libs/ardour/session_ltc.cc

   1 /*
   2   Copyright (C) 2012 Paul Davis
   3   Written by 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
  21 #include "temporal/time.h"
  22
  23 #include "ardour/audioengine.h"
  24 #include "ardour/audio_port.h"
  25 #include "ardour/debug.h"
  26 #include "ardour/io.h"
  27 #include "ardour/session.h"
  28 #include "ardour/transport_master.h"
  29 #include "ardour/transport_master_manager.h"
  30
  31 #include "pbd/i18n.h"
  32
  33 using namespace std;
  34 using namespace ARDOUR;
  35 using namespace PBD;
  36 using namespace Timecode;
  37
  38 /* really verbose timing debug */
  39 //#define LTC_GEN_FRAMEDBUG
  40 //#define LTC_GEN_TXDBUG
  41
  42 #ifndef MAX
  43 #define MAX(a,b) ( (a) > (b) ? (a) : (b) )
  44 #endif
  45 #ifndef MIN
  46 #define MIN(a,b) ( (a) < (b) ? (a) : (b) )
  47 #endif
  48
  49 /* LTC signal should have a rise time of 25 us +/- 5 us.
  50  * yet with most sound-cards a square-wave of 1-2 sample
  51  * introduces ringing and small oscillations.
  52  * https://en.wikipedia.org/wiki/Gibbs_phenomenon
  53  * A low-pass filter in libltc can reduce this at
  54  * the cost of being slightly out of spec WRT to rise-time.
  55  *
  56  * This filter is adaptive so that fast vari-speed signals
  57  * will not be affected by it.
  58  */
  59 #define LTC_RISE_TIME(speed) MIN (100, MAX(40, (4000000 / ((speed==0)?1:speed) / engine().sample_rate())))
  60
  61 #define TV_STANDARD(tcf) \
  62         (timecode_to_frames_per_second(tcf)==25.0 ? LTC_TV_625_50 : \
  63          timecode_has_drop_frames(tcf)? LTC_TV_525_60 : LTC_TV_FILM_24)
  64
  65 void
  66 Session::ltc_tx_initialize()
  67 {
  68         assert (!ltc_encoder && !ltc_enc_buf);
  69         ltc_enc_tcformat = config.get_timecode_format();
  70
  71         ltc_tx_parse_offset();
  72         DEBUG_TRACE (DEBUG::TXLTC, string_compose("LTC TX init sr: %1 fps: %2\n", nominal_sample_rate(), timecode_to_frames_per_second(ltc_enc_tcformat)));
  73         ltc_encoder = ltc_encoder_create(nominal_sample_rate(),
  74                         timecode_to_frames_per_second(ltc_enc_tcformat),
  75                         TV_STANDARD(ltc_enc_tcformat), 0);
  76
  77         ltc_encoder_set_bufsize(ltc_encoder, nominal_sample_rate(), 23.0);
  78         ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(1.0));
  79
  80         /* buffersize for 1 LTC sample: (1 + sample-rate / fps) bytes
  81          * usually returned by ltc_encoder_get_buffersize(encoder)
  82          *
  83          * since the fps can change and A3's  min fps: 24000/1001 */
  84         ltc_enc_buf = (ltcsnd_sample_t*) calloc((nominal_sample_rate() / 23), sizeof(ltcsnd_sample_t));
  85         ltc_speed = 0;
  86         ltc_prev_cycle = -1;
  87         ltc_tx_reset();
  88         ltc_tx_resync_latency();
  89         Xrun.connect_same_thread (ltc_tx_connections, boost::bind (&Session::ltc_tx_reset, this));
  90         engine().GraphReordered.connect_same_thread (ltc_tx_connections, boost::bind (&Session::ltc_tx_resync_latency, this));
  91         restarting = false;
  92 }
  93
  94 void
  95 Session::ltc_tx_cleanup()
  96 {
  97         DEBUG_TRACE (DEBUG::TXLTC, "cleanup\n");
  98         ltc_tx_connections.drop_connections ();
  99         free(ltc_enc_buf);
