flac_parser.c
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1 /*
2  * FLAC parser
3  * Copyright (c) 2010 Michael Chinen
4  *
5  * This file is part of Libav.
6  *
7  * Libav is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * Libav is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with Libav; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
35 #include "libavutil/crc.h"
36 #include "libavutil/fifo.h"
37 #include "bytestream.h"
38 #include "parser.h"
39 #include "flac.h"
40 
42 #define FLAC_MAX_SEQUENTIAL_HEADERS 3
43 
44 #define FLAC_MIN_HEADERS 10
45 
46 #define FLAC_AVG_FRAME_SIZE 8192
47 
49 #define FLAC_HEADER_BASE_SCORE 10
50 #define FLAC_HEADER_CHANGED_PENALTY 7
51 #define FLAC_HEADER_CRC_FAIL_PENALTY 50
52 #define FLAC_HEADER_NOT_PENALIZED_YET 100000
53 #define FLAC_HEADER_NOT_SCORED_YET -100000
54 
56 #define MAX_FRAME_HEADER_SIZE 16
57 
58 typedef struct FLACHeaderMarker {
59  int offset;
60  int *link_penalty;
62  int max_score;
72 
73 typedef struct FLACParseContext {
85  int end_padded;
86  uint8_t *wrap_buf;
89 
90 static int frame_header_is_valid(AVCodecContext *avctx, const uint8_t *buf,
91  FLACFrameInfo *fi)
92 {
93  GetBitContext gb;
94  init_get_bits(&gb, buf, MAX_FRAME_HEADER_SIZE * 8);
95  return !ff_flac_decode_frame_header(avctx, &gb, fi, 127);
96 }
97 
111 static uint8_t* flac_fifo_read_wrap(FLACParseContext *fpc, int offset, int len,
112  uint8_t** wrap_buf, int* allocated_size)
113 {
114  AVFifoBuffer *f = fpc->fifo_buf;
115  uint8_t *start = f->rptr + offset;
116  uint8_t *tmp_buf;
117 
118  if (start >= f->end)
119  start -= f->end - f->buffer;
120  if (f->end - start >= len)
121  return start;
122 
123  tmp_buf = av_fast_realloc(*wrap_buf, allocated_size, len);
124 
125  if (!tmp_buf) {
126  av_log(fpc->avctx, AV_LOG_ERROR,
127  "couldn't reallocate wrap buffer of size %d", len);
128  return NULL;
129  }
130  *wrap_buf = tmp_buf;
131  do {
132  int seg_len = FFMIN(f->end - start, len);
133  memcpy(tmp_buf, start, seg_len);
134  tmp_buf = (uint8_t*)tmp_buf + seg_len;
135 // memory barrier needed for SMP here in theory
136 
137  start += seg_len - (f->end - f->buffer);
138  len -= seg_len;
139  } while (len > 0);
140 
141  return *wrap_buf;
142 }
143 
151 static uint8_t* flac_fifo_read(FLACParseContext *fpc, int offset, int *len)
152 {
153  AVFifoBuffer *f = fpc->fifo_buf;
154  uint8_t *start = f->rptr + offset;
155 
156  if (start >= f->end)
157  start -= f->end - f->buffer;
158  *len = FFMIN(*len, f->end - start);
159  return start;
160 }
161 
162 static int find_headers_search_validate(FLACParseContext *fpc, int offset)
163 {
164  FLACFrameInfo fi;
165  uint8_t *header_buf;
166  int size = 0;
167  header_buf = flac_fifo_read_wrap(fpc, offset,
169  &fpc->wrap_buf,
171  if (frame_header_is_valid(fpc->avctx, header_buf, &fi)) {
172  FLACHeaderMarker **end_handle = &fpc->headers;
173  int i;
174 
175  size = 0;
176  while (*end_handle) {
177  end_handle = &(*end_handle)->next;
178  size++;
179  }
180 
181  *end_handle = av_mallocz(sizeof(FLACHeaderMarker));
182  if (!*end_handle) {
183  av_log(fpc->avctx, AV_LOG_ERROR,
184  "couldn't allocate FLACHeaderMarker\n");
185  return AVERROR(ENOMEM);
186  }
187  (*end_handle)->fi = fi;
188  (*end_handle)->offset = offset;
189  (*end_handle)->link_penalty = av_malloc(sizeof(int) *
191  for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++)
192  (*end_handle)->link_penalty[i] = FLAC_HEADER_NOT_PENALIZED_YET;
193 
194  fpc->nb_headers_found++;
195  size++;
196  }
197  return size;
198 }
199 
200 static int find_headers_search(FLACParseContext *fpc, uint8_t *buf, int buf_size,
201  int search_start)
202 
203 {
204  int size = 0, mod_offset = (buf_size - 1) % 4, i, j;
205  uint32_t x;
206 
207  for (i = 0; i < mod_offset; i++) {
208  if ((AV_RB16(buf + i) & 0xFFFE) == 0xFFF8)
209  size = find_headers_search_validate(fpc, search_start + i);
210  }
211 
212  for (; i < buf_size - 1; i += 4) {
213  x = AV_RB32(buf + i);
214  if (((x & ~(x + 0x01010101)) & 0x80808080)) {
215  for (j = 0; j < 4; j++) {
216  if ((AV_RB16(buf + i + j) & 0xFFFE) == 0xFFF8)
217  size = find_headers_search_validate(fpc, search_start + i + j);
218  }
