1 /*****************************************************************************
2 * input_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>
35 #include "input_clock.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 */
148 static mtime_t ClockStreamToSystem( input_clock_t *, mtime_t i_stream );
149 static mtime_t ClockSystemToStream( input_clock_t *, mtime_t i_system );
151 /*****************************************************************************
152 * input_clock_New: create a new clock
153 *****************************************************************************/
154 input_clock_t *input_clock_New( int i_cr_average, int i_rate )
156 input_clock_t *cl = malloc( sizeof(*cl) );
160 vlc_mutex_init( &cl->lock );
161 cl->b_has_reference = false;
162 cl->ref = clock_point_Create( 0, 0 );
164 cl->last = clock_point_Create( 0, 0 );
168 cl->i_next_drift_update = 0;
169 AvgInit( &cl->drift, i_cr_average );
176 /*****************************************************************************
177 * input_clock_Delete: destroy a new clock
178 *****************************************************************************/
179 void input_clock_Delete( input_clock_t *cl )
181 AvgClean( &cl->drift );
182 vlc_mutex_destroy( &cl->lock );
186 /*****************************************************************************
187 * input_clock_Update: manages a clock reference
189 * i_ck_stream: date in stream clock
190 * i_ck_system: date in system clock
191 *****************************************************************************/
192 void input_clock_Update( input_clock_t *cl,
193 vlc_object_t *p_log, bool b_can_pace_control,
194 mtime_t i_ck_stream, mtime_t i_ck_system )
196 bool b_reset_reference = false;
198 vlc_mutex_lock( &cl->lock );
199 if( ( !cl->b_has_reference ) ||
200 ( i_ck_stream == 0 && cl->last.i_stream != 0 ) )
203 b_reset_reference= true;
205 else if( cl->last.i_stream != 0 &&
206 ( (cl->last.i_stream - i_ck_stream) > CR_MAX_GAP ||
207 (cl->last.i_stream - i_ck_stream) < -CR_MAX_GAP ) )
209 /* Stream discontinuity, for which we haven't received a
210 * warning from the stream control facilities (dd-edited
212 msg_Warn( p_log, "clock gap, unexpected stream discontinuity" );
216 msg_Warn( p_log, "feeding synchro with a new reference point trying to recover from clock gap" );
217 b_reset_reference= true;
219 if( b_reset_reference )
221 cl->i_next_drift_update = 0;
222 AvgReset( &cl->drift );
224 /* Feed synchro with a new reference point. */
225 cl->b_has_reference = true;
226 cl->ref = clock_point_Create( i_ck_stream,
227 __MAX( cl->i_ts_max + CR_MEAN_PTS_GAP, i_ck_system ) );
230 if( !b_can_pace_control && cl->i_next_drift_update < i_ck_system )
232 const mtime_t i_converted = ClockSystemToStream( cl, i_ck_system );
234 AvgUpdate( &cl->drift, i_converted - i_ck_stream );
236 cl->i_next_drift_update = i_ck_system + CLOCK_FREQ/5; /* FIXME why that */
238 cl->last = clock_point_Create( i_ck_stream, i_ck_system );
240 vlc_mutex_unlock( &cl->lock );
243 /*****************************************************************************
245 *****************************************************************************/
246 void input_clock_Reset( input_clock_t *cl )
248 vlc_mutex_lock( &cl->lock );
250 cl->b_has_reference = false;
251 cl->ref = clock_point_Create( 0, 0 );
254 vlc_mutex_unlock( &cl->lock );
257 /*****************************************************************************
258 * input_clock_ChangeRate:
259 *****************************************************************************/
260 void input_clock_ChangeRate( input_clock_t *cl, int i_rate )
262 vlc_mutex_lock( &cl->lock );
264 /* Move the reference point */
265 if( cl->b_has_reference )
270 vlc_mutex_unlock( &cl->lock );
273 /*****************************************************************************
274 * input_clock_GetWakeup
275 *****************************************************************************/
276 mtime_t input_clock_GetWakeup( input_clock_t *cl )
278 mtime_t i_wakeup = 0;
280 vlc_mutex_lock( &cl->lock );
282 /* Synchronized, we can wait */
283 if( cl->b_has_reference )
284 i_wakeup = ClockStreamToSystem( cl, cl->last.i_stream );
286 vlc_mutex_unlock( &cl->lock );
291 /*****************************************************************************
292 * input_clock_GetTS: manages a PTS or DTS
293 *****************************************************************************/
294 mtime_t input_clock_GetTS( input_clock_t *cl,
295 mtime_t i_pts_delay, mtime_t i_ts )
297 mtime_t i_converted_ts;
299 vlc_mutex_lock( &cl->lock );
301 if( !cl->b_has_reference )
303 vlc_mutex_unlock( &cl->lock );
308 i_converted_ts = ClockStreamToSystem( cl, i_ts + AvgGet( &cl->drift ) );
309 if( i_converted_ts > cl->i_ts_max )
310 cl->i_ts_max = i_converted_ts;
312 vlc_mutex_unlock( &cl->lock );
314 return i_converted_ts + i_pts_delay;
317 /*****************************************************************************
318 * ClockStreamToSystem: converts a movie clock to system date
319 *****************************************************************************/
320 static mtime_t ClockStreamToSystem( input_clock_t *cl, mtime_t i_stream )
322 if( !cl->b_has_reference )
325 return ( i_stream - cl->ref.i_stream ) * cl->i_rate / INPUT_RATE_DEFAULT +
329 /*****************************************************************************
330 * ClockSystemToStream: converts a system date to movie clock
331 *****************************************************************************
332 * Caution : a valid reference point is needed for this to operate.
333 *****************************************************************************/
334 static mtime_t ClockSystemToStream( input_clock_t *cl, mtime_t i_system )
336 assert( cl->b_has_reference );
337 return ( i_system - cl->ref.i_system ) * INPUT_RATE_DEFAULT / cl->i_rate +
341 /*****************************************************************************
342 * Long term average helpers
343 *****************************************************************************/
344 static void AvgInit( average_t *p_avg, int i_divider )
346 p_avg->i_divider = i_divider;
349 static void AvgClean( average_t *p_avg )
353 static void AvgReset( average_t *p_avg )
356 p_avg->i_residue = 0;
359 static void AvgUpdate( average_t *p_avg, mtime_t i_value )
361 const int i_f0 = __MIN( p_avg->i_divider - 1, p_avg->i_count );
362 const int i_f1 = p_avg->i_divider - i_f0;
364 const mtime_t i_tmp = i_f0 * p_avg->i_value + i_f1 * i_value + p_avg->i_residue;
366 p_avg->i_value = i_tmp / p_avg->i_divider;
367 p_avg->i_residue = i_tmp % p_avg->i_divider;
371 static mtime_t AvgGet( average_t *p_avg )
373 return p_avg->i_value;