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 "pbd/i18n.h"
  31
  32 using namespace std;
  33 using namespace ARDOUR;
  34 using namespace PBD;
  35 using namespace Timecode;
  36
  37 /* really verbose timing debug */
  38 //#define LTC_GEN_FRAMEDBUG
  39 //#define LTC_GEN_TXDBUG
  40
  41 #ifndef MAX
  42 #define MAX(a,b) ( (a) > (b) ? (a) : (b) )
  43 #endif
  44 #ifndef MIN
  45 #define MIN(a,b) ( (a) < (b) ? (a) : (b) )
  46 #endif
  47
  48 /* LTC signal should have a rise time of 25 us +/- 5 us.
  49  * yet with most sound-cards a square-wave of 1-2 sample
  50  * introduces ringing and small oscillations.
  51  * https://en.wikipedia.org/wiki/Gibbs_phenomenon
  52  * A low-pass filter in libltc can reduce this at
  53  * the cost of being slightly out of spec WRT to rise-time.
  54  *
  55  * This filter is adaptive so that fast vari-speed signals
  56  * will not be affected by it.
  57  */
  58 #define LTC_RISE_TIME(speed) MIN (100, MAX(40, (4000000 / ((speed==0)?1:speed) / engine().sample_rate())))
  59
  60 #define TV_STANDARD(tcf) \
  61         (timecode_to_frames_per_second(tcf)==25.0 ? LTC_TV_625_50 : \
  62          timecode_has_drop_frames(tcf)? LTC_TV_525_60 : LTC_TV_FILM_24)
  63
  64 void
  65 Session::ltc_tx_initialize()
  66 {
  67         ltc_enc_tcformat = config.get_timecode_format();
  68
  69         ltc_tx_parse_offset();
  70         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)));
  71         ltc_encoder = ltc_encoder_create(nominal_frame_rate(),
  72                         timecode_to_frames_per_second(ltc_enc_tcformat),
  73                         TV_STANDARD(ltc_enc_tcformat), 0);
  74
  75         ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
  76         ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(1.0));
  77
  78         /* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
  79          * usually returned by ltc_encoder_get_buffersize(encoder)
  80          *
  81          * since the fps can change and A3's  min fps: 24000/1001 */
  82         ltc_enc_buf = (ltcsnd_sample_t*) calloc((nominal_frame_rate() / 23), sizeof(ltcsnd_sample_t));
  83         ltc_speed = 0;
  84         ltc_prev_cycle = -1;
  85         ltc_tx_reset();
  86         ltc_tx_resync_latency();
  87         Xrun.connect_same_thread (ltc_tx_connections, boost::bind (&Session::ltc_tx_reset, this));
  88         engine().GraphReordered.connect_same_thread (ltc_tx_connections, 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         ltc_tx_connections.drop_connections ();
 101 }
 102
 103 void
 104 Session::ltc_tx_resync_latency()
 105 {
 106         DEBUG_TRACE (DEBUG::LTC, "LTC TX resync latency\n");
 107         if (!deletion_in_progress()) {
 108                 boost::shared_ptr<Port> ltcport = ltc_output_port();
 109                 if (ltcport) {
 110                         ltcport->get_connected_latency_range(ltc_out_latency, true);
 111                 }
 112         }
 113 }
 114
 115 void
 116 Session::ltc_tx_reset()
 117 {
 118         DEBUG_TRACE (DEBUG::LTC, "LTC TX reset\n");
 119         assert (ltc_encoder);
 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         ltc_prev_cycle = -1;
 138 }
 139
 140 void
 141 Session::ltc_tx_recalculate_position()
 142 {
 143         SMPTETimecode enctc;
 144         Timecode::Time a3tc;
 145         ltc_encoder_get_timecode(ltc_encoder, &enctc);
 146
 147         a3tc.hours   = enctc.hours;
 148         a3tc.minutes = enctc.mins;
 149         a3tc.seconds = enctc.secs;
 150         a3tc.frames  = enctc.frame;
 151         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
 152         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
 153
 154         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
 155                 (double)frame_rate(),
 156                 config.get_subframes_per_frame(),
 157                 ltc_timecode_negative_offset, ltc_timecode_offset
 158                 );
 159         restarting = false;
 160 }
 161
 162 void
 163 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 164                                           double target_speed, double current_speed,
 165                                           pframes_t nframes)
 166 {
 167         assert (nframes > 0);
 168
 169         Sample *out;
 170         pframes_t txf = 0;
 171         boost::shared_ptr<Port> ltcport = ltc_output_port();
 172
 173         Buffer& buf (ltcport->get_buffer (nframes));
 174
 175         if (!ltc_encoder || !ltc_enc_buf) {
 176                 return;
 177         }
 178
 179         SyncSource sync_src = Config->get_sync_source();
 180         if (engine().freewheeling() || !Config->get_send_ltc()
 181             /* TODO
 182              * decide which time-sources we can generated LTC from.
