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         free(ltc_enc_buf);
  97         ltc_enc_buf = NULL;
  98         ltc_encoder_free(ltc_encoder);
  99         ltc_encoder = NULL;
 100 }
 101
 102 void
 103 Session::ltc_tx_resync_latency()
 104 {
 105         DEBUG_TRACE (DEBUG::LTC, "LTC TX resync latency\n");
 106         if (!deletion_in_progress()) {
 107                 boost::shared_ptr<Port> ltcport = ltc_output_port();
 108                 if (ltcport) {
 109                         ltcport->get_connected_latency_range(ltc_out_latency, true);
 110                 }
 111         }
 112 }
 113
 114 void
 115 Session::ltc_tx_reset()
 116 {
 117         DEBUG_TRACE (DEBUG::LTC, "LTC TX reset\n");
 118         ltc_enc_pos = -9999; // force re-start
 119         ltc_buf_len = 0;
 120         ltc_buf_off = 0;
 121         ltc_enc_byte = 0;
 122         ltc_enc_cnt = 0;
 123
 124         ltc_encoder_reset(ltc_encoder);
 125 }
 126
 127 void
 128 Session::ltc_tx_parse_offset() {
 129         Timecode::Time offset_tc;
 130         Timecode::parse_timecode_format(config.get_timecode_generator_offset(), offset_tc);
 131         offset_tc.rate = timecode_frames_per_second();
 132         offset_tc.drop = timecode_drop_frames();
 133         timecode_to_sample(offset_tc, ltc_timecode_offset, false, false);
 134         ltc_timecode_negative_offset = !offset_tc.negative;
 135 }
 136
 137 void
 138 Session::ltc_tx_recalculate_position()
 139 {
 140         SMPTETimecode enctc;
 141         Timecode::Time a3tc;
 142         ltc_encoder_get_timecode(ltc_encoder, &enctc);
 143
 144         a3tc.hours   = enctc.hours;
 145         a3tc.minutes = enctc.mins;
 146         a3tc.seconds = enctc.secs;
 147         a3tc.frames  = enctc.frame;
 148         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
 149         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
 150
 151         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
 152                 (double)frame_rate(),
 153                 config.get_subframes_per_frame(),
 154                 ltc_timecode_negative_offset, ltc_timecode_offset
 155                 );
 156         restarting = false;
 157 }
 158
 159 void
 160 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 161                                           double target_speed, double current_speed,
 162                                           pframes_t nframes)
 163 {
 164         assert (nframes > 0);
 165
 166         Sample *out;
 167         pframes_t txf = 0;
 168         boost::shared_ptr<Port> ltcport = ltc_output_port();
 169
 170         Buffer& buf (ltcport->get_buffer (nframes));
 171
 172         if (!ltc_encoder || !ltc_enc_buf) {
 173                 return;
 174         }
 175
 176         SyncSource sync_src = Config->get_sync_source();
 177         if (engine().freewheeling() || !Config->get_send_ltc()
 178             /* TODO
 179              * decide which time-sources we can generated LTC from.
 180              * Internal, JACK or sample-synced slaves should be fine.
 181              * talk to oofus.
 182              *
 183              || (config.get_external_sync() && sync_src == LTC)
 184              || (config.get_external_sync() && sync_src == MTC)
 185             */
 186              ||(config.get_external_sync() && sync_src == MIDIClock)
 187                 ) {
 188                 return;
 189         }
 190
 191         out = dynamic_cast<AudioBuffer*>(&buf)->data ();
 192
 193         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 194         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 195
 196         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_out_latency.max));
 197
 198         /* all systems go. Now here's the plan:
 199          *
 200          *  1) check if fps has changed
 201          *  2) check direction of encoding, calc speed, re-sample existing buffer
 202          *  3) calculate frame and byte to send aligned to jack-period size
 203          *  4) check if it's the frame/byte that is already in the queue
 204          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 205          *  6) actual LTC audio output
 206          *  6a) send remaining part of already queued frame; break on nframes
 207          *  6b) encode new LTC-frame byte
 208          *  6c) goto 6a
 209          *  7) done
 210          */
 211
 212         // (1) check fps
 213         TimecodeFormat cur_timecode = config.get_timecode_format();
 214         if (cur_timecode != ltc_enc_tcformat) {
 215                 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)));
 216                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(),
 217                                         timecode_to_frames_per_second(cur_timecode),
 218                                         TV_STANDARD(cur_timecode), 0
 219                                         )) {
 220                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 221                         ltc_tx_cleanup();
 222                         return;
 223                 }
 224                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
 225                 ltc_enc_tcformat = cur_timecode;
 226                 ltc_tx_parse_offset();
 227                 ltc_tx_reset();
 228         }
 229
 230         /* LTC is max. 30 fps */
 231         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 232                 return;
 233         }
 234
 235         // (2) speed & direction
 236
 237         /* speed 0 aka transport stopped is interpreted as rolling forward.
