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 (video && decode_video_packet ()) {}
 115
 116         if (audio) {
 117                 decode_audio_packet ();
 118                 audio->flush ();
 119         }
 120 }
 121
 122 bool
 123 FFmpegDecoder::pass (PassReason reason, bool accurate)
 124 {
 125         int r = av_read_frame (_format_context, &_packet);
 126
 127         /* AVERROR_INVALIDDATA can apparently be returned sometimes even when av_read_frame
 128            has pretty-much succeeded (and hence generated data which should be processed).
 129            Hence it makes sense to continue here in that case.
 130         */
 131         if (r < 0 && r != AVERROR_INVALIDDATA) {
 132                 if (r != AVERROR_EOF) {
 133                         /* Maybe we should fail here, but for now we'll just finish off instead */
 134                         char buf[256];
 135                         av_strerror (r, buf, sizeof(buf));
 136                         LOG_ERROR (N_("error on av_read_frame (%1) (%2)"), buf, r);
 137                 }
 138
 139                 flush ();
 140                 return true;
 141         }
 142
 143         int const si = _packet.stream_index;
 144         shared_ptr<const FFmpegContent> fc = _ffmpeg_content;
 145
 146         if (_video_stream && si == _video_stream.get() && !video->ignore() && (accurate || reason != PASS_REASON_SUBTITLE)) {
 147                 decode_video_packet ();
 148         } else if (fc->subtitle_stream() && fc->subtitle_stream()->uses_index (_format_context, si)) {
 149                 decode_subtitle_packet ();
 150         } else if (accurate || reason != PASS_REASON_SUBTITLE) {
 151                 decode_audio_packet ();
 152         }
 153
 154         av_packet_unref (&_packet);
 155         return false;
 156 }
 157
 158 /** @param data pointer to array of pointers to buffers.
 159  *  Only the first buffer will be used for non-planar data, otherwise there will be one per channel.
 160  */
 161 shared_ptr<AudioBuffers>
 162 FFmpegDecoder::deinterleave_audio (shared_ptr<FFmpegAudioStream> stream) const
 163 {
 164         DCPOMATIC_ASSERT (bytes_per_audio_sample (stream));
 165
 166         int const size = av_samples_get_buffer_size (
 167                 0, stream->stream(_format_context)->codec->channels, _frame->nb_samples, audio_sample_format (stream), 1
 168                 );
 169
 170         /* Deinterleave and convert to float */
 171
 172         /* total_samples and frames will be rounded down here, so if there are stray samples at the end
 173            of the block that do not form a complete sample or frame they will be dropped.
 174         */
 175         int const total_samples = size / bytes_per_audio_sample (stream);
 176         int const frames = total_samples / stream->channels();
 177         shared_ptr<AudioBuffers> audio (new AudioBuffers (stream->channels(), frames));
 178
 179         switch (audio_sample_format (stream)) {
 180         case AV_SAMPLE_FMT_U8:
 181         {
 182                 uint8_t* p = reinterpret_cast<uint8_t *> (_frame->data[0]);
 183                 int sample = 0;
 184                 int channel = 0;
 185                 for (int i = 0; i < total_samples; ++i) {
 186                         audio->data(channel)[sample] = float(*p++) / (1 << 23);
 187
 188                         ++channel;
 189                         if (channel == stream->channels()) {
 190                                 channel = 0;
 191                                 ++sample;
 192                         }
 193                 }
 194         }
 195         break;
 196
 197         case AV_SAMPLE_FMT_S16:
 198         {
 199                 int16_t* p = reinterpret_cast<int16_t *> (_frame->data[0]);
 200                 int sample = 0;
 201                 int channel = 0;
 202                 for (int i = 0; i < total_samples; ++i) {
 203                         audio->data(channel)[sample] = float(*p++) / (1 << 15);
 204
 205                         ++channel;
 206                         if (channel == stream->channels()) {