 183              * Internal, JACK or sample-synced slaves should be fine.
 184              * talk to oofus.
 185              *
 186              || (config.get_external_sync() && sync_src == LTC)
 187              || (config.get_external_sync() && sync_src == MTC)
 188             */
 189              ||(config.get_external_sync() && sync_src == MIDIClock)
 190                 ) {
 191                 return;
 192         }
 193
 194         out = dynamic_cast<AudioBuffer*>(&buf)->data ();
 195
 196         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 197         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 198
 199         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_out_latency.max));
 200
 201         /* all systems go. Now here's the plan:
 202          *
 203          *  1) check if fps has changed
 204          *  2) check direction of encoding, calc speed, re-sample existing buffer
 205          *  3) calculate frame and byte to send aligned to jack-period size
 206          *  4) check if it's the frame/byte that is already in the queue
 207          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 208          *  6) actual LTC audio output
 209          *  6a) send remaining part of already queued frame; break on nframes
 210          *  6b) encode new LTC-frame byte
 211          *  6c) goto 6a
 212          *  7) done
 213          */
 214
 215         // (1) check fps
 216         TimecodeFormat cur_timecode = config.get_timecode_format();
 217         if (cur_timecode != ltc_enc_tcformat) {
 218                 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)));
 219                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(),
 220                                         timecode_to_frames_per_second(cur_timecode),
 221                                         TV_STANDARD(cur_timecode), 0
 222                                         )) {
 223                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 224                         ltc_tx_cleanup();
 225                         return;
 226                 }
 227                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
 228                 ltc_enc_tcformat = cur_timecode;
 229                 ltc_tx_parse_offset();
 230                 ltc_tx_reset();
 231         }
 232
 233         /* LTC is max. 30 fps */
 234         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 235                 return;
 236         }
 237
 238         // (2) speed & direction
 239
 240         /* speed 0 aka transport stopped is interpreted as rolling forward.
 241          * keep repeating current frame
 242          */
 243 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 244         bool speed_changed = false;
 245
 246         /* port latency compensation:
 247          * The _generated timecode_ is offset by the port-latency,
 248          * therefore the offset depends on the direction of transport.
 249          *
 250          * latency is compensated by adding it to the timecode to
 251          * be generated. e.g. if the signal will reach the output in
 252          * N samples time from now, generate the timecode for (now + N).
 253          *
 254          * sample-sync is achieved by further calculating the difference
 255          * between the timecode and the session-transport and offsetting the
 256          * buffer.
 257          *
 258          * The timecode is generated directly in the Session process callback
 259          * using _transport_frame. It requires that the session has set the
 260          * port's playback latency to worst_playback_latency() prior to
 261          * calling ltc_tx_send_time_code_for_cycle().
 262          */
 263         framepos_t cycle_start_frame;
 264
 265         if (current_speed < 0) {
 266                 cycle_start_frame = (start_frame - ltc_out_latency.max + worst_playback_latency());
 267         } else if (current_speed > 0) {
 268                 cycle_start_frame = (start_frame + ltc_out_latency.max - worst_playback_latency());
 269         } else {
 270                 /* There is no need to compensate for latency when not rolling
 271                  * rather send the accurate NOW timecode
 272                  * (LTC encoder compenates latency by sending earlier timecode)
 273                  */
 274                 cycle_start_frame = start_frame;
 275         }
 276
 277         /* LTC TV standard offset */
 278         if (current_speed != 0) {
 279                 /* ditto - send "NOW" if not rolling */
 280                 cycle_start_frame -= ltc_frame_alignment(samples_per_timecode_frame(), TV_STANDARD(cur_timecode));
 281         }
 282
 283         /* cycle-start may become negative due to latency compensation */
 284         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 285
 286         double new_ltc_speed = (double)(labs(end_frame - start_frame) * SIGNUM(current_speed)) / (double)nframes;
 287         if (nominal_frame_rate() != frame_rate()) {
 288                 new_ltc_speed *= (double)nominal_frame_rate() / (double)frame_rate();
 289         }
 290
 291         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 292                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 293                 ltc_tx_reset();
 294         }
 295
 296         if (ltc_speed != new_ltc_speed
 297                         /* but only once if, current_speed changes to 0. In that case
 298                          * new_ltc_speed is > 0 because (end_frame - start_frame) == jack-period for no-roll
 299                          * but ltc_speed will still be 0
 300                          */
 301                         && (current_speed != 0 || ltc_speed != current_speed)
 302                         ) {
 303                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 304                  * if target_speed != current_speed we should interpolate, too.
