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 <poll.h>
  23 #include <sys/types.h>
  24 #include <unistd.h>
  25
  26 #include "pbd/error.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 == "subframes-per-frame"
  99                         || p == "timecode-format"
 100                         ) {
 101                 parse_timecode_offset();
 102         }
 103 }
 104
 105 ARDOUR::framecnt_t
 106 LTC_Slave::resolution () const
 107 {
 108         return (framecnt_t) (session.frame_rate() / 1000);
 109 }
 110
 111 bool
 112 LTC_Slave::locked () const
 113 {
 114         return (delayedlocked < 5);
 115 }
 116
 117 bool
 118 LTC_Slave::ok() const
 119 {
 120         return true;
 121 }
 122
 123 void
 124 LTC_Slave::resync_xrun()
 125 {
 126         DEBUG_TRACE (DEBUG::LTC, "LTC resync_xrun()\n");
 127         engine_dll_initstate = 0;
 128 }
 129
 130 void
 131 LTC_Slave::resync_latency()
 132 {
 133         DEBUG_TRACE (DEBUG::LTC, "LTC resync_latency()\n");
 134         engine_dll_initstate = 0;
 135
 136         if (!session.deletion_in_progress() && session.ltc_output_io()) { /* check if Port exits */
 137                 boost::shared_ptr<Port> ltcport = session.ltc_input_port();
 138                 ltcport->get_connected_latency_range(ltc_slave_latency, false);
 139         }
 140 }
 141
 142 void
 143 LTC_Slave::reset()
 144 {
 145         DEBUG_TRACE (DEBUG::LTC, "LTC reset()\n");
 146         last_timestamp = 0;
 147         current_delta = 0;
 148         transport_direction = 0;
 149         ltc_speed = 0;
 150         engine_dll_initstate = 0;
 151 }
 152
 153 void
 154 LTC_Slave::parse_ltc(const jack_nframes_t nframes, const jack_default_audio_sample_t * const in, const framecnt_t posinfo)
 155 {
 156         jack_nframes_t i;
 157         unsigned char sound[8192];
 158         if (nframes > 8192) {
 159                 /* TODO warn once or wrap, loop conversion below
 160                  * does jack/A3 support > 8192 spp anyway?
 161                  */
 162                 return;
 163         }
 164
 165         for (i = 0; i < nframes; i++) {
 166                 const int snd=(int)rint((127.0*in[i])+128.0);
 167                 sound[i] = (unsigned char) (snd&0xff);
 168         }
 169         ltc_decoder_write(decoder, sound, nframes, posinfo);
 170         return;
 171 }
 172
 173 bool
 174 LTC_Slave::equal_ltc_frame_time(LTCFrame *a, LTCFrame *b) {
 175         if (       a->frame_units != b->frame_units
 176                 || a->frame_tens  != b->frame_tens
 177                 || a->dfbit       != b->dfbit
 178                 || a->secs_units  != b->secs_units
 179                 || a->secs_tens   != b->secs_tens
 180                 || a->mins_units  != b->mins_units
 181                 || a->mins_tens   != b->mins_tens
 182                 || a->hours_units != b->hours_units
 183                 || a->hours_tens  != b->hours_tens
 184              ) {
 185                 return false;
 186         }
 187         return true;
 188 }
 189
 190 bool
 191 LTC_Slave::detect_discontinuity(LTCFrameExt *frame, int fps, bool fuzzy) {
 192         bool discontinuity_detected = false;
 193
 194         if (fuzzy && (
 195                   ( frame->reverse && prev_frame.ltc.frame_units == 0)
 196                 ||(!frame->reverse && frame->ltc.frame_units == 0)
 197                 )) {
 198                 memcpy(&prev_frame, frame, sizeof(LTCFrameExt));
 199                 return false;
 200         }
 201
 202         if (frame->reverse) {
 203                 ltc_frame_decrement(&prev_frame.ltc, fps, LTC_TV_525_60, 0);
 204         } else {
 205                 ltc_frame_increment(&prev_frame.ltc, fps, LTC_TV_525_60, 0);
 206         }
 207         if (!equal_ltc_frame_time(&prev_frame.ltc, &frame->ltc)) {
 208                 discontinuity_detected = true;
 209         }
 210
 211     memcpy(&prev_frame, frame, sizeof(LTCFrameExt));
 212     return discontinuity_detected;
 213 }
 214
 215 bool
 216 LTC_Slave::detect_ltc_fps(int frameno, bool df)
 217 {
 218         bool fps_changed = false;
 219         double detected_fps = 0;
 220         if (frameno > ltc_detect_fps_max)
 221         {
 222                 ltc_detect_fps_max = frameno;
 223         }
 224         ltc_detect_fps_cnt++;
 225
 226         if (ltc_detect_fps_cnt > 40) {
 227                 if (ltc_detect_fps_cnt > ltc_detect_fps_max) {
 228                         detected_fps = ltc_detect_fps_max + 1;
 229                         if (df) {
 230                                 /* LTC df -> indicates fractional framerate */
 231                                 if (Config->get_timecode_source_2997()) {
 232                                         detected_fps = detected_fps * 999.0 / 1000.0;
 233                                 } else {
 234                                         detected_fps = detected_fps * 1000.0 / 1001.0;
 235                                 }
 236                         }
 237
 238                         if (timecode.rate != detected_fps || timecode.drop != df) {
