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 "timecode/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/slave.h"
  29
  30 #include "i18n.h"
  31
  32 using namespace std;
  33 using namespace ARDOUR;
  34 using namespace MIDI;
  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().frame_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         ltc_enc_tcformat = config.get_timecode_format();
  69
  70         ltc_tx_parse_offset();
  71         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX init sr: %1 fps: %2\n", nominal_frame_rate(), timecode_to_frames_per_second(ltc_enc_tcformat)));
  72         ltc_encoder = ltc_encoder_create(nominal_frame_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_frame_rate(), 23.0);
  77         ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(1.0));
  78
  79         /* buffersize for 1 LTC frame: (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_frame_rate() / 23), sizeof(ltcsnd_sample_t));
  84         ltc_speed = 0;
  85         ltc_tx_reset();
  86         ltc_tx_resync_latency();
  87         Xrun.connect_same_thread (*this, boost::bind (&Session::ltc_tx_reset, this));
  88         engine().GraphReordered.connect_same_thread (*this, boost::bind (&Session::ltc_tx_resync_latency, this));
  89         restarting = false;
  90 }
  91
  92 void
  93 Session::ltc_tx_cleanup()
  94 {
  95         DEBUG_TRACE (DEBUG::LTC, "LTC TX cleanup\n");
  96         if (ltc_enc_buf) {
  97                 free(ltc_enc_buf);
  98                 ltc_enc_buf = 0;
  99         }
 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::LTC, "LTC TX 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::LTC, "LTC TX reset\n");
 120         ltc_enc_pos = -9999; // force re-start
 121         ltc_buf_len = 0;
 122         ltc_buf_off = 0;
 123         ltc_enc_byte = 0;
 124         ltc_enc_cnt = 0;
 125
 126         ltc_encoder_reset(ltc_encoder);
 127 }
 128
 129 void
 130 Session::ltc_tx_parse_offset() {
 131         Timecode::Time offset_tc;
 132         Timecode::parse_timecode_format(config.get_timecode_generator_offset(), offset_tc);
 133         offset_tc.rate = timecode_frames_per_second();
 134         offset_tc.drop = timecode_drop_frames();
 135         timecode_to_sample(offset_tc, ltc_timecode_offset, false, false);
 136         ltc_timecode_negative_offset = !offset_tc.negative;
 137 }
 138
 139 void
 140 Session::ltc_tx_recalculate_position()
 141 {
 142         SMPTETimecode enctc;
 143         Timecode::Time a3tc;
 144         ltc_encoder_get_timecode(ltc_encoder, &enctc);
 145
 146         a3tc.hours   = enctc.hours;
 147         a3tc.minutes = enctc.mins;
 148         a3tc.seconds = enctc.secs;
 149         a3tc.frames  = enctc.frame;
 150         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
 151         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
 152
 153         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
 154                 (double)frame_rate(),
 155                 config.get_subframes_per_frame(),
 156                 ltc_timecode_negative_offset, ltc_timecode_offset
 157                 );
 158         restarting = false;
 159 }
 160
 161 void
 162 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 163                                           double target_speed, double current_speed,
 164                                           pframes_t nframes)
 165 {
 166         assert (nframes > 0);
 167
 168         Sample *out;
 169         pframes_t txf = 0;
 170         boost::shared_ptr<Port> ltcport = ltc_output_port();
 171
 172         Buffer& buf (ltcport->get_buffer (nframes));
 173
 174         if (!ltc_encoder || !ltc_enc_buf) {
 175                 return;
 176         }
 177
 178         SyncSource sync_src = Config->get_sync_source();
 179         if (engine().freewheeling() || !Config->get_send_ltc()
 180             /* TODO
 181              * decide which time-sources we can generated LTC from.
 182              * Internal, JACK or sample-synced slaves should be fine.
 183              * talk to oofus.
 184              *
 185              || (config.get_external_sync() && sync_src == LTC)
 186              || (config.get_external_sync() && sync_src == MTC)
 187             */
 188              ||(config.get_external_sync() && sync_src == MIDIClock)
 189                 ) {
 190                 return;
 191         }
 192
 193         out = dynamic_cast<AudioBuffer*>(&buf)->data ();
 194
 195         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 196         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 197
 198         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_out_latency.max));
 199
 200         /* all systems go. Now here's the plan:
 201          *
 202          *  1) check if fps has changed
 203          *  2) check direction of encoding, calc speed, re-sample existing buffer
 204          *  3) calculate frame and byte to send aligned to jack-period size
 205          *  4) check if it's the frame/byte that is already in the queue
 206          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 207          *  6) actual LTC audio output
 208          *  6a) send remaining part of already queued frame; break on nframes
 209          *  6b) encode new LTC-frame byte
 210          *  6c) goto 6a
 211          *  7) done
 212          */
 213
 214         // (1) check fps
 215         TimecodeFormat cur_timecode = config.get_timecode_format();
 216         if (cur_timecode != ltc_enc_tcformat) {
 217                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX1: TC format mismatch - reinit sr: %1 fps: %2\n", nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode)));
 218                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(),
 219                                         timecode_to_frames_per_second(cur_timecode),
 220                                         TV_STANDARD(cur_timecode), 0
 221                                         )) {
 222                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 223                         ltc_tx_cleanup();
 224                         return;
 225                 }
 226                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
 227                 ltc_enc_tcformat = cur_timecode;
 228                 ltc_tx_parse_offset();
 229                 ltc_tx_reset();
 230         }
 231
 232         /* LTC is max. 30 fps */
 233         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 234                 return;
 235         }
 236
 237         // (2) speed & direction
 238
 239         /* speed 0 aka transport stopped is interpreted as rolling forward.
