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         restarting = false;
  85 }
  86
  87 void
  88 Session::ltc_tx_cleanup()
  89 {
  90         DEBUG_TRACE (DEBUG::LTC, "LTC TX cleanup\n");
  91         if (ltc_enc_buf) free(ltc_enc_buf);
  92         ltc_encoder_free(ltc_encoder);
  93         ltc_encoder = NULL;
  94 }
  95
  96 void
  97 Session::ltc_tx_resync_latency()
  98 {
  99         DEBUG_TRACE (DEBUG::LTC, "LTC TX resync latency\n");
 100         if (!deletion_in_progress()) {
 101                 boost::shared_ptr<Port> ltcport = ltc_output_port();
 102                 if (ltcport) {
 103                         ltcport->get_connected_latency_range(ltc_out_latency, true);
 104                 }
 105         }
 106 }
 107
 108 void
 109 Session::ltc_tx_reset()
 110 {
 111         DEBUG_TRACE (DEBUG::LTC, "LTC TX reset\n");
 112         ltc_enc_pos = -9999; // force re-start
 113         ltc_buf_len = 0;
 114         ltc_buf_off = 0;
 115         ltc_enc_byte = 0;
 116         ltc_enc_cnt = 0;
 117
 118         ltc_encoder_reset(ltc_encoder);
 119 }
 120
 121 void
 122 Session::ltc_tx_recalculate_position()
 123 {
 124         SMPTETimecode enctc;
 125         Timecode::Time a3tc;
 126         ltc_encoder_get_timecode(ltc_encoder, &enctc);
 127
 128         a3tc.hours   = enctc.hours;
 129         a3tc.minutes = enctc.mins;
 130         a3tc.seconds = enctc.secs;
 131         a3tc.frames  = enctc.frame;
 132         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
 133         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
 134
 135         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
 136                 (double)frame_rate(),
 137                 config.get_subframes_per_frame(),
 138                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 139                 );
 140         restarting = false;
 141 }
 142
 143 void
 144 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 145                                           double target_speed, double current_speed,
 146                                           pframes_t nframes)
 147 {
 148         assert (nframes > 0);
 149
 150         Sample *out;
 151         pframes_t txf = 0;
 152         boost::shared_ptr<Port> ltcport = ltc_output_port();
 153
 154         Buffer& buf (ltcport->get_buffer (nframes));
 155
 156         if (!ltc_encoder || !ltc_enc_buf) {
 157                 return;
 158         }
 159
 160         SyncSource sync_src = Config->get_sync_source();
 161         if (engine().freewheeling() || !Config->get_send_ltc()
 162             /* TODO
 163              * decide which time-sources we can generated LTC from.
 164              * Internal, JACK or sample-synced slaves should be fine.
 165              * talk to oofus.
 166              *
 167              || (config.get_external_sync() && sync_src == LTC)
 168              || (config.get_external_sync() && sync_src == MTC)
 169             */
 170              ||(config.get_external_sync() && sync_src == MIDIClock)
 171                 ) {
 172                 return;
 173         }
 174
 175         out = dynamic_cast<AudioBuffer*>(&buf)->data ();
 176
 177         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 178         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 179
 180         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_out_latency.max));
 181
 182         /* all systems go. Now here's the plan:
 183          *
 184          *  1) check if fps has changed
 185          *  2) check direction of encoding, calc speed, re-sample existing buffer
 186          *  3) calculate frame and byte to send aligned to jack-period size
 187          *  4) check if it's the frame/byte that is already in the queue
 188          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 189          *  6) actual LTC audio output
 190          *  6a) send remaining part of already queued frame; break on nframes
 191          *  6b) encode new LTC-frame byte
 192          *  6c) goto 6a
 193          *  7) done
 194          */
 195
 196         // (1) check fps
 197         TimecodeFormat cur_timecode = config.get_timecode_format();
 198         if (cur_timecode != ltc_enc_tcformat) {
 199                 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)));
 200                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode), -2)) {
 201                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 202                         ltc_tx_cleanup();
 203                         return;
 204                 }
 205                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
 206                 ltc_enc_tcformat = cur_timecode;
 207                 ltc_tx_reset();
 208         }
 209
 210         /* LTC is max. 30 fps */
 211         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 212                 return;
 213         }
 214
 215         // (2) speed & direction
 216
 217         /* speed 0 aka transport stopped is interpreted as rolling forward.