 100         ltc_enc_buf = NULL;
 101         ltc_encoder_free(ltc_encoder);
 102         ltc_encoder = NULL;
 103 }
 104
 105 void
 106 Session::ltc_tx_resync_latency()
 107 {
 108         DEBUG_TRACE (DEBUG::TXLTC, "resync latency\n");
 109         if (!deletion_in_progress()) {
 110                 boost::shared_ptr<Port> ltcport = ltc_output_port();
 111                 if (ltcport) {
 112                         ltcport->get_connected_latency_range(ltc_out_latency, true);
 113                 }
 114         }
 115 }
 116
 117 void
 118 Session::ltc_tx_reset()
 119 {
 120         DEBUG_TRACE (DEBUG::TXLTC, "reset\n");
 121         assert (ltc_encoder);
 122         ltc_enc_pos = -9999; // force re-start
 123         ltc_buf_len = 0;
 124         ltc_buf_off = 0;
 125         ltc_enc_byte = 0;
 126         ltc_enc_cnt = 0;
 127
 128         ltc_encoder_reset(ltc_encoder);
 129 }
 130
 131 void
 132 Session::ltc_tx_parse_offset() {
 133         Timecode::Time offset_tc;
 134         Timecode::parse_timecode_format(config.get_timecode_generator_offset(), offset_tc);
 135         offset_tc.rate = timecode_frames_per_second();
 136         offset_tc.drop = timecode_drop_frames();
 137         timecode_to_sample(offset_tc, ltc_timecode_offset, false, false);
 138         ltc_timecode_negative_offset = !offset_tc.negative;
 139         ltc_prev_cycle = -1;
 140 }
 141
 142 void
 143 Session::ltc_tx_recalculate_position()
 144 {
 145         SMPTETimecode enctc;
 146         Timecode::Time a3tc;
 147         ltc_encoder_get_timecode(ltc_encoder, &enctc);
 148
 149         a3tc.hours   = enctc.hours;
 150         a3tc.minutes = enctc.mins;
 151         a3tc.seconds = enctc.secs;
 152         a3tc.frames  = enctc.frame;
 153         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
 154         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
 155
 156         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
 157                 (double)sample_rate(),
 158                 config.get_subframes_per_frame(),
 159                 ltc_timecode_negative_offset, ltc_timecode_offset
 160                 );
 161         restarting = false;
 162 }
 163
 164 void
 165 Session::ltc_tx_send_time_code_for_cycle (samplepos_t start_sample, samplepos_t end_sample,
 166                                           double target_speed, double current_speed,
 167                                           pframes_t nframes)
 168 {
 169         assert (nframes > 0);
 170
 171         Sample *out;
 172         pframes_t txf = 0;
 173         boost::shared_ptr<Port> ltcport = ltc_output_port();
 174
 175         if (!ltcport) {
 176                 assert (deletion_in_progress ());
 177                 return;
 178         }
 179
 180         /* marks buffer as not written */
 181         Buffer& buf (ltcport->get_buffer (nframes));
 182
 183         if (!ltc_encoder || !ltc_enc_buf) {
 184                 return;
 185         }
 186
 187         SyncSource sync_src = TransportMasterManager::instance().current()->type();
 188         if (engine().freewheeling() || !Config->get_send_ltc()
 189             /* TODO
 190              * decide which time-sources we can generated LTC from.
 191              * Internal, JACK or sample-synced slaves should be fine.
 192              * talk to oofus.
