git.sesse.net Git - nageru/blob - futatabi/jpeg_frame_view.cpp

   1 #include "jpeg_frame_view.h"
   2
   3 #include "defs.h"
   4 #include "flags.h"
   5 #include "jpeg_destroyer.h"
   6 #include "jpeglib_error_wrapper.h"
   7 #include "shared/metrics.h"
   8 #include "shared/post_to_main_thread.h"
   9 #include "video_stream.h"
  10 #include "ycbcr_converter.h"
  11
  12 #include <QMouseEvent>
  13 #include <QScreen>
  14 #include <atomic>
  15 #include <condition_variable>
  16 #include <deque>
  17 #include <jpeglib.h>
  18 #include <movit/init.h>
  19 #include <movit/resource_pool.h>
  20 #include <movit/util.h>
  21 #include <mutex>
  22 #include <stdint.h>
  23 #include <thread>
  24 #include <unistd.h>
  25 #include <utility>
  26
  27 // Must come after the Qt stuff.
  28 #include "vaapi_jpeg_decoder.h"
  29
  30 using namespace movit;
  31 using namespace std;
  32
  33 namespace {
  34
  35 // Just an arbitrary order for std::map.
  36 struct FrameOnDiskLexicalOrder
  37 {
  38         bool operator() (const FrameOnDisk &a, const FrameOnDisk &b) const
  39         {
  40                 if (a.pts != b.pts)
  41                         return a.pts < b.pts;
  42                 if (a.offset != b.offset)
  43                         return a.offset < b.offset;
  44                 if (a.filename_idx != b.filename_idx)
  45                         return a.filename_idx < b.filename_idx;
  46                 assert(a.size == b.size);
  47                 return false;
  48         }
  49 };
  50
  51 inline size_t frame_size(const Frame &frame)
  52 {
  53         size_t y_size = frame.width * frame.height;
  54         size_t cbcr_size = y_size / frame.chroma_subsampling_x / frame.chroma_subsampling_y;
  55         return y_size + cbcr_size * 2;
  56 }
  57
  58 struct LRUFrame {
  59         shared_ptr<Frame> frame;
  60         size_t last_used;
  61 };
  62
  63 struct PendingDecode {
  64         JPEGFrameView *destination;
  65
  66         // For actual decodes (only if frame below is nullptr).
  67         FrameOnDisk primary, secondary;
  68         float fade_alpha;  // Irrelevant if secondary.stream_idx == -1.
  69
  70         // Already-decoded frames are also sent through PendingDecode,
  71         // so that they get drawn in the right order. If frame is nullptr,
  72         // it's a real decode.
  73         shared_ptr<Frame> frame;
  74 };
  75
  76 // There can be multiple JPEGFrameView instances, so make all the metrics static.
  77 once_flag jpeg_metrics_inited;
  78 atomic<int64_t> metric_jpeg_cache_used_bytes{0};  // Same value as cache_bytes_used.
  79 atomic<int64_t> metric_jpeg_cache_limit_bytes{size_t(CACHE_SIZE_MB) * 1024 * 1024};
  80 atomic<int64_t> metric_jpeg_cache_given_up_frames{0};
  81 atomic<int64_t> metric_jpeg_cache_hit_frames{0};
  82 atomic<int64_t> metric_jpeg_cache_miss_frames{0};
  83 atomic<int64_t> metric_jpeg_software_decode_frames{0};
  84 atomic<int64_t> metric_jpeg_software_fail_frames{0};
  85 atomic<int64_t> metric_jpeg_vaapi_decode_frames{0};
  86 atomic<int64_t> metric_jpeg_vaapi_fail_frames{0};
  87
  88 }  // namespace
  89
  90 thread JPEGFrameView::jpeg_decoder_thread;
  91 mutex cache_mu;
  92 map<FrameOnDisk, LRUFrame, FrameOnDiskLexicalOrder> cache;  // Under cache_mu.
  93 size_t cache_bytes_used = 0;  // Under cache_mu.
  94 condition_variable any_pending_decodes;
  95 deque<PendingDecode> pending_decodes;  // Under cache_mu.
