src/lib/ffmpeg_decoder.cc

   1 /*
   2     Copyright (C) 2012-2016 Carl Hetherington <cth@carlh.net>
   3
   4     This program is free software; you can redistribute it and/or modify
   5     it under the terms of the GNU General Public License as published by
   6     the Free Software Foundation; either version 2 of the License, or
   7     (at your option) any later version.
   8
   9     This program is distributed in the hope that it will be useful,
  10     but WITHOUT ANY WARRANTY; without even the implied warranty of
  11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12     GNU General Public License for more details.
  13
  14     You should have received a copy of the GNU General Public License
  15     along with this program; if not, write to the Free Software
  16     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17
  18 */
  19
  20 /** @file  src/ffmpeg_decoder.cc
  21  *  @brief A decoder using FFmpeg to decode content.
  22  */
  23
  24 #include "filter.h"
  25 #include "exceptions.h"
  26 #include "image.h"
  27 #include "util.h"
  28 #include "log.h"
  29 #include "ffmpeg_decoder.h"
  30 #include "subtitle_decoder.h"
  31 #include "ffmpeg_audio_stream.h"
  32 #include "ffmpeg_subtitle_stream.h"
  33 #include "video_filter_graph.h"
  34 #include "audio_buffers.h"
  35 #include "ffmpeg_content.h"
  36 #include "raw_image_proxy.h"
  37 #include "video_decoder.h"
  38 #include "film.h"
  39 #include "md5_digester.h"
  40 #include "audio_decoder.h"
  41 #include "compose.hpp"
  42 #include <dcp/subtitle_string.h>
  43 #include <sub/ssa_reader.h>
  44 #include <sub/subtitle.h>
  45 #include <sub/collect.h>
  46 extern "C" {
  47 #include <libavcodec/avcodec.h>
  48 #include <libavformat/avformat.h>
  49 }
  50 #include <boost/foreach.hpp>
  51 #include <boost/algorithm/string.hpp>
  52 #include <vector>
  53 #include <iomanip>
  54 #include <iostream>
  55 #include <stdint.h>
  56
  57 #include "i18n.h"
  58
  59 #define LOG_GENERAL(...) _log->log (String::compose (__VA_ARGS__), LogEntry::TYPE_GENERAL);
  60 #define LOG_ERROR(...) _log->log (String::compose (__VA_ARGS__), LogEntry::TYPE_ERROR);
  61 #define LOG_WARNING_NC(...) _log->log (__VA_ARGS__, LogEntry::TYPE_WARNING);
  62 #define LOG_WARNING(...) _log->log (String::compose (__VA_ARGS__), LogEntry::TYPE_WARNING);
  63
  64 using std::cout;
  65 using std::string;
  66 using std::vector;
  67 using std::list;
  68 using std::min;
  69 using std::pair;
  70 using std::max;
  71 using std::map;
  72 using boost::shared_ptr;
  73 using boost::is_any_of;
  74 using boost::split;
  75 using dcp::Size;
  76
  77 FFmpegDecoder::FFmpegDecoder (shared_ptr<const FFmpegContent> c, shared_ptr<Log> log, bool fast)
  78         : FFmpeg (c)
  79         , _log (log)
  80 {
  81         if (c->video) {
  82                 video.reset (new VideoDecoder (this, c, log));
  83                 _pts_offset = pts_offset (c->ffmpeg_audio_streams(), c->first_video(), c->active_video_frame_rate());
  84         } else {
  85                 _pts_offset = ContentTime ();
  86         }
  87
  88         if (c->audio) {
  89                 audio.reset (new AudioDecoder (this, c->audio, fast, log));
  90         }
  91
  92         if (c->subtitle) {
  93                 subtitle.reset (
  94                         new SubtitleDecoder (
  95                                 this,
  96                                 c->subtitle,
  97                                 bind (&FFmpegDecoder::image_subtitles_during, this, _1, _2),
  98                                 bind (&FFmpegDecoder::text_subtitles_during, this, _1, _2)
  99                                 )
 100                         );
 101         }
 102 }
 103
 104 void
 105 FFmpegDecoder::flush ()
 106 {
 107         /* Get any remaining frames */
 108
 109         _packet.data = 0;
 110         _packet.size = 0;
 111
 112         /* XXX: should we reset _packet.data and size after each *_decode_* call? */
 113
 114         while (decode_video_packet ()) {}
 115
 116         decode_audio_packet ();
 117         audio->flush ();
 118 }
 119
 120 bool
 121 FFmpegDecoder::pass (PassReason reason, bool accurate)
 122 {
 123         int r = av_read_frame (_format_context, &_packet);
 124
 125         /* AVERROR_INVALIDDATA can apparently be returned sometimes even when av_read_frame
 126            has pretty-much succeeded (and hence generated data which should be processed).