 238          * keep repeating current frame
 239          */
 240 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 241         bool speed_changed = false;
 242
 243         /* port latency compensation:
 244          * The _generated timecode_ is offset by the port-latency,
 245          * therefore the offset depends on the direction of transport.
 246          */
 247         framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame - ltc_out_latency.max) : (start_frame + ltc_out_latency.max);
 248
 249         /* LTC TV standard offset */
 250         cycle_start_frame -= ltc_frame_alignment(frames_per_timecode_frame(), TV_STANDARD(cur_timecode));
 251
 252         /* cycle-start may become negative due to latency compensation */
 253         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 254
 255         double new_ltc_speed = (double)(labs(end_frame - start_frame) * SIGNUM(current_speed)) / (double)nframes;
 256         if (nominal_frame_rate() != frame_rate()) {
 257                 new_ltc_speed *= (double)nominal_frame_rate() / (double)frame_rate();
 258         }
 259
 260         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 261                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 262                 ltc_tx_reset();
 263         }
 264
 265         if (ltc_speed != new_ltc_speed) {
 266                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 267                  * if target_speed != current_speed we should interpolate, too.
 268                  *
 269                  * However, currency in A3 target_speed == current_speed for each process cycle
 270                  * (except for the sign and if target_speed > 8.0).
 271                  * Besides, above speed calculation uses the difference (end_frame - start_frame).
 272                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 273                  * so we're good.
 274                  */
 275                 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));
 276                 speed_changed = true;
 277                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
 278         }
 279
 280         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 281                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 282                 /* keep repeating current frame
 283                  *
 284                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 285                  * some machines do odd things if LTC goes away:
 286                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 287                  * so unspool the tape from the playhead. That might be inconvenient.
 288                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 289                  */
 290                 new_ltc_speed = 0;
 291                 if (!Config->get_ltc_send_continuously()) {
 292                         ltc_speed = new_ltc_speed;
 293                         return;
 294                 }
 295         }
 296
 297         if (fabs(new_ltc_speed) > 10.0) {
 298                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 299                 ltc_tx_reset();
 300                 return;
 301         }
 302
 303         if (ltc_speed == 0 && new_ltc_speed != 0) {
 304                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 305                 ltc_tx_reset();
 306         }
 307
 308         /* the timecode duration corresponding to the samples that are still
 309          * in the buffer. Here, the speed of previous cycle is used to calculate
 310          * the alignment at the beginning of this cycle later.
 311          */
 312         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 313
 314         if (speed_changed && new_ltc_speed != 0) {
 315                 /* we need to re-sample the existing buffer.
 316                  * "make space for the en-coder to catch up to the new speed"
 317                  *
 318                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 319                  * by removing samples or duplicating samples /here and there/.
 320                  *
 321                  * There may be a more elegant way to do this, in fact one could
 322                  * simply re-render the buffer using ltc_encoder_encode_byte()
 323                  * but that'd require some timecode offset buffer magic,
 324                  * which is left for later..