  96 atomic<size_t> event_counter{0};
  97 extern QGLWidget *global_share_widget;
  98 extern atomic<bool> should_quit;
  99
 100 shared_ptr<Frame> decode_jpeg(const string &jpeg)
 101 {
 102         shared_ptr<Frame> frame;
 103         if (vaapi_jpeg_decoding_usable) {
 104                 frame = decode_jpeg_vaapi(jpeg);
 105                 if (frame != nullptr) {
 106                         ++metric_jpeg_vaapi_decode_frames;
 107                         return frame;
 108                 }
 109                 fprintf(stderr, "VA-API hardware decoding failed; falling back to software.\n");
 110                 ++metric_jpeg_vaapi_fail_frames;
 111         }
 112
 113         frame.reset(new Frame);
 114
 115         jpeg_decompress_struct dinfo;
 116         JPEGWrapErrorManager error_mgr(&dinfo);
 117         if (!error_mgr.run([&dinfo]{ jpeg_create_decompress(&dinfo); })) {
 118                 return get_black_frame();
 119         }
 120         JPEGDestroyer destroy_dinfo(&dinfo);
 121
 122         if (!error_mgr.run([&dinfo, &jpeg]{
 123                 jpeg_mem_src(&dinfo, reinterpret_cast<const unsigned char *>(jpeg.data()), jpeg.size());
 124                 jpeg_read_header(&dinfo, true);
 125         })) {
 126                 return get_black_frame();
 127         }
 128
 129         if (dinfo.num_components != 3) {
 130                 fprintf(stderr, "Not a color JPEG. (%d components, Y=%dx%d, Cb=%dx%d, Cr=%dx%d)\n",
 131                         dinfo.num_components,
 132                         dinfo.comp_info[0].h_samp_factor, dinfo.comp_info[0].v_samp_factor,
 133                         dinfo.comp_info[1].h_samp_factor, dinfo.comp_info[1].v_samp_factor,
 134                         dinfo.comp_info[2].h_samp_factor, dinfo.comp_info[2].v_samp_factor);
 135                 return get_black_frame();
 136         }
 137         if (dinfo.comp_info[0].h_samp_factor != dinfo.max_h_samp_factor ||
 138             dinfo.comp_info[0].v_samp_factor != dinfo.max_v_samp_factor ||  // Y' must not be subsampled.
 139             dinfo.comp_info[1].h_samp_factor != dinfo.comp_info[2].h_samp_factor ||
 140             dinfo.comp_info[1].v_samp_factor != dinfo.comp_info[2].v_samp_factor ||  // Cb and Cr must be identically subsampled.
 141             (dinfo.max_h_samp_factor % dinfo.comp_info[1].h_samp_factor) != 0 ||
 142             (dinfo.max_v_samp_factor % dinfo.comp_info[1].v_samp_factor) != 0) {  // No 2:3 subsampling or other weirdness.
 143                 fprintf(stderr, "Unsupported subsampling scheme. (Y=%dx%d, Cb=%dx%d, Cr=%dx%d)\n",
 144                         dinfo.comp_info[0].h_samp_factor, dinfo.comp_info[0].v_samp_factor,
 145                         dinfo.comp_info[1].h_samp_factor, dinfo.comp_info[1].v_samp_factor,
 146                         dinfo.comp_info[2].h_samp_factor, dinfo.comp_info[2].v_samp_factor);
 147                 exit(1);
 148         }
 149         dinfo.raw_data_out = true;
 150
 151         if (!error_mgr.run([&dinfo]{
 152                 jpeg_start_decompress(&dinfo);
 153         })) {
 154                 return get_black_frame();
 155         }
 156
 157         frame->width = dinfo.output_width;
 158         frame->height = dinfo.output_height;
 159         frame->chroma_subsampling_x = dinfo.max_h_samp_factor / dinfo.comp_info[1].h_samp_factor;
 160         frame->chroma_subsampling_y = dinfo.max_v_samp_factor / dinfo.comp_info[1].v_samp_factor;
 161
 162         unsigned h_mcu_size = DCTSIZE * dinfo.max_h_samp_factor;
 163         unsigned v_mcu_size = DCTSIZE * dinfo.max_v_samp_factor;
 164         unsigned mcu_width_blocks = (dinfo.output_width + h_mcu_size - 1) / h_mcu_size;
 165         unsigned mcu_height_blocks = (dinfo.output_height + v_mcu_size - 1) / v_mcu_size;
 166
 167         unsigned luma_width_blocks = mcu_width_blocks * dinfo.comp_info[0].h_samp_factor;
 168         unsigned chroma_width_blocks = mcu_width_blocks * dinfo.comp_info[1].h_samp_factor;
 169         unsigned luma_height_blocks = mcu_height_blocks * dinfo.comp_info[0].v_samp_factor;
 170         unsigned chroma_height_blocks = mcu_height_blocks * dinfo.comp_info[1].v_samp_factor;
 171
 172         // TODO: Decode into a PBO.
