xref: /aosp_15_r20/external/libvpx/vp9/decoder/vp9_decoder.c (revision fb1b10ab9aebc7c7068eedab379b749d7e3900be)
1 /*
2  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
3  *
4  *  Use of this source code is governed by a BSD-style license
5  *  that can be found in the LICENSE file in the root of the source
6  *  tree. An additional intellectual property rights grant can be found
7  *  in the file PATENTS.  All contributing project authors may
8  *  be found in the AUTHORS file in the root of the source tree.
9  */
10 
11 #include <assert.h>
12 #include <limits.h>
13 #include <stdio.h>
14 
15 #include "./vp9_rtcd.h"
16 #include "./vpx_dsp_rtcd.h"
17 #include "./vpx_scale_rtcd.h"
18 
19 #include "vpx_mem/vpx_mem.h"
20 #include "vpx_ports/system_state.h"
21 #include "vpx_ports/vpx_once.h"
22 #include "vpx_ports/vpx_timer.h"
23 #include "vpx_scale/vpx_scale.h"
24 #include "vpx_util/vpx_pthread.h"
25 #include "vpx_util/vpx_thread.h"
26 
27 #include "vp9/common/vp9_alloccommon.h"
28 #include "vp9/common/vp9_loopfilter.h"
29 #include "vp9/common/vp9_onyxc_int.h"
30 #if CONFIG_VP9_POSTPROC
31 #include "vp9/common/vp9_postproc.h"
32 #endif
33 #include "vp9/common/vp9_quant_common.h"
34 #include "vp9/common/vp9_reconintra.h"
35 
36 #include "vp9/decoder/vp9_decodeframe.h"
37 #include "vp9/decoder/vp9_decoder.h"
38 #include "vp9/decoder/vp9_detokenize.h"
39 
initialize_dec(void)40 static void initialize_dec(void) {
41   static volatile int init_done = 0;
42 
43   if (!init_done) {
44     vp9_rtcd();
45     vpx_dsp_rtcd();
46     vpx_scale_rtcd();
47     vp9_init_intra_predictors();
48     init_done = 1;
49   }
50 }
51 
vp9_dec_setup_mi(VP9_COMMON * cm)52 static void vp9_dec_setup_mi(VP9_COMMON *cm) {
53   cm->mi = cm->mip + cm->mi_stride + 1;
54   cm->mi_grid_visible = cm->mi_grid_base + cm->mi_stride + 1;
55   memset(cm->mi_grid_base, 0,
56          cm->mi_stride * (cm->mi_rows + 1) * sizeof(*cm->mi_grid_base));
57 }
58 
vp9_dec_alloc_row_mt_mem(RowMTWorkerData * row_mt_worker_data,VP9_COMMON * cm,int num_sbs,int max_threads,int num_jobs)59 void vp9_dec_alloc_row_mt_mem(RowMTWorkerData *row_mt_worker_data,
60                               VP9_COMMON *cm, int num_sbs, int max_threads,
61                               int num_jobs) {
62   int plane;
63   const size_t dqcoeff_size = (num_sbs << DQCOEFFS_PER_SB_LOG2) *
64                               sizeof(*row_mt_worker_data->dqcoeff[0]);
65   row_mt_worker_data->num_jobs = num_jobs;
66 #if CONFIG_MULTITHREAD
67   {
68     int i;
69     CHECK_MEM_ERROR(
70         &cm->error, row_mt_worker_data->recon_sync_mutex,
71         vpx_malloc(sizeof(*row_mt_worker_data->recon_sync_mutex) * num_jobs));
72     if (row_mt_worker_data->recon_sync_mutex) {
73       for (i = 0; i < num_jobs; ++i) {
74         pthread_mutex_init(&row_mt_worker_data->recon_sync_mutex[i], NULL);
75       }
76     }
77 
78     CHECK_MEM_ERROR(
79         &cm->error, row_mt_worker_data->recon_sync_cond,
80         vpx_malloc(sizeof(*row_mt_worker_data->recon_sync_cond) * num_jobs));
81     if (row_mt_worker_data->recon_sync_cond) {
82       for (i = 0; i < num_jobs; ++i) {
83         pthread_cond_init(&row_mt_worker_data->recon_sync_cond[i], NULL);
84       }
85     }