 193              *
 194              || (config.get_external_sync() && sync_src == LTC)
 195              || (config.get_external_sync() && sync_src == MTC)
 196             */
 197              ||(config.get_external_sync() && sync_src == MIDIClock)
 198                 ) {
 199                 return;
 200         }
 201
 202         out = dynamic_cast<AudioBuffer*>(&buf)->data ();
 203
 204         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 205         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 206
 207         DEBUG_TRACE (DEBUG::TXLTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_sample, end_sample, nframes, ltc_out_latency.max));
 208
 209         /* all systems go. Now here's the plan:
 210          *
 211          *  1) check if fps has changed
 212          *  2) check direction of encoding, calc speed, re-sample existing buffer
 213          *  3) calculate sample and byte to send aligned to jack-period size
 214          *  4) check if it's the sample/byte that is already in the queue
 215          *  5) if (4) mismatch, re-calculate offset of LTC sample relative to period size
 216          *  6) actual LTC audio output
 217          *  6a) send remaining part of already queued sample; break on nframes
 218          *  6b) encode new LTC-sample byte
 219          *  6c) goto 6a
 220          *  7) done
 221          */
 222
 223         // (1) check fps
 224         TimecodeFormat cur_timecode = config.get_timecode_format();
 225         if (cur_timecode != ltc_enc_tcformat) {
 226                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("1: TC format mismatch - reinit sr: %1 fps: %2\n", nominal_sample_rate(), timecode_to_frames_per_second(cur_timecode)));
 227                 if (ltc_encoder_reinit(ltc_encoder, nominal_sample_rate(),
 228                                         timecode_to_frames_per_second(cur_timecode),
 229                                         TV_STANDARD(cur_timecode), 0
 230                                         )) {
 231                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 232                         ltc_tx_cleanup();
 233                         return;
 234                 }
 235                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
 236                 ltc_enc_tcformat = cur_timecode;
 237                 ltc_tx_parse_offset();
 238                 ltc_tx_reset();
 239         }
 240
 241         /* LTC is max. 30 fps */
 242         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 243                 return;
 244         }
 245
 246         // (2) speed & direction
 247
 248         /* speed 0 aka transport stopped is interpreted as rolling forward.
 249          * keep repeating current sample
 250          */
 251 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 252         bool speed_changed = false;
 253
 254         /* port latency compensation:
 255          * The _generated timecode_ is offset by the port-latency,
 256          * therefore the offset depends on the direction of transport.
 257          *
 258          * latency is compensated by adding it to the timecode to
 259          * be generated. e.g. if the signal will reach the output in
 260          * N samples time from now, generate the timecode for (now + N).
 261          *
 262          * sample-sync is achieved by further calculating the difference
 263          * between the timecode and the session-transport and offsetting the
 264          * buffer.
 265          *
 266          * The timecode is generated directly in the Session process callback
 267          * using _transport_sample (which is the audible frame at the
 268          * output).
 269          */
 270         samplepos_t cycle_start_sample;
 271
 272         if (current_speed < 0) {
 273                 cycle_start_sample = (start_sample + ltc_out_latency.max);
 274         } else if (current_speed > 0) {
 275                 cycle_start_sample = (start_sample - ltc_out_latency.max);
 276         } else {
 277                 /* There is no need to compensate for latency when not rolling
 278                  * rather send the accurate NOW timecode
 279                  * (LTC encoder compenates latency by sending earlier timecode)
 280                  */
 281                 cycle_start_sample = start_sample;
 282         }
 283
 284         /* LTC TV standard offset */
 285         if (current_speed != 0) {
 286                 /* ditto - send "NOW" if not rolling */
 287                 cycle_start_sample -= ltc_frame_alignment(samples_per_timecode_frame(), TV_STANDARD(cur_timecode));
 288         }
 289
 290         /* cycle-start may become negative due to latency compensation */
 291         if (cycle_start_sample < 0) { cycle_start_sample = 0; }
 292
 293         double new_ltc_speed = (double)(labs(end_sample - start_sample) * SIGNUM(current_speed)) / (double)nframes;
 294         if (nominal_sample_rate() != sample_rate()) {
 295                 new_ltc_speed *= (double)nominal_sample_rate() / (double)sample_rate();
 296         }
 297
 298         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 299                 DEBUG_TRACE (DEBUG::TXLTC, "transport changed direction\n");
 300                 ltc_tx_reset();
 301         }
 302
 303         if (ltc_speed != new_ltc_speed
 304                         /* but only once if, current_speed changes to 0. In that case
 305                          * new_ltc_speed is > 0 because (end_sample - start_sample) == jack-period for no-roll
 306                          * but ltc_speed will still be 0
 307                          */
 308                         && (current_speed != 0 || ltc_speed != current_speed)
 309                         ) {
 310                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 311                  * if target_speed != current_speed we should interpolate, too.