 218          * keep repeating current frame
 219          */
 220 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 221         bool speed_changed = false;
 222
 223         /* port latency compensation:
 224          * The _generated timecode_ is offset by the port-latency,
 225          * therefore the offset depends on the direction of transport.
 226          */
 227         framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame - ltc_out_latency.max) : (start_frame + ltc_out_latency.max);
 228
 229         /* cycle-start may become negative due to latency compensation */
 230         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 231
 232         double new_ltc_speed = (double)(labs(end_frame - start_frame) * SIGNUM(current_speed)) / (double)nframes;
 233         if (nominal_frame_rate() != frame_rate()) {
 234                 new_ltc_speed *= (double)nominal_frame_rate() / (double)frame_rate();
 235         }
 236
 237         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 238                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 239                 ltc_tx_reset();
 240         }
 241
 242         if (ltc_speed != new_ltc_speed) {
 243                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 244                  * if target_speed != current_speed we should interpolate, too.
 245                  *
 246                  * However, currency in A3 target_speed == current_speed for each process cycle
 247                  * (except for the sign and if target_speed > 8.0).
 248                  * Besides, above speed calculation uses the difference (end_frame - start_frame).
 249                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 250                  * so we're good.
 251                  */
 252                 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));
 253                 speed_changed = true;
 254                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
 255         }
 256
 257         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 258                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 259                 /* keep repeating current frame
 260                  *
 261                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 262                  * some machines do odd things if LTC goes away:
 263                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 264                  * so unspool the tape from the playhead. That might be inconvenient.
 265                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 266                  */
 267                 new_ltc_speed = 0;
 268                 if (!Config->get_ltc_send_continuously()) {
 269                         ltc_speed = new_ltc_speed;
 270                         return;
 271                 }
 272         }
 273
 274         if (fabs(new_ltc_speed) > 10.0) {
 275                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 276                 ltc_tx_reset();
 277                 return;
 278         }
 279
 280         if (ltc_speed == 0 && new_ltc_speed != 0) {
 281                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 282                 ltc_tx_reset();
 283         }
 284
 285         /* the timecode duration corresponding to the samples that are still
 286          * in the buffer. Here, the speed of previous cycle is used to calculate
 287          * the alignment at the beginning of this cycle later.
 288          */
 289         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 290
 291         if (speed_changed && new_ltc_speed != 0) {
 292                 /* we need to re-sample the existing buffer.
 293                  * "make space for the en-coder to catch up to the new speed"
 294                  *
 295                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 296                  * by removing samples or duplicating samples /here and there/.
 297                  *
 298                  * There may be a more elegant way to do this, in fact one could
 299                  * simply re-render the buffer using ltc_encoder_encode_byte()
 300                  * but that'd require some timecode offset buffer magic,
 301                  * which is left for later..
 302                  */
 303
 304                 double oldbuflen = (double)(ltc_buf_len - ltc_buf_off);
 305                 double newbuflen = (double)(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 306
 307                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 308                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 309                                         ));
 310
 311                 double bufrspdiff = rint(newbuflen - oldbuflen);
 312
 313                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 314                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 315                         ltc_tx_reset();
 316                         poff = 0;
 317                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 318                         int incnt = 0;
 319                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 320                         double avg_distance = newbuflen / samples_to_insert;
 321                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 322
 323                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 324                                 const int ro = rp - ltc_buf_off;
 325                                 if (ro < (incnt*avg_distance)) continue;
 326                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 327                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 328                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 329                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 330                                 incnt++;
 331                                 ltc_buf_len++;
 332                         }
 333                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 334                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 335                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 336                         if (oldbuflen <= samples_to_remove) {
 337                                 ltc_buf_off = ltc_buf_len= 0;
 338                         } else {
 339                                 double avg_distance = newbuflen / samples_to_remove;
 340                                 int rmcnt = 0;
 341                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 342                                         const int ro = rp - ltc_buf_off;
 343                                         if (ro < (rmcnt*avg_distance)) continue;
 344                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 345                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 346                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 347                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 348                                         ltc_buf_len--;
 349                                         rmcnt++;
 350                                 }
 351                         }
 352                 }
 353         }
 354
 355         ltc_speed = new_ltc_speed;
 356         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 357
 358         // (3) bit/sample alignment
 359         Timecode::Time tc_start;
 360         framepos_t tc_sample_start;
 361
 362         /* calc timecode frame from current position - round down to nearest timecode */
 363         Timecode::sample_to_timecode(cycle_start_frame, tc_start, true, false,
 364                         timecode_frames_per_second(),
 365                         timecode_drop_frames(),
 366                         (double)frame_rate(),
 367                         config.get_subframes_per_frame(),
 368                         config.get_timecode_offset_negative(), config.get_timecode_offset()
 369                         );
 370
 371         /* convert timecode back to sample-position */
 372         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 373                 (double)frame_rate(),
 374                 config.get_subframes_per_frame(),
 375                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 376                 );
 377
 378         /* difference between current frame and TC frame in samples */
 379         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 380         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 381                                 cycle_start_frame, tc_sample_start, soff));
 382
 383
 384         // (4) check if alignment matches
 385         const double fptcf = frames_per_timecode_frame();
 386
 387         /* maximum difference of bit alignment in audio-samples.
