1 /*****************************************************************************
2 * input_clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999-2001 VideoLAN
5 * $Id: input_clock.c,v 1.34 2002/11/11 14:39:12 sam Exp $
7 * Authors: Christophe Massiot <massiot@via.ecp.fr>
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License as published by
11 * the Free Software Foundation; either version 2 of the License, or
12 * (at your option) any later version.
14 * This program is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 * GNU General Public License for more details.
19 * You should have received a copy of the GNU General Public License
20 * along with this program; if not, write to the Free Software
21 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
22 *****************************************************************************/
24 /*****************************************************************************
26 *****************************************************************************/
27 #include <string.h> /* memcpy(), memset() */
31 #include "stream_control.h"
32 #include "input_ext-intf.h"
33 #include "input_ext-dec.h"
34 #include "input_ext-plugins.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 /*****************************************************************************
66 *****************************************************************************/
68 /* Maximum number of samples used to compute the dynamic average value.
69 * We use the following formula :
70 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
72 #define CR_MAX_AVERAGE_COUNTER 40
74 /* Maximum gap allowed between two CRs. */
75 #define CR_MAX_GAP 1000000
77 /*****************************************************************************
78 * ClockToSysdate: converts a movie clock to system date
79 *****************************************************************************/
80 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
81 mtime_t i_clock, mtime_t i_sysdate );
82 static mtime_t ClockToSysdate( input_thread_t * p_input,
83 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
85 mtime_t i_sysdate = 0;
87 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
89 i_sysdate = (mtime_t)(i_clock - p_pgrm->cr_ref)
90 * (mtime_t)p_input->stream.control.i_rate
94 i_sysdate += (mtime_t)p_pgrm->sysdate_ref;
100 /*****************************************************************************
101 * ClockCurrent: converts current system date to clock units
102 *****************************************************************************
103 * Caution : the synchro state must be SYNCHRO_OK for this to operate.
104 *****************************************************************************/
105 static mtime_t ClockCurrent( input_thread_t * p_input,
106 pgrm_descriptor_t * p_pgrm )
108 return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
109 / p_input->stream.control.i_rate / 300
113 /*****************************************************************************
114 * ClockNewRef: writes a new clock reference
115 *****************************************************************************/
116 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
117 mtime_t i_clock, mtime_t i_sysdate )
119 p_pgrm->cr_ref = i_clock;
120 /* this is actually a kludge, but it gives better results when scr
121 * is zero in DVDs: we are 3-4 ms in advance instead of sometimes
123 p_pgrm->sysdate_ref = ( p_pgrm->last_syscr && !i_clock )
128 /*****************************************************************************
129 * input_ClockInit: reinitializes the clock reference after a stream
131 *****************************************************************************/
132 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
135 p_pgrm->last_syscr = 0;
137 p_pgrm->sysdate_ref = 0;
138 p_pgrm->delta_cr = 0;
139 p_pgrm->c_average_count = 0;
142 /*****************************************************************************
143 * input_ClockManageControl: handles the messages from the interface
144 *****************************************************************************
145 * Returns UNDEF_S if nothing happened, PAUSE_S if the stream was paused
146 *****************************************************************************/
147 int input_ClockManageControl( input_thread_t * p_input,
148 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
150 int i_return_value = UNDEF_S;
152 vlc_mutex_lock( &p_input->stream.stream_lock );
154 if( p_input->stream.i_new_status == PAUSE_S )
158 vlc_mutex_lock( &p_input->stream.control.control_lock );
159 i_old_status = p_input->stream.control.i_status;
160 p_input->stream.control.i_status = PAUSE_S;