219  }
220  }
221  return size;
222 }
223 
224 static int find_new_headers(FLACParseContext *fpc, int search_start)
225 {
226  FLACHeaderMarker *end;
227  int search_end, size = 0, read_len, temp;
228  uint8_t *buf;
229  fpc->nb_headers_found = 0;
230 
231  /* Search for a new header of at most 16 bytes. */
232  search_end = av_fifo_size(fpc->fifo_buf) - (MAX_FRAME_HEADER_SIZE - 1);
233  read_len = search_end - search_start + 1;
234  buf = flac_fifo_read(fpc, search_start, &read_len);
235  size = find_headers_search(fpc, buf, read_len, search_start);
236  search_start += read_len - 1;
237 
238  /* If fifo end was hit do the wrap around. */
239  if (search_start != search_end) {
240  uint8_t wrap[2];
241 
242  wrap[0] = buf[read_len - 1];
243  read_len = search_end - search_start + 1;
244 
245  /* search_start + 1 is the post-wrap offset in the fifo. */
246  buf = flac_fifo_read(fpc, search_start + 1, &read_len);
247  wrap[1] = buf[0];
248 
249  if ((AV_RB16(wrap) & 0xFFFE) == 0xFFF8) {
250  temp = find_headers_search_validate(fpc, search_start);
251  size = FFMAX(size, temp);
252  }
253  search_start++;
254 
255  /* Continue to do the last half of the wrap. */
256  temp = find_headers_search(fpc, buf, read_len, search_start);
257  size = FFMAX(size, temp);
258  search_start += read_len - 1;
259  }
260 
261  /* Return the size even if no new headers were found. */
262  if (!size && fpc->headers)
263  for (end = fpc->headers; end; end = end->next)
264  size++;
265  return size;
266 }
267 
269  FLACHeaderMarker *header,
270  FLACHeaderMarker *child,
271  int log_level_offset)
272 {
273  FLACFrameInfo *header_fi = &header->fi, *child_fi = &child->fi;
274  int deduction = 0, deduction_expected = 0, i;
275  if (child_fi->samplerate != header_fi->samplerate) {
276  deduction += FLAC_HEADER_CHANGED_PENALTY;
277  av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
278  "sample rate change detected in adjacent frames\n");
279  }
280  if (child_fi->bps != header_fi->bps) {
281  deduction += FLAC_HEADER_CHANGED_PENALTY;
282  av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
283  "bits per sample change detected in adjacent frames\n");
284  }
285  if (child_fi->is_var_size != header_fi->is_var_size) {
286  /* Changing blocking strategy not allowed per the spec */
287  deduction += FLAC_HEADER_BASE_SCORE;
288  av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
289  "blocking strategy change detected in adjacent frames\n");
290  }
291  if (child_fi->channels != header_fi->channels) {
292  deduction += FLAC_HEADER_CHANGED_PENALTY;
293  av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
294  "number of channels change detected in adjacent frames\n");
295  }
296  /* Check sample and frame numbers. */
297  if ((child_fi->frame_or_sample_num - header_fi->frame_or_sample_num
298  != header_fi->blocksize) &&
299  (child_fi->frame_or_sample_num
300  != header_fi->frame_or_sample_num + 1)) {
301  FLACHeaderMarker *curr;
302  int expected_frame_num, expected_sample_num;
303  /* If there are frames in the middle we expect this deduction,
304  as they are probably valid and this one follows it */
305 
306  expected_frame_num = expected_sample_num = header_fi->frame_or_sample_num;
307  curr = header;
308  while (curr != child) {
309  /* Ignore frames that failed all crc checks */
310  for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++) {
312  expected_frame_num++;
313  expected_sample_num += curr->fi.blocksize;
314  break;
315  }
316  }
317  curr = curr->next;
318  }
319 
320  if (expected_frame_num == child_fi->frame_or_sample_num ||
321  expected_sample_num == child_fi->frame_or_sample_num)
322  deduction_expected = deduction ? 0 : 1;
323 
324  deduction += FLAC_HEADER_CHANGED_PENALTY;
325  av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
326  "sample/frame number mismatch in adjacent frames\n");
327  }
328 
329  /* If we have suspicious headers, check the CRC between them */
330  if (deduction && !deduction_expected) {
331  FLACHeaderMarker *curr;
332  int read_len;
333  uint8_t *buf;
334  uint32_t crc = 1;
335  int inverted_test = 0;
336 
337  /* Since CRC is expensive only do it if we haven't yet.
