libs/ardour/ltc_slave.cc

   1 /*
   2     Copyright (C) 2012 Paul Davis
   3     Witten by 2012 Robin Gareus <robin@gareus.org>
   4
   5     This program is free software; you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation; either version 2 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License
  16     along with this program; if not, write to the Free Software
  17     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  18
  19 */
  20 #include <iostream>
  21 #include <errno.h>
  22 #include <sys/types.h>
  23 #include <unistd.h>
  24
  25 #include "pbd/error.h"
  26 #include "pbd/pthread_utils.h"
  27
  28 #include "ardour/debug.h"
  29 #include "ardour/slave.h"
  30 #include "ardour/session.h"
  31 #include "ardour/audioengine.h"
  32 #include "ardour/audio_port.h"
  33
  34 #include "i18n.h"
  35
  36 using namespace std;
  37 using namespace ARDOUR;
  38 using namespace MIDI;
  39 using namespace PBD;
  40 using namespace Timecode;
  41
  42 #define FLYWHEEL_TIMEOUT ( 1 * session.frame_rate() )
  43
  44 LTC_Slave::LTC_Slave (Session& s)
  45         : session (s)
  46 {
  47         frames_per_ltc_frame = session.frames_per_timecode_frame();
  48         timecode.rate = session.timecode_frames_per_second();
  49         timecode.drop  = session.timecode_drop_frames();
  50
  51         did_reset_tc_format = false;
  52         delayedlocked = 10;
  53         monotonic_cnt = 0;
  54         fps_detected=false;
  55
  56         ltc_timecode = session.config.get_timecode_format();
  57         a3e_timecode = session.config.get_timecode_format();
  58         printed_timecode_warning = false;
  59         ltc_detect_fps_cnt = ltc_detect_fps_max = 0;
  60         memset(&prev_frame, 0, sizeof(LTCFrameExt));
  61
  62         decoder = ltc_decoder_create((int) frames_per_ltc_frame, 128 /*queue size*/);
  63
  64         session.config.ParameterChanged.connect_same_thread (config_connection, boost::bind (&LTC_Slave::parameter_changed, this, _1));
  65         parse_timecode_offset();
  66         reset();
  67         resync_latency();
  68         session.Xrun.connect_same_thread (port_connections, boost::bind (&LTC_Slave::resync_xrun, this));
  69         session.engine().GraphReordered.connect_same_thread (port_connections, boost::bind (&LTC_Slave::resync_latency, this));
  70 }
  71
  72 LTC_Slave::~LTC_Slave()
  73 {
  74         port_connections.drop_connections();
  75         config_connection.disconnect();
  76
  77         if (did_reset_tc_format) {
  78                 session.config.set_timecode_format (saved_tc_format);
  79         }
  80
  81         ltc_decoder_free(decoder);
  82 }
  83
  84 void
  85 LTC_Slave::parse_timecode_offset() {
  86         Timecode::Time offset_tc;
  87         Timecode::parse_timecode_format(session.config.get_slave_timecode_offset(), offset_tc);
  88         offset_tc.rate = session.timecode_frames_per_second();
  89         offset_tc.drop = session.timecode_drop_frames();
  90         session.timecode_to_sample(offset_tc, timecode_offset, false, false);
  91         timecode_negative_offset = offset_tc.negative;
  92 }
  93
  94 void
  95 LTC_Slave::parameter_changed (std::string const & p)
  96 {
  97         if (p == "slave-timecode-offset"
  98                         || p == "timecode-format"
  99                         ) {
 100                 parse_timecode_offset();
 101         }
 102 }
 103
 104 ARDOUR::framecnt_t
 105 LTC_Slave::resolution () const
 106 {
 107         return (framecnt_t) (session.frame_rate() / 1000);
 108 }
 109
 110 bool
 111 LTC_Slave::locked () const
 112 {
 113         return (delayedlocked < 5);
 114 }
 115
 116 bool
 117 LTC_Slave::ok() const
 118 {
 119         return true;
 120 }
 121
 122 void
 123 LTC_Slave::resync_xrun()
 124 {
 125         DEBUG_TRACE (DEBUG::LTC, "LTC resync_xrun()\n");
 126         engine_dll_initstate = 0;
 127 }
 128
 129 void
 130 LTC_Slave::resync_latency()
 131 {
 132         DEBUG_TRACE (DEBUG::LTC, "LTC resync_latency()\n");
 133         engine_dll_initstate = 0;
 134
 135         if (!session.deletion_in_progress() && session.ltc_output_io()) { /* check if Port exits */
 136                 boost::shared_ptr<Port> ltcport = session.ltc_input_port();
 137                 ltcport->get_connected_latency_range (ltc_slave_latency, false);
 138         }
 139 }
 140
 141 void
 142 LTC_Slave::reset()
 143 {
 144         DEBUG_TRACE (DEBUG::LTC, "LTC reset()\n");
 145         last_timestamp = 0;
 146         current_delta = 0;
 147         transport_direction = 0;
 148         ltc_speed = 0;
 149         engine_dll_initstate = 0;
 150 }
 151
 152 void
 153 LTC_Slave::parse_ltc(const ARDOUR::pframes_t nframes, const Sample* const in, const ARDOUR::framecnt_t posinfo)
 154 {
 155         pframes_t i;
 156         unsigned char sound[8192];
 157         if (nframes > 8192) {
 158                 /* TODO warn once or wrap, loop conversion below
 159                  * does jack/A3 support > 8192 spp anyway?
