1 /*****************************************************************************
2 * input_clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999, 2000 VideoLAN
5 * $Id: input_clock.c,v 1.23 2001/11/08 14:45:44 stef 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 *****************************************************************************/
29 #include <string.h> /* memcpy(), memset() */
30 #include <sys/types.h> /* off_t */
38 #include "stream_control.h"
39 #include "input_ext-intf.h"
40 #include "input_ext-dec.h"
41 #include "input_ext-plugins.h"
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 /*****************************************************************************
73 *****************************************************************************/
75 /* Maximum number of samples used to compute the dynamic average value.
76 * We use the following formula :
77 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
79 #define CR_MAX_AVERAGE_COUNTER 40
81 /* Maximum gap allowed between two CRs. */
82 #define CR_MAX_GAP 1000000
84 /*****************************************************************************
85 * ClockToSysdate: converts a movie clock to system date
86 *****************************************************************************/
87 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
88 mtime_t i_clock, mtime_t i_sysdate );
89 static mtime_t ClockToSysdate( input_thread_t * p_input,
90 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
92 mtime_t i_sysdate = 0;
94 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
96 i_sysdate = (mtime_t)(i_clock - p_pgrm->cr_ref)
97 * (mtime_t)p_input->stream.control.i_rate
101 i_sysdate += (mtime_t)p_pgrm->sysdate_ref;
107 /*****************************************************************************
108 * ClockCurrent: converts current system date to clock units
109 *****************************************************************************
110 * Caution : the synchro state must be SYNCHRO_OK for this to operate.
111 *****************************************************************************/
112 static mtime_t ClockCurrent( input_thread_t * p_input,
113 pgrm_descriptor_t * p_pgrm )
115 return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
116 / p_input->stream.control.i_rate / 300
120 /*****************************************************************************
121 * ClockNewRef: writes a new clock reference
122 *****************************************************************************/
123 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
124 mtime_t i_clock, mtime_t i_sysdate )
126 p_pgrm->cr_ref = i_clock;
127 /* this is actually a kludge, but it gives better results when scr
128 * is zero in DVDs: we are 3-4 ms in advance instead of sometimes
130 p_pgrm->sysdate_ref = ( p_pgrm->last_syscr && !i_clock )
135 /*****************************************************************************
136 * input_ClockInit: reinitializes the clock reference after a stream
138 *****************************************************************************/
139 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
142 p_pgrm->last_syscr = 0;
144 p_pgrm->sysdate_ref = 0;
145 p_pgrm->delta_cr = 0;
146 p_pgrm->c_average_count = 0;
149 /*****************************************************************************
150 * input_ClockManageControl: handles the messages from the interface
151 *****************************************************************************
152 * Returns UNDEF_S if nothing happened, PAUSE_S if the stream was paused
153 *****************************************************************************/
154 int input_ClockManageControl( input_thread_t * p_input,
155 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
157 int i_return_value = UNDEF_S;
159 vlc_mutex_lock( &p_input->stream.stream_lock );
161 if( p_input->stream.i_new_status == PAUSE_S )
164 vlc_mutex_lock( &p_input->stream.control.control_lock );
165 i_old_status = p_input->stream.control.i_status;
167 p_input->stream.control.i_status = PAUSE_S;
168 vlc_cond_wait( &p_input->stream.stream_wait,
169 &p_input->stream.stream_lock );
170 p_pgrm->last_syscr = 0;
171 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