338  This assumes a CRC penalty is greater than all other check penalties */
339  curr = header->next;
340  for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS && curr != child; i++)
341  curr = curr->next;
342 
343  if (header->link_penalty[i] < FLAC_HEADER_CRC_FAIL_PENALTY ||
345  FLACHeaderMarker *start, *end;
346 
347  /* Although overlapping chains are scored, the crc should never
348  have to be computed twice for a single byte. */
349  start = header;
350  end = child;
351  if (i > 0 &&
352  header->link_penalty[i - 1] >= FLAC_HEADER_CRC_FAIL_PENALTY) {
353  while (start->next != child)
354  start = start->next;
355  inverted_test = 1;
356  } else if (i > 0 &&
357  header->next->link_penalty[i-1] >=
359  end = header->next;
360  inverted_test = 1;
361  }
362 
363  read_len = end->offset - start->offset;
364  buf = flac_fifo_read(fpc, start->offset, &read_len);
365  crc = av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, buf, read_len);
366  read_len = (end->offset - start->offset) - read_len;
367 
368  if (read_len) {
369  buf = flac_fifo_read(fpc, end->offset - read_len, &read_len);
370  crc = av_crc(av_crc_get_table(AV_CRC_16_ANSI), crc, buf, read_len);
371  }
372  }
373 
374  if (!crc ^ !inverted_test) {
375  deduction += FLAC_HEADER_CRC_FAIL_PENALTY;
376  av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
377  "crc check failed from offset %i (frame %"PRId64") to %i (frame %"PRId64")\n",
378  header->offset, header_fi->frame_or_sample_num,
379  child->offset, child_fi->frame_or_sample_num);
380  }
381  }
382  return deduction;
383 }
384 
396 {
397  FLACHeaderMarker *child;
398  int dist = 0;
399  int child_score;
400 
401  if (header->max_score != FLAC_HEADER_NOT_SCORED_YET)
402  return header->max_score;
403 
405 
406  /* Check and compute the children's scores. */
407  child = header->next;
408  for (dist = 0; dist < FLAC_MAX_SEQUENTIAL_HEADERS && child; dist++) {
409  /* Look at the child's frame header info and penalize suspicious
410  changes between the headers. */
411  if (header->link_penalty[dist] == FLAC_HEADER_NOT_PENALIZED_YET) {
412  header->link_penalty[dist] = check_header_mismatch(fpc, header,
413  child, AV_LOG_DEBUG);
414  }
415  child_score = score_header(fpc, child) - header->link_penalty[dist];
416 
417  if (FLAC_HEADER_BASE_SCORE + child_score > header->max_score) {
418  /* Keep the child because the frame scoring is dynamic. */
419  header->best_child = child;
420  header->max_score = FLAC_HEADER_BASE_SCORE + child_score;
421  }
422  child = child->next;
423  }
424 
425  return header->max_score;
426 }
427 
429 {
430  FLACHeaderMarker *curr;
431  int best_score = FLAC_HEADER_NOT_SCORED_YET;
432  /* First pass to clear all old scores. */
433  for (curr = fpc->headers; curr; curr = curr->next)
435 
436  /* Do a second pass to score them all. */
437  for (curr = fpc->headers; curr; curr = curr->next) {
438  if (score_header(fpc, curr) > best_score) {
439  fpc->best_header = curr;
440  best_score = curr->max_score;
441  }
442  }
443 }
444 
445 static int get_best_header(FLACParseContext* fpc, const uint8_t **poutbuf,
446  int *poutbuf_size)
447 {
448  FLACHeaderMarker *header = fpc->best_header;
449  FLACHeaderMarker *child = header->best_child;
450  if (!child) {
451  *poutbuf_size = av_fifo_size(fpc->fifo_buf) - header->offset;
452  } else {
453  *poutbuf_size = child->offset - header->offset;
454 
455  /* If the child has suspicious changes, log them */
456  check_header_mismatch(fpc, header, child, 0);
457  }
458 
459  fpc->avctx->sample_rate = header->fi.samplerate;
460  fpc->avctx->channels = header->fi.channels;
461  fpc->avctx->frame_size = header->fi.blocksize;
462  *poutbuf = flac_fifo_read_wrap(fpc, header->offset, *poutbuf_size,
463  &fpc->wrap_buf,
465 
466  fpc->best_header_valid = 0;
467  /* Return the negative overread index so the client can compute pos.