 173         frame->y.reset(new uint8_t[luma_width_blocks * luma_height_blocks * DCTSIZE2]);
 174         frame->cb.reset(new uint8_t[chroma_width_blocks * chroma_height_blocks * DCTSIZE2]);
 175         frame->cr.reset(new uint8_t[chroma_width_blocks * chroma_height_blocks * DCTSIZE2]);
 176         frame->pitch_y = luma_width_blocks * DCTSIZE;
 177         frame->pitch_chroma = chroma_width_blocks * DCTSIZE;
 178
 179         if (!error_mgr.run([&dinfo, &frame, v_mcu_size, mcu_height_blocks] {
 180                 JSAMPROW yptr[v_mcu_size], cbptr[v_mcu_size], crptr[v_mcu_size];
 181                 JSAMPARRAY data[3] = { yptr, cbptr, crptr };
 182                 for (unsigned y = 0; y < mcu_height_blocks; ++y) {
 183                         // NOTE: The last elements of cbptr/crptr will be unused for vertically subsampled chroma.
 184                         for (unsigned yy = 0; yy < v_mcu_size; ++yy) {
 185                                 yptr[yy] = frame->y.get() + (y * DCTSIZE * dinfo.max_v_samp_factor + yy) * frame->pitch_y;
 186                                 cbptr[yy] = frame->cb.get() + (y * DCTSIZE * dinfo.comp_info[1].v_samp_factor + yy) * frame->pitch_chroma;
 187                                 crptr[yy] = frame->cr.get() + (y * DCTSIZE * dinfo.comp_info[1].v_samp_factor + yy) * frame->pitch_chroma;
 188                         }
 189
 190                         jpeg_read_raw_data(&dinfo, data, v_mcu_size);
 191                 }
 192
 193                 (void)jpeg_finish_decompress(&dinfo);
 194         })) {
 195                 return get_black_frame();
 196         }
 197
 198         ++metric_jpeg_software_decode_frames;
 199         return frame;
 200 }
 201
 202 void prune_cache()
 203 {
 204         // Assumes cache_mu is held.
 205         int64_t bytes_still_to_remove = cache_bytes_used - (size_t(CACHE_SIZE_MB) * 1024 * 1024) * 9 / 10;
 206         if (bytes_still_to_remove <= 0) return;
 207
 208         vector<pair<size_t, size_t>> lru_timestamps_and_size;
 209         for (const auto &key_and_value : cache) {
 210                 lru_timestamps_and_size.emplace_back(
 211                         key_and_value.second.last_used,
 212                         frame_size(*key_and_value.second.frame));
 213         }
 214         sort(lru_timestamps_and_size.begin(), lru_timestamps_and_size.end());
 215
 216         // Remove the oldest ones until we are below 90% of the cache used.
