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(25, (4000000 / ((speed==0)?1:speed) / engine().frame_rate())))
  60
  61 void
  62 Session::ltc_tx_initialize()
  63 {
  64         ltc_enc_tcformat = config.get_timecode_format();
  65
  66         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)));
  67         ltc_encoder = ltc_encoder_create(nominal_frame_rate(),
  68                         timecode_to_frames_per_second(ltc_enc_tcformat),
  69                         -2);
  70
  71         ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
  72         ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(1.0));
  73
  74         /* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
  75          * usually returned by ltc_encoder_get_buffersize(encoder)
  76          *
  77          * since the fps can change and A3's  min fps: 24000/1001 */
  78         ltc_enc_buf = (ltcsnd_sample_t*) calloc((nominal_frame_rate() / 23), sizeof(ltcsnd_sample_t));
  79         ltc_speed = 0;
  80         ltc_tx_reset();
  81         ltc_tx_resync_latency();
  82         Xrun.connect_same_thread (*this, boost::bind (&Session::ltc_tx_reset, this));
  83         engine().GraphReordered.connect_same_thread (*this, boost::bind (&Session::ltc_tx_resync_latency, this));
  84 }
  85
  86 void
  87 Session::ltc_tx_cleanup()
  88 {
  89         DEBUG_TRACE (DEBUG::LTC, "LTC TX cleanup\n");
  90         if (ltc_enc_buf) free(ltc_enc_buf);
  91         ltc_encoder_free(ltc_encoder);
  92         ltc_encoder = NULL;
  93 }
  94
  95 void
  96 Session::ltc_tx_resync_latency()
  97 {
  98         DEBUG_TRACE (DEBUG::LTC, "LTC TX resync latency\n");
  99         if (!deletion_in_progress()) {
 100                 boost::shared_ptr<Port> ltcport = ltc_output_port();
 101                 if (ltcport) {
 102                         ltcport->get_connected_latency_range(ltc_out_latency, true);
 103                 }
 104         }
 105 }
 106
 107 void
 108 Session::ltc_tx_reset()
 109 {
 110         DEBUG_TRACE (DEBUG::LTC, "LTC TX reset\n");
 111         ltc_enc_pos = -9999; // force re-start
 112         ltc_buf_len = 0;
 113         ltc_buf_off = 0;
 114         ltc_enc_byte = 0;
 115         ltc_enc_cnt = 0;
 116
 117         ltc_encoder_reset(ltc_encoder);
 118 }
 119
 120 void
 121 Session::ltc_tx_recalculate_position()
 122 {
 123         SMPTETimecode enctc;
 124         Timecode::Time a3tc;
 125         ltc_encoder_get_timecode(ltc_encoder, &enctc);
 126
 127         a3tc.hours   = enctc.hours;
 128         a3tc.minutes = enctc.mins;
 129         a3tc.seconds = enctc.secs;
 130         a3tc.frames  = enctc.frame;
 131         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
 132         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
 133
 134         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
 135                 (double)frame_rate(),
 136                 config.get_subframes_per_frame(),
 137                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 138                 );
 139 }
 140
 141 void
 142 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 143                                           double target_speed, double current_speed,
 144                                           pframes_t nframes)
 145 {
 146         assert (nframes > 0);
 147
 148         Sample *out;
 149         pframes_t txf = 0;
 150         boost::shared_ptr<Port> ltcport = ltc_output_port();
 151
 152         Buffer& buf (ltcport->get_buffer (nframes));
 153
 154         if (!ltc_encoder || !ltc_enc_buf) {
 155                 return;
 156         }
 157
 158         SyncSource sync_src = Config->get_sync_source();
 159         if (engine().freewheeling() || !Config->get_send_ltc()
 160             /* TODO
 161              * decide which time-sources we can generated LTC from.
 162              * Internal, JACK or sample-synced slaves should be fine.
 163              * talk to oofus.