86   }
87 #endif
88   row_mt_worker_data->num_sbs = num_sbs;
89   for (plane = 0; plane < 3; ++plane) {
90     CHECK_MEM_ERROR(&cm->error, row_mt_worker_data->dqcoeff[plane],
91                     vpx_memalign(32, dqcoeff_size));
92     memset(row_mt_worker_data->dqcoeff[plane], 0, dqcoeff_size);
93     CHECK_MEM_ERROR(&cm->error, row_mt_worker_data->eob[plane],
94                     vpx_calloc(num_sbs << EOBS_PER_SB_LOG2,
95                                sizeof(*row_mt_worker_data->eob[plane])));
96   }
97   CHECK_MEM_ERROR(&cm->error, row_mt_worker_data->partition,
98                   vpx_calloc(num_sbs * PARTITIONS_PER_SB,
99                              sizeof(*row_mt_worker_data->partition)));
100   CHECK_MEM_ERROR(&cm->error, row_mt_worker_data->recon_map,
101                   vpx_calloc(num_sbs, sizeof(*row_mt_worker_data->recon_map)));
102 
103   // allocate memory for thread_data
104   if (row_mt_worker_data->thread_data == NULL) {
105     const size_t thread_size =
106         max_threads * sizeof(*row_mt_worker_data->thread_data);
107     CHECK_MEM_ERROR(&cm->error, row_mt_worker_data->thread_data,
108                     vpx_memalign(32, thread_size));
109   }
110 }
111 
vp9_dec_free_row_mt_mem(RowMTWorkerData * row_mt_worker_data)112 void vp9_dec_free_row_mt_mem(RowMTWorkerData *row_mt_worker_data) {
113   if (row_mt_worker_data != NULL) {
114     int plane;
115 #if CONFIG_MULTITHREAD
116     int i;
117     if (row_mt_worker_data->recon_sync_mutex != NULL) {
118       for (i = 0; i < row_mt_worker_data->num_jobs; ++i) {
119         pthread_mutex_destroy(&row_mt_worker_data->recon_sync_mutex[i]);
120       }
121       vpx_free(row_mt_worker_data->recon_sync_mutex);
122       row_mt_worker_data->recon_sync_mutex = NULL;
123     }
124     if (row_mt_worker_data->recon_sync_cond != NULL) {
125       for (i = 0; i < row_mt_worker_data->num_jobs; ++i) {
126         pthread_cond_destroy(&row_mt_worker_data->recon_sync_cond[i]);
127       }
128       vpx_free(row_mt_worker_data->recon_sync_cond);
129       row_mt_worker_data->recon_sync_cond = NULL;
130     }
131 #endif
132     for (plane = 0; plane < 3; ++plane) {
133       vpx_free(row_mt_worker_data->eob[plane]);
134       row_mt_worker_data->eob[plane] = NULL;
135       vpx_free(row_mt_worker_data->dqcoeff[plane]);
136       row_mt_worker_data->dqcoeff[plane] = NULL;
137     }
138     vpx_free(row_mt_worker_data->partition);
139     row_mt_worker_data->partition = NULL;
140     vpx_free(row_mt_worker_data->recon_map);
141     row_mt_worker_data->recon_map = NULL;
142     vpx_free(row_mt_worker_data->thread_data);
143     row_mt_worker_data->thread_data = NULL;
144   }
145 }
146 
vp9_dec_alloc_mi(VP9_COMMON * cm,int mi_size)147 static int vp9_dec_alloc_mi(VP9_COMMON *cm, int mi_size) {
148   cm->mip = vpx_calloc(mi_size, sizeof(*cm->mip));
149   if (!cm->mip) return 1;
150   cm->mi_alloc_size = mi_size;
151   cm->mi_grid_base = (MODE_INFO **)vpx_calloc(mi_size, sizeof(MODE_INFO *));
152   if (!cm->mi_grid_base) return 1;
153   return 0;
154 }
155 
vp9_dec_free_mi(VP9_COMMON * cm)156 static void vp9_dec_free_mi(VP9_COMMON *cm) {
157 #if CONFIG_VP9_POSTPROC
158   // MFQE allocates an additional mip and swaps it with cm->mip.