 312                  *
 313                  * However, currency in A3 target_speed == current_speed for each process cycle
 314                  * (except for the sign and if target_speed > 8.0).
 315                  * Besides, above speed calculation uses the difference (end_sample - start_sample).
 316                  * end_sample is calculated from 'samples_moved' which includes the interpolation.
 317                  * so we're good.
 318                  */
 319                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("2: speed change old: %1 cur: %2 tgt: %3 ctd: %4\n", ltc_speed, current_speed, target_speed, fabs(current_speed) - target_speed, new_ltc_speed));
 320                 speed_changed = true;
 321                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
 322         }
 323
 324         if (end_sample == start_sample || fabs(current_speed) < 0.1 ) {
 325                 DEBUG_TRACE (DEBUG::TXLTC, "transport is not rolling or absolute-speed < 0.1\n");
 326                 /* keep repeating current sample
 327                  *
 328                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 329                  * some machines do odd things if LTC goes away:
 330                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 331                  * so unspool the tape from the playhead. That might be inconvenient.
 332                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 333                  */
 334                 new_ltc_speed = 0;
 335                 if (!Config->get_ltc_send_continuously()) {
 336                         ltc_speed = new_ltc_speed;
 337                         return;
 338                 }
 339                 if (start_sample != ltc_prev_cycle) {
 340                         DEBUG_TRACE (DEBUG::TXLTC, string_compose("2: no-roll seek from %1 to %2 (%3)\n", ltc_prev_cycle, start_sample, cycle_start_sample));
 341                         ltc_tx_reset();
 342                 }
 343         }
 344
 345         if (fabs(new_ltc_speed) > 10.0) {
 346                 DEBUG_TRACE (DEBUG::TXLTC, "speed is out of bounds.\n");
 347                 ltc_tx_reset();
 348                 return;
 349         }
 350
 351         if (ltc_speed == 0 && new_ltc_speed != 0) {
 352                 DEBUG_TRACE (DEBUG::TXLTC, "transport started rolling - reset\n");
 353                 ltc_tx_reset();
 354         }
 355
 356         /* the timecode duration corresponding to the samples that are still
 357          * in the buffer. Here, the speed of previous cycle is used to calculate
 358          * the alignment at the beginning of this cycle later.
 359          */
 360         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 361
 362         if (speed_changed && new_ltc_speed != 0) {
 363                 /* we need to re-sample the existing buffer.
 364                  * "make space for the en-coder to catch up to the new speed"
 365                  *
 366                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 367                  * by removing samples or duplicating samples /here and there/.
 368                  *
 369                  * There may be a more elegant way to do this, in fact one could
 370                  * simply re-render the buffer using ltc_encoder_encode_byte()
 371                  * but that'd require some timecode offset buffer magic,
 372                  * which is left for later..