 164              *
 165              || (config.get_external_sync() && sync_src == LTC)
 166              || (config.get_external_sync() && sync_src == MTC)
 167             */
 168              ||(config.get_external_sync() && sync_src == MIDIClock)
 169                 ) {
 170                 return;
 171         }
 172
 173         out = dynamic_cast<AudioBuffer*>(&buf)->data ();
 174
 175         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 176         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 177
 178         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_out_latency.max));
 179
 180         /* all systems go. Now here's the plan:
 181          *
 182          *  1) check if fps has changed
 183          *  2) check direction of encoding, calc speed, re-sample existing buffer
 184          *  3) calculate frame and byte to send aligned to jack-period size
 185          *  4) check if it's the frame/byte that is already in the queue
 186          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 187          *  6) actual LTC audio output
 188          *  6a) send remaining part of already queued frame; break on nframes
 189          *  6b) encode new LTC-frame byte
 190          *  6c) goto 6a
 191          *  7) done
 192          */
 193
 194         // (1) check fps
 195         TimecodeFormat cur_timecode = config.get_timecode_format();
 196         if (cur_timecode != ltc_enc_tcformat) {
 197                 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)));
 198                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode), -2)) {
 199                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 200                         ltc_tx_cleanup();
 201                         return;
 202                 }
 203                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
 204                 ltc_enc_tcformat = cur_timecode;
 205                 ltc_tx_reset();
 206         }
 207
 208         /* LTC is max. 30 fps */
 209         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 210                 return;
 211         }
 212
 213         // (2) speed & direction
 214
 215         /* speed 0 aka transport stopped is interpreted as rolling forward.
 216          * keep repeating current frame
 217          */
 218 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 219         bool speed_changed = false;
 220
 221         /* port latency compensation:
 222          * The _generated timecode_ is offset by the port-latency,
 223          * therefore the offset depends on the direction of transport.
 224          */
 225         framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame - ltc_out_latency.max) : (start_frame + ltc_out_latency.max);
 226
 227         /* cycle-start may become negative due to latency compensation */
 228         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 229
 230         double new_ltc_speed = (double)(labs(end_frame - start_frame) * SIGNUM(current_speed)) / (double)nframes;
 231         if (nominal_frame_rate() != frame_rate()) {
 232                 new_ltc_speed *= (double)nominal_frame_rate() / (double)frame_rate();
 233         }
 234
 235         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 236                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 237                 ltc_tx_reset();
 238         }
 239
 240         if (ltc_speed != new_ltc_speed) {
 241                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 242                  * if target_speed != current_speed we should interpolate, too.
 243                  *
 244                  * However, currency in A3 target_speed == current_speed for each process cycle
 245                  * (except for the sign and if target_speed > 8.0).
 246                  * Besides, above speed calculation uses the difference (end_frame - start_frame).
 247                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 248                  * so we're good.
 249                  */
 250                 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));
 251                 speed_changed = true;
 252                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
 253         }
 254
 255         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 256                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 257                 /* keep repeating current frame
 258                  *
 259                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 260                  * some machines do odd things if LTC goes away:
 261                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 262                  * so unspool the tape from the playhead. That might be inconvenient.
 263                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 264                  */
 265                 new_ltc_speed = 0;
 266                 if (!Config->get_ltc_send_continuously()) {
 267                         ltc_speed = new_ltc_speed;
 268                         return;
 269                 }
 270         }
 271
 272         if (fabs(new_ltc_speed) > 10.0) {
 273                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 274                 ltc_tx_reset();
 275                 return;
 276         }
 277
 278         if (ltc_speed == 0 && new_ltc_speed != 0) {
 279                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 280                 ltc_tx_reset();
 281         }
 282
 283         /* the timecode duration corresponding to the samples that are still
 284          * in the buffer. Here, the speed of previous cycle is used to calculate
 285          * the alignment at the beginning of this cycle later.
 286          */
 287         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 288
 289         if (speed_changed && new_ltc_speed != 0) {
 290                 /* we need to re-sample the existing buffer.
 291                  * "make space for the en-coder to catch up to the new speed"
 292                  *
 293                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 294                  * by removing samples or duplicating samples /here and there/.
 295                  *
 296                  * There may be a more elegant way to do this, in fact one could
 297                  * simply re-render the buffer using ltc_encoder_encode_byte()
 298                  * but that'd require some timecode offset buffer magic,
 299                  * which is left for later..
