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 void
  43 Session::ltc_tx_initialize()
  44 {
  45         ltc_enc_tcformat = config.get_timecode_format();
  46
  47         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)));
  48         ltc_encoder = ltc_encoder_create(nominal_frame_rate(),
  49                         timecode_to_frames_per_second(ltc_enc_tcformat),
  50                         0);
  51
  52         ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
  53
  54         /* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
  55          * usually returned by ltc_encoder_get_buffersize(encoder)
  56          *
  57          * since the fps can change and A3's  min fps: 24000/1001 */
  58         ltc_enc_buf = (ltcsnd_sample_t*) calloc((nominal_frame_rate() / 23), sizeof(ltcsnd_sample_t));
  59         ltc_speed = 0;
  60         ltc_tx_reset();
  61 }
  62
  63 void
  64 Session::ltc_tx_cleanup()
  65 {
  66         DEBUG_TRACE (DEBUG::LTC, "LTC TX cleanup\n");
  67         if (ltc_enc_buf) free(ltc_enc_buf);
  68         ltc_encoder_free(ltc_encoder);
  69         ltc_encoder = NULL;
  70 }
  71
  72 void
  73 Session::ltc_tx_reset()
  74 {
  75         DEBUG_TRACE (DEBUG::LTC, "LTC TX reset\n");
  76         ltc_enc_pos = -9999; // force re-start
  77         ltc_buf_len = 0;
  78         ltc_buf_off = 0;
  79         ltc_enc_byte = 0;
  80         ltc_enc_cnt = 0;
  81 }
  82
  83 void
  84 Session::ltc_tx_recalculate_position()
  85 {
  86         SMPTETimecode enctc;
  87         Timecode::Time a3tc;
  88         ltc_encoder_get_timecode(ltc_encoder, &enctc);
  89
  90         a3tc.hours   = enctc.hours;
  91         a3tc.minutes = enctc.mins;
  92         a3tc.seconds = enctc.secs;
  93         a3tc.frames  = enctc.frame;
  94         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
  95         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
  96
  97         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
  98                 double(frame_rate()),
  99                 config.get_subframes_per_frame(),
 100                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 101                 );
 102 }
 103
 104 int
 105 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 106                                           double target_speed, double current_speed,
 107                                           pframes_t nframes)
 108 {
 109         assert (nframes > 0);
 110
 111         Sample *out;
 112         pframes_t txf = 0;
 113         boost::shared_ptr<Port> ltcport = ltc_output_port();
 114         int ret = -1;
 115
 116         Buffer& buf (ltcport->get_buffer (nframes));
 117
 118         if (!ltc_encoder || !ltc_enc_buf) {
 119                 ret = nframes;
 120                 goto out;
 121         }
 122
 123         SyncSource sync_src = Config->get_sync_source();
 124         if (engine().freewheeling() || !Config->get_send_ltc() ||
 125             /* TODO
 126              * decide which time-sources we can generated LTC from.
 127              * Internal, JACK or sample-synced slaves should be fine.
 128              *
 129              *
 130              || (config.get_external_sync() && sync_src == LTC)
 131              || (config.get_external_sync() && sync_src == MTC)
 132             */
 133             (config.get_external_sync() && sync_src == MIDIClock)
 134                 ) {
 135                 ret = nframes;
 136                 goto out;
 137         }
 138
 139         out = dynamic_cast<AudioBuffer*>(&buf)->data ();
 140
 141         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 142         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 143
 144         jack_latency_range_t ltc_latency;
 145         ltcport->get_connected_latency_range(ltc_latency, true);
 146         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_latency.max));
 147
 148         /* all systems go. Now here's the plan:
 149          *
 150          *  1) check if fps has changed
 151          *  2) check direction of encoding, calc speed, re-sample existing buffer
 152          *  3) calculate frame and byte to send aligned to jack-period size
 153          *  4) check if it's the frame/byte that is already in the queue
 154          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 155          *  6) actual LTC audio output
 156          *  6a) send remaining part of already queued frame; break on nframes
 157          *  6b) encode new LTC-frame byte
 158          *  6c) goto 6a
 159          *  7) done
 160          */
 161
 162         // (1) check fps
 163         TimecodeFormat cur_timecode = config.get_timecode_format();
 164         if (cur_timecode != ltc_enc_tcformat) {
 165                 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)));
 166                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode), 0)) {
 167                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 168                         ltc_tx_cleanup();
 169                         ret = 0;
 170                         goto out;
 171                 }
 172                 ltc_enc_tcformat = cur_timecode;
 173                 ltc_tx_reset();
 174         }
 175
 176         /* LTC is max. 30 fps */
 177         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 178                 ret = nframes;
 179                 goto out;
 180         }
 181
 182         // (2) speed & direction
 183 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 184         bool speed_changed = false;
 185
 186         /* use port latency compensation */
 187 #if 1
 188         /* The generated timecode is offset by the port-latency,
 189          * therefore the offset depends on the direction of transport.