 160                  */
 161                 return;
 162         }
 163
 164         for (i = 0; i < nframes; i++) {
 165                 const int snd=(int)rint((127.0*in[i])+128.0);
 166                 sound[i] = (unsigned char) (snd&0xff);
 167         }
 168         ltc_decoder_write(decoder, sound, nframes, posinfo);
 169         return;
 170 }
 171
 172 bool
 173 LTC_Slave::equal_ltc_frame_time(LTCFrame *a, LTCFrame *b) {
 174         if (       a->frame_units != b->frame_units
 175                 || a->frame_tens  != b->frame_tens
 176                 || a->dfbit       != b->dfbit
 177                 || a->secs_units  != b->secs_units
 178                 || a->secs_tens   != b->secs_tens
 179                 || a->mins_units  != b->mins_units
 180                 || a->mins_tens   != b->mins_tens
 181                 || a->hours_units != b->hours_units
 182                 || a->hours_tens  != b->hours_tens
 183              ) {
 184                 return false;
 185         }
 186         return true;
 187 }
 188
 189 bool
 190 LTC_Slave::detect_discontinuity(LTCFrameExt *frame, int fps, bool fuzzy) {
 191         bool discontinuity_detected = false;
 192
 193         if (fuzzy && (
 194                   ( frame->reverse && prev_frame.ltc.frame_units == 0)
 195                 ||(!frame->reverse && frame->ltc.frame_units == 0)
 196                 )) {
 197                 memcpy(&prev_frame, frame, sizeof(LTCFrameExt));
 198                 return false;
 199         }
 200
 201         if (frame->reverse) {
 202                 ltc_frame_decrement(&prev_frame.ltc, fps, LTC_TV_525_60, 0);
 203         } else {
 204                 ltc_frame_increment(&prev_frame.ltc, fps, LTC_TV_525_60, 0);
 205         }
 206         if (!equal_ltc_frame_time(&prev_frame.ltc, &frame->ltc)) {
 207                 discontinuity_detected = true;
 208         }
 209
 210     memcpy(&prev_frame, frame, sizeof(LTCFrameExt));
 211     return discontinuity_detected;
 212 }
 213
 214 bool
 215 LTC_Slave::detect_ltc_fps(int frameno, bool df)
 216 {
 217         bool fps_changed = false;
 218         double detected_fps = 0;
 219         if (frameno > ltc_detect_fps_max)
 220         {
 221                 ltc_detect_fps_max = frameno;
 222         }
 223         ltc_detect_fps_cnt++;
 224
 225         if (ltc_detect_fps_cnt > 40) {
 226                 if (ltc_detect_fps_cnt > ltc_detect_fps_max) {
 227                         detected_fps = ltc_detect_fps_max + 1;
 228                         if (df) {
 229                                 /* LTC df -> indicates fractional framerate */
 230                                 if (Config->get_timecode_source_2997()) {
 231                                         detected_fps = detected_fps * 999.0 / 1000.0;
 232                                 } else {
 233                                         detected_fps = detected_fps * 1000.0 / 1001.0;
 234                                 }
 235                         }
 236
 237                         if (timecode.rate != detected_fps || timecode.drop != df) {
 238                                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC detected FPS: %1%2\n", detected_fps, df?"df":"ndf"));
 239                         } else {
 240                                 detected_fps = 0; /* no cange */
 241                         }
 242                 }
 243                 ltc_detect_fps_cnt = ltc_detect_fps_max = 0;
 244         }
 245
 246         /* when changed */
 247         if (detected_fps != 0 && (detected_fps != timecode.rate || df != timecode.drop)) {
 248                 timecode.rate = detected_fps;
 249                 timecode.drop = df;
 250                 frames_per_ltc_frame = double(session.frame_rate()) / timecode.rate;
 251                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC reset to FPS: %1%2 ; audio-frames per LTC: %3\n",
 252                                 detected_fps, df?"df":"ndf", frames_per_ltc_frame));
 253                 fps_changed=true;
 254         }
 255