 373                  */
 374
 375                 double oldbuflen = (double)(ltc_buf_len - ltc_buf_off);
 376                 double newbuflen = (double)(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 377
 378                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("2: bufOld %1 bufNew %2 | diff %3\n",
 379                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 380                                         ));
 381
 382                 double bufrspdiff = rint(newbuflen - oldbuflen);
 383
 384                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 385                         DEBUG_TRACE (DEBUG::TXLTC, "resampling buffer would destroy information.\n");
 386                         ltc_tx_reset();
 387                         poff = 0;
 388                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 389                         int incnt = 0;
 390                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 391                         double avg_distance = newbuflen / samples_to_insert;
 392                         DEBUG_TRACE (DEBUG::TXLTC, string_compose("2: resample buffer insert: %1\n", samples_to_insert));
 393
 394                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 395                                 const int ro = rp - ltc_buf_off;
 396                                 if (ro < (incnt*avg_distance)) continue;
 397                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 398                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 399                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 400                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 401                                 incnt++;
 402                                 ltc_buf_len++;
 403                         }
 404                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 405                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 406                         DEBUG_TRACE (DEBUG::TXLTC, string_compose("2: resample buffer - remove: %1\n", samples_to_remove));
 407                         if (oldbuflen <= samples_to_remove) {
 408                                 ltc_buf_off = ltc_buf_len= 0;
 409                         } else {
 410                                 double avg_distance = newbuflen / samples_to_remove;
 411                                 int rmcnt = 0;
 412                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 413                                         const int ro = rp - ltc_buf_off;
 414                                         if (ro < (rmcnt*avg_distance)) continue;
 415                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 416                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 417                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 418                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 419                                         ltc_buf_len--;
 420                                         rmcnt++;
 421                                 }
 422                         }
 423                 }
 424         }
 425
 426         ltc_prev_cycle = start_sample;
 427         ltc_speed = new_ltc_speed;
 428         DEBUG_TRACE (DEBUG::TXLTC, string_compose("2: transport speed %1.\n", ltc_speed));
 429
 430         // (3) bit/sample alignment
 431         Timecode::Time tc_start;
 432         samplepos_t tc_sample_start;
 433
 434         /* calc timecode frame from current position - round down to nearest timecode */
 435         Timecode::sample_to_timecode(cycle_start_sample, tc_start, true, false,
 436                         timecode_frames_per_second(),
 437                         timecode_drop_frames(),
 438                         (double)sample_rate(),
 439                         config.get_subframes_per_frame(),
 440                         ltc_timecode_negative_offset, ltc_timecode_offset
 441                         );
 442
 443         /* convert timecode back to sample-position */
 444         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 445                 (double)sample_rate(),
 446                 config.get_subframes_per_frame(),
 447                 ltc_timecode_negative_offset, ltc_timecode_offset
 448                 );
 449
 450         /* difference between current sample and TC sample in samples */
 451         sampleoffset_t soff = cycle_start_sample - tc_sample_start;
 452         if (current_speed == 0) {
 453                 soff = 0;
 454         }
 455         DEBUG_TRACE (DEBUG::TXLTC, string_compose("3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 456                                 cycle_start_sample, tc_sample_start, soff));
 457
 458
 459         // (4) check if alignment matches
 460         const double fptcf = samples_per_timecode_frame();
 461
 462         /* maximum difference of bit alignment in audio-samples.
 463          *
 464          * if transport and LTC generator differs more than this, the LTC
 465          * generator will be re-initialized
 466          *
 467          * due to rounding error and variations in LTC-bit duration depending
 468          * on the speed, it can be off by +- ltc_speed audio-samples.
 469          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 470          * in the cycle _after_ the speed changed. The average delta however is 0.
