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