1 /*****************************************************************************
2 * input_clock.c: Clock/System date convertions, stream management
3 *****************************************************************************
4 * Copyright (C) 1999-2001 VideoLAN
5 * $Id: input_clock.c,v 1.26 2001/12/06 10:53:42 massiot 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"
46 * DISCUSSION : SYNCHRONIZATION METHOD
48 * In some cases we can impose the pace of reading (when reading from a
49 * file or a pipe), and for the synchronization we simply sleep() until
50 * it is time to deliver the packet to the decoders. When reading from
51 * the network, we must be read at the same pace as the server writes,
52 * otherwise the kernel's buffer will trash packets. The risk is now to
53 * overflow the input buffers in case the server goes too fast, that is
54 * why we do these calculations :
56 * We compute a mean for the pcr because we want to eliminate the
57 * network jitter and keep the low frequency variations. The mean is
58 * in fact a low pass filter and the jitter is a high frequency signal
59 * that is why it is eliminated by the filter/average.
61 * The low frequency variations enable us to synchronize the client clock
62 * with the server clock because they represent the time variation between
63 * the 2 clocks. Those variations (ie the filtered pcr) are used to compute
64 * the presentation dates for the audio and video frames. With those dates
65 * we can decode (or trash) the MPEG2 stream at "exactly" the same rate
66 * as it is sent by the server and so we keep the synchronization between
67 * the server and the client.
69 * It is a very important matter if you want to avoid underflow or overflow
70 * in all the FIFOs, but it may be not enough.
73 /*****************************************************************************
75 *****************************************************************************/
77 /* Maximum number of samples used to compute the dynamic average value.
78 * We use the following formula :
79 * new_average = (old_average * c_average + new_sample_value) / (c_average +1)
81 #define CR_MAX_AVERAGE_COUNTER 40
83 /* Maximum gap allowed between two CRs. */
84 #define CR_MAX_GAP 1000000
86 /*****************************************************************************
87 * ClockToSysdate: converts a movie clock to system date
88 *****************************************************************************/
89 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
90 mtime_t i_clock, mtime_t i_sysdate );
91 static mtime_t ClockToSysdate( input_thread_t * p_input,
92 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
94 mtime_t i_sysdate = 0;
96 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
98 i_sysdate = (mtime_t)(i_clock - p_pgrm->cr_ref)
99 * (mtime_t)p_input->stream.control.i_rate
103 i_sysdate += (mtime_t)p_pgrm->sysdate_ref;
109 /*****************************************************************************
110 * ClockCurrent: converts current system date to clock units
111 *****************************************************************************
112 * Caution : the synchro state must be SYNCHRO_OK for this to operate.
113 *****************************************************************************/
114 static mtime_t ClockCurrent( input_thread_t * p_input,
115 pgrm_descriptor_t * p_pgrm )
117 return( (mdate() - p_pgrm->sysdate_ref) * 27 * DEFAULT_RATE
118 / p_input->stream.control.i_rate / 300
122 /*****************************************************************************
123 * ClockNewRef: writes a new clock reference
124 *****************************************************************************/
125 static void ClockNewRef( input_thread_t * p_input, pgrm_descriptor_t * p_pgrm,
126 mtime_t i_clock, mtime_t i_sysdate )
128 p_pgrm->cr_ref = i_clock;
129 /* this is actually a kludge, but it gives better results when scr
130 * is zero in DVDs: we are 3-4 ms in advance instead of sometimes
132 p_pgrm->sysdate_ref = ( p_pgrm->last_syscr && !i_clock )
137 /*****************************************************************************
138 * input_ClockInit: reinitializes the clock reference after a stream
140 *****************************************************************************/
141 void input_ClockInit( pgrm_descriptor_t * p_pgrm )
144 p_pgrm->last_syscr = 0;
146 p_pgrm->sysdate_ref = 0;
147 p_pgrm->delta_cr = 0;
148 p_pgrm->c_average_count = 0;
151 /*****************************************************************************
152 * input_ClockManageControl: handles the messages from the interface
153 *****************************************************************************
154 * Returns UNDEF_S if nothing happened, PAUSE_S if the stream was paused