 127            Hence it makes sense to continue here in that case.
 128         */
 129         if (r < 0 && r != AVERROR_INVALIDDATA) {
 130                 if (r != AVERROR_EOF) {
 131                         /* Maybe we should fail here, but for now we'll just finish off instead */
 132                         char buf[256];
 133                         av_strerror (r, buf, sizeof(buf));
 134                         LOG_ERROR (N_("error on av_read_frame (%1) (%2)"), buf, r);
 135                 }
 136
 137                 flush ();
 138                 return true;
 139         }
 140
 141         int const si = _packet.stream_index;
 142         shared_ptr<const FFmpegContent> fc = _ffmpeg_content;
 143
 144         if (_video_stream && si == _video_stream.get() && !video->ignore() && (accurate || reason != PASS_REASON_SUBTITLE)) {
 145                 decode_video_packet ();
 146         } else if (fc->subtitle_stream() && fc->subtitle_stream()->uses_index (_format_context, si)) {
 147                 decode_subtitle_packet ();
 148         } else if (accurate || reason != PASS_REASON_SUBTITLE) {
 149                 decode_audio_packet ();
 150         }
 151
 152         av_packet_unref (&_packet);
 153         return false;
 154 }
 155
 156 /** @param data pointer to array of pointers to buffers.
 157  *  Only the first buffer will be used for non-planar data, otherwise there will be one per channel.
 158  */
 159 shared_ptr<AudioBuffers>
 160 FFmpegDecoder::deinterleave_audio (shared_ptr<FFmpegAudioStream> stream) const
 161 {
 162         DCPOMATIC_ASSERT (bytes_per_audio_sample (stream));
 163
 164         int const size = av_samples_get_buffer_size (
 165                 0, stream->stream(_format_context)->codec->channels, _frame->nb_samples, audio_sample_format (stream), 1
 166                 );
 167
 168         /* Deinterleave and convert to float */
 169
 170         /* total_samples and frames will be rounded down here, so if there are stray samples at the end
 171            of the block that do not form a complete sample or frame they will be dropped.