468  This should be the amount overread to the beginning of the child */
469  if (child)
470  return child->offset - av_fifo_size(fpc->fifo_buf);
471  return 0;
472 }
473 
475  const uint8_t **poutbuf, int *poutbuf_size,
476  const uint8_t *buf, int buf_size)
477 {
478  FLACParseContext *fpc = s->priv_data;
479  FLACHeaderMarker *curr;
480  int nb_headers;
481  const uint8_t *read_end = buf;
482  const uint8_t *read_start = buf;
483 
485  FLACFrameInfo fi;
486  if (frame_header_is_valid(avctx, buf, &fi))
487  avctx->frame_size = fi.blocksize;
488  *poutbuf = buf;
489  *poutbuf_size = buf_size;
490  return buf_size;
491  }
492 
493  fpc->avctx = avctx;
494  if (fpc->best_header_valid)
495  return get_best_header(fpc, poutbuf, poutbuf_size);
496 
497  /* If a best_header was found last call remove it with the buffer data. */
498  if (fpc->best_header && fpc->best_header->best_child) {
499  FLACHeaderMarker *temp;
500  FLACHeaderMarker *best_child = fpc->best_header->best_child;
501 
502  /* Remove headers in list until the end of the best_header. */
503  for (curr = fpc->headers; curr != best_child; curr = temp) {
504  if (curr != fpc->best_header) {
505  av_log(avctx, AV_LOG_DEBUG,
506  "dropping low score %i frame header from offset %i to %i\n",
507  curr->max_score, curr->offset, curr->next->offset);
508  }
509  temp = curr->next;
510  av_freep(&curr->link_penalty);
511  av_free(curr);
512  fpc->nb_headers_buffered--;
513  }
514  /* Release returned data from ring buffer. */
515  av_fifo_drain(fpc->fifo_buf, best_child->offset);
516 
517  /* Fix the offset for the headers remaining to match the new buffer. */
518  for (curr = best_child->next; curr; curr = curr->next)
519  curr->offset -= best_child->offset;
520 
521  fpc->nb_headers_buffered--;
522  best_child->offset = 0;
523  fpc->headers = best_child;
525  fpc->best_header = best_child;
526  return get_best_header(fpc, poutbuf, poutbuf_size);
527  }
528  fpc->best_header = NULL;
529  } else if (fpc->best_header) {
530  /* No end frame no need to delete the buffer; probably eof */
531  FLACHeaderMarker *temp;
532 
533  for (curr = fpc->headers; curr != fpc->best_header; curr = temp) {
534  temp = curr->next;
535  av_freep(&curr->link_penalty);
536  av_free(curr);
537  }
538  fpc->headers = fpc->best_header->next;
540  av_freep(&fpc->best_header);
541  }
542 
543  /* Find and score new headers. */
544  while ((buf && read_end < buf + buf_size &&
546  || (!buf && !fpc->end_padded)) {
547  int start_offset;
548 
549  /* Pad the end once if EOF, to check the final region for headers. */
550  if (!buf) {
551  fpc->end_padded = 1;
552  buf_size = MAX_FRAME_HEADER_SIZE;
553  read_end = read_start + MAX_FRAME_HEADER_SIZE;
554  } else {
555  /* The maximum read size is the upper-bound of what the parser
556  needs to have the required number of frames buffered */
557  int nb_desired = FLAC_MIN_HEADERS - fpc->nb_headers_buffered + 1;
558  read_end = read_end + FFMIN(buf + buf_size - read_end,
559  nb_desired * FLAC_AVG_FRAME_SIZE);
560  }
561 
562  /* Fill the buffer. */
563  if (av_fifo_realloc2(fpc->fifo_buf,
564  (read_end - read_start) + av_fifo_size(fpc->fifo_buf)) < 0) {
565  av_log(avctx, AV_LOG_ERROR,
566  "couldn't reallocate buffer of size %td\n",
