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 #include "ardour/slave.h"
  26
  27 #include "i18n.h"
  28
  29 using namespace std;
  30 using namespace ARDOUR;
  31 using namespace MIDI;
  32 using namespace PBD;
  33 using namespace Timecode;
  34
  35 /* really verbose timing debug */
  36 //#define LTC_GEN_FRAMEDBUG
  37 //#define LTC_GEN_TXDBUG
  38
  39 void
  40 Session::ltc_tx_initialize()
  41 {
  42         ltc_enc_tcformat = config.get_timecode_format();
  43
  44         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)));
  45         ltc_encoder = ltc_encoder_create(nominal_frame_rate(),
  46                         timecode_to_frames_per_second(ltc_enc_tcformat),
  47                         0);
  48
  49         ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
  50
  51         /* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
  52          * usually returned by ltc_encoder_get_buffersize(encoder)
  53          *
  54          * since the fps can change and A3's  min fps: 24000/1001 */
  55         ltc_enc_buf = (ltcsnd_sample_t*) calloc((nominal_frame_rate() / 23), sizeof(ltcsnd_sample_t));
  56         ltc_speed = 0;
  57         ltc_tx_reset();
  58 }
  59
  60 void
  61 Session::ltc_tx_cleanup()
  62 {
  63         DEBUG_TRACE (DEBUG::LTC, "LTC TX cleanup\n");
  64         if (ltc_enc_buf) free(ltc_enc_buf);
  65         ltc_encoder_free(ltc_encoder);
  66         ltc_encoder = NULL;
  67 }
  68
  69 void
  70 Session::ltc_tx_reset()
  71 {
  72         DEBUG_TRACE (DEBUG::LTC, "LTC TX reset\n");
  73         ltc_enc_pos = -9999; // force re-start
  74         ltc_buf_len = 0;
  75         ltc_buf_off = 0;
  76         ltc_enc_byte = 0;
  77         ltc_enc_cnt = 0;
  78 }
  79
  80 void
  81 Session::ltc_tx_recalculate_position()
  82 {
  83         SMPTETimecode enctc;
  84         Timecode::Time a3tc;
  85         ltc_encoder_get_timecode(ltc_encoder, &enctc);
  86
  87         a3tc.hours   = enctc.hours;
  88         a3tc.minutes = enctc.mins;
  89         a3tc.seconds = enctc.secs;
  90         a3tc.frames  = enctc.frame;
  91         a3tc.rate = timecode_to_frames_per_second(ltc_enc_tcformat);
  92         a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
  93
  94         Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
  95                 double(frame_rate()),
  96                 config.get_subframes_per_frame(),
  97                 config.get_timecode_offset_negative(), config.get_timecode_offset()
  98                 );
  99 }
 100
 101 int
 102 Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end_frame,
 103                 double target_speed, double current_speed,
 104                 pframes_t nframes)
 105 {
 106         assert(nframes > 0);
 107
 108         jack_default_audio_sample_t *out;
 109         pframes_t txf = 0;
 110         boost::shared_ptr<Port> ltcport = engine().ltc_output_port();
 111
 112         if (!ltc_encoder || !ltc_enc_buf || !ltcport || ! ltcport->jack_port()) return 0;
 113
 114         out = (jack_default_audio_sample_t*) jack_port_get_buffer (ltcport->jack_port(), nframes);
 115         if (!out) return 0;
 116
 117         SyncSource sync_src = Config->get_sync_source();
 118         if (engine().freewheeling()
 119                         || !Config->get_send_ltc()
 120                         /* TODO
 121                          * decide which time-sources we can generated LTC from.
 122                          * Internal, JACK or sample-synced slaves should be fine.