 305                  *
 306                  * However, currency in A3 target_speed == current_speed for each process cycle
 307                  * (except for the sign and if target_speed > 8.0).
 308                  * Besides, above speed calculation uses the difference (end_frame - start_frame).
 309                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 310                  * so we're good.
 311                  */
 312                 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, new_ltc_speed));
 313                 speed_changed = true;
 314                 ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
 315         }
 316
 317         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 318                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 319                 /* keep repeating current frame
 320                  *
 321                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 322                  * some machines do odd things if LTC goes away:
 323                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 324                  * so unspool the tape from the playhead. That might be inconvenient.
 325                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 326                  */
 327                 new_ltc_speed = 0;
 328                 if (!Config->get_ltc_send_continuously()) {
 329                         ltc_speed = new_ltc_speed;
 330                         return;
 331                 }
 332                 if (start_frame != ltc_prev_cycle) {
 333                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: no-roll seek from %1 to %2 (%3)\n", ltc_prev_cycle, start_frame, cycle_start_frame));
 334                         ltc_tx_reset();
 335                 }
 336         }
 337
 338         if (fabs(new_ltc_speed) > 10.0) {
 339                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 340                 ltc_tx_reset();
 341                 return;
 342         }
 343
 344         if (ltc_speed == 0 && new_ltc_speed != 0) {
 345                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 346                 ltc_tx_reset();
 347         }
 348
 349         /* the timecode duration corresponding to the samples that are still
 350          * in the buffer. Here, the speed of previous cycle is used to calculate
 351          * the alignment at the beginning of this cycle later.
 352          */
 353         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 354
 355         if (speed_changed && new_ltc_speed != 0) {
 356                 /* we need to re-sample the existing buffer.
 357                  * "make space for the en-coder to catch up to the new speed"
 358                  *
 359                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 360                  * by removing samples or duplicating samples /here and there/.
 361                  *
 362                  * There may be a more elegant way to do this, in fact one could
 363                  * simply re-render the buffer using ltc_encoder_encode_byte()
 364                  * but that'd require some timecode offset buffer magic,
 365                  * which is left for later..
 366                  */
 367
 368                 double oldbuflen = (double)(ltc_buf_len - ltc_buf_off);
 369                 double newbuflen = (double)(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 370
 371                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 372                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 373                                         ));
 374
 375                 double bufrspdiff = rint(newbuflen - oldbuflen);
 376
 377                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 378                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 379                         ltc_tx_reset();
 380                         poff = 0;
 381                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 382                         int incnt = 0;
 383                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 384                         double avg_distance = newbuflen / samples_to_insert;
 385                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 386
 387                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 388                                 const int ro = rp - ltc_buf_off;
 389                                 if (ro < (incnt*avg_distance)) continue;
 390                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 391                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 392                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 393                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 394                                 incnt++;
 395                                 ltc_buf_len++;
 396                         }
 397                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 398                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 399                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 400                         if (oldbuflen <= samples_to_remove) {
 401                                 ltc_buf_off = ltc_buf_len= 0;
 402                         } else {
 403                                 double avg_distance = newbuflen / samples_to_remove;
 404                                 int rmcnt = 0;
 405                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 406                                         const int ro = rp - ltc_buf_off;
 407                                         if (ro < (rmcnt*avg_distance)) continue;
 408                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 409                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 410                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 411                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 412                                         ltc_buf_len--;
 413                                         rmcnt++;
 414                                 }
 415                         }
 416                 }
 417         }
 418
 419         ltc_prev_cycle = start_frame;
 420         ltc_speed = new_ltc_speed;
 421         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 422
 423         // (3) bit/sample alignment
 424         Timecode::Time tc_start;
 425         framepos_t tc_sample_start;
 426
 427         /* calc timecode frame from current position - round down to nearest timecode */
 428         Timecode::sample_to_timecode(cycle_start_frame, tc_start, true, false,
 429                         timecode_frames_per_second(),
 430                         timecode_drop_frames(),
 431                         (double)frame_rate(),
 432                         config.get_subframes_per_frame(),
 433                         ltc_timecode_negative_offset, ltc_timecode_offset
 434                         );
 435
 436         /* convert timecode back to sample-position */
 437         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 438                 (double)frame_rate(),
 439                 config.get_subframes_per_frame(),
 440                 ltc_timecode_negative_offset, ltc_timecode_offset
 441                 );
 442
 443         /* difference between current frame and TC frame in samples */
 444         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 445         if (current_speed == 0) {
 446                 soff = 0;
 447         }
 448         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 449                                 cycle_start_frame, tc_sample_start, soff));
 450
 451
 452         // (4) check if alignment matches
 453         const double fptcf = samples_per_timecode_frame();
 454
 455         /* maximum difference of bit alignment in audio-samples.
