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 #include "ardour/debug.h"
  21 #include "timecode/time.h"
  22 #include "ardour/session.h"
  23 #include "ardour/audioengine.h"
  24 #include "ardour/audio_port.h"
  25
  26 #include "i18n.h"
  27
  28 using namespace std;
  29 using namespace ARDOUR;
  30 using namespace MIDI;
  31 using namespace PBD;
  32 using namespace Timecode;
  33
  34 /* really verbose timing debug */
  35 //#define LTC_GEN_FRAMEDBUG
  36 //#define LTC_GEN_TXDBUG
  37
  38 void
  39 Session::ltc_tx_initialize()
  40 {
  41         ltc_enc_tcformat = config.get_timecode_format();
  42
  43         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)));
  44         ltc_encoder = ltc_encoder_create(nominal_frame_rate(),
  45                         timecode_to_frames_per_second(ltc_enc_tcformat),
  46                         0);
  47
  48         ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
  49
  50         /* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
  51          * usually returned by ltc_encoder_get_buffersize(encoder)
  52          *
  53          * since the fps can change and A3's  min fps: 24000/1001 */
  54         ltc_enc_buf = (ltcsnd_sample_t*) calloc((nominal_frame_rate() / 23), sizeof(ltcsnd_sample_t));
  55         ltc_speed = 0;
  56         ltc_tx_reset();
  57 }
  58
  59 void
  60 Session::ltc_tx_cleanup()
  61 {
  62         DEBUG_TRACE (DEBUG::LTC, "LTC TX cleanup\n");
  63         if (ltc_enc_buf) free(ltc_enc_buf);
  64         ltc_encoder_free(ltc_encoder);
  65         ltc_encoder = NULL;
  66 }
  67
  68 void
  69 Session::ltc_tx_reset()
  70 {
  71         DEBUG_TRACE (DEBUG::LTC, "LTC TX reset\n");
  72         ltc_enc_pos = -9999; // force re-start
  73         ltc_buf_len = 0;
  74         ltc_buf_off = 0;
  75         ltc_enc_byte = 0;
  76         ltc_enc_cnt = 0;
  77 }
  78
  79 void
  80 Session::ltc_tx_recalculate_position()
  81 {
  82         SMPTETimecode enctc;
  83         Timecode::Time a3tc;
  84         ltc_encoder_get_timecode(ltc_encoder, &enctc);
  85
  86         a3tc.hours   = enctc.hours;
  87         a3tc.minutes = enctc.mins;
  88         a3tc.seconds = enctc.secs;
  89         a3tc.frames  = enctc.frame;
  90         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
  91         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
  92
  93         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
  94                 double(frame_rate()),
  95                 config.get_subframes_per_frame(),
  96                 config.get_timecode_offset_negative(), config.get_timecode_offset()
  97                 );
  98 }
  99
 100 int
 101 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 102                 double target_speed, double current_speed,
 103                 pframes_t nframes)
 104 {
 105         assert(nframes > 0);
 106
 107         jack_default_audio_sample_t *out;
 108         pframes_t txf = 0;
 109         boost::shared_ptr<Port> ltcport = engine().ltc_output_port();
 110
 111         if (!ltc_encoder || !ltc_enc_buf || !ltcport || ! ltcport->jack_port()) return 0;
 112
 113         out = (jack_default_audio_sample_t*) jack_port_get_buffer (ltcport->jack_port(), nframes);
 114         if (!out) return 0;
 115
 116         if (engine().freewheeling()|| !Config->get_send_ltc()
 117                         /* TODO
 118                          * we can relax this a bit, JACK or sample-synced slaves should be fine.
 119                          * test before allowing it, do the same for MTC generator in
 120                          * libs/ardour/session_midi.cc
 121                          * */
 122                 //      || config.get_external_sync()  // XXX XXX
 123                         ) {
 124                 memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 125                 return nframes;
 126         }
 127
 128         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 129         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 130
 131         jack_latency_range_t ltc_latency;
 132         ltcport->get_connected_latency_range(ltc_latency, true);
 133         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_latency.max));
 134
 135         /* all systems go. Now here's the plan:
 136          *
 137          *  1) check if fps has changed
 138          *  2) check direction of encoding, calc speed, resample existing buffer
 139          *  3) calculate frame and byte to send aligned to jack-period size
 140          *  4) check if it's the frame/byte that is already in the queue
 141          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 142          *  6) actual LTC audio output
 143          *  6a) send remaining part of already queued frame; break on nframes
 144          *  6b) encode new LTC-frame byte
 145          *  6c) goto 6a
 146          *  7) done
 147          */
 148
 149         // (1) check fps
 150         TimecodeFormat cur_timecode = config.get_timecode_format();
 151         if (cur_timecode != ltc_enc_tcformat) {
 152                 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)));
 153                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode), 0)) {
 154                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 155                         ltc_tx_cleanup();
 156                         return 0;
 157                 }
 158                 ltc_enc_tcformat = cur_timecode;
 159                 ltc_tx_reset();
 160         }
 161
 162         /* LTC is max. 30 fps */
 163         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 164                 memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 165                 return nframes;
 166         }
 167
 168         // (2) speed & direction
 169 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 170         bool speed_changed = false;
 171
 172         // XXX
 173         //framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame - ltc_latency.max) : (start_frame + ltc_latency.max);
 174         framepos_t cycle_start_frame = start_frame;
 175
 176         /* cycle-start may become negative due to latency comensation */
 177         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 178
 179         double new_ltc_speed = double(labs(end_frame - start_frame) * SIGNUM(current_speed)) / double(nframes);
 180
 181         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 182                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 183                 ltc_tx_reset();
 184         }
 185
 186         if (ltc_speed != new_ltc_speed) {
 187                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 188                  * if target_speed != current_speed we should interpolate, too.