 207                                 channel = 0;
 208                                 ++sample;
 209                         }
 210                 }
 211         }
 212         break;
 213
 214         case AV_SAMPLE_FMT_S16P:
 215         {
 216                 int16_t** p = reinterpret_cast<int16_t **> (_frame->data);
 217                 for (int i = 0; i < stream->channels(); ++i) {
 218                         for (int j = 0; j < frames; ++j) {
 219                                 audio->data(i)[j] = static_cast<float>(p[i][j]) / (1 << 15);
 220                         }
 221                 }
 222         }
 223         break;
 224
 225         case AV_SAMPLE_FMT_S32:
 226         {
 227                 int32_t* p = reinterpret_cast<int32_t *> (_frame->data[0]);
 228                 int sample = 0;
 229                 int channel = 0;
 230                 for (int i = 0; i < total_samples; ++i) {
 231                         audio->data(channel)[sample] = static_cast<float>(*p++) / 2147483648;
 232
 233                         ++channel;
 234                         if (channel == stream->channels()) {
 235                                 channel = 0;
 236                                 ++sample;
 237                         }
 238                 }
 239         }
 240         break;
 241
 242         case AV_SAMPLE_FMT_S32P:
 243         {
 244                 int32_t** p = reinterpret_cast<int32_t **> (_frame->data);
 245                 for (int i = 0; i < stream->channels(); ++i) {
 246                         for (int j = 0; j < frames; ++j) {
 247                                 audio->data(i)[j] = static_cast<float>(p[i][j]) / 2147483648;
 248                         }
 249                 }
 250         }
 251         break;
 252
 253         case AV_SAMPLE_FMT_FLT:
 254         {
 255                 float* p = reinterpret_cast<float*> (_frame->data[0]);
 256                 int sample = 0;
 257                 int channel = 0;
 258                 for (int i = 0; i < total_samples; ++i) {
 259                         audio->data(channel)[sample] = *p++;
 260
 261                         ++channel;
 262                         if (channel == stream->channels()) {
 263                                 channel = 0;
 264                                 ++sample;
 265                         }
 266                 }
 267         }
 268         break;
 269
 270         case AV_SAMPLE_FMT_FLTP:
 271         {
 272                 float** p = reinterpret_cast<float**> (_frame->data);
 273                 /* Sometimes there aren't as many channels in the _frame as in the stream */
 274                 for (int i = 0; i < _frame->channels; ++i) {
 275                         memcpy (audio->data(i), p[i], frames * sizeof(float));
 276                 }
 277                 for (int i = _frame->channels; i < stream->channels(); ++i) {
 278                         audio->make_silent (i);
 279                 }
 280         }
 281         break;
 282
 283         default:
 284                 throw DecodeError (String::compose (_("Unrecognised audio sample format (%1)"), static_cast<int> (audio_sample_format (stream))));
 285         }
 286
 287         return audio;
 288 }
 289
 290 AVSampleFormat
 291 FFmpegDecoder::audio_sample_format (shared_ptr<FFmpegAudioStream> stream) const
 292 {
 293         return stream->stream (_format_context)->codec->sample_fmt;
 294 }
 295
 296 int
 297 FFmpegDecoder::bytes_per_audio_sample (shared_ptr<FFmpegAudioStream> stream) const
 298 {
 299         return av_get_bytes_per_sample (audio_sample_format (stream));
 300 }
 301
 302 void
 303 FFmpegDecoder::seek (ContentTime time, bool accurate)
 304 {
 305         if (video) {
 306                 video->seek (time, accurate);
 307         }
 308
 309         if (audio) {
 310                 audio->seek (time, accurate);
 311         }
 312
 313         if (subtitle) {
 314                 subtitle->seek (time, accurate);
 315         }
 316
 317         /* If we are doing an `accurate' seek, we need to use pre-roll, as
 318            we don't really know what the seek will give us.
