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 * DISCUSSION : SYNCHRONIZATION METHOD
40 * In some cases we can impose the pace of reading (when reading from a
41 * file or a pipe), and for the synchronization we simply sleep() until
42 * it is time to deliver the packet to the decoders. When reading from
43 * the network, we must be read at the same pace as the server writes,
44 * otherwise the kernel's buffer will trash packets. The risk is now to
45 * overflow the input buffers in case the server goes too fast, that is
46 * why we do these calculations :
48 * We compute a mean for the pcr because we want to eliminate the
49 * network jitter and keep the low frequency variations. The mean is
50 * in fact a low pass filter and the jitter is a high frequency signal
51 * that is why it is eliminated by the filter/average.
53 * The low frequency variations enable us to synchronize the client clock
54 * with the server clock because they represent the time variation between
55 * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
56 * the presentation dates for the audio and video frames. With those dates
57 * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
58 * as it is sent by the server and so we keep the synchronization between
59 * the server and the client.
61 * It is a very important matter if you want to avoid underflow or overflow
62 * in all the FIFOs, but it may be not enough.
65 /* p_input->p->i_cr_average : Maximum number of samples used to compute the
66 * dynamic average value.
67 * We use the following formula :
68 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
71 /*****************************************************************************
73 *****************************************************************************/
75 /* Maximum gap allowed between two CRs. */
76 #define CR_MAX_GAP (INT64_C(2000000)*100/9)
78 /* Latency introduced on DVDs with CR == 0 on chapter change - this is from
80 #define CR_MEAN_PTS_GAP (300000)
82 /*****************************************************************************
84 *****************************************************************************/
87 * This structure holds long term average
97 static void AvgInit( average_t *, int i_divider );
98 static void AvgClean( average_t * );
100 static void AvgReset( average_t * );
101 static void AvgUpdate( average_t *, mtime_t i_value );
102 static mtime_t AvgGet( average_t * );
111 static inline clock_point_t clock_point_Create( mtime_t i_stream, mtime_t i_system )
113 clock_point_t p = { .i_stream = i_stream, .i_system = i_system };
120 /* Reference point */
121 bool b_has_reference;
125 * It is used to detect unexpected stream discontinuities */
128 /* Maximal timestamp returned by input_clock_GetTS (in system unit) */
132 mtime_t i_next_drift_update;
135 /* Current modifiers */
139 static mtime_t ClockStreamToSystem( input_clock_t *, mtime_t i_stream );
140 static mtime_t ClockSystemToStream( input_clock_t *, mtime_t i_system );
142 /*****************************************************************************
143 * input_clock_New: create a new clock
144 *****************************************************************************/
145 input_clock_t *input_clock_New( int i_cr_average, int i_rate )
147 input_clock_t *cl = malloc( sizeof(*cl) );
151 cl->b_has_reference = false;
152 cl->ref = clock_point_Create( 0, 0 );
154 cl->last = clock_point_Create( 0, 0 );
158 cl->i_next_drift_update = 0;
159 AvgInit( &cl->drift, i_cr_average );
166 /*****************************************************************************
167 * input_clock_Delete: destroy a new clock
168 *****************************************************************************/
169 void input_clock_Delete( input_clock_t *cl )
171 AvgClean( &cl->drift );
175 /*****************************************************************************
176 * input_clock_Update: manages a clock reference
178 * i_ck_stream: date in stream clock
179 * i_ck_system: date in system clock
180 *****************************************************************************/
181 void input_clock_Update( input_clock_t *cl,
182 vlc_object_t *p_log, bool b_can_pace_control,