 325                  */
 326
 327                 double oldbuflen = (double)(ltc_buf_len - ltc_buf_off);
 328                 double newbuflen = (double)(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 329
 330                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 331                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 332                                         ));
 333
 334                 double bufrspdiff = rint(newbuflen - oldbuflen);
 335
 336                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 337                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 338                         ltc_tx_reset();
 339                         poff = 0;
 340                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 341                         int incnt = 0;
 342                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 343                         double avg_distance = newbuflen / samples_to_insert;
 344                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 345
 346                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 347                                 const int ro = rp - ltc_buf_off;
 348                                 if (ro < (incnt*avg_distance)) continue;
 349                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 350                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 351                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 352                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 353                                 incnt++;
 354                                 ltc_buf_len++;
 355                         }
 356                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 357                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 358                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 359                         if (oldbuflen <= samples_to_remove) {
 360                                 ltc_buf_off = ltc_buf_len= 0;
 361                         } else {
 362                                 double avg_distance = newbuflen / samples_to_remove;
 363                                 int rmcnt = 0;
 364                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 365                                         const int ro = rp - ltc_buf_off;
 366                                         if (ro < (rmcnt*avg_distance)) continue;
 367                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 368                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 369                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 370                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 371                                         ltc_buf_len--;
 372                                         rmcnt++;
 373                                 }
 374                         }
 375                 }
 376         }
 377
 378         ltc_speed = new_ltc_speed;
 379         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 380
 381         // (3) bit/sample alignment
 382         Timecode::Time tc_start;
 383         framepos_t tc_sample_start;
 384
 385         /* calc timecode frame from current position - round down to nearest timecode */
 386         Timecode::sample_to_timecode(cycle_start_frame, tc_start, true, false,
 387                         timecode_frames_per_second(),
 388                         timecode_drop_frames(),
 389                         (double)frame_rate(),
 390                         config.get_subframes_per_frame(),
 391                         ltc_timecode_negative_offset, ltc_timecode_offset
 392                         );
 393
 394         /* convert timecode back to sample-position */
 395         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 396                 (double)frame_rate(),
 397                 config.get_subframes_per_frame(),
 398                 ltc_timecode_negative_offset, ltc_timecode_offset
 399                 );
 400
 401         /* difference between current frame and TC frame in samples */
 402         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 403         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 404                                 cycle_start_frame, tc_sample_start, soff));
 405
 406
 407         // (4) check if alignment matches
 408         const double fptcf = frames_per_timecode_frame();
 409
 410         /* maximum difference of bit alignment in audio-samples.
 411          *
 412          * if transport and LTC generator differs more than this, the LTC
 413          * generator will be re-initialized
 414          *
 415          * due to rounding error and variations in LTC-bit duration depending
 416          * on the speed, it can be off by +- ltc_speed audio-samples.
 417          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 418          * in the cycle _after_ the speed changed. The average delta however is 0.
 419          */
 420         double maxdiff;
 421
 422         if (config.get_external_sync() && slave()) {
 423                 maxdiff = slave()->resolution();
 424         } else {
 425                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 426                 if (nominal_frame_rate() != frame_rate()) {
 427                         maxdiff *= 3.0;
 428                 }
 429                 if (ltc_enc_tcformat == Timecode::timecode_23976 || ltc_enc_tcformat == Timecode::timecode_24976) {
 430                         maxdiff *= 15.0;
 431                 }
 432         }
 433
 434         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 435                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 436
 437         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 438                                 ltc_enc_pos + ltc_enc_cnt - poff,
 439                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 440                                 ));
 441
 442         if (ltc_enc_pos < 0
 443                         || (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff)
 444                         ) {
 445
 446                 // (5) re-align
 447                 ltc_tx_reset();
 448
 449                 /* set frame to encode */
 450                 SMPTETimecode tc;
 451                 tc.hours = tc_start.hours;
 452                 tc.mins = tc_start.minutes;
 453                 tc.secs = tc_start.seconds;
 454                 tc.frame = tc_start.frames;
 455                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 456
 457                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 458                  * In A3 30000/1001 or 30 fps can be drop-frame.
 459                  */
 460                 LTCFrame ltcframe;
 461                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 462                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 463                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 464
 465
 466                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 467
 468                 uint32_t cyc_off;
 469                 if (soff < 0 || soff >= fptcf) {
 470                         /* session framerate change between (2) and now */
 471                         ltc_tx_reset();
 472                         return;
 473                 }
 474
 475                 if (ltc_speed < 0 ) {
 476                         /* calculate the byte that starts at or after the current position */
 477                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 478                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 479
 480                         /* calculate difference between the current position and the byte to send */
 481                         cyc_off = soff- ceil(ltc_enc_cnt);
 482
 483                 } else {
 484                         /* calculate the byte that starts at or after the current position */
 485                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 486                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 487
 488                         /* calculate difference between the current position and the byte to send */
 489                         cyc_off = ceil(ltc_enc_cnt) - soff;
 490
 491                         if (ltc_enc_byte == 10) {
 492                                 ltc_enc_byte = 0;
 493                                 ltc_encoder_inc_timecode(ltc_encoder);
 494                         }
 495                 }
 496
 497                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 498                                         soff, ltc_enc_byte, cyc_off));
 499
 500                 if ( (ltc_speed < 0 && ltc_enc_byte !=9 ) || (ltc_speed >= 0 && ltc_enc_byte !=0 ) ) {
 501                         restarting = true;
 502                 }
 503
 504                 if (cyc_off > 0 && cyc_off <= nframes) {
 505                         /* offset in this cycle */
 506                         txf= rint(cyc_off / fabs(ltc_speed));
 507                         memset(out, 0, cyc_off * sizeof(Sample));
 508                 } else {
 509                         /* resync next cycle */
 510                         memset(out, 0, nframes * sizeof(Sample));
 511                         return;
 512                 }
 513
 514                 ltc_enc_pos = tc_sample_start;
 515
 516                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 517                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 518         }
 519         else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
 520                 /* reduce (low freq) jitter.