159   vpx_free(cm->postproc_state.prev_mip);
160   cm->postproc_state.prev_mip = NULL;
161 #endif
162   vpx_free(cm->mip);
163   cm->mip = NULL;
164   vpx_free(cm->mi_grid_base);
165   cm->mi_grid_base = NULL;
166   cm->mi_alloc_size = 0;
167 }
168 
vp9_decoder_create(BufferPool * const pool)169 VP9Decoder *vp9_decoder_create(BufferPool *const pool) {
170   VP9Decoder *volatile const pbi = vpx_memalign(32, sizeof(*pbi));
171   VP9_COMMON *volatile const cm = pbi ? &pbi->common : NULL;
172 
173   if (!cm) return NULL;
174 
175   vp9_zero(*pbi);
176 
177   if (setjmp(cm->error.jmp)) {
178     cm->error.setjmp = 0;
179     vp9_decoder_remove(pbi);
180     return NULL;
181   }
182 
183   cm->error.setjmp = 1;
184 
185   CHECK_MEM_ERROR(&cm->error, cm->fc,
186                   (FRAME_CONTEXT *)vpx_calloc(1, sizeof(*cm->fc)));
187   CHECK_MEM_ERROR(
188       &cm->error, cm->frame_contexts,
189       (FRAME_CONTEXT *)vpx_calloc(FRAME_CONTEXTS, sizeof(*cm->frame_contexts)));
190 
191   pbi->need_resync = 1;
192   once(initialize_dec);
193 
194   // Initialize the references to not point to any frame buffers.
195   memset(&cm->ref_frame_map, -1, sizeof(cm->ref_frame_map));
196   memset(&cm->next_ref_frame_map, -1, sizeof(cm->next_ref_frame_map));
197 
198   init_frame_indexes(cm);
199   pbi->ready_for_new_data = 1;
200   pbi->common.buffer_pool = pool;
201 
202   cm->bit_depth = VPX_BITS_8;
203   cm->dequant_bit_depth = VPX_BITS_8;
204 
205   cm->alloc_mi = vp9_dec_alloc_mi;
206   cm->free_mi = vp9_dec_free_mi;
207   cm->setup_mi = vp9_dec_setup_mi;
208 
209   vp9_loop_filter_init(cm);
210 
211   cm->error.setjmp = 0;
212 
213   vpx_get_worker_interface()->init(&pbi->lf_worker);
214   pbi->lf_worker.thread_name = "vpx lf worker";
215 
216   return pbi;
217 }
218 
vp9_decoder_remove(VP9Decoder * pbi)219 void vp9_decoder_remove(VP9Decoder *pbi) {
220   int i;
221 
222   if (!pbi) return;
223 
224   vpx_get_worker_interface()->end(&pbi->lf_worker);
225   vpx_free(pbi->lf_worker.data1);
226 
227   for (i = 0; i < pbi->num_tile_workers; ++i) {
228     VPxWorker *const worker = &pbi->tile_workers[i];
229     vpx_get_worker_interface()->end(worker);
230   }
231 
232   vpx_free(pbi->tile_worker_data);
233   vpx_free(pbi->tile_workers);
234 
235   if (pbi->num_tile_workers > 0) {
236     vp9_loop_filter_dealloc(&pbi->lf_row_sync);
237   }
238 
239   if (pbi->row_mt == 1) {
240     vp9_dec_free_row_mt_mem(pbi->row_mt_worker_data);
241     if (pbi->row_mt_worker_data != NULL) {
242       vp9_jobq_deinit(&pbi->row_mt_worker_data->jobq);
243       vpx_free(pbi->row_mt_worker_data->jobq_buf);
244 #if CONFIG_MULTITHREAD
245       pthread_mutex_destroy(&pbi->row_mt_worker_data->recon_done_mutex);
246 #endif
247     }
248     vpx_free(pbi->row_mt_worker_data);
249   }
250 
251   vp9_remove_common(&pbi->common);
252   vpx_free(pbi);
253 }
254 
equal_dimensions(const YV12_BUFFER_CONFIG * a,const YV12_BUFFER_CONFIG * b)255 static int equal_dimensions(const YV12_BUFFER_CONFIG *a,
256                             const YV12_BUFFER_CONFIG *b) {