173 if( p_input->stream.i_new_status == PAUSE_S )
175 /* PAUSE_S undoes the pause state: Return to old state. */
176 p_input->stream.control.i_status = i_old_status;
177 p_input->stream.i_new_status = UNDEF_S;
178 p_input->stream.i_new_rate = UNDEF_S;
181 /* We handle i_new_status != PAUSE_S below... */
182 vlc_mutex_unlock( &p_input->stream.control.control_lock );
184 i_return_value = PAUSE_S;
187 if( p_input->stream.i_new_status != UNDEF_S )
189 vlc_mutex_lock( &p_input->stream.control.control_lock );
191 p_input->stream.control.i_status = p_input->stream.i_new_status;
193 ClockNewRef( p_input, p_pgrm, i_clock,
194 ClockToSysdate( p_input, p_pgrm, i_clock ) );
196 if( p_input->stream.control.i_status == PLAYING_S )
198 p_input->stream.control.i_rate = DEFAULT_RATE;
199 p_input->stream.control.b_mute = 0;
203 p_input->stream.control.i_rate = p_input->stream.i_new_rate;
204 p_input->stream.control.b_mute = 1;
206 /* Feed the audio decoders with a NULL packet to avoid
207 * discontinuities. */
208 input_EscapeAudioDiscontinuity( p_input );
211 p_input->stream.i_new_status = UNDEF_S;
212 p_input->stream.i_new_rate = UNDEF_S;
214 vlc_mutex_unlock( &p_input->stream.control.control_lock );
217 vlc_mutex_unlock( &p_input->stream.stream_lock );
219 return( i_return_value );
222 /*****************************************************************************
223 * input_ClockManageRef: manages a clock reference
224 *****************************************************************************/
225 void input_ClockManageRef( input_thread_t * p_input,
226 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
228 if( ( p_pgrm->i_synchro_state != SYNCHRO_OK ) || ( i_clock == 0 ) )
230 /* Feed synchro with a new reference point. */
231 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
232 p_pgrm->i_synchro_state = SYNCHRO_OK;
234 if( p_input->stream.b_pace_control
235 && p_input->stream.pp_programs[0] == p_pgrm )
237 p_pgrm->last_cr = i_clock;
238 mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
243 p_pgrm->last_syscr = 0;
244 p_pgrm->delta_cr = 0;
245 p_pgrm->c_average_count = 0;
250 if ( p_pgrm->last_cr != 0 &&
251 ( (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
252 || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
254 /* Stream discontinuity, for which we haven't received a
255 * warning from the stream control facilities (dd-edited
257 intf_WarnMsg( 1, "Clock gap, unexpected stream discontinuity" );
258 input_ClockInit( p_pgrm );
259 p_pgrm->i_synchro_state = SYNCHRO_START;
260 input_EscapeDiscontinuity( p_input, p_pgrm );
263 p_pgrm->last_cr = i_clock;
265 if( p_input->stream.b_pace_control
266 && p_input->stream.pp_programs[0] == p_pgrm )
268 /* We remember the last system date to be able to restart
269 * the synchro we statistically better continuity, after
271 p_pgrm->last_syscr = ClockToSysdate( p_input, p_pgrm, i_clock );
273 /* Wait a while before delivering the packets to the decoder.
274 * In case of multiple programs, we arbitrarily follow the
275 * clock of the first program. */
276 mwait( p_pgrm->last_syscr );
278 /* Now take into account interface changes. */
279 input_ClockManageControl( p_input, p_pgrm, i_clock );
283 /* Smooth clock reference variations. */
284 mtime_t i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
286 /* Bresenham algorithm to smooth variations. */
287 if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
289 p_pgrm->delta_cr = ( p_pgrm->delta_cr
290 * (CR_MAX_AVERAGE_COUNTER - 1)
291 + ( i_extrapoled_clock - i_clock ) )
292 / CR_MAX_AVERAGE_COUNTER;
296 p_pgrm->delta_cr = ( p_pgrm->delta_cr
297 * p_pgrm->c_average_count
298 + ( i_extrapoled_clock - i_clock ) )
299 / (p_pgrm->c_average_count + 1);
300 p_pgrm->c_average_count++;
306 /*****************************************************************************
307 * input_ClockGetTS: manages a PTS or DTS
308 *****************************************************************************/
309 mtime_t input_ClockGetTS( input_thread_t * p_input,
310 pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
312 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
314 return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
315 + DEFAULT_PTS_DELAY );