 172         */
 173         int const total_samples = size / bytes_per_audio_sample (stream);
 174         int const frames = total_samples / stream->channels();
 175         shared_ptr<AudioBuffers> audio (new AudioBuffers (stream->channels(), frames));
 176
 177         switch (audio_sample_format (stream)) {
 178         case AV_SAMPLE_FMT_U8:
 179         {
 180                 uint8_t* p = reinterpret_cast<uint8_t *> (_frame->data[0]);
 181                 int sample = 0;
 182                 int channel = 0;
 183                 for (int i = 0; i < total_samples; ++i) {
 184                         audio->data(channel)[sample] = float(*p++) / (1 << 23);
 185
 186                         ++channel;
 187                         if (channel == stream->channels()) {
 188                                 channel = 0;
 189                                 ++sample;
 190                         }
 191                 }
 192         }
 193         break;
 194
 195         case AV_SAMPLE_FMT_S16:
 196         {
 197                 int16_t* p = reinterpret_cast<int16_t *> (_frame->data[0]);
 198                 int sample = 0;
 199                 int channel = 0;
 200                 for (int i = 0; i < total_samples; ++i) {
 201                         audio->data(channel)[sample] = float(*p++) / (1 << 15);
 202
 203                         ++channel;
 204                         if (channel == stream->channels()) {
 205                                 channel = 0;
 206                                 ++sample;
 207                         }
 208                 }
 209         }
 210         break;
 211
 212         case AV_SAMPLE_FMT_S16P:
 213         {
 214                 int16_t** p = reinterpret_cast<int16_t **> (_frame->data);
 215                 for (int i = 0; i < stream->channels(); ++i) {
 216                         for (int j = 0; j < frames; ++j) {
 217                                 audio->data(i)[j] = static_cast<float>(p[i][j]) / (1 << 15);
 218                         }
 219                 }
 220         }
 221         break;
 222
 223         case AV_SAMPLE_FMT_S32:
 224         {
 225                 int32_t* p = reinterpret_cast<int32_t *> (_frame->data[0]);
 226                 int sample = 0;
 227                 int channel = 0;
 228                 for (int i = 0; i < total_samples; ++i) {
 229                         audio->data(channel)[sample] = static_cast<float>(*p++) / (1 << 31);
 230
 231                         ++channel;
 232                         if (channel == stream->channels()) {
 233                                 channel = 0;
 234                                 ++sample;
 235                         }
 236                 }
 237         }
 238         break;
 239
 240         case AV_SAMPLE_FMT_S32P:
 241         {
 242                 int32_t** p = reinterpret_cast<int32_t **> (_frame->data);
 243                 for (int i = 0; i < stream->channels(); ++i) {
 244                         for (int j = 0; j < frames; ++j) {
 245                                 audio->data(i)[j] = static_cast<float>(p[i][j]) / (1 << 31);
 246                         }
 247                 }
 248         }
 249         break;
 250
 251         case AV_SAMPLE_FMT_FLT:
 252         {
 253                 float* p = reinterpret_cast<float*> (_frame->data[0]);
 254                 int sample = 0;
 255                 int channel = 0;
 256                 for (int i = 0; i < total_samples; ++i) {
 257                         audio->data(channel)[sample] = *p++;
 258
 259                         ++channel;
 260                         if (channel == stream->channels()) {
 261                                 channel = 0;
 262                                 ++sample;
 263                         }
 264                 }
 265         }
 266         break;
 267
 268         case AV_SAMPLE_FMT_FLTP:
 269         {
 270                 float** p = reinterpret_cast<float**> (_frame->data);
 271                 /* Sometimes there aren't as many channels in the _frame as in the stream */
 272                 for (int i = 0; i < _frame->channels; ++i) {
 273                         memcpy (audio->data(i), p[i], frames * sizeof(float));
 274                 }
 275                 for (int i = _frame->channels; i < stream->channels(); ++i) {
 276                         audio->make_silent (i);
 277                 }
 278         }
 279         break;
 280
 281         default:
 282                 throw DecodeError (String::compose (_("Unrecognised audio sample format (%1)"), static_cast<int> (audio_sample_format (stream))));
 283         }
 284
 285         return audio;
 286 }
 287
 288 AVSampleFormat
 289 FFmpegDecoder::audio_sample_format (shared_ptr<FFmpegAudioStream> stream) const
 290 {
 291         return stream->stream (_format_context)->codec->sample_fmt;
 292 }
 293
 294 int
 295 FFmpegDecoder::bytes_per_audio_sample (shared_ptr<FFmpegAudioStream> stream) const
 296 {
 297         return av_get_bytes_per_sample (audio_sample_format (stream));
 298 }
 299
 300 void
 301 FFmpegDecoder::seek (ContentTime time, bool accurate)
 302 {
 303         video->seek (time, accurate);
 304         audio->seek (time, accurate);
 305         subtitle->seek (time, accurate);
 306
 307         /* If we are doing an `accurate' seek, we need to use pre-roll, as
 308            we don't really know what the seek will give us.