 256         /* poll and check session TC */
 257         TimecodeFormat tc_format = apparent_timecode_format();
 258         TimecodeFormat cur_timecode = session.config.get_timecode_format();
 259
 260         if (Config->get_timecode_sync_frame_rate()) {
 261                 /* enforce time-code */
 262                 if (!did_reset_tc_format) {
 263                         saved_tc_format = cur_timecode;
 264                         did_reset_tc_format = true;
 265                 }
 266                 if (cur_timecode != tc_format) {
 267                         if (ceil(Timecode::timecode_to_frames_per_second(cur_timecode)) != ceil(Timecode::timecode_to_frames_per_second(tc_format))) {
 268                                 warning << string_compose(_("Session framerate adjusted from %1 to LTC's %2."),
 269                                                 Timecode::timecode_format_name(cur_timecode),
 270                                                 Timecode::timecode_format_name(tc_format))
 271                                         << endmsg;
 272                         }
 273                         session.config.set_timecode_format (tc_format);
 274                 }
 275         } else {
 276                 /* only warn about TC mismatch */
 277                 if (ltc_timecode != tc_format) printed_timecode_warning = false;
 278                 if (a3e_timecode != cur_timecode) printed_timecode_warning = false;
 279
 280                 if (cur_timecode != tc_format && ! printed_timecode_warning) {
 281                         if (ceil(Timecode::timecode_to_frames_per_second(cur_timecode)) != ceil(Timecode::timecode_to_frames_per_second(tc_format))) {
 282                                 warning << string_compose(_("Session and LTC framerate mismatch: LTC:%1 Session:%2."),
 283                                                 Timecode::timecode_format_name(tc_format),
 284                                                 Timecode::timecode_format_name(cur_timecode))
 285                                         << endmsg;
 286                         }
 287                         printed_timecode_warning = true;
 288                 }
 289         }
 290         ltc_timecode = tc_format;
 291         a3e_timecode = cur_timecode;
 292
 293         return fps_changed;
 294 }
 295
 296 void
 297 LTC_Slave::process_ltc(framepos_t const /*now*/)
 298 {
 299         LTCFrameExt frame;
 300         enum LTC_TV_STANDARD tv_standard = LTC_TV_625_50;
 301         while (ltc_decoder_read(decoder, &frame)) {
 302                 SMPTETimecode stime;
 303
 304                 ltc_frame_to_time(&stime, &frame.ltc, 0);
 305                 timecode.negative  = false;
 306                 timecode.subframes  = 0;
 307
 308                 /* set timecode.rate and timecode.drop: */
 309                 bool ltc_is_static = equal_ltc_frame_time(&prev_frame.ltc, &frame.ltc);
 310
 311                 if (detect_discontinuity(&frame, ceil(timecode.rate), !fps_detected)) {
 312                         if (fps_detected) { ltc_detect_fps_cnt = ltc_detect_fps_max = 0; }
 313                         fps_detected=false;
 314                 }
 315
 316                 if (!ltc_is_static && detect_ltc_fps(stime.frame, (frame.ltc.dfbit)? true : false)) {
 317                         reset();
 318                         fps_detected=true;
 319                 }
 320
 321 #if 0 // Devel/Debug
 322                 fprintf(stdout, "LTC %02d:%02d:%02d%c%02d | %8lld %8lld%s\n",
 323                         stime.hours,
 324                         stime.mins,
 325                         stime.secs,
 326                         (frame.ltc.dfbit) ? '.' : ':',
 327                         stime.frame,
 328                         frame.off_start,
 329                         frame.off_end,
 330                         frame.reverse ? " R" : "  "
 331                         );
 332 #endif
 333
 334                 /* when a full LTC frame is decoded, the timecode the LTC frame
 335                  * is referring has just passed.
