Libav
alac.c
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1 /*
2  * ALAC (Apple Lossless Audio Codec) decoder
3  * Copyright (c) 2005 David Hammerton
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 
49 #include "avcodec.h"
50 #include "get_bits.h"
51 #include "bytestream.h"
52 #include "internal.h"
53 #include "unary.h"
54 #include "mathops.h"
55 #include "alac_data.h"
56 
57 #define ALAC_EXTRADATA_SIZE 36
58 
59 typedef struct {
62  int channels;
63 
64  int32_t *predict_error_buffer[2];
65  int32_t *output_samples_buffer[2];
66  int32_t *extra_bits_buffer[2];
67 
73 
74  int extra_bits;
75  int nb_samples;
76 } ALACContext;
77 
78 static inline unsigned int decode_scalar(GetBitContext *gb, int k, int bps)
79 {
80  unsigned int x = get_unary_0_9(gb);
81 
82  if (x > 8) { /* RICE THRESHOLD */
83  /* use alternative encoding */
84  x = get_bits_long(gb, bps);
85  } else if (k != 1) {
86  int extrabits = show_bits(gb, k);
87 
88  /* multiply x by 2^k - 1, as part of their strange algorithm */
89  x = (x << k) - x;
90 
91  if (extrabits > 1) {
92  x += extrabits - 1;
93  skip_bits(gb, k);
94  } else
95  skip_bits(gb, k - 1);
96  }
97  return x;
98 }
99 
101  int nb_samples, int bps, int rice_history_mult)
102 {
103  int i;
104  unsigned int history = alac->rice_initial_history;
105  int sign_modifier = 0;
106 
107  for (i = 0; i < nb_samples; i++) {
108  int k;
109  unsigned int x;
110 
111  /* calculate rice param and decode next value */
112  k = av_log2((history >> 9) + 3);
113  k = FFMIN(k, alac->rice_limit);
114  x = decode_scalar(&alac->gb, k, bps);
115  x += sign_modifier;
116  sign_modifier = 0;
117  output_buffer[i] = (x >> 1) ^ -(x & 1);
118 
119  /* update the history */
120  if (x > 0xffff)
121  history = 0xffff;
122  else
123  history += x * rice_history_mult -
124  ((history * rice_history_mult) >> 9);
125 
126  /* special case: there may be compressed blocks of 0 */
127  if ((history < 128) && (i + 1 < nb_samples)) {
128  int block_size;
129 
130  /* calculate rice param and decode block size */
131  k = 7 - av_log2(history) + ((history + 16) >> 6);
132  k = FFMIN(k, alac->rice_limit);
133  block_size = decode_scalar(&alac->gb, k, 16);
134 
135  if (block_size > 0) {
136  if (block_size >= nb_samples - i) {
137  av_log(alac->avctx, AV_LOG_ERROR,
138  "invalid zero block size of %d %d %d\n", block_size,
139  nb_samples, i);
140  block_size = nb_samples - i - 1;
141  }
142  memset(&output_buffer[i + 1], 0,
143  block_size * sizeof(*output_buffer));
144  i += block_size;
145  }
146  if (block_size <= 0xffff)
147  sign_modifier = 1;
148  history = 0;
149  }
150  }
151 }
152 
153 static inline int sign_only(int v)
154 {
155  return v ? FFSIGN(v) : 0;
156 }
157 
158 static void lpc_prediction(int32_t *error_buffer, int32_t *buffer_out,
159  int nb_samples, int bps, int16_t *lpc_coefs,
160  int lpc_order, int lpc_quant)
161 {
162  int i;
163  int32_t *pred = buffer_out;
164 
165  /* first sample always copies */
166  *buffer_out = *error_buffer;
167 
168  if (nb_samples <= 1)
169  return;
170 
171  if (!lpc_order) {
172  memcpy(&buffer_out[1], &error_buffer[1],
173  (nb_samples - 1) * sizeof(*buffer_out));
174  return;
175  }
176 
177  if (lpc_order == 31) {
178  /* simple 1st-order prediction */
179  for (i = 1; i < nb_samples; i++) {
180  buffer_out[i] = sign_extend(buffer_out[i - 1] + error_buffer[i],
181  bps);
182  }
183  return;
184  }
185 
186  /* read warm-up samples */
187  for (i = 1; i <= lpc_order; i++)
188  buffer_out[i] = sign_extend(buffer_out[i - 1] + error_buffer[i], bps);
189 