 319         */
 320
 321         ContentTime pre_roll = accurate ? ContentTime::from_seconds (2) : ContentTime (0);
 322         time -= pre_roll;
 323
 324         /* XXX: it seems debatable whether PTS should be used here...
 325            http://www.mjbshaw.com/2012/04/seeking-in-ffmpeg-know-your-timestamp.html
 326         */
 327
 328         DCPOMATIC_ASSERT (_video_stream);
 329
 330         ContentTime u = time - _pts_offset;
 331         if (u < ContentTime ()) {
 332                 u = ContentTime ();
 333         }
 334         av_seek_frame (
 335                 _format_context,
 336                 _video_stream.get(),
 337                 u.seconds() / av_q2d (_format_context->streams[_video_stream.get()]->time_base),
 338                 AVSEEK_FLAG_BACKWARD
 339                 );
 340
 341         avcodec_flush_buffers (video_codec_context());
 342
 343         /* XXX: should be flushing audio buffers? */
 344
 345         if (subtitle_codec_context ()) {
 346                 avcodec_flush_buffers (subtitle_codec_context ());
 347         }
 348 }
 349
 350 void
 351 FFmpegDecoder::decode_audio_packet ()
 352 {
 353         /* Audio packets can contain multiple frames, so we may have to call avcodec_decode_audio4
 354            several times.
 355         */
 356
 357         AVPacket copy_packet = _packet;
 358
 359         /* XXX: inefficient */
 360         vector<shared_ptr<FFmpegAudioStream> > streams = ffmpeg_content()->ffmpeg_audio_streams ();
 361         vector<shared_ptr<FFmpegAudioStream> >::const_iterator stream = streams.begin ();
 362         while (stream != streams.end () && !(*stream)->uses_index (_format_context, copy_packet.stream_index)) {
 363                 ++stream;
 364         }
 365
 366         if (stream == streams.end ()) {
 367                 /* The packet's stream may not be an audio one; just ignore it in this method if so */
 368                 return;
 369         }
 370
 371         while (copy_packet.size > 0) {
 372
 373                 int frame_finished;
 374                 int decode_result = avcodec_decode_audio4 ((*stream)->stream (_format_context)->codec, _frame, &frame_finished, &copy_packet);
 375                 if (decode_result < 0) {
 376                         /* avcodec_decode_audio4 can sometimes return an error even though it has decoded
 377                            some valid data; for example dca_subframe_footer can return AVERROR_INVALIDDATA
 378                            if it overreads the auxiliary data.  ffplay carries on if frame_finished is true,
 379                            even in the face of such an error, so I think we should too.
 380
 381                            Returning from the method here caused mantis #352.
 382                         */
 383                         LOG_WARNING ("avcodec_decode_audio4 failed (%1)", decode_result);
 384
 385                         /* Fudge decode_result so that we come out of the while loop when
 386                            we've processed this data.
