1 /*****************************************************************************
2 * input_clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999-2001 VideoLAN
5 * $Id: input_clock.c,v 1.33 2002/11/10 18:04:23 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 #ifdef HAVE_SYS_TYPES_H
32 # include <sys/types.h> /* off_t */
35 #include "stream_control.h"
36 #include "input_ext-intf.h"
37 #include "input_ext-dec.h"
38 #include "input_ext-plugins.h"
41 * DISCUSSION : SYNCHRONIZATION METHOD
43 * In some cases we can impose the pace of reading (when reading from a
44 * file or a pipe), and for the synchronization we simply sleep() until
45 * it is time to deliver the packet to the decoders. When reading from
46 * the network, we must be read at the same pace as the server writes,
47 * otherwise the kernel's buffer will trash packets. The risk is now to
48 * overflow the input buffers in case the server goes too fast, that is
49 * why we do these calculations :
51 * We compute a mean for the pcr because we want to eliminate the
52 * network jitter and keep the low frequency variations. The mean is
53 * in fact a low pass filter and the jitter is a high frequency signal
54 * that is why it is eliminated by the filter/average.
56 * The low frequency variations enable us to synchronize the client clock
57 * with the server clock because they represent the time variation between
58 * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
59 * the presentation dates for the audio and video frames. With those dates
60 * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
61 * as it is sent by the server and so we keep the synchronization between
62 * the server and the client.
64 * It is a very important matter if you want to avoid underflow or overflow
65 * in all the FIFOs, but it may be not enough.
68 /*****************************************************************************
70 *****************************************************************************/
72 /* Maximum number of samples used to compute the dynamic average value.
73 * We use the following formula :
74 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
76 #define CR_MAX_AVERAGE_COUNTER 40
78 /* Maximum gap allowed between two CRs. */
79 #define CR_MAX_GAP 1000000
81 /*****************************************************************************
82 * ClockToSysdate: converts a movie clock to system date
83 *****************************************************************************/
84 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
85 mtime_t i_clock, mtime_t i_sysdate );
86 static mtime_t ClockToSysdate( input_thread_t * p_input,
87 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
89 mtime_t i_sysdate = 0;
91 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
93 i_sysdate = (mtime_t)(i_clock - p_pgrm->cr_ref)
94 * (mtime_t)p_input->stream.control.i_rate
98 i_sysdate += (mtime_t)p_pgrm->sysdate_ref;
104 /*****************************************************************************
105 * ClockCurrent: converts current system date to clock units
106 *****************************************************************************
107 * Caution : the synchro state must be SYNCHRO_OK for this to operate.
108 *****************************************************************************/
109 static mtime_t ClockCurrent( input_thread_t * p_input,
110 pgrm_descriptor_t * p_pgrm )
112 return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
113 / p_input->stream.control.i_rate / 300
117 /*****************************************************************************
118 * ClockNewRef: writes a new clock reference
119 *****************************************************************************/
120 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
121 mtime_t i_clock, mtime_t i_sysdate )
123 p_pgrm->cr_ref = i_clock;
124 /* this is actually a kludge, but it gives better results when scr
125 * is zero in DVDs: we are 3-4 ms in advance instead of sometimes
127 p_pgrm->sysdate_ref = ( p_pgrm->last_syscr && !i_clock )
132 /*****************************************************************************
133 * input_ClockInit: reinitializes the clock reference after a stream
135 *****************************************************************************/
136 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
139 p_pgrm->last_syscr = 0;
141 p_pgrm->sysdate_ref = 0;
142 p_pgrm->delta_cr = 0;
143 p_pgrm->c_average_count = 0;
146 /*****************************************************************************
147 * input_ClockManageControl: handles the messages from the interface
148 *****************************************************************************
149 * Returns UNDEF_S if nothing happened, PAUSE_S if the stream was paused
150 *****************************************************************************/
151 int input_ClockManageControl( input_thread_t * p_input,
152 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
154 int i_return_value = UNDEF_S;