 123                          *
 124                          *
 125                          || (config.get_external_sync() && sync_src == LTC)
 126                          || (config.get_external_sync() && sync_src == MTC)
 127                          */
 128                          || (config.get_external_sync() && sync_src == MIDIClock)
 129                         ) {
 130                 memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 131                 return nframes;
 132         }
 133
 134         /* range from libltc (38..218) || - 128.0  -> (-90..90) */
 135         const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 136
 137         jack_latency_range_t ltc_latency;
 138         ltcport->get_connected_latency_range(ltc_latency, true);
 139         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_latency.max));
 140
 141         /* all systems go. Now here's the plan:
 142          *
 143          *  1) check if fps has changed
 144          *  2) check direction of encoding, calc speed, re-sample existing buffer
 145          *  3) calculate frame and byte to send aligned to jack-period size
 146          *  4) check if it's the frame/byte that is already in the queue
 147          *  5) if (4) mismatch, re-calculate offset of LTC frame relative to period size
 148          *  6) actual LTC audio output
 149          *  6a) send remaining part of already queued frame; break on nframes
 150          *  6b) encode new LTC-frame byte
 151          *  6c) goto 6a
 152          *  7) done
 153          */
 154
 155         // (1) check fps
 156         TimecodeFormat cur_timecode = config.get_timecode_format();
 157         if (cur_timecode != ltc_enc_tcformat) {
 158                 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)));
 159                 if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode), 0)) {
 160                         PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
 161                         ltc_tx_cleanup();
 162                         return 0;
 163                 }
 164                 ltc_enc_tcformat = cur_timecode;
 165                 ltc_tx_reset();
 166         }
 167
 168         /* LTC is max. 30 fps */
 169         if (timecode_to_frames_per_second(cur_timecode) > 30) {
 170                 memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 171                 return nframes;
 172         }
 173
 174         // (2) speed & direction
 175 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 176         bool speed_changed = false;
 177
 178         /* use port latency compensation */
 179 #if 1
 180         /* The generated timecode is offset by the port-latency,
 181          * therefore the offset depends on the direction of transport.
 182          */
 183         framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame + ltc_latency.max) : (start_frame - ltc_latency.max);
 184 #else
 185         /* This comes in handy when testing sync - record output on an A3 track
 186          * see also http://tracker.ardour.org/view.php?id=5073
 187          */
 188         framepos_t cycle_start_frame = start_frame;
 189 #endif
 190
 191         /* cycle-start may become negative due to latency compensation */
 192         if (cycle_start_frame < 0) { cycle_start_frame = 0; }
 193
 194         double new_ltc_speed = double(labs(end_frame - start_frame) * SIGNUM(current_speed)) / double(nframes);
 195
 196         if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
 197                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
 198                 ltc_tx_reset();
 199         }
 200
 201         if (ltc_speed != new_ltc_speed) {
 202                 /* check ./libs/ardour/interpolation.cc  CubicInterpolation::interpolate
 203                  * if target_speed != current_speed we should interpolate, too.
 204                  *
 205                  * However, currency in A3 target_speed == current_speed for each process cycle
 206                  * (except for the sign and if target_speed > 8.0).
 207                  * Besides, above speed calculation uses the difference (end_frame - start_frame).
 208                  * end_frame is calculated from 'frames_moved' which includes the interpolation.
 209                  * so we're good.
 210                  */
 211                 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));
 212                 speed_changed = true;
 213         }
 214
 215         if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
 216                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport is not rolling or absolute-speed < 0.1\n");
 217                 /* keep repeating current frame
 218                  *
 219                  * an LTC generator must be able to continue generating LTC when Ardours transport is in stop
 220                  * some machines do odd things if LTC goes away:
 221                  * e.g. a tape based machine (video or audio), some think they have gone into park if LTC goes away,
 222                  * so unspool the tape from the playhead. That might be inconvenient.
 223                  * If LTC keeps arriving they remain in a stop position with the tape on the playhead.
 224                  */
 225                 new_ltc_speed = 0;
 226                 if (!Config->get_ltc_send_continuously()) {
 227                         ltc_speed = new_ltc_speed;
 228                         memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 229                         return nframes;
 230                 }
 231         }
 232
 233         if (fabs(new_ltc_speed) > 10.0) {
 234                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: speed is out of bounds.\n");
 235                 ltc_tx_reset();
 236                 memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 237                 return nframes;
 238         }
 239
 240         if (ltc_speed == 0 && new_ltc_speed != 0) {
 241                 DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport started rolling - reset\n");
 242                 ltc_tx_reset();
 243         }
 244
 245         /* the timecode duration corresponding to the samples that are still
 246          * in the buffer. Here, the speed of previous cycle is used to calculate
 247          * the alignment at the beginning of this cycle later.