 240          * keep repeating current frame
 241          */
 242 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 243         bool speed_changed = false;
 244
 245         /* port latency compensation:
 246          * The _generated timecode_ is offset by the port-latency,
 247          * therefore the offset depends on the direction of transport.
 248          */
 249         framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame - ltc_out_latency.max) : (start_frame + ltc_out_latency.max);
 250
 251         /* LTC TV standard offset */
 252         cycle_start_frame -= ltc_frame_alignment(frames_per_timecode_frame(), TV_STANDARD(cur_timecode));
 253
 254         /* cycle-start may become negative due to latency compensation */
 255         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 256
 257         double new_ltc_speed = (double)(labs(end_frame - start_frame) * SIGNUM(current_speed)) / (double)nframes;
 258         if (nominal_frame_rate() != frame_rate()) {
 259                 new_ltc_speed *= (double)nominal_frame_rate() / (double)frame_rate();
 260         }
 261
 262         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 263                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 264                 ltc_tx_reset();
 265         }
 266
 267         if (ltc_speed != new_ltc_speed) {
 268                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 269                  * if target_speed != current_speed we should interpolate, too.
 270                  *
 271                  * However, currency in A3 target_speed == current_speed for each process cycle
 272                  * (except for the sign and if target_speed > 8.0).
 273                  * Besides, above speed calculation uses the difference (end_frame - start_frame).
 274                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 275                  * so we're good.
 276                  */
 277                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: speed change old: %1 cur: %2 tgt: %3 ctd: %4\n", ltc_speed, current_speed, target_speed, fabs(current_speed) - target_speed));
 278                 speed_changed = true;
 279                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
 280         }
 281
 282         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 283                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 284                 /* keep repeating current frame
 285                  *
 286                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 287                  * some machines do odd things if LTC goes away:
 288                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 289                  * so unspool the tape from the playhead. That might be inconvenient.
 290                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 291                  */
 292                 new_ltc_speed = 0;
 293                 if (!Config->get_ltc_send_continuously()) {
 294                         ltc_speed = new_ltc_speed;
 295                         return;
 296                 }
 297         }
 298
 299         if (fabs(new_ltc_speed) > 10.0) {
 300                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 301                 ltc_tx_reset();
 302                 return;
 303         }
 304
 305         if (ltc_speed == 0 && new_ltc_speed != 0) {
 306                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 307                 ltc_tx_reset();
 308         }
 309
 310         /* the timecode duration corresponding to the samples that are still
 311          * in the buffer. Here, the speed of previous cycle is used to calculate
 312          * the alignment at the beginning of this cycle later.
 313          */
 314         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 315
 316         if (speed_changed && new_ltc_speed != 0) {
 317                 /* we need to re-sample the existing buffer.
 318                  * "make space for the en-coder to catch up to the new speed"
 319                  *
 320                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 321                  * by removing samples or duplicating samples /here and there/.
 322                  *
 323                  * There may be a more elegant way to do this, in fact one could
 324                  * simply re-render the buffer using ltc_encoder_encode_byte()
 325                  * but that'd require some timecode offset buffer magic,
 326                  * which is left for later..