 217         size_t lru_cutoff_point = 0;
 218         for (const pair<size_t, size_t> &it : lru_timestamps_and_size) {
 219                 lru_cutoff_point = it.first;
 220                 bytes_still_to_remove -= it.second;
 221                 if (bytes_still_to_remove <= 0) break;
 222         }
 223
 224         for (auto it = cache.begin(); it != cache.end(); ) {
 225                 if (it->second.last_used <= lru_cutoff_point) {
 226                         cache_bytes_used -= frame_size(*it->second.frame);
 227                         metric_jpeg_cache_used_bytes = cache_bytes_used;
 228                         it = cache.erase(it);
 229                 } else {
 230                         ++it;
 231                 }
 232         }
 233 }
 234
 235 shared_ptr<Frame> decode_jpeg_with_cache(FrameOnDisk frame_spec, CacheMissBehavior cache_miss_behavior, FrameReader *frame_reader, bool *did_decode)
 236 {
 237         *did_decode = false;
 238         {
 239                 unique_lock<mutex> lock(cache_mu);
 240                 auto it = cache.find(frame_spec);
 241                 if (it != cache.end()) {
 242                         ++metric_jpeg_cache_hit_frames;
 243                         it->second.last_used = event_counter++;
 244                         return it->second.frame;
 245                 }
 246         }
 247
 248         if (cache_miss_behavior == RETURN_NULLPTR_IF_NOT_IN_CACHE) {
 249                 ++metric_jpeg_cache_given_up_frames;
 250                 return nullptr;
 251         }
 252
 253         ++metric_jpeg_cache_miss_frames;
 254
 255         *did_decode = true;
 256         shared_ptr<Frame> frame = decode_jpeg(frame_reader->read_frame(frame_spec));
 257
 258         unique_lock<mutex> lock(cache_mu);
 259         cache_bytes_used += frame_size(*frame);
 260         metric_jpeg_cache_used_bytes = cache_bytes_used;
 261         cache[frame_spec] = LRUFrame{ frame, event_counter++ };
 262
 263         if (cache_bytes_used > size_t(CACHE_SIZE_MB) * 1024 * 1024) {
 264                 prune_cache();
 265         }
 266         return frame;
 267 }
 268
 269 void JPEGFrameView::jpeg_decoder_thread_func()
 270 {
 271         size_t num_decoded = 0, num_dropped = 0;
 272
 273         pthread_setname_np(pthread_self(), "JPEGDecoder");
 274         while (!should_quit.load()) {
 275                 PendingDecode decode;
 276                 CacheMissBehavior cache_miss_behavior = DECODE_IF_NOT_IN_CACHE;
 277                 {
 278                         unique_lock<mutex> lock(cache_mu);  // TODO: Perhaps under another lock?
 279                         any_pending_decodes.wait(lock, [] {
 280                                 return !pending_decodes.empty() || should_quit.load();
 281                         });
 282                         if (should_quit.load())
 283                                 break;
 284                         decode = pending_decodes.front();
 285                         pending_decodes.pop_front();
 286
 287                         size_t num_pending = 0;
 288                         for (const PendingDecode &other_decode : pending_decodes) {
 289                                 if (other_decode.destination == decode.destination) {
 290                                         ++num_pending;
 291                                 }
 292                         }
 293                         if (num_pending > 3) {
 294                                 cache_miss_behavior = RETURN_NULLPTR_IF_NOT_IN_CACHE;
 295                         }
 296                 }
 297
 298                 if (decode.frame != nullptr) {
 299                         // Already decoded, so just show it.
 300                         decode.destination->setDecodedFrame(decode.frame, nullptr, 1.0f);
 301                         continue;
 302                 }
 303
 304                 shared_ptr<Frame> primary_frame, secondary_frame;
 305                 bool drop = false;
 306                 for (int subframe_idx = 0; subframe_idx < 2; ++subframe_idx) {
 307                         const FrameOnDisk &frame_spec = (subframe_idx == 0 ? decode.primary : decode.secondary);
 308                         if (frame_spec.pts == -1) {
 309                                 // No secondary frame.
 310                                 continue;
 311                         }
 312
 313                         bool found_in_cache;
 314                         shared_ptr<Frame> frame = decode_jpeg_with_cache(frame_spec, cache_miss_behavior, &decode.destination->frame_reader, &found_in_cache);
 315
 316                         if (frame == nullptr) {
 317                                 assert(cache_miss_behavior == RETURN_NULLPTR_IF_NOT_IN_CACHE);
 318                                 drop = true;
 319                                 break;
 320                         }
 321
 322                         if (!found_in_cache) {
 323                                 ++num_decoded;
 324                                 if (num_decoded % 1000 == 0) {
 325                                         fprintf(stderr, "Decoded %zu images, dropped %zu (%.2f%% dropped)\n",
 326                                                 num_decoded, num_dropped, (100.0 * num_dropped) / (num_decoded + num_dropped));
 327                                 }
 328                         }
 329                         if (subframe_idx == 0) {
 330                                 primary_frame = std::move(frame);
 331                         } else {
 332                                 secondary_frame = std::move(frame);
 333                         }
 334                 }
 335                 if (drop) {
 336                         ++num_dropped;
 337                         continue;
 338                 }
 339
 340                 // TODO: Could we get jitter between non-interpolated and interpolated frames here?