 239                                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC detected FPS: %1%2\n", detected_fps, df?"df":"ndf"));
 240                         } else {
 241                                 detected_fps = 0; /* no cange */
 242                         }
 243                 }
 244                 ltc_detect_fps_cnt = ltc_detect_fps_max = 0;
 245         }
 246
 247         /* when changed */
 248         if (detected_fps != 0 && (detected_fps != timecode.rate || df != timecode.drop)) {
 249                 timecode.rate = detected_fps;
 250                 timecode.drop = df;
 251                 frames_per_ltc_frame = double(session.frame_rate()) / timecode.rate;
 252                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC reset to FPS: %1%2 ; audio-frames per LTC: %3\n",
 253                                 detected_fps, df?"df":"ndf", frames_per_ltc_frame));
 254                 fps_changed=true;
 255         }
 256
 257         /* poll and check session TC */
 258         TimecodeFormat tc_format = apparent_timecode_format();
 259         TimecodeFormat cur_timecode = session.config.get_timecode_format();
 260
 261         if (Config->get_timecode_sync_frame_rate()) {
 262                 /* enforce time-code */
 263                 if (!did_reset_tc_format) {
 264                         saved_tc_format = cur_timecode;
 265                         did_reset_tc_format = true;
 266                 }
 267                 if (cur_timecode != tc_format) {
 268                         if (ceil(Timecode::timecode_to_frames_per_second(cur_timecode)) != ceil(Timecode::timecode_to_frames_per_second(tc_format))) {
 269                                 warning << string_compose(_("Session framerate adjusted from %1 to LTC's %2."),
 270                                                 Timecode::timecode_format_name(cur_timecode),
 271                                                 Timecode::timecode_format_name(tc_format))
 272                                         << endmsg;
 273                         }
 274                         session.config.set_timecode_format (tc_format);
 275                 }
 276         } else {
 277                 /* only warn about TC mismatch */
 278                 if (ltc_timecode != tc_format) printed_timecode_warning = false;
 279                 if (a3e_timecode != cur_timecode) printed_timecode_warning = false;
 280
 281                 if (cur_timecode != tc_format && ! printed_timecode_warning) {
 282                         if (ceil(Timecode::timecode_to_frames_per_second(cur_timecode)) != ceil(Timecode::timecode_to_frames_per_second(tc_format))) {
 283                                 warning << string_compose(_("Session and LTC framerate mismatch: LTC:%1 Session:%2."),
 284                                                 Timecode::timecode_format_name(tc_format),
 285                                                 Timecode::timecode_format_name(cur_timecode))
 286                                         << endmsg;
 287                         }
 288                         printed_timecode_warning = true;
 289                 }
 290         }
 291         ltc_timecode = tc_format;
 292         a3e_timecode = cur_timecode;
 293
 294         return fps_changed;
 295 }
 296
 297 void
 298 LTC_Slave::process_ltc(framepos_t const now)
 299 {
 300         LTCFrameExt frame;
 301         enum LTC_TV_STANDARD tv_standard = LTC_TV_625_50;
 302         while (ltc_decoder_read(decoder, &frame)) {
 303                 SMPTETimecode stime;
 304
 305                 ltc_frame_to_time(&stime, &frame.ltc, 0);
 306                 timecode.negative  = false;
 307                 timecode.subframes  = 0;
 308
 309                 /* set timecode.rate and timecode.drop: */
 310                 bool ltc_is_static = equal_ltc_frame_time(&prev_frame.ltc, &frame.ltc);
 311
 312                 if (detect_discontinuity(&frame, ceil(timecode.rate), !fps_detected)) {
 313                         if (fps_detected) { ltc_detect_fps_cnt = ltc_detect_fps_max = 0; }
 314                         fps_detected=false;
 315                 }
 316
 317                 if (!ltc_is_static && detect_ltc_fps(stime.frame, (frame.ltc.dfbit)? true : false)) {
 318                         reset();
 319                         fps_detected=true;
 320                 }
 321
 322 #if 0 // Devel/Debug
 323                 fprintf(stdout, "LTC %02d:%02d:%02d%c%02d | %8lld %8lld%s\n",
 324                         stime.hours,
 325                         stime.mins,
 326                         stime.secs,
 327                         (frame.ltc.dfbit) ? '.' : ':',
 328                         stime.frame,
 329                         frame.off_start,
 330                         frame.off_end,
 331                         frame.reverse ? " R" : "  "
 332                         );
 333 #endif
 334
 335                 /* when a full LTC frame is decoded, the timecode the LTC frame
 336                  * is referring has just passed.
