate +
426 /*****************************************************************************
427 * Long term average helpers
428 *****************************************************************************/
429 static void AvgInit( average_t *p_avg, int i_divider )
431 p_avg->i_divider = i_divider;
434 static void AvgClean( average_t *p_avg )
438 static void AvgReset( average_t *p_avg )
441 p_avg->i_residue = 0;
444 static void AvgUpdate( average_t *p_avg, mtime_t i_value )
446 const int i_f0 = __MIN( p_avg->i_divider - 1, p_avg->i_count );
447 const int i_f1 = p_avg->i_divider - i_f0;
449 const mtime_t i_tmp = i_f0 * p_avg->i_value + i_f1 * i_value + p_avg->i_residue;
451 p_avg->i_value = i_tmp / p_avg->i_divider;
452 p_avg->i_residue = i_tmp % p_avg->i_divider;
456 static mtime_t AvgGet( average_t *p_avg )
458 return p_avg->i_value;