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>
38 * - clean up locking once clock code is stable
43 * DISCUSSION : SYNCHRONIZATION METHOD
45 * In some cases we can impose the pace of reading (when reading from a
46 * file or a pipe), and for the synchronization we simply sleep() until
47 * it is time to deliver the packet to the decoders. When reading from
48 * the network, we must be read at the same pace as the server writes,
49 * otherwise the kernel's buffer will trash packets. The risk is now to
50 * overflow the input buffers in case the server goes too fast, that is
51 * why we do these calculations :
53 * We compute a mean for the pcr because we want to eliminate the
54 * network jitter and keep the low frequency variations. The mean is
55 * in fact a low pass filter and the jitter is a high frequency signal
56 * that is why it is eliminated by the filter/average.
58 * The low frequency variations enable us to synchronize the client clock
59 * with the server clock because they represent the time variation between
60 * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
61 * the presentation dates for the audio and video frames. With those dates
62 * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
63 * as it is sent by the server and so we keep the synchronization between
64 * the server and the client.
66 * It is a very important matter if you want to avoid underflow or overflow
67 * in all the FIFOs, but it may be not enough.
70 /* p_input->p->i_cr_average : Maximum number of samples used to compute the
71 * dynamic average value.
72 * We use the following formula :
73 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
77 /*****************************************************************************
79 *****************************************************************************/
81 /* Maximum gap allowed between two CRs. */
82 #define CR_MAX_GAP (INT64_C(2000000)*100/9)
84 /* Latency introduced on DVDs with CR == 0 on chapter change - this is from
86 #define CR_MEAN_PTS_GAP (300000)
88 /*****************************************************************************
90 *****************************************************************************/
93 * This structure holds long term average
103 static void AvgInit( average_t *, int i_divider );
104 static void AvgClean( average_t * );
106 static void AvgReset( average_t * );
107 static void AvgUpdate( average_t *, mtime_t i_value );
108 static mtime_t AvgGet( average_t * );
117 static inline clock_point_t clock_point_Create( mtime_t i_stream, mtime_t i_system )
119 clock_point_t p = { .i_stream = i_stream, .i_system = i_system };
129 /* Reference point */
130 bool b_has_reference;
134 * It is used to detect unexpected stream discontinuities */
137 /* Maximal timestamp returned by input_clock_GetTS (in system unit) */
141 mtime_t i_next_drift_update;
144 /* Current modifiers */
147 mtime_t i_pause_date;
150 static mtime_t ClockStreamToSystem( input_clock_t *, mtime_t i_stream );
151 static mtime_t ClockSystemToStream( input_clock_t *, mtime_t i_system );
153 /*****************************************************************************
154 * input_clock_New: create a new clock
155 *****************************************************************************/
156 input_clock_t *input_clock_New( int i_cr_average, int i_rate )
158 input_clock_t *cl = malloc( sizeof(*cl) );
162 vlc_mutex_init( &cl->lock );
163 cl->b_has_reference = false;
164 cl->ref = clock_point_Create( 0, 0 );
166 cl->last = clock_point_Create( 0, 0 );
170 cl->i_next_drift_update = 0;
171 AvgInit( &cl->drift, i_cr_average );
174 cl->b_paused = false;
175 cl->i_pause_date = 0;
180 /*****************************************************************************
181 * input_clock_Delete: destroy a new clock
182 *****************************************************************************/
183 void input_clock_Delete( input_clock_t *cl )
185 AvgClean( &cl->drift );
186 vlc_mutex_destroy( &cl->lock );
190 /*****************************************************************************
191 * input_clock_Update: manages a clock reference
193 * i_ck_stream: date in stream clock
194 * i_ck_system: date in system clock
195 *****************************************************************************/
196 void input_clock_Update( input_clock_t *cl,
197 vlc_object_t *p_log, bool b_can_pace_control,
198 mtime_t i_ck_stream, mtime_t i_ck_system )
200 bool b_reset_reference = false;
202 vlc_mutex_lock( &cl->lock );
204 if( ( !cl->b_has_reference ) ||
205 ( i_ck_stream == 0 && cl->last.i_stream != 0 ) )
208 b_reset_reference= true;
210 else if( cl->last.i_stream != 0 &&
211 ( (cl->last.i_stream - i_ck_stream) > CR_MAX_GAP ||
212 (cl->last.i_stream - i_ck_stream) < -CR_MAX_GAP ) )
214 /* Stream discontinuity, for which we haven't received a
215 * warning from the stream control facilities (dd-edited
217 msg_Warn( p_log, "clock gap, unexpected stream discontinuity" );
221 msg_Warn( p_log, "feeding synchro with a new reference point trying to recover from clock gap" );
222 b_reset_reference= true;
224 if( b_reset_reference )
226 cl->i_next_drift_update = 0;
227 AvgReset( &cl->drift );
229 /* Feed synchro with a new reference point. */
230 cl->b_has_reference = true;
231 cl->ref = clock_point_Create( i_ck_stream,
232 __MAX( cl->i_ts_max + CR_MEAN_PTS_GAP, i_ck_system ) );
235 if( !b_can_pace_control && cl->i_next_drift_update < i_ck_system )
237 const mtime_t i_converted = ClockSystemToStream( cl, i_ck_system );
239 AvgUpdate( &cl->drift, i_converted - i_ck_stream );
241 cl->i_next_drift_update = i_ck_system + CLOCK_FREQ/5; /* FIXME why that */