 337                  * So we send the _next_ timecode which
 338                  * is expected to start at the end of the current frame
 339                  */
 340                 int fps_i = ceil(timecode.rate);
 341
 342                 switch(fps_i) {
 343                         case 30:
 344                                 if (timecode.drop) {
 345                                         tv_standard = LTC_TV_525_60;
 346                                 } else {
 347                                         tv_standard = LTC_TV_1125_60;
 348                                 }
 349                                 break;
 350                         case 25:
 351                                 tv_standard = LTC_TV_625_50;
 352                                 break;
 353                         default:
 354                                 tv_standard = LTC_TV_FILM_24; /* == LTC_TV_1125_60 == no offset, 24,30fps BGF */
 355                                 break;
 356                 }
 357
 358                 if (!frame.reverse) {
 359                         ltc_frame_increment(&frame.ltc, fps_i, tv_standard, 0);
 360                         ltc_frame_to_time(&stime, &frame.ltc, 0);
 361                         transport_direction = 1;
 362                         frame.off_start -= ltc_frame_alignment(session.frame_rate(), tv_standard);
 363                         frame.off_end -= ltc_frame_alignment(session.frame_rate(), tv_standard);
 364                 } else {
 365                         ltc_frame_decrement(&frame.ltc, fps_i, tv_standard, 0);
 366                         int off = frame.off_end - frame.off_start;
 367                         frame.off_start += off - ltc_frame_alignment(session.frame_rate(), tv_standard);
 368                         frame.off_end += off - ltc_frame_alignment(session.frame_rate(), tv_standard);
 369                         transport_direction = -1;
 370                 }
 371
 372                 timecode.hours   = stime.hours;
 373                 timecode.minutes = stime.mins;
 374                 timecode.seconds = stime.secs;
 375                 timecode.frames  = stime.frame;
 376
 377                 /* map LTC timecode to session TC setting */
 378                 framepos_t ltc_frame; ///< audio-frame corresponding to LTC frame
 379                 Timecode::timecode_to_sample (timecode, ltc_frame, true, false,
 380                         double(session.frame_rate()),
 381                         session.config.get_subframes_per_frame(),
 382                         timecode_negative_offset, timecode_offset
 383                         );
 384
 385                 framepos_t cur_timestamp = frame.off_end + 1;
 386                 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));
 387                 if (frame.off_end + 1 <= last_timestamp || last_timestamp == 0) {
 388                         DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC speed: UNCHANGED: %1\n", ltc_speed));
 389                 } else {
 390                         ltc_speed = double(ltc_frame - last_ltc_frame) / double(cur_timestamp - last_timestamp);
 391                         DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC speed: %1\n", ltc_speed));
 392                 }
 393
 394                 if (fabs(ltc_speed) > 10.0) {
 395                         ltc_speed = 0;
 396                 }
 397
 398                 last_timestamp = frame.off_end + 1;
 399                 last_ltc_frame = ltc_frame;
 400         } /* end foreach decoded LTC frame */
 401 }
 402
 403 void
 404 LTC_Slave::init_engine_dll (framepos_t pos, int32_t inc)
 405 {
 406         double omega = 2.0 * M_PI * double(inc) / double(session.frame_rate());
 407         b = 1.4142135623730950488 * omega;
 408         c = omega * omega;
 409
 410         e2 = double(ltc_speed * inc);
 411         t0 = double(pos);
 412         t1 = t0 + e2;
 413         DEBUG_TRACE (DEBUG::LTC, string_compose ("[re-]init Engine DLL %1 %2 %3\n", t0, t1, e2));
 414 }
 415
 416 /* main entry point from session_process.cc
 417  * called from jack_process callback context
 418  * so it is OK to use jack_port_get_buffer()
 419  */
 420 bool