257   return a->y_height == b->y_height && a->y_width == b->y_width &&
258          a->uv_height == b->uv_height && a->uv_width == b->uv_width;
259 }
260 
vp9_copy_reference_dec(VP9Decoder * pbi,VP9_REFFRAME ref_frame_flag,YV12_BUFFER_CONFIG * sd)261 vpx_codec_err_t vp9_copy_reference_dec(VP9Decoder *pbi,
262                                        VP9_REFFRAME ref_frame_flag,
263                                        YV12_BUFFER_CONFIG *sd) {
264   VP9_COMMON *cm = &pbi->common;
265 
266   /* TODO(jkoleszar): The decoder doesn't have any real knowledge of what the
267    * encoder is using the frame buffers for. This is just a stub to keep the
268    * vpxenc --test-decode functionality working, and will be replaced in a
269    * later commit that adds VP9-specific controls for this functionality.
270    */
271   if (ref_frame_flag == VP9_LAST_FLAG) {
272     const YV12_BUFFER_CONFIG *const cfg = get_ref_frame(cm, 0);
273     if (cfg == NULL) {
274       vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
275                          "No 'last' reference frame");
276       return VPX_CODEC_ERROR;
277     }
278     if (!equal_dimensions(cfg, sd))
279       vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
280                          "Incorrect buffer dimensions");
281     else
282       vpx_yv12_copy_frame(cfg, sd);
283   } else {
284     vpx_internal_error(&cm->error, VPX_CODEC_ERROR, "Invalid reference frame");
285   }
286 
287   return cm->error.error_code;
288 }
289 
vp9_set_reference_dec(VP9_COMMON * cm,VP9_REFFRAME ref_frame_flag,YV12_BUFFER_CONFIG * sd)290 vpx_codec_err_t vp9_set_reference_dec(VP9_COMMON *cm,
291                                       VP9_REFFRAME ref_frame_flag,
292                                       YV12_BUFFER_CONFIG *sd) {
293   int idx;
294   YV12_BUFFER_CONFIG *ref_buf = NULL;
295 
296   // TODO(jkoleszar): The decoder doesn't have any real knowledge of what the
297   // encoder is using the frame buffers for. This is just a stub to keep the
298   // vpxenc --test-decode functionality working, and will be replaced in a
299   // later commit that adds VP9-specific controls for this functionality.
300   // (Yunqing) The set_reference control depends on the following setting in
301   // encoder.
302   // cpi->lst_fb_idx = 0;
303   // cpi->gld_fb_idx = 1;
304   // cpi->alt_fb_idx = 2;
305   if (ref_frame_flag == VP9_LAST_FLAG) {
306     idx = cm->ref_frame_map[0];
307   } else if (ref_frame_flag == VP9_GOLD_FLAG) {
308     idx = cm->ref_frame_map[1];
309   } else if (ref_frame_flag == VP9_ALT_FLAG) {
310     idx = cm->ref_frame_map[2];
311   } else {
312     vpx_internal_error(&cm->error, VPX_CODEC_ERROR, "Invalid reference frame");
313     return cm->error.error_code;
314   }
315 
316   if (idx < 0 || idx >= FRAME_BUFFERS) {
317     vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
318                        "Invalid reference frame map");
319     return cm->error.error_code;
320   }
321 
322   // Get the destination reference buffer.