 190          */
 191         framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame + ltc_latency.max) : (start_frame - ltc_latency.max);
 192 #else
 193         /* This comes in handy when testing sync - record output on an A3 track
 194          * see also http://tracker.ardour.org/view.php?id=5073
 195          */
 196         framepos_t cycle_start_frame = start_frame;
 197 #endif
 198
 199         /* cycle-start may become negative due to latency compensation */
 200         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 201
 202         double new_ltc_speed = double(labs(end_frame - start_frame) * SIGNUM(current_speed)) / double(nframes);
 203
 204         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 205                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 206                 ltc_tx_reset();
 207         }
 208
 209         if (ltc_speed != new_ltc_speed) {
 210                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 211                  * if target_speed != current_speed we should interpolate, too.
 212                  *
 213                  * However, currency in A3 target_speed == current_speed for each process cycle
 214                  * (except for the sign and if target_speed > 8.0).
 215                  * Besides, above speed calculation uses the difference (end_frame - start_frame).
 216                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 217                  * so we're good.
 218                  */
 219                 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));
 220                 speed_changed = true;
 221         }
 222
 223         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 224                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 225                 /* keep repeating current frame
 226                  *
 227                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 228                  * some machines do odd things if LTC goes away:
 229                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 230                  * so unspool the tape from the playhead. That might be inconvenient.
 231                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 232                  */
 233                 new_ltc_speed = 0;
 234                 if (!Config->get_ltc_send_continuously()) {
 235                         ltc_speed = new_ltc_speed;
 236                         ret = nframes;
 237                         goto out;
 238                 }
 239         }
 240
 241         if (fabs(new_ltc_speed) > 10.0) {
 242                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 243                 ltc_tx_reset();
 244                 ret = nframes;
 245                 goto out;
 246         }
 247
 248         if (ltc_speed == 0 && new_ltc_speed != 0) {
 249                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 250                 ltc_tx_reset();
 251         }
 252
 253         /* the timecode duration corresponding to the samples that are still
 254          * in the buffer. Here, the speed of previous cycle is used to calculate
 255          * the alignment at the beginning of this cycle later.
 256          */
 257         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 258
 259         if (speed_changed && new_ltc_speed != 0) {
 260                 /* we need to re-sample the existing buffer.
 261                  * "make space for the en-coder to catch up to the new speed"
 262                  *
 263                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 264                  * by removing samples or duplicating samples /here and there/.
 265                  *
 266                  * There may be a more elegant way to do this, in fact one could
 267                  * simply re-render the buffer using ltc_encoder_encode_byte()
 268                  * but that'd require some timecode offset buffer magic,
 269                  * which is left for later..
 270                  */
 271
 272                 double oldbuflen = double(ltc_buf_len - ltc_buf_off);
 273                 double newbuflen = double(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 274
 275                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 276                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 277                                         ));
 278
 279                 double bufrspdiff = rint(newbuflen - oldbuflen);
 280
 281                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 282                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 283                         ltc_tx_reset();
 284                         poff = 0;
 285                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 286                         int incnt = 0;
 287                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 288                         double avg_distance = newbuflen / samples_to_insert;
 289                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 290
 291                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 292                                 const int ro = rp - ltc_buf_off;
 293                                 if (ro < (incnt*avg_distance)) continue;
 294                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 295                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 296                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 297                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 298                                 incnt++;
 299                                 ltc_buf_len++;
 300                         }
 301                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 302                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 303                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 304                         if (oldbuflen <= samples_to_remove) {
 305                                 ltc_buf_off = ltc_buf_len= 0;
 306                         } else {
 307                                 double avg_distance = newbuflen / samples_to_remove;
 308                                 int rmcnt = 0;
 309                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 310                                         const int ro = rp - ltc_buf_off;
 311                                         if (ro < (rmcnt*avg_distance)) continue;
 312                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 313                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 314                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 315                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 316                                         ltc_buf_len--;
 317                                         rmcnt++;
 318                                 }
 319                         }
 320                 }
 321         }
 322
 323         ltc_speed = new_ltc_speed;
 324         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 325
 326         // (3) bit/sample alignment
 327         Timecode::Time tc_start;
 328         framepos_t tc_sample_start;
 329
 330         /* calc timecode frame from current position - round down to nearest timecode */
 331         sample_to_timecode(cycle_start_frame, tc_start, true, false);
 332
 333         /* convert timecode back to sample-position */
 334         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 335                 double(frame_rate()),
 336                 config.get_subframes_per_frame(),
 337                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 338                 );
 339
 340         /* difference between current frame and TC frame in samples */
 341         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 342         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 343                                 cycle_start_frame, tc_sample_start, soff));
 344
 345
 346         // (4) check if alignment matches
 347         const double fptcf = frames_per_timecode_frame(); // convenient, used a lot below.
 348
 349         /* maximum difference of bit alignment in audio-samples.
 350          *
 351          * if transport and LTC generator differs more than this, the LTC
 352          * generator will be re-initialized
 353          *
 354          * due to rounding error and variations in LTC-bit duration depending
 355          * on the speed, it can be off by +- ltc_speed audio-samples.