 388          *
 389          * if transport and LTC generator differs more than this, the LTC
 390          * generator will be re-initialized
 391          *
 392          * due to rounding error and variations in LTC-bit duration depending
 393          * on the speed, it can be off by +- ltc_speed audio-samples.
 394          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 395          * in the cycle _after_ the speed changed. The average delta however is 0.
 396          */
 397         double maxdiff;
 398
 399         if (config.get_external_sync() && slave()) {
 400                 maxdiff = slave()->resolution();
 401         } else {
 402                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 403                 if (nominal_frame_rate() != frame_rate()) {
 404                         maxdiff *= 3.0;
 405                 }
 406                 if (ltc_enc_tcformat == Timecode::timecode_23976 || ltc_enc_tcformat == Timecode::timecode_24976) {
 407                         maxdiff *= 15.0;
 408                 }
 409         }
 410
 411         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 412                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 413
 414         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 415                                 ltc_enc_pos + ltc_enc_cnt - poff,
 416                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 417                                 ));
 418
 419         if (ltc_enc_pos < 0
 420                         || (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff)
 421                         ) {
 422
 423                 // (5) re-align
 424                 ltc_tx_reset();
 425
 426                 /* set frame to encode */
 427                 SMPTETimecode tc;
 428                 tc.hours = tc_start.hours;
 429                 tc.mins = tc_start.minutes;
 430                 tc.secs = tc_start.seconds;
 431                 tc.frame = tc_start.frames;
 432                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 433
 434                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 435                  * In A3 30000/1001 or 30 fps can be drop-frame.
 436                  */
 437                 LTCFrame ltcframe;
 438                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 439                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 440                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 441
 442
 443                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 444
 445                 uint32_t cyc_off;
 446                 if (soff < 0 || soff >= fptcf) {
 447                         /* session framerate change between (2) and now */
 448                         ltc_tx_reset();
 449                         return;
 450                 }
 451
 452                 if (ltc_speed < 0 ) {
 453                         /* calculate the byte that starts at or after the current position */
 454                         ltc_enc_byte = floor((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 = soff- ceil(ltc_enc_cnt);
 459
 460                 } else {
 461                         /* calculate the byte that starts at or after the current position */
 462                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 463                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 464
 465                         /* calculate difference between the current position and the byte to send */
 466                         cyc_off = ceil(ltc_enc_cnt) - soff;
 467
 468                         if (ltc_enc_byte == 10) {
 469                                 ltc_enc_byte = 0;
 470                                 ltc_encoder_inc_timecode(ltc_encoder);
 471                         }
 472                 }
 473
 474                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 475                                         soff, ltc_enc_byte, cyc_off));
 476
 477                 if ( (ltc_speed < 0 && ltc_enc_byte !=9 ) || (ltc_speed >= 0 && ltc_enc_byte !=0 ) ) {
 478                         restarting = true;
 479                 }
 480
 481                 if (cyc_off > 0 && cyc_off <= nframes) {
 482                         /* offset in this cycle */
 483                         txf= rint(cyc_off / fabs(ltc_speed));
 484                         memset(out, 0, cyc_off * sizeof(Sample));
 485                 } else {
 486                         /* resync next cycle */
 487                         memset(out, 0, nframes * sizeof(Sample));
 488                         return;
 489                 }
 490
 491                 ltc_enc_pos = tc_sample_start;
 492
 493                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 494                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 495         }
 496         else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
 497                 /* reduce (low freq) jitter.