 248          */
 249         double poff = (ltc_buf_len - ltc_buf_off) * ltc_speed;
 250
 251         if (speed_changed && new_ltc_speed != 0) {
 252                 /* we need to re-sample the existing buffer.
 253                  * "make space for the en-coder to catch up to the new speed"
 254                  *
 255                  * since the LTC signal is a rectangular waveform we can simply squeeze it
 256                  * by removing samples or duplicating samples /here and there/.
 257                  *
 258                  * There may be a more elegant way to do this, in fact one could
 259                  * simply re-render the buffer using ltc_encoder_encode_byte()
 260                  * but that'd require some timecode offset buffer magic,
 261                  * which is left for later..
 262                  */
 263
 264                 double oldbuflen = double(ltc_buf_len - ltc_buf_off);
 265                 double newbuflen = double(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
 266
 267                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
 268                                         (ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
 269                                         ));
 270
 271                 double bufrspdiff = rint(newbuflen - oldbuflen);
 272
 273                 if (abs(bufrspdiff) > newbuflen || abs(bufrspdiff) > oldbuflen) {
 274                         DEBUG_TRACE (DEBUG::LTC, "LTC TX2: resampling buffer would destroy information.\n");
 275                         ltc_tx_reset();
 276                         poff = 0;
 277                 } else if (bufrspdiff != 0 && newbuflen > oldbuflen) {
 278                         int incnt = 0;
 279                         double samples_to_insert = ceil(newbuflen - oldbuflen);
 280                         double avg_distance = newbuflen / samples_to_insert;
 281                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer insert: %1\n", samples_to_insert));
 282
 283                         for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 284                                 const int ro = rp - ltc_buf_off;
 285                                 if (ro < (incnt*avg_distance)) continue;
 286                                 const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 287                                 const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 288                                 if (v1 != v2 && ro < ((incnt+1)*avg_distance)) continue;
 289                                 memmove(&ltc_enc_buf[rp+1], &ltc_enc_buf[rp], ltc_buf_len-rp);
 290                                 incnt++;
 291                                 ltc_buf_len++;
 292                         }
 293                 } else if (bufrspdiff != 0 && newbuflen < oldbuflen) {
 294                         double samples_to_remove = ceil(oldbuflen - newbuflen);
 295                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: resample buffer - remove: %1\n", samples_to_remove));
 296                         if (oldbuflen <= samples_to_remove) {
 297                                 ltc_buf_off = ltc_buf_len= 0;
 298                         } else {
 299                                 double avg_distance = newbuflen / samples_to_remove;
 300                                 int rmcnt = 0;
 301                                 for (int rp = ltc_buf_off; rp < ltc_buf_len - 1; ++rp) {
 302                                         const int ro = rp - ltc_buf_off;
 303                                         if (ro < (rmcnt*avg_distance)) continue;
 304                                         const ltcsnd_sample_t v1 = ltc_enc_buf[rp];
 305                                         const ltcsnd_sample_t v2 = ltc_enc_buf[rp+1];
 306                                         if (v1 != v2 && ro < ((rmcnt+1)*avg_distance)) continue;
 307                                         memmove(&ltc_enc_buf[rp], &ltc_enc_buf[rp+1], ltc_buf_len-rp-1);
 308                                         ltc_buf_len--;
 309                                         rmcnt++;
 310                                 }
 311                         }
 312                 }
 313         }
 314
 315         ltc_speed = new_ltc_speed;
 316         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: transport speed %1.\n", ltc_speed));
 317
 318
 319         // (3) bit/sample alignment
 320         Timecode::Time tc_start;
 321         framepos_t tc_sample_start;
 322
 323         /* calc timecode frame from current position - round down to nearest timecode */
 324         sample_to_timecode(cycle_start_frame, tc_start, true, false);
 325
 326         /* convert timecode back to sample-position */
 327         Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
 328                 double(frame_rate()),
 329                 config.get_subframes_per_frame(),
 330                 config.get_timecode_offset_negative(), config.get_timecode_offset()
 331                 );
 332
 333         /* difference between current frame and TC frame in samples */
 334         frameoffset_t soff = cycle_start_frame - tc_sample_start;
 335         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX3: A3cycle: %1 = A3tc: %2 +off: %3\n",
 336                                 cycle_start_frame, tc_sample_start, soff));
 337
 338
 339         // (4) check if alignment matches
 340         const double fptcf = frames_per_timecode_frame(); // convenient, used a lot below.