 327                  */
 328
 329                 double oldbuflen = (double)(ltc_buf_len - ltc_buf_off);
 330                 double newbuflen = (double)(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 331
 332                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 333                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 334                                         ));
 335
 336                 double bufrspdiff = rint(newbuflen - oldbuflen);
 337
 338                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 339                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 340                         ltc_tx_reset();
 341                         poff = 0;
 342                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 343                         int incnt = 0;
 344                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 345                         double avg_distance = newbuflen / samples_to_insert;
 346                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 347
 348                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 349                                 const int ro = rp - ltc_buf_off;
 350                                 if (ro < (incnt*avg_distance)) continue;
 351                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 352                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 353                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 354                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 355                                 incnt++;
 356                                 ltc_buf_len++;
 357                         }
 358                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 359                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 360                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 361                         if (oldbuflen <= samples_to_remove) {
 362                                 ltc_buf_off = ltc_buf_len= 0;
 363                         } else {
 364                                 double avg_distance = newbuflen / samples_to_remove;
 365                                 int rmcnt = 0;
 366                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 367                                         const int ro = rp - ltc_buf_off;
 368                                         if (ro < (rmcnt*avg_distance)) continue;
 369                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 370                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 371                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 372                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 373                                         ltc_buf_len--;
 374                                         rmcnt++;
 375                                 }
 376                         }
 377                 }
 378         }
 379
 380         ltc_speed = new_ltc_speed;
 381         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 382
 383         // (3) bit/sample alignment
 384         Timecode::Time tc_start;
 385         framepos_t tc_sample_start;
 386
 387         /* calc timecode frame from current position - round down to nearest timecode */
 388         Timecode::sample_to_timecode(cycle_start_frame, tc_start, true, false,
 389                         timecode_frames_per_second(),
 390                         timecode_drop_frames(),
 391                         (double)frame_rate(),
 392                         config.get_subframes_per_frame(),
 393                         ltc_timecode_negative_offset, ltc_timecode_offset
 394                         );
 395
 396         /* convert timecode back to sample-position */
 397         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 398                 (double)frame_rate(),
 399                 config.get_subframes_per_frame(),
 400                 ltc_timecode_negative_offset, ltc_timecode_offset
 401                 );
 402
 403         /* difference between current frame and TC frame in samples */
 404         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 405         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 406                                 cycle_start_frame, tc_sample_start, soff));
 407
 408
 409         // (4) check if alignment matches
 410         const double fptcf = frames_per_timecode_frame();
 411
 412         /* maximum difference of bit alignment in audio-samples.
 413          *
 414          * if transport and LTC generator differs more than this, the LTC
 415          * generator will be re-initialized
 416          *
 417          * due to rounding error and variations in LTC-bit duration depending
 418          * on the speed, it can be off by +- ltc_speed audio-samples.
 419          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 420          * in the cycle _after_ the speed changed. The average delta however is 0.
 421          */
 422         double maxdiff;
 423
 424         if (config.get_external_sync() && slave()) {
 425                 maxdiff = slave()->resolution();
 426         } else {
 427                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 428                 if (nominal_frame_rate() != frame_rate()) {
 429                         maxdiff *= 3.0;
 430                 }
 431                 if (ltc_enc_tcformat == Timecode::timecode_23976 || ltc_enc_tcformat == Timecode::timecode_24976) {
 432                         maxdiff *= 15.0;
 433                 }
 434         }
 435
 436         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 437                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 438
 439         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 440                                 ltc_enc_pos + ltc_enc_cnt - poff,
 441                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 442                                 ));
 443
 444         if (ltc_enc_pos < 0
 445                         || (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff)
 446                         ) {
 447
 448                 // (5) re-align
 449                 ltc_tx_reset();
 450
 451                 /* set frame to encode */
 452                 SMPTETimecode tc;
 453                 tc.hours = tc_start.hours;
 454                 tc.mins = tc_start.minutes;
 455                 tc.secs = tc_start.seconds;
 456                 tc.frame = tc_start.frames;
 457                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 458
 459                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 460                  * In A3 30000/1001 or 30 fps can be drop-frame.
 461                  */
 462                 LTCFrame ltcframe;
 463                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 464                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 465                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 466
 467
 468                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 469
 470                 uint32_t cyc_off;
 471                 if (soff < 0 || soff >= fptcf) {
 472                         /* session framerate change between (2) and now */
 473                         ltc_tx_reset();
 474                         return;
 475                 }
 476
 477                 if (ltc_speed < 0 ) {
 478                         /* calculate the byte that starts at or after the current position */
 479                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 480                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 481
 482                         /* calculate difference between the current position and the byte to send */
 483                         cyc_off = soff- ceil(ltc_enc_cnt);
 484
 485                 } else {
 486                         /* calculate the byte that starts at or after the current position */
 487                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 488                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 489
 490                         /* calculate difference between the current position and the byte to send */
 491                         cyc_off = ceil(ltc_enc_cnt) - soff;
 492
 493                         if (ltc_enc_byte == 10) {
 494                                 ltc_enc_byte = 0;
 495                                 ltc_encoder_inc_timecode(ltc_encoder);
 496                         }
 497                 }
 498
 499                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 500                                         soff, ltc_enc_byte, cyc_off));
 501
 502                 if ( (ltc_speed < 0 && ltc_enc_byte !=9 ) || (ltc_speed >= 0 && ltc_enc_byte !=0 ) ) {
 503                         restarting = true;
 504                 }
 505
 506                 if (cyc_off > 0 && cyc_off <= nframes) {
 507                         /* offset in this cycle */
 508                         txf= rint(cyc_off / fabs(ltc_speed));
 509                         memset(out, 0, cyc_off * sizeof(Sample));
 510                 } else {
 511                         /* resync next cycle */
 512                         memset(out, 0, nframes * sizeof(Sample));
 513                         return;
 514                 }
 515
 516                 ltc_enc_pos = tc_sample_start;
 517
 518                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 519                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 520         }
 521         else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
 522                 /* reduce (low freq) jitter.