 309         */
 310
 311         ContentTime pre_roll = accurate ? ContentTime::from_seconds (2) : ContentTime (0);
 312         time -= pre_roll;
 313
 314         /* XXX: it seems debatable whether PTS should be used here...
 315            http://www.mjbshaw.com/2012/04/seeking-in-ffmpeg-know-your-timestamp.html
 316         */
 317
 318         DCPOMATIC_ASSERT (_video_stream);
 319
 320         ContentTime u = time - _pts_offset;
 321         if (u < ContentTime ()) {
 322                 u = ContentTime ();
 323         }
 324         av_seek_frame (
 325                 _format_context,
 326                 _video_stream.get(),
 327                 u.seconds() / av_q2d (_format_context->streams[_video_stream.get()]->time_base),
 328                 AVSEEK_FLAG_BACKWARD
 329                 );
 330
 331         avcodec_flush_buffers (video_codec_context());
 332
 333         /* XXX: should be flushing audio buffers? */
 334
 335         if (subtitle_codec_context ()) {
 336                 avcodec_flush_buffers (subtitle_codec_context ());
 337         }
 338 }
 339
 340 void
 341 FFmpegDecoder::decode_audio_packet ()
 342 {
 343         /* Audio packets can contain multiple frames, so we may have to call avcodec_decode_audio4
 344            several times.
 345         */
 346
 347         AVPacket copy_packet = _packet;
 348
 349         /* XXX: inefficient */
 350         vector<shared_ptr<FFmpegAudioStream> > streams = ffmpeg_content()->ffmpeg_audio_streams ();
 351         vector<shared_ptr<FFmpegAudioStream> >::const_iterator stream = streams.begin ();
 352         while (stream != streams.end () && !(*stream)->uses_index (_format_context, copy_packet.stream_index)) {
 353                 ++stream;
 354         }
 355
 356         if (stream == streams.end ()) {
 357                 /* The packet's stream may not be an audio one; just ignore it in this method if so */
 358                 return;
 359         }
 360
 361         while (copy_packet.size > 0) {
 362
 363                 int frame_finished;
 364                 int decode_result = avcodec_decode_audio4 ((*stream)->stream (_format_context)->codec, _frame, &frame_finished, &copy_packet);
 365                 if (decode_result < 0) {
 366                         /* avcodec_decode_audio4 can sometimes return an error even though it has decoded
 367                            some valid data; for example dca_subframe_footer can return AVERROR_INVALIDDATA
 368                            if it overreads the auxiliary data.  ffplay carries on if frame_finished is true,
 369                            even in the face of such an error, so I think we should too.
 370
 371                            Returning from the method here caused mantis #352.
 372                         */
 373                         LOG_WARNING ("avcodec_decode_audio4 failed (%1)", decode_result);
 374
 375                         /* Fudge decode_result so that we come out of the while loop when
 376                            we've processed this data.