323   ref_buf = &cm->buffer_pool->frame_bufs[idx].buf;
324 
325   if (!equal_dimensions(ref_buf, sd)) {
326     vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
327                        "Incorrect buffer dimensions");
328   } else {
329     // Overwrite the reference frame buffer.
330     vpx_yv12_copy_frame(sd, ref_buf);
331   }
332 
333   return cm->error.error_code;
334 }
335 
336 /* If any buffer updating is signaled it should be done here. */
swap_frame_buffers(VP9Decoder * pbi)337 static void swap_frame_buffers(VP9Decoder *pbi) {
338   int ref_index = 0, mask;
339   VP9_COMMON *const cm = &pbi->common;
340   BufferPool *const pool = cm->buffer_pool;
341   RefCntBuffer *const frame_bufs = cm->buffer_pool->frame_bufs;
342 
343   for (mask = pbi->refresh_frame_flags; mask; mask >>= 1) {
344     const int old_idx = cm->ref_frame_map[ref_index];
345     // Current thread releases the holding of reference frame.
346     decrease_ref_count(old_idx, frame_bufs, pool);
347 
348     // Release the reference frame in reference map.
349     if (mask & 1) {
350       decrease_ref_count(old_idx, frame_bufs, pool);
351     }
352     cm->ref_frame_map[ref_index] = cm->next_ref_frame_map[ref_index];
353     ++ref_index;
354   }
355 
356   // Current thread releases the holding of reference frame.
357   for (; ref_index < REF_FRAMES && !cm->show_existing_frame; ++ref_index) {
358     const int old_idx = cm->ref_frame_map[ref_index];
359     decrease_ref_count(old_idx, frame_bufs, pool);
360     cm->ref_frame_map[ref_index] = cm->next_ref_frame_map[ref_index];
361   }
362   pbi->hold_ref_buf = 0;
363   cm->frame_to_show = get_frame_new_buffer(cm);
364 
365   --frame_bufs[cm->new_fb_idx].ref_count;
366 
367   // Invalidate these references until the next frame starts.
368   for (ref_index = 0; ref_index < 3; ref_index++)
369     cm->frame_refs[ref_index].idx = -1;
370 }
371 
release_fb_on_decoder_exit(VP9Decoder * pbi)372 static void release_fb_on_decoder_exit(VP9Decoder *pbi) {
373   const VPxWorkerInterface *const winterface = vpx_get_worker_interface();
374   VP9_COMMON *volatile const cm = &pbi->common;
375   BufferPool *volatile const pool = cm->buffer_pool;
376   RefCntBuffer *volatile const frame_bufs = cm->buffer_pool->frame_bufs;
377   int i;
378 
379   // Synchronize all threads immediately as a subsequent decode call may
380   // cause a resize invalidating some allocations.
381   winterface->sync(&pbi->lf_worker);
382   for (i = 0; i < pbi->num_tile_workers; ++i) {
383     winterface->sync(&pbi->tile_workers[i]);
384   }
385 
386   // Release all the reference buffers if worker thread is holding them.
387   if (pbi->hold_ref_buf == 1) {
388     int ref_index = 0, mask;
389     for (mask = pbi->refresh_frame_flags; mask; mask >>= 1) {
390       const int old_idx = cm->ref_frame_map[ref_index];
391       // Current thread releases the holding of reference frame.
392       decrease_ref_count(old_idx, frame_bufs, pool);
393 
394       // Release the reference frame in reference map.
395       if (mask & 1) {
396         decrease_ref_count(old_idx, frame_bufs, pool);
397       }
398       ++ref_index;
399     }
400 
401     // Current thread releases the holding of reference frame.