 471          */
 472         double maxdiff;
 473
 474         if (transport_master_is_external()) {
 475                 maxdiff = transport_master()->resolution();
 476         } else {
 477                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 478                 if (nominal_sample_rate() != sample_rate()) {
 479                         maxdiff *= 3.0;
 480                 }
 481                 if (ltc_enc_tcformat == Timecode::timecode_23976 || ltc_enc_tcformat == Timecode::timecode_24976) {
 482                         maxdiff *= 15.0;
 483                 }
 484         }
 485
 486         DEBUG_TRACE (DEBUG::TXLTC, string_compose("4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 487                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 488
 489         DEBUG_TRACE (DEBUG::TXLTC, string_compose("4: enc-pos: %1  | d: %2\n",
 490                                 ltc_enc_pos + ltc_enc_cnt - poff,
 491                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_sample
 492                                 ));
 493
 494         const samplecnt_t wrap24h = 86400. * sample_rate();
 495         if (ltc_enc_pos < 0
 496                         || (ltc_speed != 0 && fabs(fmod(ceil(ltc_enc_pos + ltc_enc_cnt - poff), wrap24h) - (cycle_start_sample % wrap24h)) > maxdiff)
 497                         ) {
 498
 499                 // (5) re-align
 500                 ltc_tx_reset();
 501
 502                 /* set sample to encode */
 503                 SMPTETimecode tc;
 504                 tc.hours = tc_start.hours % 24;
 505                 tc.mins = tc_start.minutes;
 506                 tc.secs = tc_start.seconds;
 507                 tc.frame = tc_start.frames;
 508                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 509
 510                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-sample TC.
 511                  * In A3 30000/1001 or 30 fps can be drop-sample.
 512                  */
 513                 LTCFrame ltcframe;
 514                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 515                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 516                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 517
 518
 519                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("4: now: %1 trs: %2 toff %3\n", cycle_start_sample, tc_sample_start, soff));
 520
 521                 int32_t cyc_off;
 522                 if (soff < 0 || soff >= fptcf) {
 523                         /* session framerate change between (2) and now */
 524                         ltc_tx_reset();
 525                         return;
 526                 }
 527
 528                 if (ltc_speed < 0 ) {
 529                         /* calculate the byte that starts at or after the current position */
 530                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 531                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 532
 533                         /* calculate difference between the current position and the byte to send */
 534                         cyc_off = soff- ceil(ltc_enc_cnt);
 535
 536                 } else {
 537                         /* calculate the byte that starts at or after the current position */
 538                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 539                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 540
 541                         /* calculate difference between the current position and the byte to send */
 542                         cyc_off = ceil(ltc_enc_cnt) - soff;
 543
 544                         if (ltc_enc_byte == 10) {
 545                                 ltc_enc_byte = 0;
 546                                 ltc_encoder_inc_timecode(ltc_encoder);
 547                         }
 548                 }
 549
 550                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("5 restart encoder: soff %1 byte %2 cycoff %3\n",
 551                                         soff, ltc_enc_byte, cyc_off));
 552
 553                 if ( (ltc_speed < 0 && ltc_enc_byte !=9 ) || (ltc_speed >= 0 && ltc_enc_byte !=0 ) ) {
 554                         restarting = true;
 555                 }
 556
 557                 if (cyc_off >= 0 && cyc_off <= (int32_t) nframes) {
 558                         /* offset in this cycle */
 559                         txf= rint(cyc_off / fabs(ltc_speed));
 560                         memset(out, 0, cyc_off * sizeof(Sample));
 561                 } else {
 562                         /* resync next cycle */
 563                         memset(out, 0, nframes * sizeof(Sample));
 564                         return;
 565                 }
 566
 567                 ltc_enc_pos = tc_sample_start % wrap24h;
 568
 569                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("5 restart @ %1 + %2 - %3 |  byte %4\n",
 570                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 571         }
 572         else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
 573                 /* reduce (low freq) jitter.
 574                  * The granularity of the LTC encoder speed is 1 byte =
 575                  * (samples-per-timecode-sample / 10) audio-samples.
 576                  * Thus, tiny speed changes [as produced by some transport masters]
 577                  * may not have any effect in the cycle when they occur,
 578                  * but they will add up over time.
 579                  *
 580                  * This is a linear approx to compensate for this jitter
 581                  * and prempt re-sync when the drift builds up.
 582                  *
 583                  * However, for very fast speeds - when 1 LTC bit is
 584                  * <= 3 audio-sample - adjusting speed may lead to
 585                  * invalid samples.
 586                  *
 587                  * To do better than this, resampling (or a rewrite of the
 588                  * encoder) is required.