156 vlc_mutex_lock( &p_input->stream.stream_lock );
158 if( p_input->stream.i_new_status == PAUSE_S )
162 vlc_mutex_lock( &p_input->stream.control.control_lock );
163 i_old_status = p_input->stream.control.i_status;
164 p_input->stream.control.i_status = PAUSE_S;
165 vlc_mutex_unlock( &p_input->stream.control.control_lock );
167 vlc_cond_wait( &p_input->stream.stream_wait,
168 &p_input->stream.stream_lock );
169 p_pgrm->last_syscr = 0;
170 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
172 if( p_input->stream.i_new_status == PAUSE_S )
174 /* PAUSE_S undoes the pause state: Return to old state. */
175 vlc_mutex_lock( &p_input->stream.control.control_lock );
176 p_input->stream.control.i_status = i_old_status;
177 vlc_mutex_unlock( &p_input->stream.control.control_lock );
179 p_input->stream.i_new_status = UNDEF_S;
180 p_input->stream.i_new_rate = UNDEF_S;
183 /* We handle i_new_status != PAUSE_S below... */
185 i_return_value = PAUSE_S;
188 if( p_input->stream.i_new_status != UNDEF_S )
190 vlc_mutex_lock( &p_input->stream.control.control_lock );
192 p_input->stream.control.i_status = p_input->stream.i_new_status;
194 ClockNewRef( p_input, p_pgrm, i_clock,
195 ClockToSysdate( p_input, p_pgrm, i_clock ) );
197 if( p_input->stream.control.i_status == PLAYING_S )
199 p_input->stream.control.i_rate = DEFAULT_RATE;
200 p_input->stream.control.b_mute = 0;
204 p_input->stream.control.i_rate = p_input->stream.i_new_rate;
205 p_input->stream.control.b_mute = 1;
207 /* Feed the audio decoders with a NULL packet to avoid
208 * discontinuities. */
209 input_EscapeAudioDiscontinuity( p_input );
212 p_input->stream.i_new_status = UNDEF_S;
213 p_input->stream.i_new_rate = UNDEF_S;
215 vlc_mutex_unlock( &p_input->stream.control.control_lock );
218 vlc_mutex_unlock( &p_input->stream.stream_lock );
220 return( i_return_value );
223 /*****************************************************************************
224 * input_ClockManageRef: manages a clock reference
225 *****************************************************************************/
226 void input_ClockManageRef( input_thread_t * p_input,
227 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
229 /* take selected program if none specified */
232 p_pgrm = p_input->stream.p_selected_program;
235 if( ( p_pgrm->i_synchro_state != SYNCHRO_OK ) || ( i_clock == 0 ) )
237 /* Feed synchro with a new reference point. */
238 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
239 p_pgrm->i_synchro_state = SYNCHRO_OK;
241 if( p_input->stream.b_pace_control
242 && p_input->stream.p_selected_program == p_pgrm )
244 p_pgrm->last_cr = i_clock;
245 mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
250 p_pgrm->last_syscr = 0;
251 p_pgrm->delta_cr = 0;
252 p_pgrm->c_average_count = 0;
257 if ( p_pgrm->last_cr != 0 &&
258 ( (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
259 || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
261 /* Stream discontinuity, for which we haven't received a
262 * warning from the stream control facilities (dd-edited
264 msg_Warn( p_input, "clock gap, unexpected stream discontinuity" );
265 input_ClockInit( p_pgrm );
266 p_pgrm->i_synchro_state = SYNCHRO_START;
267 input_EscapeDiscontinuity( p_input );
270 p_pgrm->last_cr = i_clock;
272 if( p_input->stream.b_pace_control
273 && p_input->stream.p_selected_program == p_pgrm )
275 /* We remember the last system date to be able to restart
276 * the synchro we statistically better continuity, after
278 p_pgrm->last_syscr = ClockToSysdate( p_input, p_pgrm, i_clock );
280 /* Wait a while before delivering the packets to the decoder.
281 * In case of multiple programs, we arbitrarily follow the
282 * clock of the first program. */
283 mwait( p_pgrm->last_syscr );
285 /* Now take into account interface changes. */
286 input_ClockManageControl( p_input, p_pgrm, i_clock );
290 /* Smooth clock reference variations. */
291 mtime_t i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
293 /* Bresenham algorithm to smooth variations. */
294 if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
296 p_pgrm->delta_cr = ( p_pgrm->delta_cr
297 * (CR_MAX_AVERAGE_COUNTER - 1)
298 + ( i_extrapoled_clock - i_clock ) )
299 / CR_MAX_AVERAGE_COUNTER;
303 p_pgrm->delta_cr = ( p_pgrm->delta_cr
304 * p_pgrm->c_average_count
305 + ( i_extrapoled_clock - i_clock ) )
306 / (p_pgrm->c_average_count + 1);
307 p_pgrm->c_average_count++;
313 /*****************************************************************************
314 * input_ClockGetTS: manages a PTS or DTS
315 *****************************************************************************/
316 mtime_t input_ClockGetTS( input_thread_t * p_input,
317 pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
319 /* take selected program if none specified */
322 p_pgrm = p_input->stream.p_selected_program;
325 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
327 return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
329 + (p_input->p_vlc->i_desync > 0
330 ? p_input->p_vlc->i_desync : 0) );