 498                  * The granularity of the LTC encoder speed is 1 byte =
 499                  * (frames-per-timecode-frame / 10) audio-samples.
 500                  * Thus, tiny speed changes [as produced by some slaves]
 501                  * may not have any effect in the cycle when they occur,
 502                  * but they will add up over time.
 503                  *
 504                  * This is a linear approx to compensate for this jitter
 505                  * and prempt re-sync when the drift builds up.
 506                  *
 507                  * However, for very fast speeds - when 1 LTC bit is
 508                  * <= 3 audio-sample - adjusting speed may lead to
 509                  * invalid frames.
 510                  *
 511                  * To do better than this, resampling (or a rewrite of the
 512                  * encoder) is required.
 513                  */
 514                 ltc_speed -= ((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) / engine().frame_rate();
 515         }
 516
 517
 518         // (6) encode and output
 519         while (1) {
 520 #ifdef LTC_GEN_TXDBUG
 521                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 522 #endif
 523                 // (6a) send remaining buffer
 524                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 525                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 526                         const Sample val = (Sample) (v1*ltcvol);
 527                         out[txf++] = val;
 528                 }
 529 #ifdef LTC_GEN_TXDBUG
 530                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 531 #endif
 532
 533                 if (txf >= nframes) {
 534                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 535                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 536                         break;
 537                 }
 538
 539                 ltc_buf_len = 0;
 540                 ltc_buf_off = 0;
 541
 542                 // (6b) encode LTC, bump timecode
 543
 544                 if (ltc_speed < 0) {
 545                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 546                         if (ltc_enc_byte == 9) {
 547                                 ltc_encoder_dec_timecode(ltc_encoder);
 548                                 ltc_tx_recalculate_position();
 549                                 ltc_enc_cnt = fptcf;
 550                         }
 551                 }
 552
 553                 int enc_frames;
 554
 555                 if (restarting) {
 556                         /* write zero bytes -- don't touch encoder until we're at a frame-boundary
 557                          * otherwise the biphase polarity may be inverted.
 558                          */
 559                         enc_frames = fptcf / 10.0;
 560                         memset(&ltc_enc_buf[ltc_buf_len], 127, enc_frames * sizeof(ltcsnd_sample_t));
 561                 } else {
 562                         if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 563                                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 564                                 ltc_encoder_buffer_flush(ltc_encoder);
 565                                 ltc_tx_reset();
 566                                 return;
 567                         }
 568                         enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 569                 }
 570
 571 #ifdef LTC_GEN_FRAMEDBUG
 572                 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));
 573 #endif
 574                 if (enc_frames <=0) {
 575                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 576                         ltc_encoder_buffer_flush(ltc_encoder);
 577                         ltc_tx_reset();
 578                         return;
 579                 }
 580
 581                 ltc_buf_len += enc_frames;
 582                 if (ltc_speed < 0)
 583                         ltc_enc_cnt -= fptcf/10.0;
 584                 else
 585                         ltc_enc_cnt += fptcf/10.0;
 586
 587                 if (ltc_speed >= 0) {
 588                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 589                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 590                                 ltc_encoder_inc_timecode(ltc_encoder);
 591 #if 0 /* force fixed parity -- scope debug */
 592                                 LTCFrame f;
 593                                 ltc_encoder_get_frame(ltc_encoder, &f);
 594                                 f.biphase_mark_phase_correction=0;
 595                                 ltc_encoder_set_frame(ltc_encoder, &f);
 596 #endif
 597                                 ltc_tx_recalculate_position();
 598                                 ltc_enc_cnt = 0;
 599                         } else if (ltc_enc_byte == 0) {
 600                                 ltc_enc_cnt = 0;
 601                                 restarting=false;
 602                         }
 603                 }
 604 #ifdef LTC_GEN_FRAMEDBUG
 605                 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));
 606 #endif
 607         }
 608
 609         dynamic_cast<AudioBuffer*>(&buf)->set_written (true);
 610         return;
 611 }