 300                  */
 301
 302                 double oldbuflen = (double)(ltc_buf_len - ltc_buf_off);
 303                 double newbuflen = (double)(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 304
 305                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 306                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 307                                         ));
 308
 309                 double bufrspdiff = rint(newbuflen - oldbuflen);
 310
 311                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 312                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 313                         ltc_tx_reset();
 314                         poff = 0;
 315                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 316                         int incnt = 0;
 317                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 318                         double avg_distance = newbuflen / samples_to_insert;
 319                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 320
 321                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 322                                 const int ro = rp - ltc_buf_off;
 323                                 if (ro < (incnt*avg_distance)) continue;
 324                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 325                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 326                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 327                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 328                                 incnt++;
 329                                 ltc_buf_len++;
 330                         }
 331                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 332                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 333                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 334                         if (oldbuflen <= samples_to_remove) {
 335                                 ltc_buf_off = ltc_buf_len= 0;
 336                         } else {
 337                                 double avg_distance = newbuflen / samples_to_remove;
 338                                 int rmcnt = 0;
 339                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 340                                         const int ro = rp - ltc_buf_off;
 341                                         if (ro < (rmcnt*avg_distance)) continue;
 342                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 343                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 344                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 345                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 346                                         ltc_buf_len--;
 347                                         rmcnt++;
 348                                 }
 349                         }
 350                 }
 351         }
 352
 353         ltc_speed = new_ltc_speed;
 354         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 355
 356         // (3) bit/sample alignment
 357         Timecode::Time tc_start;
 358         framepos_t tc_sample_start;
 359
 360         /* calc timecode frame from current position - round down to nearest timecode */
 361         Timecode::sample_to_timecode(cycle_start_frame, tc_start, true, false,
 362                         timecode_frames_per_second(),
 363                         timecode_drop_frames(),
 364                         (double)frame_rate(),
 365                         config.get_subframes_per_frame(),
 366                         config.get_timecode_offset_negative(), config.get_timecode_offset()
 367                         );
 368
 369         /* convert timecode back to sample-position */
 370         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 371                 (double)frame_rate(),
 372                 config.get_subframes_per_frame(),
 373                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 374                 );
 375
 376         /* difference between current frame and TC frame in samples */
 377         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 378         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 379                                 cycle_start_frame, tc_sample_start, soff));
 380
 381
 382         // (4) check if alignment matches
 383         const double fptcf = frames_per_timecode_frame();
 384
 385         /* maximum difference of bit alignment in audio-samples.
 386          *
 387          * if transport and LTC generator differs more than this, the LTC
 388          * generator will be re-initialized
 389          *
 390          * due to rounding error and variations in LTC-bit duration depending
 391          * on the speed, it can be off by +- ltc_speed audio-samples.
 392          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 393          * in the cycle _after_ the speed changed. The average delta however is 0.
 394          */
 395         double maxdiff;
 396
 397         if (config.get_external_sync() && slave()) {
 398                 maxdiff = slave()->resolution();
 399         } else {
 400                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 401         }
 402
 403         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 404                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 405
 406         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 407                                 ltc_enc_pos + ltc_enc_cnt - poff,
 408                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 409                                 ));
 410
 411         if (ltc_enc_pos < 0
 412                         || (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff)
 413                         ) {
 414
 415                 // (5) re-align
 416                 ltc_tx_reset();
 417
 418                 /* set frame to encode */
 419                 SMPTETimecode tc;
 420                 tc.hours = tc_start.hours;
 421                 tc.mins = tc_start.minutes;
 422                 tc.secs = tc_start.seconds;
 423                 tc.frame = tc_start.frames;
 424                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 425
 426                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 427                  * In A3 30000/1001 or 30 fps can be drop-frame.
 428                  */
 429                 LTCFrame ltcframe;
 430                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 431                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 432                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 433
 434
 435                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 436
 437                 uint32_t cyc_off;
 438                 if (soff < 0 || soff >= fptcf) {
 439                         /* session framerate change between (2) and now */
 440                         ltc_tx_reset();
 441                         return;
 442                 }
 443
 444                 if (ltc_speed < 0 ) {
 445                         /* calculate the byte that starts at or after the current position */
 446                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 447                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 448
 449                         /* calculate difference between the current position and the byte to send */
 450                         cyc_off = soff- ceil(ltc_enc_cnt);
 451
 452                 } else {
 453                         /* calculate the byte that starts at or after the current position */
 454                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 455                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 456
 457                         /* calculate difference between the current position and the byte to send */
 458                         cyc_off = ceil(ltc_enc_cnt) - soff;
 459
 460                         if (ltc_enc_byte == 10) {
 461                                 ltc_enc_byte = 0;
 462                                 ltc_encoder_inc_timecode(ltc_encoder);
 463                         }
 464                 }
 465
 466                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 467                                         soff, ltc_enc_byte, cyc_off));
 468
 469                 if (cyc_off > 0 && cyc_off <= nframes) {
 470                         /* offset in this cycle */
 471                         txf= rint(cyc_off / fabs(ltc_speed));
 472                         memset(out, 0, cyc_off * sizeof(Sample));
 473                 } else {
 474                         /* resync next cycle */
 475                         memset(out, 0, nframes * sizeof(Sample));
 476                         return;
 477                 }
 478
 479                 ltc_enc_pos = tc_sample_start;
 480
 481                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 482                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 483         }
 484         else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
 485                 /* reduce (low freq) jitter.