 456          *
 457          * if transport and LTC generator differs more than this, the LTC
 458          * generator will be re-initialized
 459          *
 460          * due to rounding error and variations in LTC-bit duration depending
 461          * on the speed, it can be off by +- ltc_speed audio-samples.
 462          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 463          * in the cycle _after_ the speed changed. The average delta however is 0.
 464          */
 465         double maxdiff;
 466
 467         if (config.get_external_sync() && slave()) {
 468                 maxdiff = slave()->resolution();
 469         } else {
 470                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 471                 if (nominal_frame_rate() != frame_rate()) {
 472                         maxdiff *= 3.0;
 473                 }
 474                 if (ltc_enc_tcformat == Timecode::timecode_23976 || ltc_enc_tcformat == Timecode::timecode_24976) {
 475                         maxdiff *= 15.0;
 476                 }
 477         }
 478
 479         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 480                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 481
 482         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 483                                 ltc_enc_pos + ltc_enc_cnt - poff,
 484                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 485                                 ));
 486
 487         const framecnt_t wrap24h = 86400. * frame_rate();
 488         if (ltc_enc_pos < 0
 489                         || (ltc_speed != 0 && fabs(fmod(ceil(ltc_enc_pos + ltc_enc_cnt - poff), wrap24h) - (cycle_start_frame % wrap24h)) > maxdiff)
 490                         ) {
 491
 492                 // (5) re-align
 493                 ltc_tx_reset();
 494
 495                 /* set frame to encode */
 496                 SMPTETimecode tc;
 497                 tc.hours = tc_start.hours % 24;
 498                 tc.mins = tc_start.minutes;
 499                 tc.secs = tc_start.seconds;
 500                 tc.frame = tc_start.frames;
 501                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 502
 503                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 504                  * In A3 30000/1001 or 30 fps can be drop-frame.
 505                  */
 506                 LTCFrame ltcframe;
 507                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 508                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 509                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 510
 511
 512                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 513
 514                 int32_t cyc_off;
 515                 if (soff < 0 || soff >= fptcf) {
 516                         /* session framerate change between (2) and now */
 517                         ltc_tx_reset();
 518                         return;
 519                 }
 520
 521                 if (ltc_speed < 0 ) {
 522                         /* calculate the byte that starts at or after the current position */
 523                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 524                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 525
 526                         /* calculate difference between the current position and the byte to send */
 527                         cyc_off = soff- ceil(ltc_enc_cnt);
 528
 529                 } else {
 530                         /* calculate the byte that starts at or after the current position */
 531                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 532                         ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
 533
 534                         /* calculate difference between the current position and the byte to send */
 535                         cyc_off = ceil(ltc_enc_cnt) - soff;
 536
 537                         if (ltc_enc_byte == 10) {
 538                                 ltc_enc_byte = 0;
 539                                 ltc_encoder_inc_timecode(ltc_encoder);
 540                         }
 541                 }
 542
 543                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 544                                         soff, ltc_enc_byte, cyc_off));
 545
 546                 if ( (ltc_speed < 0 && ltc_enc_byte !=9 ) || (ltc_speed >= 0 && ltc_enc_byte !=0 ) ) {
 547                         restarting = true;
 548                 }
 549
 550                 if (cyc_off >= 0 && cyc_off <= (int32_t) nframes) {
 551                         /* offset in this cycle */
 552                         txf= rint(cyc_off / fabs(ltc_speed));
 553                         memset(out, 0, cyc_off * sizeof(Sample));
 554                 } else {
 555                         /* resync next cycle */
 556                         memset(out, 0, nframes * sizeof(Sample));
 557                         return;
 558                 }
 559
 560                 ltc_enc_pos = tc_sample_start % wrap24h;
 561
 562                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 563                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 564         }
 565         else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
 566                 /* reduce (low freq) jitter.