 521                  * The granularity of the LTC encoder speed is 1 byte =
 522                  * (frames-per-timecode-frame / 10) audio-samples.
 523                  * Thus, tiny speed changes [as produced by some slaves]
 524                  * may not have any effect in the cycle when they occur,
 525                  * but they will add up over time.
 526                  *
 527                  * This is a linear approx to compensate for this jitter
 528                  * and prempt re-sync when the drift builds up.
 529                  *
 530                  * However, for very fast speeds - when 1 LTC bit is
 531                  * <= 3 audio-sample - adjusting speed may lead to
 532                  * invalid frames.
 533                  *
 534                  * To do better than this, resampling (or a rewrite of the
 535                  * encoder) is required.
 536                  */
 537                 ltc_speed -= ((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) / engine().frame_rate();
 538         }
 539
 540
 541         // (6) encode and output
 542         while (1) {
 543 #ifdef LTC_GEN_TXDBUG
 544                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 545 #endif
 546                 // (6a) send remaining buffer
 547                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 548                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 549                         const Sample val = (Sample) (v1*ltcvol);
 550                         out[txf++] = val;
 551                 }
 552 #ifdef LTC_GEN_TXDBUG
 553                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 554 #endif
 555
 556                 if (txf >= nframes) {
 557                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 558                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 559                         break;
 560                 }
 561
 562                 ltc_buf_len = 0;
 563                 ltc_buf_off = 0;
 564
 565                 // (6b) encode LTC, bump timecode
 566
 567                 if (ltc_speed < 0) {
 568                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 569                         if (ltc_enc_byte == 9) {
 570                                 ltc_encoder_dec_timecode(ltc_encoder);
 571                                 ltc_tx_recalculate_position();
 572                                 ltc_enc_cnt = fptcf;
 573                         }
 574                 }
 575
 576                 int enc_frames;
 577
 578                 if (restarting) {
 579                         /* write zero bytes -- don't touch encoder until we're at a frame-boundary
 580                          * otherwise the biphase polarity may be inverted.
 581                          */
 582                         enc_frames = fptcf / 10.0;
 583                         memset(&ltc_enc_buf[ltc_buf_len], 127, enc_frames * sizeof(ltcsnd_sample_t));
 584                 } else {
 585                         if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 586                                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 587                                 ltc_encoder_buffer_flush(ltc_encoder);
 588                                 ltc_tx_reset();
 589                                 return;
 590                         }
 591                         enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 592                 }
 593
 594 #ifdef LTC_GEN_FRAMEDBUG
 595                 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));
 596 #endif
 597                 if (enc_frames <=0) {
 598                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 599                         ltc_encoder_buffer_flush(ltc_encoder);
 600                         ltc_tx_reset();
 601                         return;
 602                 }
 603
 604                 ltc_buf_len += enc_frames;
 605                 if (ltc_speed < 0)
 606                         ltc_enc_cnt -= fptcf/10.0;
 607                 else
 608                         ltc_enc_cnt += fptcf/10.0;
 609
 610                 if (ltc_speed >= 0) {
 611                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 612                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 613                                 ltc_encoder_inc_timecode(ltc_encoder);
 614 #if 0 /* force fixed parity -- scope debug */
 615                                 LTCFrame f;
 616                                 ltc_encoder_get_frame(ltc_encoder, &f);
 617                                 f.biphase_mark_phase_correction=0;
 618                                 ltc_encoder_set_frame(ltc_encoder, &f);
 619 #endif
 620                                 ltc_tx_recalculate_position();
 621                                 ltc_enc_cnt = 0;
 622                         } else if (ltc_enc_byte == 0) {
 623                                 ltc_enc_cnt = 0;
 624                                 restarting=false;
 625                         }
 626                 }
 627 #ifdef LTC_GEN_FRAMEDBUG
 628                 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));
 629 #endif
 630         }
 631
 632         dynamic_cast<AudioBuffer*>(&buf)->set_written (true);
 633         return;
 634 }