 387                         */
 388                         decode_result = copy_packet.size;
 389                 }
 390
 391                 if (frame_finished) {
 392                         ContentTime ct = ContentTime::from_seconds (
 393                                 av_frame_get_best_effort_timestamp (_frame) *
 394                                 av_q2d ((*stream)->stream (_format_context)->time_base))
 395                                 + _pts_offset;
 396
 397                         shared_ptr<AudioBuffers> data = deinterleave_audio (*stream);
 398
 399                         if (ct < ContentTime ()) {
 400                                 /* Discard audio data that comes before time 0 */
 401                                 Frame const remove = min (int64_t (data->frames()), (-ct).frames_ceil(double((*stream)->frame_rate ())));
 402                                 data->move (remove, 0, data->frames() - remove);
 403                                 data->set_frames (data->frames() - remove);
 404                                 ct += ContentTime::from_frames (remove, (*stream)->frame_rate ());
 405                         }
 406
 407                         if (data->frames() > 0) {
 408                                 audio->give (*stream, data, ct);
 409                         }
 410                 }
 411
 412                 copy_packet.data += decode_result;
 413                 copy_packet.size -= decode_result;
 414         }
 415 }
 416
 417 bool
 418 FFmpegDecoder::decode_video_packet ()
 419 {
 420         DCPOMATIC_ASSERT (_video_stream);
 421
 422         int frame_finished;
 423         if (avcodec_decode_video2 (video_codec_context(), _frame, &frame_finished, &_packet) < 0 || !frame_finished) {
 424                 return false;
 425         }
 426
 427         boost::mutex::scoped_lock lm (_filter_graphs_mutex);
 428
 429         shared_ptr<VideoFilterGraph> graph;
 430
 431         list<shared_ptr<VideoFilterGraph> >::iterator i = _filter_graphs.begin();
 432         while (i != _filter_graphs.end() && !(*i)->can_process (dcp::Size (_frame->width, _frame->height), (AVPixelFormat) _frame->format)) {
 433                 ++i;
 434         }
 435
 436         if (i == _filter_graphs.end ()) {
 437                 graph.reset (new VideoFilterGraph (dcp::Size (_frame->width, _frame->height), (AVPixelFormat) _frame->format));
 438                 graph->setup (_ffmpeg_content->filters ());
 439                 _filter_graphs.push_back (graph);
 440                 LOG_GENERAL (N_("New graph for %1x%2, pixel format %3"), _frame->width, _frame->height, _frame->format);
 441         } else {
 442                 graph = *i;
 443         }
 444
 445         list<pair<shared_ptr<Image>, int64_t> > images = graph->process (_frame);
 446
 447         for (list<pair<shared_ptr<Image>, int64_t> >::iterator i = images.begin(); i != images.end(); ++i) {
 448
 449                 shared_ptr<Image> image = i->first;
 450
 451                 if (i->second != AV_NOPTS_VALUE) {
 452                         double const pts = i->second * av_q2d (_format_context->streams[_video_stream.get()]->time_base) + _pts_offset.seconds ();
 453                         video->give (
 454                                 shared_ptr<ImageProxy> (new RawImageProxy (image)),
 455                                 llrint (pts * _ffmpeg_content->active_video_frame_rate ())
 456                                 );
 457                 } else {
 458                         LOG_WARNING_NC ("Dropping frame without PTS");
 459                 }
 460         }
 461
 462         return true;
 463 }
 464
 465 void
 466 FFmpegDecoder::decode_subtitle_packet ()
 467 {
 468         int got_subtitle;
 469         AVSubtitle sub;
 470         if (avcodec_decode_subtitle2 (subtitle_codec_context(), &sub, &got_subtitle, &_packet) < 0 || !got_subtitle) {
 471                 return;
 472         }
 473
 474         if (sub.num_rects <= 0) {
 475                 /* Sometimes we get an empty AVSubtitle, which is used by some codecs to
 476                    indicate that the previous subtitle should stop.  We can ignore it here.
 477                 */
 478                 return;
 479         }
 480
 481         /* Subtitle PTS (within the source, not taking into account any of the
 482            source that we may have chopped off for the DCP).