567  (read_end - read_start) + av_fifo_size(fpc->fifo_buf));
568  goto handle_error;
569  }
570 
571  if (buf) {
572  av_fifo_generic_write(fpc->fifo_buf, (void*) read_start,
573  read_end - read_start, NULL);
574  } else {
575  int8_t pad[MAX_FRAME_HEADER_SIZE];
576  memset(pad, 0, sizeof(pad));
577  av_fifo_generic_write(fpc->fifo_buf, (void*) pad, sizeof(pad), NULL);
578  }
579 
580  /* Tag headers and update sequences. */
581  start_offset = av_fifo_size(fpc->fifo_buf) -
582  ((read_end - read_start) + (MAX_FRAME_HEADER_SIZE - 1));
583  start_offset = FFMAX(0, start_offset);
584  nb_headers = find_new_headers(fpc, start_offset);
585 
586  if (nb_headers < 0) {
587  av_log(avctx, AV_LOG_ERROR,
588  "find_new_headers couldn't allocate FLAC header\n");
589  goto handle_error;
590  }
591 
592  fpc->nb_headers_buffered = nb_headers;
593  /* Wait till FLAC_MIN_HEADERS to output a valid frame. */
594  if (!fpc->end_padded && fpc->nb_headers_buffered < FLAC_MIN_HEADERS) {
595  if (buf && read_end < buf + buf_size) {
596  read_start = read_end;
597  continue;
598  } else {
599  goto handle_error;
600  }
601  }
602 
603  /* If headers found, update the scores since we have longer chains. */
604  if (fpc->end_padded || fpc->nb_headers_found)
605  score_sequences(fpc);
606 
607  /* restore the state pre-padding */
608  if (fpc->end_padded) {
609  /* HACK: drain the tail of the fifo */
612  if (fpc->fifo_buf->wptr < 0) {
613  fpc->fifo_buf->wptr += fpc->fifo_buf->end -
614  fpc->fifo_buf->buffer;
615  }
616  buf_size = 0;
617  read_start = read_end = NULL;
618  }
619  }
620 
621  curr = fpc->headers;
622  for (curr = fpc->headers; curr; curr = curr->next)
623  if (!fpc->best_header || curr->max_score > fpc->best_header->max_score)
624  fpc->best_header = curr;
625 
626  if (fpc->best_header) {
627  fpc->best_header_valid = 1;
628  if (fpc->best_header->offset > 0) {
629  /* Output a junk frame. */
630  av_log(avctx, AV_LOG_DEBUG, "Junk frame till offset %i\n",
631  fpc->best_header->offset);
632 
633  /* Set frame_size to 0. It is unknown or invalid in a junk frame. */
634  avctx->frame_size = 0;
635  *poutbuf_size = fpc->best_header->offset;
636  *poutbuf = flac_fifo_read_wrap(fpc, 0, *poutbuf_size,
637  &fpc->wrap_buf,
639  return buf_size ? (read_end - buf) : (fpc->best_header->offset -
640  av_fifo_size(fpc->fifo_buf));
641  }
642  if (!buf_size)
643  return get_best_header(fpc, poutbuf, poutbuf_size);
644  }
645 
646 handle_error:
647  *poutbuf = NULL;
648  *poutbuf_size = 0;
649  return read_end - buf;
650 }
651 
653 {
654  FLACParseContext *fpc = c->priv_data;
655  /* There will generally be FLAC_MIN_HEADERS buffered in the fifo before
656  it drains. This is allocated early to avoid slow reallocation. */
658  return 0;
659 }
660 
662 {
663  FLACParseContext *fpc = c->priv_data;
664  FLACHeaderMarker *curr = fpc->headers, *temp;
665 
666  while (curr) {
667  temp = curr->next;
668  av_freep(&curr->link_penalty);
669  av_free(curr);
670  curr = temp;
671  }
672  av_fifo_free(fpc->fifo_buf);
673  av_free(fpc->wrap_buf);
674 }
675 
677  .codec_ids = { CODEC_ID_FLAC },
678  .priv_data_size = sizeof(FLACParseContext),
679  .parser_init = flac_parse_init,
680  .parser_parse = flac_parse,
681  .parser_close = flac_parse_close,
682 };