 341
 342         /* maximum difference of bit alignment in audio-samples.
 343          *
 344          * if transport and LTC generator differs more than this, the LTC
 345          * generator will be re-initialized
 346          *
 347          * due to rounding error and variations in LTC-bit duration depending
 348          * on the speed, it can be off by +- ltc_speed audio-samples.
 349          * When the playback speed changes, it can actually reach +- 2 * ltc_speed
 350          * in the cycle _after_ the speed changed. The average delta however is 0.
 351          */
 352         double maxdiff;
 353
 354         if (config.get_external_sync() && slave()) {
 355                 maxdiff = slave()->resolution();
 356         } else {
 357                 maxdiff = ceil(fabs(ltc_speed))*2.0;
 358         }
 359
 360         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
 361                                 ltc_enc_pos, ltc_enc_cnt, poff, (ltc_buf_len - ltc_buf_off), poff, ltc_enc_byte));
 362
 363         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc-pos: %1  | d: %2\n",
 364                                 ltc_enc_pos + ltc_enc_cnt - poff,
 365                                 rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
 366                                 ));
 367
 368         if (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff)
 369         {
 370                 // (5) re-align
 371                 ltc_tx_reset();
 372
 373                 /* set frame to encode */
 374                 SMPTETimecode tc;
 375                 tc.hours = tc_start.hours;
 376                 tc.mins = tc_start.minutes;
 377                 tc.secs = tc_start.seconds;
 378                 tc.frame = tc_start.frames;
 379                 ltc_encoder_set_timecode(ltc_encoder, &tc);
 380
 381                 /* workaround for libltc recognizing 29.97 and 30000/1001 as drop-frame TC.
 382                  * In A3 30000/1001 or 30 fps can be drop-frame.
 383                  */
 384                 LTCFrame ltcframe;
 385                 ltc_encoder_get_frame(ltc_encoder, &ltcframe);
 386                 ltcframe.dfbit = timecode_has_drop_frames(cur_timecode)?1:0;
 387                 ltc_encoder_set_frame(ltc_encoder, &ltcframe);
 388
 389
 390                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: now: %1 trs: %2 toff %3\n", cycle_start_frame, tc_sample_start, soff));
 391
 392                 uint32_t cyc_off;
 393                 assert(soff >= 0 && soff < fptcf);
 394
 395                 if (ltc_speed < 0 ) {
 396                         /* calculate the byte that starts at or after the current position */
 397                         ltc_enc_byte = floor((10.0 * soff) / (fptcf));
 398                         ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
 399
 400                         /* calculate difference between the current position and the byte to send */
 401                         cyc_off = soff- ceil(ltc_enc_cnt);
 402
 403                 } else {
 404                         /* calculate the byte that starts at or after the current position */
 405                         ltc_enc_byte = ceil((10.0 * soff) / fptcf);
 406                         ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
 407
 408                         /* calculate difference between the current position and the byte to send */
 409                         cyc_off = ceil(ltc_enc_cnt) - soff;
 410
 411                         if (ltc_enc_byte == 10) {
 412                                 ltc_enc_byte = 0;
 413                                 ltc_encoder_inc_timecode(ltc_encoder);
 414                         }
 415                 }
 416
 417                 assert (cyc_off >= 0);
 418
 419                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
 420                                         soff, ltc_enc_byte, cyc_off));
 421
 422                 if (cyc_off > 0 && cyc_off <= nframes) {
 423                         /* offset in this cycle */
 424                         txf= rint(cyc_off / fabs(ltc_speed));
 425                         memset(out, 0, cyc_off * sizeof(jack_default_audio_sample_t));