 589                  */
 590                 ltc_speed -= fmod(((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_sample), wrap24h) / engine().sample_rate();
 591         }
 592
 593
 594         // (6) encode and output
 595         while (1) {
 596 #ifdef LTC_GEN_TXDBUG
 597                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 598 #endif
 599                 // (6a) send remaining buffer
 600                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 601                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 602                         const Sample val = (Sample) (v1*ltcvol);
 603                         out[txf++] = val;
 604                 }
 605 #ifdef LTC_GEN_TXDBUG
 606                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 607 #endif
 608
 609                 if (txf >= nframes) {
 610                         DEBUG_TRACE (DEBUG::TXLTC, string_compose("7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 611                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 612                         break;
 613                 }
 614
 615                 ltc_buf_len = 0;
 616                 ltc_buf_off = 0;
 617
 618                 // (6b) encode LTC, bump timecode
 619
 620                 if (ltc_speed < 0) {
 621                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 622                         if (ltc_enc_byte == 9) {
 623                                 ltc_encoder_dec_timecode(ltc_encoder);
 624                                 ltc_tx_recalculate_position();
 625                                 ltc_enc_cnt = fptcf;
 626                         }
 627                 }
 628
 629                 int enc_samples;
 630
 631                 if (restarting) {
 632                         /* write zero bytes -- don't touch encoder until we're at a sample-boundary
 633                          * otherwise the biphase polarity may be inverted.
 634                          */
 635                         enc_samples = fptcf / 10.0;
 636                         memset(&ltc_enc_buf[ltc_buf_len], 127, enc_samples * sizeof(ltcsnd_sample_t));
 637                 } else {
 638                         if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 639                                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("6.3 encoder error byte %1\n", ltc_enc_byte));
 640                                 ltc_encoder_buffer_flush(ltc_encoder);
 641                                 ltc_tx_reset();
 642                                 return;
 643                         }
 644                         enc_samples = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 645                 }
 646
 647 #ifdef LTC_GEN_FRAMEDBUG
 648                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("6.3 encoded %1 bytes for LTC-byte %2 at spd %3\n", enc_samples, ltc_enc_byte, ltc_speed));
 649 #endif
 650                 if (enc_samples <=0) {
 651                         DEBUG_TRACE (DEBUG::TXLTC, "6.3 encoder empty buffer.\n");
 652                         ltc_encoder_buffer_flush(ltc_encoder);
 653                         ltc_tx_reset();
 654                         return;
 655                 }
 656
 657                 ltc_buf_len += enc_samples;
 658                 if (ltc_speed < 0)
 659                         ltc_enc_cnt -= fptcf/10.0;
 660                 else
 661                         ltc_enc_cnt += fptcf/10.0;
 662
 663                 if (ltc_speed >= 0) {
 664                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 665                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 666                                 ltc_encoder_inc_timecode(ltc_encoder);
 667 #if 0 /* force fixed parity -- scope debug */
 668                                 LTCFrame f;
 669                                 ltc_encoder_get_frame(ltc_encoder, &f);
 670                                 f.biphase_mark_phase_correction=0;
 671                                 ltc_encoder_set_frame(ltc_encoder, &f);
 672 #endif
 673                                 ltc_tx_recalculate_position();
 674                                 ltc_enc_cnt = 0;
 675                         } else if (ltc_enc_byte == 0) {
 676                                 ltc_enc_cnt = 0;
 677                                 restarting=false;
 678                         }
 679                 }
 680 #ifdef LTC_GEN_FRAMEDBUG
 681                 DEBUG_TRACE (DEBUG::TXLTC, string_compose("6.4 enc-pos: %1 + %2 [ %4 / %5 ] spd %6\n", ltc_enc_pos, ltc_enc_cnt, ltc_buf_off, ltc_buf_len, ltc_speed));
 682 #endif
 683         }
 684
 685         dynamic_cast<AudioBuffer*>(&buf)->set_written (true);
 686         return;
 687 }