 483         */
 484         FFmpegSubtitlePeriod sub_period = subtitle_period (sub);
 485         ContentTimePeriod period;
 486         period.from = sub_period.from + _pts_offset;
 487         if (sub_period.to) {
 488                 /* We already know the subtitle period `to' time */
 489                 period.to = sub_period.to.get() + _pts_offset;
 490         } else {
 491                 /* We have to look up the `to' time in the stream's records */
 492                 period.to = ffmpeg_content()->subtitle_stream()->find_subtitle_to (subtitle_id (sub));
 493         }
 494
 495         for (unsigned int i = 0; i < sub.num_rects; ++i) {
 496                 AVSubtitleRect const * rect = sub.rects[i];
 497
 498                 switch (rect->type) {
 499                 case SUBTITLE_NONE:
 500                         break;
 501                 case SUBTITLE_BITMAP:
 502                         decode_bitmap_subtitle (rect, period);
 503                         break;
 504                 case SUBTITLE_TEXT:
 505                         cout << "XXX: SUBTITLE_TEXT " << rect->text << "\n";
 506                         break;
 507                 case SUBTITLE_ASS:
 508                         decode_ass_subtitle (rect->ass, period);
 509                         break;
 510                 }
 511         }
 512
 513         avsubtitle_free (&sub);
 514 }
 515
 516 list<ContentTimePeriod>
 517 FFmpegDecoder::image_subtitles_during (ContentTimePeriod p, bool starting) const
 518 {
 519         return _ffmpeg_content->image_subtitles_during (p, starting);
 520 }
 521
 522 list<ContentTimePeriod>
 523 FFmpegDecoder::text_subtitles_during (ContentTimePeriod p, bool starting) const
 524 {
 525         return _ffmpeg_content->text_subtitles_during (p, starting);
 526 }
 527
 528 void
 529 FFmpegDecoder::decode_bitmap_subtitle (AVSubtitleRect const * rect, ContentTimePeriod period)
 530 {
 531         /* Note RGBA is expressed little-endian, so the first byte in the word is R, second
 532            G, third B, fourth A.
 533         */
 534         shared_ptr<Image> image (new Image (AV_PIX_FMT_RGBA, dcp::Size (rect->w, rect->h), true));
 535
 536 #ifdef DCPOMATIC_HAVE_AVSUBTITLERECT_PICT
 537         /* Start of the first line in the subtitle */
 538         uint8_t* sub_p = rect->pict.data[0];
 539         /* sub_p looks up into a BGRA palette which is here
 540            (i.e. first byte B, second G, third R, fourth A)
 541         */
 542         uint32_t const * palette = (uint32_t *) rect->pict.data[1];
 543 #else
 544         /* Start of the first line in the subtitle */
 545         uint8_t* sub_p = rect->data[0];
 546         /* sub_p looks up into a BGRA palette which is here
 547            (i.e. first byte B, second G, third R, fourth A)
 548         */
 549         uint32_t const * palette = (uint32_t *) rect->data[1];
 550 #endif
 551         /* And the stream has a map of those palette colours to colours
 552            chosen by the user; created a `mapped' palette from those settings.
 553         */
 554         map<RGBA, RGBA> colour_map = ffmpeg_content()->subtitle_stream()->colours ();
 555         vector<RGBA> mapped_palette (rect->nb_colors);
 556         for (int i = 0; i < rect->nb_colors; ++i) {
 557                 RGBA c ((palette[i] & 0xff0000) >> 16, (palette[i] & 0xff00) >> 8, palette[i] & 0xff, (palette[i] & 0xff000000) >> 24);
 558                 map<RGBA, RGBA>::const_iterator j = colour_map.find (c);
 559                 if (j != colour_map.end ()) {
 560                         mapped_palette[i] = j->second;
 561                 } else {
 562                         /* This colour was not found in the FFmpegSubtitleStream's colour map; probably because
 563                            it is from a project that was created before this stuff was added.  Just use the
 564                            colour straight from the original palette.