 486                  * The granularity of the LTC encoder speed is 1 byte =
 487                  * (frames-per-timecode-frame / 10) audio-samples.
 488                  * Thus, tiny speed changes [as produced by the slave]
 489                  * may not have any effect in the cycle when they occur,
 490                  * but they will add up over time.
 491                  *
 492                  * This is a linear approx to compensate for this drift
 493                  * and prempt re-sync when the drift builds up.
 494                  *
 495                  * However, for very fast speeds - when 1 LTC bit is
 496                  * <= 3 audio-sample - adjusting speed may lead to
 497                  * invalid frames.
 498                  *
 499                  * To do better than this, resampling (or a rewrite of the
 500                  * encoder) is required.
 501                  */
 502                 ltc_speed -= ((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) / engine().frame_rate();
 503         }
 504
 505
 506         // (6) encode and output
 507         while (1) {
 508 #ifdef LTC_GEN_TXDBUG
 509                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 510 #endif
 511                 // (6a) send remaining buffer
 512                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 513                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 514                         const Sample val = (Sample) (v1*ltcvol);
 515                         out[txf++] = val;
 516                 }
 517 #ifdef LTC_GEN_TXDBUG
 518                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 519 #endif
 520
 521                 if (txf >= nframes) {
 522                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 523                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 524                         break;
 525                 }
 526
 527                 ltc_buf_len = 0;
 528                 ltc_buf_off = 0;
 529
 530                 // (6b) encode LTC, bump timecode
 531
 532                 if (ltc_speed < 0) {
 533                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 534                         if (ltc_enc_byte == 9) {
 535                                 ltc_encoder_dec_timecode(ltc_encoder);
 536                                 ltc_tx_recalculate_position();
 537                                 ltc_enc_cnt = fptcf;
 538                         }
 539                 }
 540
 541                 if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 542                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 543                         ltc_encoder_buffer_flush(ltc_encoder);
 544                         ltc_tx_reset();
 545                         return;
 546                 }
 547                 int enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 548 #ifdef LTC_GEN_FRAMEDBUG
 549                 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));
 550 #endif
 551                 if (enc_frames <=0) {
 552                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 553                         ltc_encoder_buffer_flush(ltc_encoder);
 554                         ltc_tx_reset();
 555                         return;
 556                 }
 557
 558                 ltc_buf_len += enc_frames;
 559                 if (ltc_speed < 0)
 560                         ltc_enc_cnt -= fptcf/10.0;
 561                 else
 562                         ltc_enc_cnt += fptcf/10.0;
 563
 564                 if (ltc_speed >= 0) {
 565                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 566                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 567                                 ltc_encoder_inc_timecode(ltc_encoder);
 568 #if 0 /* force fixed parity -- scope debug */
 569                                 LTCFrame f;
 570                                 ltc_encoder_get_frame(ltc_encoder, &f);
 571                                 f.biphase_mark_phase_correction=0;
 572                                 ltc_encoder_set_frame(ltc_encoder, &f);
 573 #endif
 574                                 ltc_tx_recalculate_position();
 575                                 ltc_enc_cnt = 0;
 576                         } else if (ltc_enc_byte == 0) {
 577                                 ltc_enc_cnt = 0;
 578                         }
 579                 }
 580 #ifdef LTC_GEN_FRAMEDBUG
 581                 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));
 582 #endif
 583         }
 584
 585         dynamic_cast<AudioBuffer*>(&buf)->set_written (true);
 586         return;
 587 }