 189                  *
 190                  * However, currenly in A3 target_speed == current_speed for each process cycle
 191                  * (except for the sign and if target_speed > 8.0).
 192                  * Besides, above speed calulation uses the difference (end_frame - start_frame).
 193                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 194                  * so we're good.
 195                  */
 196                 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));
 197                 speed_changed = true;
 198         }
 199
 200         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 201                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 202                 /* keep repeating current frame
 203                  *
 204                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 205                  * some machines do odd things if LTC goes away:
 206                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 207                  * so unspool the tape from the playhead. That might be inconvenient.
 208                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 209                  */
 210                 new_ltc_speed = 0;
 211                 if (!Config->get_ltc_send_continuously()) {
 212                         ltc_speed = new_ltc_speed;
 213                         memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 214                         return nframes;
 215                 }
 216         }
 217
 218         if (fabs(new_ltc_speed) > 10.0) {
 219                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 220                 ltc_tx_reset();
 221                 memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 222                 return nframes;
 223         }
 224
 225         if (ltc_speed == 0 && new_ltc_speed != 0) {
 226                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 227                 ltc_tx_reset();
 228         }
 229
 230         /* the timecode duration corresponding to the samples still in the buffer
 231          * here we use prev. speed to match the begining of this cycle for aligment.
 232          */
 233         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 234
 235         if (speed_changed && new_ltc_speed != 0) {
 236                 /* we need to re-sample the existing buffer.
 237                  * "make space for the en-coder to catch up to the new speed"
 238                  *
 239                  * since the LTC signal is a rect waveform we can simply squeeze it
 240                  * by removing samples or duplicating /here and there/.
 241                  *
 242                  * There may be a more elegant way to do this, in fact one could
 243                  * simply re-render the buffer using ltc_encoder_encode_byte()
 244                  * but that'd require some timecode offset buffer magic,
 245                  * which is left for later..
 246                  */
 247
 248                 double oldbuflen = double(ltc_buf_len - ltc_buf_off);
 249                 double newbuflen = double(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 250
 251                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 252                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 253                                         ));
 254
 255                 double bufrspdiff = rint(newbuflen - oldbuflen);
 256
 257                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 258                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 259                         ltc_tx_reset();
 260                         poff = 0;
 261                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 262                         int incnt = 0;
 263                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 264                         double avg_distance = newbuflen / samples_to_insert;
 265                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 266
 267                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 268                                 const int ro = rp - ltc_buf_off;
 269                                 if (ro < (incnt*avg_distance)) continue;
 270                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 271                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 272                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 273                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 274                                 incnt++;
 275                                 ltc_buf_len++;
 276                         }
 277                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 278                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 279                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 280                         if (oldbuflen <= samples_to_remove) {
 281                                 ltc_buf_off = ltc_buf_len= 0;
 282                         } else {
 283                                 double avg_distance = newbuflen / samples_to_remove;
 284                                 int rmcnt = 0;
 285                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 286                                         const int ro = rp - ltc_buf_off;
 287                                         if (ro < (rmcnt*avg_distance)) continue;
 288                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 289                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 290                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 291                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 292                                         ltc_buf_len--;
 293                                         rmcnt++;
 294                                 }
 295                         }
 296                 }
 297         }
 298
 299         ltc_speed = new_ltc_speed;
 300         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 301
 302
 303         // (3) bit/sample aligment
 304         Timecode::Time tc_start;
 305         framepos_t tc_sample_start;
 306
 307         /* calc timecode frame from current position - round down to nearest timecode */
 308         sample_to_timecode(cycle_start_frame, tc_start, true, false);
 309
 310         /* convert timecode back to sample-position */
 311         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 312                 double(frame_rate()),
 313                 config.get_subframes_per_frame(),
 314                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 315                 );
 316
 317         /* difference between current frame and TC frame in samples */
 318         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 319         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 320                                 cycle_start_frame, tc_sample_start, soff));
 321
 322
 323         // (4) check if aligment matches
 324         const double fptcf = frames_per_timecode_frame(); // convenient, used a lot below.
 325         double maxdiff;
 326
 327         /* due to rounding error and variations in LTC-bit duration depending
 328          * on the speed, we can be off by +- speed samples.
 329          * during speed-changes we can acually ready += 2*speed audio-samples
 330          * in the cycle after the speed change.  The average delta however is 0.