 565                         */
 566                         mapped_palette[i] = c;
 567                 }
 568         }
 569
 570         /* Start of the output data */
 571         uint32_t* out_p = (uint32_t *) image->data()[0];
 572
 573         for (int y = 0; y < rect->h; ++y) {
 574                 uint8_t* sub_line_p = sub_p;
 575                 uint32_t* out_line_p = out_p;
 576                 for (int x = 0; x < rect->w; ++x) {
 577                         RGBA const p = mapped_palette[*sub_line_p++];
 578                         /* XXX: this seems to be wrong to me (isn't the output image RGBA?) but it looks right on screen */
 579                         *out_line_p++ = (p.a << 24) | (p.r << 16) | (p.g << 8) | p.b;
 580                 }
 581 #ifdef DCPOMATIC_HAVE_AVSUBTITLERECT_PICT
 582                 sub_p += rect->pict.linesize[0];
 583 #else
 584                 sub_p += rect->linesize[0];
 585 #endif
 586                 out_p += image->stride()[0] / sizeof (uint32_t);
 587         }
 588
 589         dcp::Size const vs = _ffmpeg_content->video->size ();
 590         dcpomatic::Rect<double> const scaled_rect (
 591                 static_cast<double> (rect->x) / vs.width,
 592                 static_cast<double> (rect->y) / vs.height,
 593                 static_cast<double> (rect->w) / vs.width,
 594                 static_cast<double> (rect->h) / vs.height
 595                 );
 596
 597         subtitle->give_image (period, image, scaled_rect);
 598 }
 599
 600 void
 601 FFmpegDecoder::decode_ass_subtitle (string ass, ContentTimePeriod period)
 602 {
 603         /* We have no styles and no Format: line, so I'm assuming that FFmpeg
 604            produces a single format of Dialogue: lines...
 605         */
 606
 607         vector<string> bits;
 608         split (bits, ass, is_any_of (","));
 609         if (bits.size() < 10) {
 610                 return;
 611         }
 612
 613         sub::RawSubtitle base;
 614         list<sub::RawSubtitle> raw = sub::SSAReader::parse_line (base, bits[9]);
 615         list<sub::Subtitle> subs = sub::collect<list<sub::Subtitle> > (raw);
 616
 617         /* XXX: lots of this is copied from TextSubtitle; there should probably be some sharing */
 618
 619         /* Highest line index in this subtitle */
 620         int highest = 0;
 621         BOOST_FOREACH (sub::Subtitle i, subs) {
 622                 BOOST_FOREACH (sub::Line j, i.lines) {
 623                         DCPOMATIC_ASSERT (j.vertical_position.reference && j.vertical_position.reference.get() == sub::TOP_OF_SUBTITLE);
 624                         DCPOMATIC_ASSERT (j.vertical_position.line);
 625                         highest = max (highest, j.vertical_position.line.get());
 626                 }
 627         }
 628
 629         list<dcp::SubtitleString> ss;
 630
 631         BOOST_FOREACH (sub::Subtitle i, sub::collect<list<sub::Subtitle> > (sub::SSAReader::parse_line (base, bits[9]))) {
 632                 BOOST_FOREACH (sub::Line j, i.lines) {
 633                         BOOST_FOREACH (sub::Block k, j.blocks) {
 634                                 ss.push_back (
 635                                         dcp::SubtitleString (
 636                                                 boost::optional<string> (),
 637                                                 k.italic,
 638                                                 k.bold,
 639                                                 dcp::Colour (255, 255, 255),
 640                                                 /* 48pt is 1/22nd of the screen height */
 641                                                 48,
 642                                                 1,
 643                                                 dcp::Time (i.from.seconds(), 1000),
 644                                                 dcp::Time (i.to.seconds(), 1000),
 645                                                 0,
 646                                                 dcp::HALIGN_CENTER,
 647                                                 /* This 1.015 is an arbitrary value to lift the bottom sub off the bottom
 648                                                    of the screen a bit to a pleasing degree.
 649                                                 */
 650                                                 1.015 - ((1 + highest - j.vertical_position.line.get()) * 1.5 / 22),
 651                                                 dcp::VALIGN_TOP,
 652                                                 dcp::DIRECTION_LTR,
 653                                                 k.text,
 654                                                 static_cast<dcp::Effect> (0),
 655                                                 dcp::Colour (255, 255, 255),
 656                                                 dcp::Time (),
 657                                                 dcp::Time ()
 658                                                 )
 659                                         );
 660                         }
 661                 }
 662         }
 663
 664         subtitle->give_text (period, ss);
 665 }