1 /*****************************************************************************
2 * input_clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999-2001 VideoLAN
5 * $Id: input_clock.c,v 1.32 2002/06/01 12:32:01 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() */
28 #include <sys/types.h> /* off_t */
32 #include "stream_control.h"
33 #include "input_ext-intf.h"
34 #include "input_ext-dec.h"
35 #include "input_ext-plugins.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 /*****************************************************************************
67 *****************************************************************************/
69 /* Maximum number of samples used to compute the dynamic average value.
70 * We use the following formula :
71 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
73 #define CR_MAX_AVERAGE_COUNTER 40
75 /* Maximum gap allowed between two CRs. */
76 #define CR_MAX_GAP 1000000
78 /*****************************************************************************
79 * ClockToSysdate: converts a movie clock to system date
80 *****************************************************************************/
81 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
82 mtime_t i_clock, mtime_t i_sysdate );
83 static mtime_t ClockToSysdate( input_thread_t * p_input,
84 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
86 mtime_t i_sysdate = 0;
88 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
90 i_sysdate = (mtime_t)(i_clock - p_pgrm->cr_ref)
91 * (mtime_t)p_input->stream.control.i_rate
95 i_sysdate += (mtime_t)p_pgrm->sysdate_ref;
101 /*****************************************************************************
102 * ClockCurrent: converts current system date to clock units
103 *****************************************************************************
104 * Caution : the synchro state must be SYNCHRO_OK for this to operate.
105 *****************************************************************************/
106 static mtime_t ClockCurrent( input_thread_t * p_input,
107 pgrm_descriptor_t * p_pgrm )
109 return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
110 / p_input->stream.control.i_rate / 300
114 /*****************************************************************************
115 * ClockNewRef: writes a new clock reference
116 *****************************************************************************/
117 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
118 mtime_t i_clock, mtime_t i_sysdate )
120 p_pgrm->cr_ref = i_clock;
121 /* this is actually a kludge, but it gives better results when scr
122 * is zero in DVDs: we are 3-4 ms in advance instead of sometimes
124 p_pgrm->sysdate_ref = ( p_pgrm->last_syscr && !i_clock )
129 /*****************************************************************************
130 * input_ClockInit: reinitializes the clock reference after a stream
132 *****************************************************************************/
133 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
136 p_pgrm->last_syscr = 0;
138 p_pgrm->sysdate_ref = 0;
139 p_pgrm->delta_cr = 0;
140 p_pgrm->c_average_count = 0;
143 /*****************************************************************************
144 * input_ClockManageControl: handles the messages from the interface
145 *****************************************************************************
146 * Returns UNDEF_S if nothing happened, PAUSE_S if the stream was paused
147 *****************************************************************************/
148 int input_ClockManageControl( input_thread_t * p_input,
149 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
151 int i_return_value = UNDEF_S;
153 vlc_mutex_lock( &p_input->stream.stream_lock );
155 if( p_input->stream.i_new_status == PAUSE_S )
159 vlc_mutex_lock( &p_input->stream.control.control_lock );
160 i_old_status = p_input->stream.control.i_status;
161 p_input->stream.control.i_status = PAUSE_S;
162 vlc_mutex_unlock( &p_input->stream.control.control_lock );
164 vlc_cond_wait( &p_input->stream.stream_wait,
165 &p_input->stream.stream_lock );
166 p_pgrm->last_syscr = 0;
167 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
169 if( p_input->stream.i_new_status == PAUSE_S )
171 /* PAUSE_S undoes the pause state: Return to old state. */
172 vlc_mutex_lock( &p_input->stream.control.control_lock );