 356          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 357          * in the cycle _after_ the speed changed. The average delta however is 0.
 358          */
 359         double maxdiff;
 360
 361         if (config.get_external_sync() && slave()) {
 362                 maxdiff = slave()->resolution();
 363         } else {
 364                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 365         }
 366
 367         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 368                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 369
 370         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 371                                 ltc_enc_pos + ltc_enc_cnt - poff,
 372                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 373                                 ));
 374
 375         if (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff) {
 376
 377                 // (5) re-align
 378                 ltc_tx_reset();
 379
 380                 /* set frame to encode */
 381                 SMPTETimecode tc;
 382                 tc.hours = tc_start.hours;
 383                 tc.mins = tc_start.minutes;
 384                 tc.secs = tc_start.seconds;
 385                 tc.frame = tc_start.frames;
 386                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 387
 388                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 389                  * In A3 30000/1001 or 30 fps can be drop-frame.
 390                  */
 391                 LTCFrame ltcframe;
 392                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 393                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 394                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 395
 396
 397                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 398
 399                 uint32_t cyc_off;
 400                 assert(soff >= 0 && soff < fptcf);
 401
 402                 if (ltc_speed < 0 ) {
 403                         /* calculate the byte that starts at or after the current position */
 404                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 405                         ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
 406
 407                         /* calculate difference between the current position and the byte to send */
 408                         cyc_off = soff- ceil(ltc_enc_cnt);
 409
 410                 } else {
 411                         /* calculate the byte that starts at or after the current position */
 412                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 413                         ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
 414
 415                         /* calculate difference between the current position and the byte to send */
 416                         cyc_off = ceil(ltc_enc_cnt) - soff;
 417
 418                         if (ltc_enc_byte == 10) {
 419                                 ltc_enc_byte = 0;
 420                                 ltc_encoder_inc_timecode(ltc_encoder);
 421                         }
 422                 }
 423
 424                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 425                                         soff, ltc_enc_byte, cyc_off));
 426
 427                 if (cyc_off > 0 && cyc_off <= nframes) {
 428                         /* offset in this cycle */
 429                         txf= rint(cyc_off / fabs(ltc_speed));
 430                         memset(out, 0, cyc_off * sizeof(Sample));
 431                 } else {
 432                         /* resync next cycle */
 433                         memset(out, 0, cyc_off * sizeof(Sample));
 434                         ret = frames;
 435                         goto done;
 436                 }
 437
 438                 ltc_enc_pos = tc_sample_start;
 439
 440                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 441                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 442         }
 443
 444
 445         // (6) encode and output
 446         while (1) {
 447 #ifdef LTC_GEN_TXDBUG
 448                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 449 #endif
 450                 // (6a) send remaining buffer
 451                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 452                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 453                         const Sample val = (Sample) (v1*ltcvol);
 454                         out[txf++] = val;
 455                 }
 456 #ifdef LTC_GEN_TXDBUG
 457                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 458 #endif
 459
 460                 if (txf >= nframes) {
 461                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 462                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 463                         ret = nframes;
 464                         goto done;
 465                 }
 466
 467                 ltc_buf_len = 0;
 468                 ltc_buf_off = 0;
 469
 470                 // (6b) encode LTC, bump timecode
 471
 472                 if (ltc_speed < 0) {
 473                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 474                         if (ltc_enc_byte == 9) {
 475                                 ltc_encoder_dec_timecode(ltc_encoder);
 476                                 ltc_tx_recalculate_position();
 477                                 ltc_enc_cnt = fptcf;
 478                         }
 479                 }
 480
 481                 if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 482                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 483                         ltc_encoder_buffer_flush(ltc_encoder);
 484                         ltc_tx_reset();
 485                         goto out;
 486                 }
 487                 int enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 488 #ifdef LTC_GEN_FRAMEDBUG
 489                 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));
 490 #endif
 491                 if (enc_frames <=0) {
 492                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 493                         ltc_encoder_buffer_flush(ltc_encoder);
 494                         ltc_tx_reset();
 495                         goto out;;
 496                 }
 497
 498                 ltc_buf_len += enc_frames;
 499                 if (ltc_speed < 0)
 500                         ltc_enc_cnt -= fptcf/10.0;
 501                 else
 502                         ltc_enc_cnt += fptcf/10.0;
 503
 504                 if (ltc_speed >= 0) {
 505                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 506                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 507                                 ltc_encoder_inc_timecode(ltc_encoder);
 508                                 ltc_tx_recalculate_position();
 509                                 ltc_enc_cnt = 0;
 510                         } else if (ltc_enc_byte == 0) {
 511                                 ltc_enc_cnt = 0;
 512                         }
 513                 }
 514 #ifdef LTC_GEN_FRAMEDBUG
 515                 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));
 516 #endif
 517         }
 518
 519   done:
 520         dynamic_cast<AudioBuffer*>(&buf)->set_written (true);
 521         ret = nframes;
 522
 523   out:
 524         return ret;
 525 }