 341                 decode.destination->setDecodedFrame(primary_frame, secondary_frame, decode.fade_alpha);
 342         }
 343 }
 344
 345 void JPEGFrameView::shutdown()
 346 {
 347         any_pending_decodes.notify_all();
 348         jpeg_decoder_thread.join();
 349 }
 350
 351 JPEGFrameView::JPEGFrameView(QWidget *parent)
 352         : QGLWidget(parent, global_share_widget)
 353 {
 354         call_once(jpeg_metrics_inited, []{
 355                 global_metrics.add("jpeg_cache_used_bytes", &metric_jpeg_cache_used_bytes, Metrics::TYPE_GAUGE);
 356                 global_metrics.add("jpeg_cache_limit_bytes", &metric_jpeg_cache_limit_bytes, Metrics::TYPE_GAUGE);
 357                 global_metrics.add("jpeg_cache_frames", {{ "action", "given_up" }}, &metric_jpeg_cache_given_up_frames);
 358                 global_metrics.add("jpeg_cache_frames", {{ "action", "hit" }}, &metric_jpeg_cache_hit_frames);
 359                 global_metrics.add("jpeg_cache_frames", {{ "action", "miss" }}, &metric_jpeg_cache_miss_frames);
 360                 global_metrics.add("jpeg_decode_frames", {{ "decoder", "software" }, { "result", "decode" }}, &metric_jpeg_software_decode_frames);
 361                 global_metrics.add("jpeg_decode_frames", {{ "decoder", "software" }, { "result", "fail" }}, &metric_jpeg_software_fail_frames);
 362                 global_metrics.add("jpeg_decode_frames", {{ "decoder", "vaapi" }, { "result", "decode" }}, &metric_jpeg_vaapi_decode_frames);
 363                 global_metrics.add("jpeg_decode_frames", {{ "decoder", "vaapi" }, { "result", "fail" }}, &metric_jpeg_vaapi_fail_frames);
 364         });
 365 }
 366
 367 void JPEGFrameView::setFrame(unsigned stream_idx, FrameOnDisk frame, FrameOnDisk secondary_frame, float fade_alpha)
 368 {
 369         current_stream_idx = stream_idx;  // TODO: Does this interact with fades?
 370
 371         unique_lock<mutex> lock(cache_mu);
 372         PendingDecode decode;
 373         decode.primary = frame;
 374         decode.secondary = secondary_frame;
 375         decode.fade_alpha = fade_alpha;
 376         decode.destination = this;
 377         pending_decodes.push_back(decode);
 378         any_pending_decodes.notify_all();
 379 }
 380
 381 void JPEGFrameView::setFrame(shared_ptr<Frame> frame)
 382 {
 383         unique_lock<mutex> lock(cache_mu);
 384         PendingDecode decode;
 385         decode.frame = std::move(frame);
 386         decode.destination = this;
 387         pending_decodes.push_back(decode);
 388         any_pending_decodes.notify_all();
 389 }
 390
 391 ResourcePool *resource_pool = nullptr;
 392
 393 void JPEGFrameView::initializeGL()
 394 {
 395         glDisable(GL_BLEND);
 396         glDisable(GL_DEPTH_TEST);
 397         check_error();
 398
 399         static once_flag once;
 400         call_once(once, [] {
 401                 resource_pool = new ResourcePool;
 402                 jpeg_decoder_thread = std::thread(jpeg_decoder_thread_func);
 403         });
 404
 405         ycbcr_converter.reset(new YCbCrConverter(YCbCrConverter::OUTPUT_TO_RGBA, resource_pool));
 406
 407         ImageFormat inout_format;
 408         inout_format.color_space = COLORSPACE_sRGB;
 409         inout_format.gamma_curve = GAMMA_sRGB;
 410
 411         overlay_chain.reset(new EffectChain(overlay_base_width, overlay_base_height, resource_pool));
 412         overlay_input = (movit::FlatInput *)overlay_chain->add_input(new FlatInput(inout_format, FORMAT_GRAYSCALE, GL_UNSIGNED_BYTE, overlay_base_width, overlay_base_height));
 413
 414         overlay_chain->add_output(inout_format, OUTPUT_ALPHA_FORMAT_POSTMULTIPLIED);
 415         overlay_chain->finalize();
 416 }
 417
 418 void JPEGFrameView::resizeGL(int width, int height)
 419 {
 420         check_error();
 421         glViewport(0, 0, width, height);
 422         check_error();
 423
 424         // Save these, as width() and height() will lie with DPI scaling.