 331          */
 332         if (config.get_external_sync()) {
 333                 maxdiff = fptcf; // TODO get slave max delta
 334         } else {
 335                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 336         }
 337
 338         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 339                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 340
 341         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 342                                 ltc_enc_pos + ltc_enc_cnt - poff,
 343                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 344                                 ));
 345
 346         if (fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff)
 347         {
 348                 // (5) re-align
 349                 ltc_tx_reset();
 350
 351                 /* set frame to encode */
 352                 SMPTETimecode tc;
 353                 tc.hours = tc_start.hours;
 354                 tc.mins = tc_start.minutes;
 355                 tc.secs = tc_start.seconds;
 356                 tc.frame = tc_start.frames;
 357                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 358
 359                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 360                  * in A3 only 30000/1001 is drop-frame and there are also other questionable
 361                  * DF timecodes  such as 24k/1001 and 25k/1001.
 362                  */
 363                 LTCFrame ltcframe;
 364                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 365                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 366                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 367
 368
 369                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 370
 371                 uint32_t cyc_off;
 372                 assert(soff >= 0 && soff < fptcf);
 373
 374                 if (ltc_speed < 0 ) {
 375                         /* calculate the byte that starts at or after the current position */
 376                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 377                         ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
 378
 379                         /* calculate difference between the current position and the byte to send */
 380                         cyc_off = soff- ceil(ltc_enc_cnt);
 381
 382                 } else {
 383                         /* calculate the byte that starts at or after the current position */
 384                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 385                         ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
 386
 387                         /* calculate difference between the current position and the byte to send */
 388                         cyc_off = ceil(ltc_enc_cnt) - soff;
 389
 390                         if (ltc_enc_byte == 10) {
 391                                 ltc_enc_byte = 0;
 392                                 ltc_encoder_inc_timecode(ltc_encoder);
 393                         }
 394                 }
 395
 396                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 397                                         soff, ltc_enc_byte, cyc_off));
 398
 399                 if (ltc_speed == 0) {
 400                         /* don't bother to align non-moving loops */
 401                 } else if (cyc_off > 0 && cyc_off <= nframes) {
 402                         /* offset in this cycle */
 403                         txf= rint(cyc_off / fabs(ltc_speed));
 404                         memset(out, 0, cyc_off * sizeof(jack_default_audio_sample_t));
 405                 } else if (cyc_off > 0) {
 406                         /* resync next cycle */
 407                         memset(out, 0, cyc_off * sizeof(jack_default_audio_sample_t));
 408                         return nframes;
 409                 }
 410
 411                 ltc_enc_pos = tc_sample_start;
 412
 413                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 414                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 415         }
 416
 417
 418         // (6) encode and output
 419         while (1) {
 420 #ifdef LTC_GEN_TXDBUG
 421                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 422 #endif
 423                 // (6a) send remaining buffer
 424                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 425                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 426                         const jack_default_audio_sample_t val = (jack_default_audio_sample_t) (v1*ltcvol);
 427                         out[txf++] = val;
 428                 }
 429 #ifdef LTC_GEN_TXDBUG
 430                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 431 #endif
 432
 433                 if (txf >= nframes) {
 434                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 435                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 436                         return nframes;
 437                 }
 438
 439                 ltc_buf_len = 0;
 440                 ltc_buf_off = 0;
 441
 442                 // (6b) encode LTC, bump timecode
 443
 444                 if (ltc_speed < 0) {
 445                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 446                         if (ltc_enc_byte == 9) {
 447                                 ltc_encoder_dec_timecode(ltc_encoder);
 448                                 ltc_tx_recalculate_position();
 449                                 ltc_enc_cnt = fptcf;
 450                         }
 451                 }
 452
 453                 if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 454                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 455                         ltc_encoder_buffer_flush(ltc_encoder);
 456                         ltc_tx_reset();
 457                         memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 458                         return -1;
 459                 }
 460                 int enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 461 #ifdef LTC_GEN_FRAMEDBUG
 462                 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));
 463 #endif
 464                 if (enc_frames <=0) {
 465                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 466                         ltc_encoder_buffer_flush(ltc_encoder);
 467                         ltc_tx_reset();
 468                         memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 469                         return -1;
 470                 }
 471
 472                 ltc_buf_len += enc_frames;
 473                 if (ltc_speed < 0)
 474                         ltc_enc_cnt -= fptcf/10.0; //enc_frames * ltc_speed;
 475                 else
 476                         ltc_enc_cnt += fptcf/10.0; //enc_frames * ltc_speed;
 477
 478                 if (ltc_speed >= 0) {
 479                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 480                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 481                                 ltc_encoder_inc_timecode(ltc_encoder);
 482                                 ltc_tx_recalculate_position();
 483                                 ltc_enc_cnt = 0;
 484                         } else if (ltc_enc_byte == 0) {
 485                                 ltc_enc_cnt = 0;
 486                         }
 487                 }
 488 #ifdef LTC_GEN_FRAMEDBUG
 489                 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));
 490 #endif
 491         }
 492
 493         return nframes;
 494 }