243 cl->last = clock_point_Create( i_ck_stream, i_ck_system );
245 vlc_mutex_unlock( &cl->lock );
248 /*****************************************************************************
250 *****************************************************************************/
251 void input_clock_Reset( input_clock_t *cl )
253 vlc_mutex_lock( &cl->lock );
255 cl->b_has_reference = false;
256 cl->ref = clock_point_Create( 0, 0 );
259 vlc_mutex_unlock( &cl->lock );
262 /*****************************************************************************
263 * input_clock_ChangeRate:
264 *****************************************************************************/
265 void input_clock_ChangeRate( input_clock_t *cl, int i_rate )
267 vlc_mutex_lock( &cl->lock );
269 /* Move the reference point */
270 if( cl->b_has_reference )
272 cl->last.i_system = ClockStreamToSystem( cl, cl->last.i_stream );
278 vlc_mutex_unlock( &cl->lock );
281 /*****************************************************************************
282 * input_clock_ChangePause:
283 *****************************************************************************/
284 void input_clock_ChangePause( input_clock_t *cl, bool b_paused, mtime_t i_date )
286 vlc_mutex_lock( &cl->lock );
287 assert( (!cl->b_paused) != (!b_paused) );
291 const mtime_t i_duration = i_date - cl->i_pause_date;
293 if( cl->b_has_reference && i_duration > 0 )
295 cl->ref.i_system += i_duration;
296 cl->last.i_system += i_duration;
299 cl->i_pause_date = i_date;
300 cl->b_paused = b_paused;
302 vlc_mutex_unlock( &cl->lock );
305 /*****************************************************************************
306 * input_clock_GetWakeup
307 *****************************************************************************/
308 mtime_t input_clock_GetWakeup( input_clock_t *cl )
310 mtime_t i_wakeup = 0;
312 vlc_mutex_lock( &cl->lock );
314 /* Synchronized, we can wait */
315 if( cl->b_has_reference )
316 i_wakeup = ClockStreamToSystem( cl, cl->last.i_stream );
318 vlc_mutex_unlock( &cl->lock );
323 /*****************************************************************************
324 * input_clock_GetTS: manages a PTS or DTS
325 *****************************************************************************/
326 mtime_t input_clock_GetTS( input_clock_t *cl, int *pi_rate,
327 mtime_t i_pts_delay, mtime_t i_ts )
329 mtime_t i_converted_ts;
331 vlc_mutex_lock( &cl->lock );
334 *pi_rate = cl->i_rate;
336 if( !cl->b_has_reference )
338 vlc_mutex_unlock( &cl->lock );
343 i_converted_ts = ClockStreamToSystem( cl, i_ts + AvgGet( &cl->drift ) );
344 if( i_converted_ts > cl->i_ts_max )
345 cl->i_ts_max = i_converted_ts;
347 vlc_mutex_unlock( &cl->lock );
349 return i_converted_ts + i_pts_delay;
351 /*****************************************************************************
352 * input_clock_GetRate: Return current rate
353 *****************************************************************************/
354 int input_clock_GetRate( input_clock_t *cl )
358 vlc_mutex_lock( &cl->lock );
360 vlc_mutex_unlock( &cl->lock );
365 int input_clock_GetState( input_clock_t *cl,
366 mtime_t *pi_stream_start, mtime_t *pi_system_start,
367 mtime_t *pi_stream_duration, mtime_t *pi_system_duration )
369 vlc_mutex_lock( &cl->lock );
371 if( !cl->b_has_reference )
373 vlc_mutex_unlock( &cl->lock );
377 *pi_stream_start = cl->ref.i_stream;
378 *pi_system_start = cl->ref.i_system;
380 *pi_stream_duration = cl->last.i_stream - cl->ref.i_stream;
381 *pi_system_duration = cl->last.i_system - cl->ref.i_system;
383 vlc_mutex_unlock( &cl->lock );
388 void input_clock_ChangeSystemOrigin( input_clock_t *cl, mtime_t i_system )
390 vlc_mutex_lock( &cl->lock );
392 assert( cl->b_has_reference );
393 const mtime_t i_offset = i_system - cl->ref.i_system;
395 cl->ref.i_system += i_offset;
396 cl->last.i_system += i_offset;
398 vlc_mutex_unlock( &cl->lock );
401 /*****************************************************************************
402 * ClockStreamToSystem: converts a movie clock to system date
403 *****************************************************************************/
404 static mtime_t ClockStreamToSystem( input_clock_t *cl, mtime_t i_stream )
406 if( !cl->b_has_reference )
409 return ( i_stream - cl->ref.i_stream ) * cl->i_rate / INPUT_RATE_DEFAULT +
413 /*****************************************************************************
414 * ClockSystemToStream: converts a system date to movie clock
415 *****************************************************************************
416 * Caution : a valid reference point is needed for this to operate.
417 *****************************************************************************/
418 static mtime_t ClockSystemToStream( input_clock_t *cl, mtime_t i_system )
420 assert( cl->b_has_reference );
421 return ( i_system - cl->ref.i_system ) * INPUT_RATE_DEFAULT / cl->i_rate +
425 /*****************************************************************************
426 * Long term average helpers
427 *****************************************************************************/
428 static void AvgInit( average_t *p_avg, int i_divider )
430 p_avg->i_divider = i_divider;
433 static void AvgClean( average_t *p_avg )
437 static void AvgReset( average_t *p_avg )
440 p_avg->i_residue = 0;
443 static void AvgUpdate( average_t *p_avg, mtime_t i_value )
445 const int i_f0 = __MIN( p_avg->i_divider - 1, p_avg->i_count );
446 const int i_f1 = p_avg->i_divider - i_f0;
448 const mtime_t i_tmp = i_f0 * p_avg->i_value + i_f1 * i_value + p_avg->i_residue;
450 p_avg->i_value = i_tmp / p_avg->i_divider;
451 p_avg->i_residue = i_tmp % p_avg->i_divider;
455 static mtime_t AvgGet( average_t *p_avg )
457 return p_avg->i_value;