 377                         */
 378                         decode_result = copy_packet.size;
 379                 }
 380
 381                 if (frame_finished) {
 382                         ContentTime ct = ContentTime::from_seconds (
 383                                 av_frame_get_best_effort_timestamp (_frame) *
 384                                 av_q2d ((*stream)->stream (_format_context)->time_base))
 385                                 + _pts_offset;
 386
 387                         shared_ptr<AudioBuffers> data = deinterleave_audio (*stream);
 388
 389                         if (ct < ContentTime ()) {
 390                                 /* Discard audio data that comes before time 0 */
 391                                 Frame const remove = min (int64_t (data->frames()), (-ct).frames_ceil(double((*stream)->frame_rate ())));
 392                                 data->move (remove, 0, data->frames() - remove);
 393                                 data->set_frames (data->frames() - remove);
 394                                 ct += ContentTime::from_frames (remove, (*stream)->frame_rate ());
 395                         }
 396
 397                         if (data->frames() > 0) {
 398                                 audio->give (*stream, data, ct);
 399                         }
 400                 }
 401
 402                 copy_packet.data += decode_result;
 403                 copy_packet.size -= decode_result;
 404         }
 405 }
 406
 407 bool
 408 FFmpegDecoder::decode_video_packet ()
 409 {
 410         DCPOMATIC_ASSERT (_video_stream);
 411
 412         int frame_finished;
 413         if (avcodec_decode_video2 (video_codec_context(), _frame, &frame_finished, &_packet) < 0 || !frame_finished) {
 414                 return false;
 415         }
 416
 417         boost::mutex::scoped_lock lm (_filter_graphs_mutex);
 418
 419         shared_ptr<VideoFilterGraph> graph;
 420
 421         list<shared_ptr<VideoFilterGraph> >::iterator i = _filter_graphs.begin();
 422         while (i != _filter_graphs.end() && !(*i)->can_process (dcp::Size (_frame->width, _frame->height), (AVPixelFormat) _frame->format)) {
 423                 ++i;
 424         }
 425
 426         if (i == _filter_graphs.end ()) {
 427                 graph.reset (new VideoFilterGraph (dcp::Size (_frame->width, _frame->height), (AVPixelFormat) _frame->format));
 428                 graph->setup (_ffmpeg_content->filters ());
 429                 _filter_graphs.push_back (graph);
 430                 LOG_GENERAL (N_("New graph for %1x%2, pixel format %3"), _frame->width, _frame->height, _frame->format);
 431         } else {
 432                 graph = *i;
 433         }
 434
 435         list<pair<shared_ptr<Image>, int64_t> > images = graph->process (_frame);
 436
 437         for (list<pair<shared_ptr<Image>, int64_t> >::iterator i = images.begin(); i != images.end(); ++i) {
 438
 439                 shared_ptr<Image> image = i->first;
 440
 441                 if (i->second != AV_NOPTS_VALUE) {
 442                         double const pts = i->second * av_q2d (_format_context->streams[_video_stream.get()]->time_base) + _pts_offset.seconds ();
 443                         video->give (
 444                                 shared_ptr<ImageProxy> (new RawImageProxy (image)),
 445                                 llrint (pts * _ffmpeg_content->active_video_frame_rate ())
 446                                 );
 447                 } else {
 448                         LOG_WARNING_NC ("Dropping frame without PTS");
 449                 }
 450         }
 451
 452         return true;
 453 }
 454
 455 void
 456 FFmpegDecoder::decode_subtitle_packet ()
 457 {
 458         int got_subtitle;
 459         AVSubtitle sub;
 460         if (avcodec_decode_subtitle2 (subtitle_codec_context(), &sub, &got_subtitle, &_packet) < 0 || !got_subtitle) {
 461                 return;
 462         }
 463
 464         if (sub.num_rects <= 0) {
 465                 /* Sometimes we get an empty AVSubtitle, which is used by some codecs to
 466                    indicate that the previous subtitle should stop.  We can ignore it here.
 467                 */
 468                 return;
 469         }
 470
 471         /* Subtitle PTS (within the source, not taking into account any of the
 472            source that we may have chopped off for the DCP).