161 vlc_mutex_unlock( &p_input->stream.control.control_lock );
163 vlc_cond_wait( &p_input->stream.stream_wait,
164 &p_input->stream.stream_lock );
165 p_pgrm->last_syscr = 0;
166 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
168 if( p_input->stream.i_new_status == PAUSE_S )
170 /* PAUSE_S undoes the pause state: Return to old state. */
171 vlc_mutex_lock( &p_input->stream.control.control_lock );
172 p_input->stream.control.i_status = i_old_status;
173 vlc_mutex_unlock( &p_input->stream.control.control_lock );
175 p_input->stream.i_new_status = UNDEF_S;
176 p_input->stream.i_new_rate = UNDEF_S;
179 /* We handle i_new_status != PAUSE_S below... */
181 i_return_value = PAUSE_S;
184 if( p_input->stream.i_new_status != UNDEF_S )
186 vlc_mutex_lock( &p_input->stream.control.control_lock );
188 p_input->stream.control.i_status = p_input->stream.i_new_status;
190 ClockNewRef( p_input, p_pgrm, i_clock,
191 ClockToSysdate( p_input, p_pgrm, i_clock ) );
193 if( p_input->stream.control.i_status == PLAYING_S )
195 p_input->stream.control.i_rate = DEFAULT_RATE;
196 p_input->stream.control.b_mute = 0;
200 p_input->stream.control.i_rate = p_input->stream.i_new_rate;
201 p_input->stream.control.b_mute = 1;
203 /* Feed the audio decoders with a NULL packet to avoid
204 * discontinuities. */
205 input_EscapeAudioDiscontinuity( p_input );
208 p_input->stream.i_new_status = UNDEF_S;
209 p_input->stream.i_new_rate = UNDEF_S;
211 vlc_mutex_unlock( &p_input->stream.control.control_lock );
214 vlc_mutex_unlock( &p_input->stream.stream_lock );
216 return( i_return_value );
219 /*****************************************************************************
220 * input_ClockManageRef: manages a clock reference
221 *****************************************************************************/
222 void input_ClockManageRef( input_thread_t * p_input,
223 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
225 /* take selected program if none specified */
228 p_pgrm = p_input->stream.p_selected_program;
231 if( ( p_pgrm->i_synchro_state != SYNCHRO_OK ) || ( i_clock == 0 ) )
233 /* Feed synchro with a new reference point. */
234 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
235 p_pgrm->i_synchro_state = SYNCHRO_OK;
237 if( p_input->stream.b_pace_control
238 && p_input->stream.p_selected_program == p_pgrm )
240 p_pgrm->last_cr = i_clock;
241 mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
246 p_pgrm->last_syscr = 0;
247 p_pgrm->delta_cr = 0;
248 p_pgrm->c_average_count = 0;
253 if ( p_pgrm->last_cr != 0 &&
254 ( (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
255 || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
257 /* Stream discontinuity, for which we haven't received a
258 * warning from the stream control facilities (dd-edited
260 msg_Warn( p_input, "clock gap, unexpected stream discontinuity" );
261 input_ClockInit( p_pgrm );
262 p_pgrm->i_synchro_state = SYNCHRO_START;
263 input_EscapeDiscontinuity( p_input );
266 p_pgrm->last_cr = i_clock;
268 if( p_input->stream.b_pace_control
269 && p_input->stream.p_selected_program == p_pgrm )
271 /* We remember the last system date to be able to restart
272 * the synchro we statistically better continuity, after
274 p_pgrm->last_syscr = ClockToSysdate( p_input, p_pgrm, i_clock );
276 /* Wait a while before delivering the packets to the decoder.
277 * In case of multiple programs, we arbitrarily follow the
278 * clock of the first program. */
279 mwait( p_pgrm->last_syscr );
281 /* Now take into account interface changes. */
282 input_ClockManageControl( p_input, p_pgrm, i_clock );
286 /* Smooth clock reference variations. */
287 mtime_t i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
289 /* Bresenham algorithm to smooth variations. */
290 if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
292 p_pgrm->delta_cr = ( p_pgrm->delta_cr
293 * (CR_MAX_AVERAGE_COUNTER - 1)
294 + ( i_extrapoled_clock - i_clock ) )
295 / CR_MAX_AVERAGE_COUNTER;
299 p_pgrm->delta_cr = ( p_pgrm->delta_cr
300 * p_pgrm->c_average_count
301 + ( i_extrapoled_clock - i_clock ) )
302 / (p_pgrm->c_average_count + 1);
303 p_pgrm->c_average_count++;
309 /*****************************************************************************
310 * input_ClockGetTS: manages a PTS or DTS
311 *****************************************************************************/
312 mtime_t input_ClockGetTS( input_thread_t * p_input,
313 pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
315 /* take selected program if none specified */
318 p_pgrm = p_input->stream.p_selected_program;
321 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
323 return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
325 + (p_input->p_vlc->i_desync > 0
326 ? p_input->p_vlc->i_desync : 0) );