 421 LTC_Slave::speed_and_position (double& speed, framepos_t& pos)
 422 {
 423         bool engine_init_called = false;
 424         framepos_t now = session.engine().frame_time_at_cycle_start();
 425         framepos_t sess_pos = session.transport_frame(); // corresponds to now
 426         framecnt_t nframes = session.engine().frames_per_cycle();
 427
 428         jack_default_audio_sample_t *in;
 429
 430         boost::shared_ptr<Port> ltcport = session.ltc_input_port();
 431
 432         in = (jack_default_audio_sample_t*) jack_port_get_buffer (ltcport->jack_port(), nframes);
 433
 434         frameoffset_t skip = now - (monotonic_cnt + nframes);
 435         monotonic_cnt = now;
 436         DEBUG_TRACE (DEBUG::LTC, string_compose ("speed_and_position - TID:%1 | latency: %2 | skip %3\n", ::pthread_self(), ltc_slave_latency.max, skip));
 437
 438         if (last_timestamp == 0) {
 439                 engine_dll_initstate = 0;
 440                 delayedlocked++;
 441         }
 442         else if (engine_dll_initstate != transport_direction && ltc_speed != 0) {
 443                 engine_dll_initstate = transport_direction;
 444                 init_engine_dll(last_ltc_frame + rint(ltc_speed * double(2 * nframes + now - last_timestamp)),
 445                                 session.engine().frames_per_cycle());
 446                 engine_init_called = true;
 447         }
 448
 449         if (in) {
 450                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC Process eng-tme: %1 eng-pos: %2\n", now, sess_pos));
 451                 /* when the jack-graph changes and if ardour performs
 452                  * locates, the audioengine is stopped (skipping frames) while
 453                  * jack [time] moves along.
 454                  */
 455                 if (skip > 0) {
 456                         DEBUG_TRACE (DEBUG::LTC, string_compose("engine skipped %1 frames. Feeding silence to LTC parser.\n", skip));
 457                         if (skip >= 8192) skip = 8192;
 458                         unsigned char sound[8192];
 459                         memset(sound, 0, sizeof(char) * skip);
 460                         ltc_decoder_write(decoder, sound, nframes, now);
 461                 } else if (skip != 0) {
 462                         /* this should never happen. it may if monotonic_cnt, now overflow on 64bit */
 463                         DEBUG_TRACE (DEBUG::LTC, string_compose("engine skipped %1 frames\n", skip));
 464                         reset();
 465                 }
 466
 467                 parse_ltc(nframes, in, now - ltc_slave_latency.max );
 468                 process_ltc(now);
 469         }
 470
 471         if (last_timestamp == 0) {
 472                 DEBUG_TRACE (DEBUG::LTC, "last timestamp == 0\n");
 473                 speed = 0;
 474                 pos = session.transport_frame();
 475                 return true;
 476         } else if (ltc_speed != 0) {
 477                 delayedlocked = 0;
 478         }
 479
 480         if (abs(now - last_timestamp) > FLYWHEEL_TIMEOUT) {
 481                 DEBUG_TRACE (DEBUG::LTC, "flywheel timeout\n");
 482                 reset();
 483                 speed = 0;
 484                 pos = session.transport_frame();
 485                 return true;
 486         }
 487
 488         /* it take 2 cycles from naught to rolling.
 489          * during these to initial cycles the speed == 0
 490          *
 491          * the first cycle:
 492          * DEBUG::Slave: slave stopped, move to NNN
 493          * DEBUG::Transport: Request forced locate to NNN
 494          * DEBUG::Slave: slave state 0 @ NNN speed 0 cur delta VERY-LARGE-DELTA avg delta 1800
 495          * DEBUG::Slave: silent motion
 496          * DEBUG::Transport: realtime stop @ NNN
 497          * DEBUG::Transport: Butler transport work, todo = PostTransportStop,PostTransportLocate,PostTransportClearSubstate
 498          *
 499          * [engine skips frames to locate, jack time keeps rolling on]
 500          *
 501          * the second cycle:
 502          *
 503          * DEBUG::LTC: [re-]init Engine DLL
 504          * DEBUG::Slave: slave stopped, move to NNN+
 505          * ...