 473         */
 474         FFmpegSubtitlePeriod sub_period = subtitle_period (sub);
 475         ContentTimePeriod period;
 476         period.from = sub_period.from + _pts_offset;
 477         if (sub_period.to) {
 478                 /* We already know the subtitle period `to' time */
 479                 period.to = sub_period.to.get() + _pts_offset;
 480         } else {
 481                 /* We have to look up the `to' time in the stream's records */
 482                 period.to = ffmpeg_content()->subtitle_stream()->find_subtitle_to (subtitle_id (sub));
 483         }
 484
 485         for (unsigned int i = 0; i < sub.num_rects; ++i) {
 486                 AVSubtitleRect const * rect = sub.rects[i];
 487
 488                 switch (rect->type) {
 489                 case SUBTITLE_NONE:
 490                         break;
 491                 case SUBTITLE_BITMAP:
 492                         decode_bitmap_subtitle (rect, period);
 493                         break;
 494                 case SUBTITLE_TEXT:
 495                         cout << "XXX: SUBTITLE_TEXT " << rect->text << "\n";
 496                         break;
 497                 case SUBTITLE_ASS:
 498                         decode_ass_subtitle (rect->ass, period);
 499                         break;
 500                 }
 501         }
 502
 503         avsubtitle_free (&sub);
 504 }
 505
 506 list<ContentTimePeriod>
 507 FFmpegDecoder::image_subtitles_during (ContentTimePeriod p, bool starting) const
 508 {
 509         return _ffmpeg_content->image_subtitles_during (p, starting);
 510 }
 511
 512 list<ContentTimePeriod>
 513 FFmpegDecoder::text_subtitles_during (ContentTimePeriod p, bool starting) const
 514 {
 515         return _ffmpeg_content->text_subtitles_during (p, starting);
 516 }
 517
 518 void
 519 FFmpegDecoder::decode_bitmap_subtitle (AVSubtitleRect const * rect, ContentTimePeriod period)
 520 {
 521         /* Note RGBA is expressed little-endian, so the first byte in the word is R, second
 522            G, third B, fourth A.
 523         */
 524         shared_ptr<Image> image (new Image (AV_PIX_FMT_RGBA, dcp::Size (rect->w, rect->h), true));
 525
 526 #ifdef DCPOMATIC_HAVE_AVSUBTITLERECT_PICT
 527         /* Start of the first line in the subtitle */
 528         uint8_t* sub_p = rect->pict.data[0];
 529         /* sub_p looks up into a BGRA palette which is here
 530            (i.e. first byte B, second G, third R, fourth A)
 531         */
 532         uint32_t const * palette = (uint32_t *) rect->pict.data[1];
 533 #else
 534         /* Start of the first line in the subtitle */
 535         uint8_t* sub_p = rect->data[0];
 536         /* sub_p looks up into a BGRA palette which is here
 537            (i.e. first byte B, second G, third R, fourth A)
 538         */
 539         uint32_t const * palette = (uint32_t *) rect->data[1];
 540 #endif
 541         /* And the stream has a map of those palette colours to colours
 542            chosen by the user; created a `mapped' palette from those settings.
 543         */
 544         map<RGBA, RGBA> colour_map = ffmpeg_content()->subtitle_stream()->colours ();
 545         vector<RGBA> mapped_palette (rect->nb_colors);
 546         for (int i = 0; i < rect->nb_colors; ++i) {
 547                 RGBA c ((palette[i] & 0xff0000) >> 16, (palette[i] & 0xff00) >> 8, palette[i] & 0xff, (palette[i] & 0xff000000) >> 24);
 548                 map<RGBA, RGBA>::const_iterator j = colour_map.find (c);
 549                 if (j != colour_map.end ()) {
 550                         mapped_palette[i] = j->second;
 551                 } else {
 552                         /* This colour was not found in the FFmpegSubtitleStream's colour map; probably because
 553                            it is from a project that was created before this stuff was added.  Just use the
 554                            colour straight from the original palette.