 336                  * So we send the _next_ timecode which
 337                  * is expected to start at the end of the current frame
 338                  */
 339                 int fps_i = ceil(timecode.rate);
 340
 341                 switch(fps_i) {
 342                         case 30:
 343                                 if (timecode.drop) {
 344                                         tv_standard = LTC_TV_525_60;
 345                                 } else {
 346                                         tv_standard = LTC_TV_1125_60;
 347                                 }
 348                                 break;
 349                         case 25:
 350                                 tv_standard = LTC_TV_625_50;
 351                                 break;
 352                         default:
 353                                 tv_standard = LTC_TV_FILM_24; /* == LTC_TV_1125_60 == no offset, 24,30fps BGF */
 354                                 break;
 355                 }
 356
 357                 if (!frame.reverse) {
 358                         ltc_frame_increment(&frame.ltc, fps_i, tv_standard, 0);
 359                         ltc_frame_to_time(&stime, &frame.ltc, 0);
 360                         transport_direction = 1;
 361                         frame.off_start -= ltc_frame_alignment(session.frames_per_timecode_frame(), tv_standard);
 362                         frame.off_end -= ltc_frame_alignment(session.frames_per_timecode_frame(), tv_standard);
 363                 } else {
 364                         ltc_frame_decrement(&frame.ltc, fps_i, tv_standard, 0);
 365                         int off = frame.off_end - frame.off_start;
 366                         frame.off_start += off - ltc_frame_alignment(session.frames_per_timecode_frame(), tv_standard);
 367                         frame.off_end += off - ltc_frame_alignment(session.frames_per_timecode_frame(), tv_standard);
 368                         transport_direction = -1;
 369                 }
 370
 371                 timecode.hours   = stime.hours;
 372                 timecode.minutes = stime.mins;
 373                 timecode.seconds = stime.secs;
 374                 timecode.frames  = stime.frame;
 375
 376                 /* map LTC timecode to session TC setting */
 377                 framepos_t ltc_frame; ///< audio-frame corresponding to LTC frame
 378                 Timecode::timecode_to_sample (timecode, ltc_frame, true, false,
 379                         double(session.frame_rate()),
 380                         session.config.get_subframes_per_frame(),
 381                         timecode_negative_offset, timecode_offset
 382                         );
 383
 384                 framepos_t cur_timestamp = frame.off_end + 1;
 385                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC F: %1 LF: %2  N: %3 L: %4\n", ltc_frame, last_ltc_frame, cur_timestamp, last_timestamp));
 386                 if (frame.off_end + 1 <= last_timestamp || last_timestamp == 0) {
 387                         DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC speed: UNCHANGED: %1\n", ltc_speed));
 388                 } else {
 389                         ltc_speed = double(ltc_frame - last_ltc_frame) / double(cur_timestamp - last_timestamp);
 390                         DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC speed: %1\n", ltc_speed));
 391                 }
 392
 393                 if (fabs(ltc_speed) > 10.0) {
 394                         ltc_speed = 0;
 395                 }
 396
 397                 last_timestamp = frame.off_end + 1;
 398                 last_ltc_frame = ltc_frame;
 399         } /* end foreach decoded LTC frame */
 400 }
 401
 402 void
 403 LTC_Slave::init_engine_dll (framepos_t pos, int32_t inc)
 404 {
 405         double omega = 2.0 * M_PI * double(inc) / double(session.frame_rate());
 406         b = 1.4142135623730950488 * omega;
 407         c = omega * omega;
 408
 409         e2 = double(ltc_speed * inc);
 410         t0 = double(pos);
 411         t1 = t0 + e2;
 412         DEBUG_TRACE (DEBUG::LTC, string_compose ("[re-]init Engine DLL %1 %2 %3\n", t0, t1, e2));
 413 }
 414
 415 /* main entry point from session_process.cc
 416  * called from process callback context