183 mtime_t i_ck_stream, mtime_t i_ck_system )
185 bool b_reset_reference = false;
187 if( ( !cl->b_has_reference ) ||
188 ( i_ck_stream == 0 && cl->last.i_stream != 0 ) )
191 b_reset_reference= true;
193 else if( cl->last.i_stream != 0 &&
194 ( (cl->last.i_stream - i_ck_stream) > CR_MAX_GAP ||
195 (cl->last.i_stream - 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 cl->b_has_reference = true;
214 cl->ref = clock_point_Create( i_ck_stream,
215 __MAX( cl->i_ts_max + CR_MEAN_PTS_GAP, i_ck_system ) );
218 if( !b_can_pace_control && cl->i_next_drift_update < i_ck_system )
220 const mtime_t i_converted = ClockSystemToStream( cl, i_ck_system );
222 AvgUpdate( &cl->drift, i_converted - i_ck_stream );
224 cl->i_next_drift_update = i_ck_system + CLOCK_FREQ/5; /* FIXME why that */
226 cl->last = clock_point_Create( i_ck_stream, i_ck_system );
229 /*****************************************************************************
231 *****************************************************************************/
232 void input_clock_Reset( input_clock_t *cl )
234 cl->b_has_reference = false;
235 cl->ref = clock_point_Create( 0, 0 );
239 /*****************************************************************************
240 * input_clock_ChangeRate:
241 *****************************************************************************/
242 void input_clock_ChangeRate( input_clock_t *cl, int i_rate )
244 /* Move the reference point */
245 if( cl->b_has_reference )
251 /*****************************************************************************
252 * input_clock_GetWakeup
253 *****************************************************************************/
254 mtime_t input_clock_GetWakeup( input_clock_t *cl )
256 /* Not synchronized, we cannot wait */
257 if( !cl->b_has_reference )
261 return ClockStreamToSystem( cl, cl->last.i_stream );
264 /*****************************************************************************
265 * input_clock_GetTS: manages a PTS or DTS
266 *****************************************************************************/
267 mtime_t input_clock_GetTS( input_clock_t *cl,
268 mtime_t i_pts_delay, mtime_t i_ts )
270 mtime_t i_converted_ts;
272 if( !cl->b_has_reference )
276 i_converted_ts = ClockStreamToSystem( cl, i_ts + AvgGet( &cl->drift ) );
277 if( i_converted_ts > cl->i_ts_max )
278 cl->i_ts_max = i_converted_ts;
280 return i_converted_ts + i_pts_delay;
283 /*****************************************************************************
284 * ClockStreamToSystem: converts a movie clock to system date
285 *****************************************************************************/
286 static mtime_t ClockStreamToSystem( input_clock_t *cl, mtime_t i_stream )
288 if( !cl->b_has_reference )
291 return ( i_stream - cl->ref.i_stream ) * cl->i_rate / INPUT_RATE_DEFAULT +
295 /*****************************************************************************
296 * ClockSystemToStream: converts a system date to movie clock
297 *****************************************************************************
298 * Caution : a valid reference point is needed for this to operate.
299 *****************************************************************************/
300 static mtime_t ClockSystemToStream( input_clock_t *cl, mtime_t i_system )
302 assert( cl->b_has_reference );
303 return ( i_system - cl->ref.i_system ) * INPUT_RATE_DEFAULT / cl->i_rate +
307 /*****************************************************************************
308 * Long term average helpers
309 *****************************************************************************/
310 static void AvgInit( average_t *p_avg, int i_divider )
312 p_avg->i_divider = i_divider;
315 static void AvgClean( average_t *p_avg )
319 static void AvgReset( average_t *p_avg )
322 p_avg->i_residue = 0;
325 static void AvgUpdate( average_t *p_avg, mtime_t i_value )
327 const int i_f0 = __MIN( p_avg->i_divider - 1, p_avg->i_count );
328 const int i_f1 = p_avg->i_divider - i_f0;
330 const mtime_t i_tmp = i_f0 * p_avg->i_value + i_f1 * i_value + p_avg->i_residue;
332 p_avg->i_value = i_tmp / p_avg->i_divider;
333 p_avg->i_residue = i_tmp % p_avg->i_divider;
337 static mtime_t AvgGet( average_t *p_avg )
339 return p_avg->i_value;