 425         gl_width = width;
 426         gl_height = height;
 427 }
 428
 429 void JPEGFrameView::paintGL()
 430 {
 431         glViewport(0, 0, gl_width, gl_height);
 432         if (current_frame == nullptr) {
 433                 glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
 434                 glClear(GL_COLOR_BUFFER_BIT);
 435                 return;
 436         }
 437
 438         check_error();
 439         current_chain->render_to_screen();
 440
 441         if (overlay_image != nullptr) {
 442                 if (overlay_input_needs_refresh) {
 443                         overlay_input->set_width(overlay_width);
 444                         overlay_input->set_height(overlay_height);
 445                         overlay_input->set_pixel_data(overlay_image->bits());
 446                 }
 447                 glViewport(gl_width - overlay_width, 0, overlay_width, overlay_height);
 448                 overlay_chain->render_to_screen();
 449         }
 450 }
 451
 452 namespace {
 453
 454 }  // namespace
 455
 456 void JPEGFrameView::setDecodedFrame(shared_ptr<Frame> frame, shared_ptr<Frame> secondary_frame, float fade_alpha)
 457 {
 458         post_to_main_thread([this, frame, secondary_frame, fade_alpha] {
 459                 current_frame = frame;
 460                 current_secondary_frame = secondary_frame;
 461
 462                 if (secondary_frame != nullptr) {
 463                         current_chain = ycbcr_converter->prepare_chain_for_fade(frame, secondary_frame, fade_alpha);
 464                 } else {
 465                         current_chain = ycbcr_converter->prepare_chain_for_conversion(frame);
 466                 }
 467                 update();
 468         });
 469 }
 470
 471 void JPEGFrameView::mousePressEvent(QMouseEvent *event)
 472 {
 473         if (event->type() == QEvent::MouseButtonPress && event->button() == Qt::LeftButton) {
 474                 emit clicked();
 475         }
 476 }
 477
 478 void JPEGFrameView::set_overlay(const string &text)
 479 {
 480         if (text.empty()) {
 481                 overlay_image.reset();
 482                 return;
 483         }
 484
 485         float dpr = QGuiApplication::primaryScreen()->devicePixelRatio();
 486         overlay_width = lrint(overlay_base_width * dpr);
 487         overlay_height = lrint(overlay_base_height * dpr);
 488
 489         overlay_image.reset(new QImage(overlay_width, overlay_height, QImage::Format_Grayscale8));
 490         overlay_image->setDevicePixelRatio(dpr);
 491         overlay_image->fill(0);
 492         QPainter painter(overlay_image.get());
 493
 494         painter.setPen(Qt::white);
 495         QFont font = painter.font();
 496         font.setPointSize(12);
 497         painter.setFont(font);
 498
 499         painter.drawText(QRectF(0, 0, overlay_base_width, overlay_base_height), Qt::AlignCenter, QString::fromStdString(text));
 500
 501         // Don't refresh immediately; we might not have an OpenGL context here.
 502         overlay_input_needs_refresh = true;
 503 }
 504
 505 shared_ptr<Frame> get_black_frame()
 506 {
 507         static shared_ptr<Frame> black_frame;
 508         static once_flag flag;
 509         call_once(flag, [] {
 510                 black_frame.reset(new Frame);
 511                 black_frame->y.reset(new uint8_t[global_flags.width * global_flags.height]);
 512                 black_frame->cb.reset(new uint8_t[(global_flags.width / 2) * (global_flags.height / 2)]);
 513                 black_frame->cr.reset(new uint8_t[(global_flags.width / 2) * (global_flags.height / 2)]);
 514                 black_frame->width = global_flags.width;
 515                 black_frame->height = global_flags.height;
 516                 black_frame->chroma_subsampling_x = 2;
 517                 black_frame->chroma_subsampling_y = 2;
 518                 black_frame->pitch_y = global_flags.width;
 519                 black_frame->pitch_chroma = global_flags.width / 2;
 520         });
 521         ++metric_jpeg_software_fail_frames;
 522         return black_frame;
 523 }