 506          *
 507          * we need to seek two cycles ahead: 2 * nframes
 508          */
 509         if (engine_dll_initstate == 0) {
 510                 DEBUG_TRACE (DEBUG::LTC, "engine DLL not initialized. ltc_speed\n");
 511                 speed = 0;
 512                 pos = last_ltc_frame + rint(ltc_speed * double(2 * nframes + now - last_timestamp));
 513                 return true;
 514         }
 515
 516         /* interpolate position according to speed and time since last LTC-frame*/
 517         double speed_flt = ltc_speed;
 518         double elapsed = (now - last_timestamp) * speed_flt;
 519
 520         if (!engine_init_called) {
 521                 const double e = elapsed + double (last_ltc_frame - sess_pos);
 522                 t0 = t1;
 523                 t1 += b * e + e2;
 524                 e2 += c * e;
 525                 speed_flt = (t1 - t0) / double(session.engine().frames_per_cycle());
 526                 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().frames_per_cycle() ));
 527         } else {
 528                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC adjusting elapsed (no DLL) from %1 by %2\n", elapsed, (2 * nframes * ltc_speed)));
 529                 speed_flt = 0;
 530                 elapsed += 2.0 * nframes * ltc_speed; /* see note above */
 531         }
 532
 533         pos = last_ltc_frame + rint(elapsed);
 534         speed = speed_flt;
 535         current_delta = (pos - sess_pos);
 536
 537         if (((pos < 0) || (labs(current_delta) > 2 * session.frame_rate()))) {
 538                 DEBUG_TRACE (DEBUG::LTC, string_compose ("LTC large drift: %1\n", current_delta));
 539                 reset();
 540                 speed = 0;
 541                 pos = session.transport_frame();
 542                 return true;
 543         }
 544
 545         DEBUG_TRACE (DEBUG::LTC, string_compose ("LTCsync spd: %1 pos: %2 | last-pos: %3 elapsed: %4 delta: %5\n",
 546                                                  speed, pos, last_ltc_frame, elapsed, current_delta));
 547
 548         /* provide a .1% deadzone to lock the speed */
 549         if (fabs(speed - 1.0) <= 0.001) {
 550                 speed = 1.0;
 551         }
 552
 553         return true;
 554 }
 555
 556 Timecode::TimecodeFormat
 557 LTC_Slave::apparent_timecode_format () const
 558 {
 559         if      (timecode.rate == 24 && !timecode.drop)
 560                 return timecode_24;
 561         else if (timecode.rate == 25 && !timecode.drop)
 562                 return timecode_25;
 563         else if (rint(timecode.rate * 100) == 2997 && !timecode.drop)
 564                 return (Config->get_timecode_source_2997() ? timecode_2997000 : timecode_2997);
 565         else if (rint(timecode.rate * 100) == 2997 &&  timecode.drop)
 566                 return (Config->get_timecode_source_2997() ? timecode_2997000drop : timecode_2997drop);
 567         else if (timecode.rate == 30 &&  timecode.drop)
 568                 return timecode_2997drop; // timecode_30drop; // LTC counting to 30 frames w/DF *means* 29.97 df
 569         else if (timecode.rate == 30 && !timecode.drop)
 570                 return timecode_30;
 571
 572         /* XXX - unknown timecode format */
 573         return session.config.get_timecode_format();
 574 }
 575
 576 std::string
 577 LTC_Slave::approximate_current_position() const
 578 {
 579         if (last_timestamp == 0) {
 580                 return " \u2012\u2012:\u2012\u2012:\u2012\u2012:\u2012\u2012";
 581         }
 582         return Timecode::timecode_format_time(timecode);
 583 }
 584
 585 std::string
 586 LTC_Slave::approximate_current_delta() const
 587 {
 588         char delta[80];
 589         if (last_timestamp == 0 || engine_dll_initstate == 0) {
 590                 snprintf(delta, sizeof(delta), "\u2012\u2012\u2012\u2012");
 591         } else if ((monotonic_cnt - last_timestamp) > 2 * frames_per_ltc_frame) {
 592                 snprintf(delta, sizeof(delta), _("flywheel"));
 593         } else {
 594                 snprintf(delta, sizeof(delta), "\u0394<span foreground=\"green\" face=\"monospace\" >%s%s%" PRIi64 "</span> sm",
 595                                 LEADINGZERO(abs(current_delta)), PLUSMINUS(-current_delta), abs(current_delta));
 596         }
 597         return std::string(delta);
 598 }