155 *****************************************************************************/
156 int input_ClockManageControl( input_thread_t * p_input,
157 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
159 int i_return_value = UNDEF_S;
161 vlc_mutex_lock( &p_input->stream.stream_lock );
163 if( p_input->stream.i_new_status == PAUSE_S )
166 vlc_mutex_lock( &p_input->stream.control.control_lock );
167 i_old_status = p_input->stream.control.i_status;
169 p_input->stream.control.i_status = PAUSE_S;
170 vlc_cond_wait( &p_input->stream.stream_wait,
171 &p_input->stream.stream_lock );
172 p_pgrm->last_syscr = 0;
173 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
175 if( p_input->stream.i_new_status == PAUSE_S )
177 /* PAUSE_S undoes the pause state: Return to old state. */
178 p_input->stream.control.i_status = i_old_status;
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... */
184 vlc_mutex_unlock( &p_input->stream.control.control_lock );
186 i_return_value = PAUSE_S;
189 if( p_input->stream.i_new_status != UNDEF_S )
191 vlc_mutex_lock( &p_input->stream.control.control_lock );
193 p_input->stream.control.i_status = p_input->stream.i_new_status;
195 ClockNewRef( p_input, p_pgrm, i_clock,
196 ClockToSysdate( p_input, p_pgrm, i_clock ) );
198 if( p_input->stream.control.i_status == PLAYING_S )
200 p_input->stream.control.i_rate = DEFAULT_RATE;
201 p_input->stream.control.b_mute = 0;
205 p_input->stream.control.i_rate = p_input->stream.i_new_rate;
206 p_input->stream.control.b_mute = 1;
208 /* Feed the audio decoders with a NULL packet to avoid
209 * discontinuities. */
210 input_EscapeAudioDiscontinuity( p_input );
213 p_input->stream.i_new_status = UNDEF_S;
214 p_input->stream.i_new_rate = UNDEF_S;
216 vlc_mutex_unlock( &p_input->stream.control.control_lock );
219 vlc_mutex_unlock( &p_input->stream.stream_lock );
221 return( i_return_value );
224 /*****************************************************************************
225 * input_ClockManageRef: manages a clock reference
226 *****************************************************************************/
227 void input_ClockManageRef( input_thread_t * p_input,
228 pgrm_descriptor_t * p_pgrm, mtime_t i_clock )
230 if( ( p_pgrm->i_synchro_state != SYNCHRO_OK ) || ( i_clock == 0 ) )
232 /* Feed synchro with a new reference point. */
233 ClockNewRef( p_input, p_pgrm, i_clock, mdate() );
234 p_pgrm->i_synchro_state = SYNCHRO_OK;
236 if( p_input->stream.b_pace_control
237 && p_input->stream.p_selected_program == p_pgrm )
239 p_pgrm->last_cr = i_clock;
240 mwait( ClockToSysdate( p_input, p_pgrm, i_clock ) );
245 p_pgrm->last_syscr = 0;
246 p_pgrm->delta_cr = 0;
247 p_pgrm->c_average_count = 0;
252 if ( p_pgrm->last_cr != 0 &&
253 ( (p_pgrm->last_cr - i_clock) > CR_MAX_GAP
254 || (p_pgrm->last_cr - i_clock) < - CR_MAX_GAP ) )
256 /* Stream discontinuity, for which we haven't received a
257 * warning from the stream control facilities (dd-edited
259 intf_WarnMsg( 1, "Clock gap, unexpected stream discontinuity" );
260 input_ClockInit( p_pgrm );
261 p_pgrm->i_synchro_state = SYNCHRO_START;
262 input_EscapeDiscontinuity( p_input, p_pgrm );
265 p_pgrm->last_cr = i_clock;
267 if( p_input->stream.b_pace_control
268 && p_input->stream.p_selected_program == p_pgrm )
270 /* We remember the last system date to be able to restart
271 * the synchro we statistically better continuity, after
273 p_pgrm->last_syscr = ClockToSysdate( p_input, p_pgrm, i_clock );
275 /* Wait a while before delivering the packets to the decoder.
276 * In case of multiple programs, we arbitrarily follow the
277 * clock of the first program. */
278 mwait( p_pgrm->last_syscr );
280 /* Now take into account interface changes. */
281 input_ClockManageControl( p_input, p_pgrm, i_clock );
285 /* Smooth clock reference variations. */
286 mtime_t i_extrapoled_clock = ClockCurrent( p_input, p_pgrm );
288 /* Bresenham algorithm to smooth variations. */
289 if( p_pgrm->c_average_count == CR_MAX_AVERAGE_COUNTER )
291 p_pgrm->delta_cr = ( p_pgrm->delta_cr
292 * (CR_MAX_AVERAGE_COUNTER - 1)
293 + ( i_extrapoled_clock - i_clock ) )
294 / CR_MAX_AVERAGE_COUNTER;
298 p_pgrm->delta_cr = ( p_pgrm->delta_cr
299 * p_pgrm->c_average_count
300 + ( i_extrapoled_clock - i_clock ) )
301 / (p_pgrm->c_average_count + 1);
302 p_pgrm->c_average_count++;
308 /*****************************************************************************
309 * input_ClockGetTS: manages a PTS or DTS
310 *****************************************************************************/
311 mtime_t input_ClockGetTS( input_thread_t * p_input,
312 pgrm_descriptor_t * p_pgrm, mtime_t i_ts )
314 if( p_pgrm->i_synchro_state == SYNCHRO_OK )
316 return( ClockToSysdate( p_input, p_pgrm, i_ts + p_pgrm->delta_cr )
318 + (p_main->i_desync > 0 ? p_main->i_desync : 0) );