 567                  * The granularity of the LTC encoder speed is 1 byte =
 568                  * (frames-per-timecode-frame / 10) audio-samples.
 569                  * Thus, tiny speed changes [as produced by some slaves]
 570                  * may not have any effect in the cycle when they occur,
 571                  * but they will add up over time.
 572                  *
 573                  * This is a linear approx to compensate for this jitter
 574                  * and prempt re-sync when the drift builds up.
 575                  *
 576                  * However, for very fast speeds - when 1 LTC bit is
 577                  * <= 3 audio-sample - adjusting speed may lead to
 578                  * invalid frames.
 579                  *
 580                  * To do better than this, resampling (or a rewrite of the
 581                  * encoder) is required.
 582                  */
 583                 ltc_speed -= fmod(((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame), wrap24h) / engine().sample_rate();
 584         }
 585
 586
 587         // (6) encode and output
 588         while (1) {
 589 #ifdef LTC_GEN_TXDBUG
 590                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 591 #endif
 592                 // (6a) send remaining buffer
 593                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 594                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 595                         const Sample val = (Sample) (v1*ltcvol);
 596                         out[txf++] = val;
 597                 }
 598 #ifdef LTC_GEN_TXDBUG
 599                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 600 #endif
 601
 602                 if (txf >= nframes) {
 603                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 604                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 605                         break;
 606                 }
 607
 608                 ltc_buf_len = 0;
 609                 ltc_buf_off = 0;
 610
 611                 // (6b) encode LTC, bump timecode
 612
 613                 if (ltc_speed < 0) {
 614                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 615                         if (ltc_enc_byte == 9) {
 616                                 ltc_encoder_dec_timecode(ltc_encoder);
 617                                 ltc_tx_recalculate_position();
 618                                 ltc_enc_cnt = fptcf;
 619                         }
 620                 }
 621
 622                 int enc_frames;
 623
 624                 if (restarting) {
 625                         /* write zero bytes -- don't touch encoder until we're at a frame-boundary
 626                          * otherwise the biphase polarity may be inverted.
 627                          */
 628                         enc_frames = fptcf / 10.0;
 629                         memset(&ltc_enc_buf[ltc_buf_len], 127, enc_frames * sizeof(ltcsnd_sample_t));
 630                 } else {
 631                         if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 632                                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 633                                 ltc_encoder_buffer_flush(ltc_encoder);
 634                                 ltc_tx_reset();
 635                                 return;
 636                         }
 637                         enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 638                 }
 639
 640 #ifdef LTC_GEN_FRAMEDBUG
 641                 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));
 642 #endif
 643                 if (enc_frames <=0) {
 644                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 645                         ltc_encoder_buffer_flush(ltc_encoder);
 646                         ltc_tx_reset();
 647                         return;
 648                 }
 649
 650                 ltc_buf_len += enc_frames;
 651                 if (ltc_speed < 0)
 652                         ltc_enc_cnt -= fptcf/10.0;
 653                 else
 654                         ltc_enc_cnt += fptcf/10.0;
 655
 656                 if (ltc_speed >= 0) {
 657                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 658                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 659                                 ltc_encoder_inc_timecode(ltc_encoder);
 660 #if 0 /* force fixed parity -- scope debug */
 661                                 LTCFrame f;
 662                                 ltc_encoder_get_frame(ltc_encoder, &f);
 663                                 f.biphase_mark_phase_correction=0;
 664                                 ltc_encoder_set_frame(ltc_encoder, &f);
 665 #endif
 666                                 ltc_tx_recalculate_position();
 667                                 ltc_enc_cnt = 0;
 668                         } else if (ltc_enc_byte == 0) {
 669                                 ltc_enc_cnt = 0;
 670                                 restarting=false;
 671                         }
 672                 }
 673 #ifdef LTC_GEN_FRAMEDBUG
 674                 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));
 675 #endif
 676         }
 677
 678         dynamic_cast<AudioBuffer*>(&buf)->set_written (true);
 679         return;
 680 }