 417  * so it is OK to use get_buffer()
 418  */
 419 bool
 420 LTC_Slave::speed_and_position (double& speed, framepos_t& pos)
 421 {
 422         bool engine_init_called = false;
 423         framepos_t now = session.engine().sample_time_at_cycle_start();
 424         framepos_t sess_pos = session.transport_frame(); // corresponds to now
 425         framecnt_t nframes = session.engine().samples_per_cycle();
 426
 427         Sample* in;
 428
 429         boost::shared_ptr<Port> ltcport = session.ltc_input_port();
 430
 431         in = (Sample*) AudioEngine::instance()->port_engine().get_buffer (ltcport->port_handle(), nframes);
 432
 433         frameoffset_t skip = now - (monotonic_cnt + nframes);
 434         monotonic_cnt = now;
 435         DEBUG_TRACE (DEBUG::LTC, string_compose ("speed_and_position - TID:%1 | latency: %2 | skip %3\n", pthread_name(), ltc_slave_latency.max, skip));
 436
 437         if (last_timestamp == 0) {
 438                 engine_dll_initstate = 0;
 439                 delayedlocked++;
 440         }
 441         else if (engine_dll_initstate != transport_direction && ltc_speed != 0) {
 442                 engine_dll_initstate = transport_direction;
 443                 init_engine_dll(last_ltc_frame + rint(ltc_speed * double(2 * nframes + now - last_timestamp)),
 444                                 session.engine().samples_per_cycle());
 445                 engine_init_called = true;
 446         }
 447
 448         if (in) {
 449                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC Process eng-tme: %1 eng-pos: %2\n", now, sess_pos));
 450                 /* when the jack-graph changes and if ardour performs
 451                  * locates, the audioengine is stopped (skipping frames) while
 452                  * jack [time] moves along.
 453                  */
 454                 if (skip > 0) {
 455                         DEBUG_TRACE (DEBUG::LTC, string_compose("engine skipped %1 frames. Feeding silence to LTC parser.\n", skip));
 456                         if (skip >= 8192) skip = 8192;
 457                         unsigned char sound[8192];
 458                         memset(sound, 0, sizeof(char) * skip);
 459                         ltc_decoder_write(decoder, sound, nframes, now);
 460                 } else if (skip != 0) {
 461                         /* this should never happen. it may if monotonic_cnt, now overflow on 64bit */
 462                         DEBUG_TRACE (DEBUG::LTC, string_compose("engine skipped %1 frames\n", skip));
 463                         reset();
 464                 }
 465
 466                 parse_ltc(nframes, in, now - ltc_slave_latency.max );
 467                 process_ltc(now);
 468         }
 469
 470         if (last_timestamp == 0) {
 471                 DEBUG_TRACE (DEBUG::LTC, "last timestamp == 0\n");
 472                 speed = 0;
 473                 pos = session.transport_frame();
 474                 return true;
 475         } else if (ltc_speed != 0) {
 476                 delayedlocked = 0;
 477         }
 478
 479         if (abs(now - last_timestamp) > FLYWHEEL_TIMEOUT) {
 480                 DEBUG_TRACE (DEBUG::LTC, "flywheel timeout\n");
 481                 reset();
 482                 speed = 0;
 483                 pos = session.transport_frame();
 484                 return true;
 485         }
 486
 487         /* it take 2 cycles from naught to rolling.
 488          * during these to initial cycles the speed == 0
 489          *
 490          * the first cycle:
 491          * DEBUG::Slave: slave stopped, move to NNN
 492          * DEBUG::Transport: Request forced locate to NNN
 493          * DEBUG::Slave: slave state 0 @ NNN speed 0 cur delta VERY-LARGE-DELTA avg delta 1800
 494          * DEBUG::Slave: silent motion
 495          * DEBUG::Transport: realtime stop @ NNN
 496          * DEBUG::Transport: Butler transport work, todo = PostTransportStop,PostTransportLocate,PostTransportClearSubstate
 497          *
 498          * [engine skips frames to locate, jack time keeps rolling on]
 499          *
 500          * the second cycle:
 501          *
 502          * DEBUG::LTC: [re-]init Engine DLL
 503          * DEBUG::Slave: slave stopped, move to NNN+
 504          * ...