173 p_input->stream.control.i_status = i_old_status;
174 vlc_mutex_unlock( &p_input->stream.control.control_lock );
176 p_input->stream.i_new_status = UNDEF_S;
177 p_input->stream.i_new_rate = UNDEF_S;
180 /* We handle i_new_status != PAUSE_S below... */
182 i_return_value = PAUSE_S;
185 if( p_input->stream.i_new_status != UNDEF_S )
187 vlc_mutex_lock( &p_input->stream.control.control_lock );
189 p_input->stream.control.i_status = p_input->stream.i_new_status;
191 ClockNewRef( p_input, p_pgrm, i_clock,
192 ClockToSysdate( p_input, p_pgrm, i_clock ) );
194 if( p_input->stream.control.i_status == PLAYING_S )
196 p_input->stream.control.i_rate = DEFAULT_RATE;
197 p_input->stream.control.b_mute = 0;
201 p_input->stream.control.i_rate = p_input->stream.i_new_rate;
202 p_input->stream.control.b_mute = 1;
204 /* Feed the audio decoders with a NULL packet to avoid
205 * discontinuities. */
206 input_EscapeAudioDiscontinuity( p_input );
209 p_input->stream.i_new_status = UNDEF_S;
210 p_input->stream.i_new_rate = UNDEF_S;
212 vlc_mutex_unlock( &p_input->stream.control.control_lock );
215 vlc_mutex_unlock( &p_input->stream.stream_lock );
217 return( i_return_value );
220 /*****************************************************************************
221 * input_ClockManageRef: manages a clock reference
222 *****************************************************************************/
223 void input_ClockManageRef( input_thread_t * p_input,
224 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
226 /* take selected program if none specified */
229 p_pgrm = p_input->stream.p_selected_program;
232 if( ( p_pgrm->i_synchro_state != SYNCHRO_OK ) || ( i_clock == 0 ) )
234 /* Feed synchro with a new reference point. */
235 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
236 p_pgrm->i_synchro_state = SYNCHRO_OK;
238 if( p_input->stream.b_pace_control
239 && p_input->stream.p_selected_program == p_pgrm )
241 p_pgrm->last_cr = i_clock;
242 mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
247 p_pgrm->last_syscr = 0;
248 p_pgrm->delta_cr = 0;
249 p_pgrm->c_average_count = 0;
254 if ( p_pgrm->last_cr != 0 &&
255 ( (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
256 || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
258 /* Stream discontinuity, for which we haven't received a
259 * warning from the stream control facilities (dd-edited
261 msg_Warn( p_input, "clock gap, unexpected stream discontinuity" );
262 input_ClockInit( p_pgrm );
263 p_pgrm->i_synchro_state = SYNCHRO_START;
264 input_EscapeDiscontinuity( p_input );
267 p_pgrm->last_cr = i_clock;
269 if( p_input->stream.b_pace_control
270 && p_input->stream.p_selected_program == p_pgrm )
272 /* We remember the last system date to be able to restart
273 * the synchro we statistically better continuity, after
275 p_pgrm->last_syscr = ClockToSysdate( p_input, p_pgrm, i_clock );
277 /* Wait a while before delivering the packets to the decoder.
278 * In case of multiple programs, we arbitrarily follow the
279 * clock of the first program. */
280 mwait( p_pgrm->last_syscr );
282 /* Now take into account interface changes. */
283 input_ClockManageControl( p_input, p_pgrm, i_clock );
287 /* Smooth clock reference variations. */
288 mtime_t i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
290 /* Bresenham algorithm to smooth variations. */
291 if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
293 p_pgrm->delta_cr = ( p_pgrm->delta_cr
294 * (CR_MAX_AVERAGE_COUNTER - 1)
295 + ( i_extrapoled_clock - i_clock ) )
296 / CR_MAX_AVERAGE_COUNTER;
300 p_pgrm->delta_cr = ( p_pgrm->delta_cr
301 * p_pgrm->c_average_count
302 + ( i_extrapoled_clock - i_clock ) )
303 / (p_pgrm->c_average_count + 1);
304 p_pgrm->c_average_count++;
310 /*****************************************************************************
311 * input_ClockGetTS: manages a PTS or DTS
312 *****************************************************************************/
313 mtime_t input_ClockGetTS( input_thread_t * p_input,
314 pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
316 /* take selected program if none specified */
319 p_pgrm = p_input->stream.p_selected_program;
322 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
324 return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
326 + (p_input->p_vlc->i_desync > 0
327 ? p_input->p_vlc->i_desync : 0) );