402     for (; ref_index < REF_FRAMES && !cm->show_existing_frame; ++ref_index) {
403       const int old_idx = cm->ref_frame_map[ref_index];
404       decrease_ref_count(old_idx, frame_bufs, pool);
405     }
406     pbi->hold_ref_buf = 0;
407   }
408 }
409 
vp9_receive_compressed_data(VP9Decoder * pbi,size_t size,const uint8_t ** psource)410 int vp9_receive_compressed_data(VP9Decoder *pbi, size_t size,
411                                 const uint8_t **psource) {
412   VP9_COMMON *volatile const cm = &pbi->common;
413   BufferPool *volatile const pool = cm->buffer_pool;
414   RefCntBuffer *volatile const frame_bufs = cm->buffer_pool->frame_bufs;
415   const uint8_t *source = *psource;
416   int retcode = 0;
417   cm->error.error_code = VPX_CODEC_OK;
418 
419   if (size == 0) {
420     // This is used to signal that we are missing frames.
421     // We do not know if the missing frame(s) was supposed to update
422     // any of the reference buffers, but we act conservative and
423     // mark only the last buffer as corrupted.
424     //
425     // TODO(jkoleszar): Error concealment is undefined and non-normative
426     // at this point, but if it becomes so, [0] may not always be the correct
427     // thing to do here.
428     if (cm->frame_refs[0].idx > 0) {
429       assert(cm->frame_refs[0].buf != NULL);
430       cm->frame_refs[0].buf->corrupted = 1;
431     }
432   }
433 
434   pbi->ready_for_new_data = 0;
435 
436   // Check if the previous frame was a frame without any references to it.
437   if (cm->new_fb_idx >= 0 && frame_bufs[cm->new_fb_idx].ref_count == 0 &&
438       !frame_bufs[cm->new_fb_idx].released) {
439     pool->release_fb_cb(pool->cb_priv,
440                         &frame_bufs[cm->new_fb_idx].raw_frame_buffer);
441     frame_bufs[cm->new_fb_idx].released = 1;
442   }
443 
444   // Find a free frame buffer. Return error if can not find any.
445   cm->new_fb_idx = get_free_fb(cm);
446   if (cm->new_fb_idx == INVALID_IDX) {
447     pbi->ready_for_new_data = 1;
448     release_fb_on_decoder_exit(pbi);
449     vpx_clear_system_state();
450     vpx_internal_error(&cm->error, VPX_CODEC_MEM_ERROR,
451                        "Unable to find free frame buffer");
452     return cm->error.error_code;
453   }
454 
455   // Assign a MV array to the frame buffer.
456   cm->cur_frame = &pool->frame_bufs[cm->new_fb_idx];
457 
458   pbi->hold_ref_buf = 0;
459   pbi->cur_buf = &frame_bufs[cm->new_fb_idx];
460 
461   if (setjmp(cm->error.jmp)) {
462     cm->error.setjmp = 0;
463     pbi->ready_for_new_data = 1;
464     release_fb_on_decoder_exit(pbi);
465     // Release current frame.
466     decrease_ref_count(cm->new_fb_idx, frame_bufs, pool);
467     vpx_clear_system_state();
468     return -1;
469   }
470 
471   cm->error.setjmp = 1;
472   vp9_decode_frame(pbi, source, source + size, psource);
473 
474   swap_frame_buffers(pbi);
475 
476   vpx_clear_system_state();
477 
478   if (!cm->show_existing_frame) {
479     cm->last_show_frame = cm->show_frame;
480     cm->prev_frame = cm->cur_frame;
481     if (cm->seg.enabled) vp9_swap_current_and_last_seg_map(cm);
482   }
483 
484   if (cm->show_frame) cm->cur_show_frame_fb_idx = cm->new_fb_idx;
485 
486   // Update progress in frame parallel decode.