 426                 } else {
 427                         /* resync next cycle */
 428                         memset(out, 0, cyc_off * sizeof(jack_default_audio_sample_t));
 429                         return nframes;
 430                 }
 431
 432                 ltc_enc_pos = tc_sample_start;
 433
 434                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 435                                         ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 436         }
 437
 438
 439         // (6) encode and output
 440         while (1) {
 441 #ifdef LTC_GEN_TXDBUG
 442                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.1 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 443 #endif
 444                 // (6a) send remaining buffer
 445                 while ((ltc_buf_off < ltc_buf_len) && (txf < nframes)) {
 446                         const float v1 = ltc_enc_buf[ltc_buf_off++] - 128.0;
 447                         const jack_default_audio_sample_t val = (jack_default_audio_sample_t) (v1*ltcvol);
 448                         out[txf++] = val;
 449                 }
 450 #ifdef LTC_GEN_TXDBUG
 451                 DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.2 @%1  [ %2 / %3 ]\n", txf, ltc_buf_off, ltc_buf_len));
 452 #endif
 453
 454                 if (txf >= nframes) {
 455                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX7 enc: %1 [ %2 / %3 ] byte: %4 spd %5 fpp %6 || nf: %7\n",
 456                                                 ltc_enc_pos, ltc_buf_off, ltc_buf_len, ltc_enc_byte, ltc_speed, nframes, txf));
 457                         return nframes;
 458                 }
 459
 460                 ltc_buf_len = 0;
 461                 ltc_buf_off = 0;
 462
 463                 // (6b) encode LTC, bump timecode
 464
 465                 if (ltc_speed < 0) {
 466                         ltc_enc_byte = (ltc_enc_byte + 9)%10;
 467                         if (ltc_enc_byte == 9) {
 468                                 ltc_encoder_dec_timecode(ltc_encoder);
 469                                 ltc_tx_recalculate_position();
 470                                 ltc_enc_cnt = fptcf;
 471                         }
 472                 }
 473
 474                 if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
 475                         DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
 476                         ltc_encoder_buffer_flush(ltc_encoder);
 477                         ltc_tx_reset();
 478                         memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 479                         return -1;
 480                 }
 481                 int enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
 482 #ifdef LTC_GEN_FRAMEDBUG
 483                 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));
 484 #endif
 485                 if (enc_frames <=0) {
 486                         DEBUG_TRACE (DEBUG::LTC, "LTC TX6.3 encoder empty buffer.\n");
 487                         ltc_encoder_buffer_flush(ltc_encoder);
 488                         ltc_tx_reset();
 489                         memset(out, 0, nframes * sizeof(jack_default_audio_sample_t));
 490                         return -1;
 491                 }
 492
 493                 ltc_buf_len += enc_frames;
 494                 if (ltc_speed < 0)
 495                         ltc_enc_cnt -= fptcf/10.0;
 496                 else
 497                         ltc_enc_cnt += fptcf/10.0;
 498
 499                 if (ltc_speed >= 0) {
 500                         ltc_enc_byte = (ltc_enc_byte + 1)%10;
 501                         if (ltc_enc_byte == 0 && ltc_speed != 0) {
 502                                 ltc_encoder_inc_timecode(ltc_encoder);
 503                                 ltc_tx_recalculate_position();
 504                                 ltc_enc_cnt = 0;
 505                         } else if (ltc_enc_byte == 0) {
 506                                 ltc_enc_cnt = 0;
 507                         }
 508                 }
 509 #ifdef LTC_GEN_FRAMEDBUG
 510                 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));
 511 #endif
 512         }
 513
 514         return nframes;
 515 }