 555                         */
 556                         mapped_palette[i] = c;
 557                 }
 558         }
 559
 560         /* Start of the output data */
 561         uint32_t* out_p = (uint32_t *) image->data()[0];
 562
 563         for (int y = 0; y < rect->h; ++y) {
 564                 uint8_t* sub_line_p = sub_p;
 565                 uint32_t* out_line_p = out_p;
 566                 for (int x = 0; x < rect->w; ++x) {
 567                         RGBA const p = mapped_palette[*sub_line_p++];
 568                         /* XXX: this seems to be wrong to me (isn't the output image RGBA?) but it looks right on screen */
 569                         *out_line_p++ = (p.a << 24) | (p.r << 16) | (p.g << 8) | p.b;
 570                 }
 571 #ifdef DCPOMATIC_HAVE_AVSUBTITLERECT_PICT
 572                 sub_p += rect->pict.linesize[0];
 573 #else
 574                 sub_p += rect->linesize[0];
 575 #endif
 576                 out_p += image->stride()[0] / sizeof (uint32_t);
 577         }
 578
 579         dcp::Size const vs = _ffmpeg_content->video->size ();
 580         dcpomatic::Rect<double> const scaled_rect (
 581                 static_cast<double> (rect->x) / vs.width,
 582                 static_cast<double> (rect->y) / vs.height,
 583                 static_cast<double> (rect->w) / vs.width,
 584                 static_cast<double> (rect->h) / vs.height
 585                 );
 586
 587         subtitle->give_image (period, image, scaled_rect);
 588 }
 589
 590 void
 591 FFmpegDecoder::decode_ass_subtitle (string ass, ContentTimePeriod period)
 592 {
 593         /* We have no styles and no Format: line, so I'm assuming that FFmpeg
 594            produces a single format of Dialogue: lines...
 595         */
 596
 597         vector<string> bits;
 598         split (bits, ass, is_any_of (","));
 599         if (bits.size() < 10) {
 600                 return;
 601         }
 602
 603         sub::RawSubtitle base;
 604         list<sub::RawSubtitle> raw = sub::SSAReader::parse_line (base, bits[9]);
 605         list<sub::Subtitle> subs = sub::collect<list<sub::Subtitle> > (raw);
 606
 607         /* XXX: lots of this is copied from TextSubtitle; there should probably be some sharing */
 608
 609         /* Highest line index in this subtitle */
 610         int highest = 0;
 611         BOOST_FOREACH (sub::Subtitle i, subs) {
 612                 BOOST_FOREACH (sub::Line j, i.lines) {
 613                         DCPOMATIC_ASSERT (j.vertical_position.reference && j.vertical_position.reference.get() == sub::TOP_OF_SUBTITLE);
 614                         DCPOMATIC_ASSERT (j.vertical_position.line);
 615                         highest = max (highest, j.vertical_position.line.get());
 616                 }
 617         }
 618
 619         list<dcp::SubtitleString> ss;
 620
 621         BOOST_FOREACH (sub::Subtitle i, sub::collect<list<sub::Subtitle> > (sub::SSAReader::parse_line (base, bits[9]))) {
 622                 BOOST_FOREACH (sub::Line j, i.lines) {
 623                         BOOST_FOREACH (sub::Block k, j.blocks) {
 624                                 ss.push_back (
 625                                         dcp::SubtitleString (
 626                                                 boost::optional<string> (),
 627                                                 k.italic,
 628                                                 k.bold,
 629                                                 dcp::Colour (255, 255, 255),
 630                                                 /* 48pt is 1/22nd of the screen height */
 631                                                 48,
 632                                                 1,
 633                                                 dcp::Time (i.from.seconds(), 1000),
 634                                                 dcp::Time (i.to.seconds(), 1000),
 635                                                 0,
 636                                                 dcp::HALIGN_CENTER,
 637                                                 /* This 1.015 is an arbitrary value to lift the bottom sub off the bottom
 638                                                    of the screen a bit to a pleasing degree.
 639                                                 */
 640                                                 1.015 - ((1 + highest - j.vertical_position.line.get()) * 1.5 / 22),
 641                                                 dcp::VALIGN_TOP,
 642                                                 dcp::DIRECTION_LTR,
 643                                                 k.text,
 644                                                 static_cast<dcp::Effect> (0),
 645                                                 dcp::Colour (255, 255, 255),
 646                                                 dcp::Time (),
 647                                                 dcp::Time ()
 648                                                 )
 649                                         );
 650                         }
 651                 }
 652         }
 653
 654         subtitle->give_text (period, ss);
 655 }