487   cm->last_width = cm->width;
488   cm->last_height = cm->height;
489   if (cm->show_frame) {
490     cm->current_video_frame++;
491   }
492 
493   cm->error.setjmp = 0;
494   return retcode;
495 }
496 
vp9_get_raw_frame(VP9Decoder * pbi,YV12_BUFFER_CONFIG * sd,vp9_ppflags_t * flags)497 int vp9_get_raw_frame(VP9Decoder *pbi, YV12_BUFFER_CONFIG *sd,
498                       vp9_ppflags_t *flags) {
499   VP9_COMMON *const cm = &pbi->common;
500   int ret = -1;
501 #if !CONFIG_VP9_POSTPROC
502   (void)*flags;
503 #endif
504 
505   if (pbi->ready_for_new_data == 1) return ret;
506 
507   pbi->ready_for_new_data = 1;
508 
509   /* no raw frame to show!!! */
510   if (!cm->show_frame) return ret;
511 
512   pbi->ready_for_new_data = 1;
513 
514 #if CONFIG_VP9_POSTPROC
515   if (!cm->show_existing_frame) {
516     ret = vp9_post_proc_frame(cm, sd, flags, cm->width);
517   } else {
518     *sd = *cm->frame_to_show;
519     ret = 0;
520   }
521 #else
522   *sd = *cm->frame_to_show;
523   ret = 0;
524 #endif /*!CONFIG_POSTPROC*/
525   vpx_clear_system_state();
526   return ret;
527 }
528 
vp9_parse_superframe_index(const uint8_t * data,size_t data_sz,uint32_t sizes[8],int * count,vpx_decrypt_cb decrypt_cb,void * decrypt_state)529 vpx_codec_err_t vp9_parse_superframe_index(const uint8_t *data, size_t data_sz,
530                                            uint32_t sizes[8], int *count,
531                                            vpx_decrypt_cb decrypt_cb,
532                                            void *decrypt_state) {
533   // A chunk ending with a byte matching 0xc0 is an invalid chunk unless
534   // it is a super frame index. If the last byte of real video compression
535   // data is 0xc0 the encoder must add a 0 byte. If we have the marker but
536   // not the associated matching marker byte at the front of the index we have
537   // an invalid bitstream and need to return an error.
538 
539   uint8_t marker;
540 
541   assert(data_sz);
542   marker = read_marker(decrypt_cb, decrypt_state, data + data_sz - 1);
543   *count = 0;
544 
545   if ((marker & 0xe0) == 0xc0) {
546     const uint32_t frames = (marker & 0x7) + 1;
547     const uint32_t mag = ((marker >> 3) & 0x3) + 1;
548     const size_t index_sz = 2 + mag * frames;
549 
550     // This chunk is marked as having a superframe index but doesn't have
551     // enough data for it, thus it's an invalid superframe index.
552     if (data_sz < index_sz) return VPX_CODEC_CORRUPT_FRAME;
553 
554     {
555       const uint8_t marker2 =
556           read_marker(decrypt_cb, decrypt_state, data + data_sz - index_sz);
557 
558       // This chunk is marked as having a superframe index but doesn't have
559       // the matching marker byte at the front of the index therefore it's an
560       // invalid chunk.
561       if (marker != marker2) return VPX_CODEC_CORRUPT_FRAME;
562     }
563 
564     {
565       // Found a valid superframe index.
566       uint32_t i, j;
567       const uint8_t *x = &data[data_sz - index_sz + 1];
568 
569       // Frames has a maximum of 8 and mag has a maximum of 4.
570       uint8_t clear_buffer[32];
571       assert(sizeof(clear_buffer) >= frames * mag);
572       if (decrypt_cb) {
573         decrypt_cb(decrypt_state, x, clear_buffer, frames * mag);
574         x = clear_buffer;
575       }
576 
577       for (i = 0; i < frames; ++i) {
578         uint32_t this_sz = 0;
579 
580         for (j = 0; j < mag; ++j) this_sz |= ((uint32_t)(*x++)) << (j * 8);
581         sizes[i] = this_sz;
582       }
583       *count = frames;
584     }
585   }
586   return VPX_CODEC_OK;
587 }
588