 505          *
 506          * we need to seek two cycles ahead: 2 * nframes
 507          */
 508         if (engine_dll_initstate == 0) {
 509                 DEBUG_TRACE (DEBUG::LTC, "engine DLL not initialized. ltc_speed\n");
 510                 speed = 0;
 511                 pos = last_ltc_frame + rint(ltc_speed * double(2 * nframes + now - last_timestamp));
 512                 return true;
 513         }
 514
 515         /* interpolate position according to speed and time since last LTC-frame*/
 516         double speed_flt = ltc_speed;
 517         double elapsed = (now - last_timestamp) * speed_flt;
 518
 519         if (!engine_init_called) {
 520                 const double e = elapsed + double (last_ltc_frame - sess_pos);
 521                 t0 = t1;
 522                 t1 += b * e + e2;
 523                 e2 += c * e;
 524                 speed_flt = (t1 - t0) / double(session.engine().samples_per_cycle());
 525                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC engine DLL t0:%1 t1:%2 err:%3 spd:%4 ddt:%5\n", t0, t1, e, speed_flt, e2 - session.engine().samples_per_cycle() ));
 526         } else {
 527                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC adjusting elapsed (no DLL) from %1 by %2\n", elapsed, (2 * nframes * ltc_speed)));
 528                 speed_flt = 0;
 529                 elapsed += 2.0 * nframes * ltc_speed; /* see note above */
 530         }
 531
 532         pos = last_ltc_frame + rint(elapsed);
 533         speed = speed_flt;
 534         current_delta = (pos - sess_pos);
 535
 536         if (((pos < 0) || (labs(current_delta) > 2 * session.frame_rate()))) {
 537                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC large drift: %1\n", current_delta));
 538                 reset();
 539                 speed = 0;
 540                 pos = session.transport_frame();
 541                 return true;
 542         }
 543
 544         DEBUG_TRACE (DEBUG::LTC, string_compose ("LTCsync spd: %1 pos: %2 | last-pos: %3 elapsed: %4 delta: %5\n",
 545                                                  speed, pos, last_ltc_frame, elapsed, current_delta));
 546
 547         /* provide a .1% deadzone to lock the speed */
 548         if (fabs(speed - 1.0) <= 0.001) {
 549                 speed = 1.0;
 550         }
 551
 552         return true;
 553 }
 554
 555 Timecode::TimecodeFormat
 556 LTC_Slave::apparent_timecode_format () const
 557 {
 558         if      (timecode.rate == 24 && !timecode.drop)
 559                 return timecode_24;
 560         else if (timecode.rate == 25 && !timecode.drop)
 561                 return timecode_25;
 562         else if (rint(timecode.rate * 100) == 2997 && !timecode.drop)
 563                 return (Config->get_timecode_source_2997() ? timecode_2997000 : timecode_2997);
 564         else if (rint(timecode.rate * 100) == 2997 &&  timecode.drop)
 565                 return (Config->get_timecode_source_2997() ? timecode_2997000drop : timecode_2997drop);
 566         else if (timecode.rate == 30 &&  timecode.drop)
 567                 return timecode_2997drop; // timecode_30drop; // LTC counting to 30 frames w/DF *means* 29.97 df
 568         else if (timecode.rate == 30 && !timecode.drop)
 569                 return timecode_30;
 570
 571         /* XXX - unknown timecode format */
 572         return session.config.get_timecode_format();
 573 }
 574
 575 std::string
 576 LTC_Slave::approximate_current_position() const
 577 {
 578         if (last_timestamp == 0) {
 579                 return " --:--:--:--";
 580         }
 581         return Timecode::timecode_format_time(timecode);
 582 }
 583
 584 std::string
 585 LTC_Slave::approximate_current_delta() const
 586 {
 587         char delta[80];
 588         if (last_timestamp == 0 || engine_dll_initstate == 0) {
 589                 snprintf(delta, sizeof(delta), "\u2012\u2012\u2012\u2012");
 590         } else if ((monotonic_cnt - last_timestamp) > 2 * frames_per_ltc_frame) {
 591                 snprintf(delta, sizeof(delta), "%s", _("flywheel"));
 592         } else {
 593                 snprintf(delta, sizeof(delta), "\u0394<span foreground=\"green\" face=\"monospace\" >%s%s%" PRIi64 "</span>sm",
 594                                 LEADINGZERO(llabs(current_delta)), PLUSMINUS(-current_delta), llabs(current_delta));
 595         }
 596         return std::string(delta);
 597 }