 523                  * The granularity of the LTC encoder speed is 1 byte =
 524                  * (frames-per-timecode-frame / 10) audio-samples.
 525                  * Thus, tiny speed changes [as produced by some slaves]
 526                  * may not have any effect in the cycle when they occur,
 527                  * but they will add up over time.
 528                  *
 529                  * This is a linear approx to compensate for this jitter
 530                  * and prempt re-sync when the drift builds up.
 531                  *
 532                  * However, for very fast speeds - when 1 LTC bit is
 533                  * <= 3 audio-sample - adjusting speed may lead to
 534                  * invalid frames.
 535                  *
 536                  * To do better than this, resampling (or a rewrite of the
 537                  * encoder) is required.
 538                  */
 539                 ltc_speed -= ((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) / engine().frame_rate();
 540         }
 541
 542
 543         // (6) encode and output
 544         while (1) {
 545 #ifdef LTC_GEN_TXDBUG
 546                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 547 #endif
 548                 // (6a) send remaining buffer
 549                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 550                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 551                         const Sample val = (Sample) (v1*ltcvol);
 552                         out[txf++] = val;
 553                 }
 554 #ifdef LTC_GEN_TXDBUG
 555                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 556 #endif
 557
 558                 if (txf >= nframes) {
 559                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 560                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 561                         break;
 562                 }
 563
 564                 ltc_buf_len = 0;
 565                 ltc_buf_off = 0;
 566
 567                 // (6b) encode LTC, bump timecode
 568
 569                 if (ltc_speed < 0) {
 570                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 571                         if (ltc_enc_byte == 9) {
 572                                 ltc_encoder_dec_timecode(ltc_encoder);
 573                                 ltc_tx_recalculate_position();
 574                                 ltc_enc_cnt = fptcf;
 575                         }
 576                 }
 577
 578                 int enc_frames;
 579
 580                 if (restarting) {
 581                         /* write zero bytes -- don't touch encoder until we're at a frame-boundary
 582                          * otherwise the biphase polarity may be inverted.
 583                          */
 584                         enc_frames = fptcf / 10.0;
 585                         memset(&ltc_enc_buf[ltc_buf_len], 127, enc_frames * sizeof(ltcsnd_sample_t));
 586                 } else {
 587                         if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 588                                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 589                                 ltc_encoder_buffer_flush(ltc_encoder);
 590                                 ltc_tx_reset();
 591                                 return;
 592                         }
 593                         enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 594                 }
 595
 596 #ifdef LTC_GEN_FRAMEDBUG
 597                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoded %1 bytes for LTC-byte %2 at spd %3\n", enc_frames, ltc_enc_byte, ltc_speed));
 598 #endif
 599                 if (enc_frames <=0) {
 600                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 601                         ltc_encoder_buffer_flush(ltc_encoder);
 602                         ltc_tx_reset();
 603                         return;
 604                 }
 605
 606                 ltc_buf_len += enc_frames;
 607                 if (ltc_speed < 0)
 608                         ltc_enc_cnt -= fptcf/10.0;
 609                 else
 610                         ltc_enc_cnt += fptcf/10.0;
 611
 612                 if (ltc_speed >= 0) {
 613                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 614                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 615                                 ltc_encoder_inc_timecode(ltc_encoder);
 616 #if 0 /* force fixed parity -- scope debug */
 617                                 LTCFrame f;
 618                                 ltc_encoder_get_frame(ltc_encoder, &f);
 619                                 f.biphase_mark_phase_correction=0;
 620                                 ltc_encoder_set_frame(ltc_encoder, &f);
 621 #endif
 622                                 ltc_tx_recalculate_position();
 623                                 ltc_enc_cnt = 0;
 624                         } else if (ltc_enc_byte == 0) {
 625                                 ltc_enc_cnt = 0;
 626                                 restarting=false;
 627                         }
 628                 }
 629 #ifdef LTC_GEN_FRAMEDBUG
 630                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.4 enc-pos: %1 + %2 [ %4 / %5 ] spd %6\n", ltc_enc_pos, ltc_enc_cnt, ltc_buf_off, ltc_buf_len, ltc_speed));
 631 #endif
 632         }
 633
 634         dynamic_cast<AudioBuffer*>(&buf)->set_written (true);
 635         return;
 636 }