190  /* NOTE: 4 and 8 are very common cases that could be optimized. */
191 
192  for (; i < nb_samples; i++) {
193  int j;
194  int val = 0;
195  int error_val = error_buffer[i];
196  int error_sign;
197  int d = *pred++;
198 
199  /* LPC prediction */
200  for (j = 0; j < lpc_order; j++)
201  val += (pred[j] - d) * lpc_coefs[j];
202  val = (val + (1 << (lpc_quant - 1))) >> lpc_quant;
203  val += d + error_val;
204  buffer_out[i] = sign_extend(val, bps);
205 
206  /* adapt LPC coefficients */
207  error_sign = sign_only(error_val);
208  if (error_sign) {
209  for (j = 0; j < lpc_order && error_val * error_sign > 0; j++) {
210  int sign;
211  val = d - pred[j];
212  sign = sign_only(val) * error_sign;
213  lpc_coefs[j] -= sign;
214  val *= sign;
215  error_val -= (val >> lpc_quant) * (j + 1);
216  }
217  }
218  }
219 }
220 
221 static void decorrelate_stereo(int32_t *buffer[2], int nb_samples,
222  int decorr_shift, int decorr_left_weight)
223 {
224  int i;
225 
226  for (i = 0; i < nb_samples; i++) {
227  int32_t a, b;
228 
229  a = buffer[0][i];
230  b = buffer[1][i];
231 
232  a -= (b * decorr_left_weight) >> decorr_shift;
233  b += a;
234 
235  buffer[0][i] = b;
236  buffer[1][i] = a;
237  }
238 }
239 
240 static void append_extra_bits(int32_t *buffer[2], int32_t *extra_bits_buffer[2],
241  int extra_bits, int channels, int nb_samples)
242 {
243  int i, ch;
244 
245  for (ch = 0; ch < channels; ch++)
246  for (i = 0; i < nb_samples; i++)
247  buffer[ch][i] = (buffer[ch][i] << extra_bits) | extra_bits_buffer[ch][i];
248 }
249 
250 static int decode_element(AVCodecContext *avctx, AVFrame *frame, int ch_index,
251  int channels)
252 {
253  ALACContext *alac = avctx->priv_data;
254  int has_size, bps, is_compressed, decorr_shift, decorr_left_weight, ret;
255  uint32_t output_samples;
256  int i, ch;
257 
258  skip_bits(&alac->gb, 4); /* element instance tag */
259  skip_bits(&alac->gb, 12); /* unused header bits */
260 
261  /* the number of output samples is stored in the frame */
262  has_size = get_bits1(&alac->gb);
263 
264  alac->extra_bits = get_bits(&alac->gb, 2) << 3;
265  bps = alac->sample_size - alac->extra_bits + channels - 1;
266  if (bps > 32) {
267  av_log(avctx, AV_LOG_ERROR, "bps is unsupported: %d\n", bps);
268  return AVERROR_PATCHWELCOME;
269  }
270 
271  /* whether the frame is compressed */
272  is_compressed = !get_bits1(&alac->gb);
273 
274  if (has_size)
275  output_samples = get_bits_long(&alac->gb, 32);
276  else
277  output_samples = alac->max_samples_per_frame;
278  if (!output_samples || output_samples > alac->max_samples_per_frame) {
279  av_log(avctx, AV_LOG_ERROR, "invalid samples per frame: %d\n",
280  output_samples);
281  return AVERROR_INVALIDDATA;
282  }
283  if (!alac->nb_samples) {
284  /* get output buffer */
285  frame->nb_samples = output_samples;
286  if ((ret = ff_get_buffer(avctx, frame, 0)) < 0) {
287  av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
288  return ret;
289  }
290  } else if (output_samples != alac->nb_samples) {
291  av_log(avctx, AV_LOG_ERROR, "sample count mismatch: %u != %d\n",
292  output_samples, alac->nb_samples);
293  return AVERROR_INVALIDDATA;
294  }
295  alac->nb_samples = output_samples;
296  if (alac->sample_size > 16) {
297  for (ch = 0; ch < channels; ch++)
298  alac->output_samples_buffer[ch] = (int32_t *)frame->extended_data[ch_index + ch];
299  }
300 
301  if (is_compressed) {
302  int16_t lpc_coefs[2][32];
303  int lpc_order[2];
304  int prediction_type[2];
305  int lpc_quant[2];
306  int rice_history_mult[2];
307 
308  decorr_shift = get_bits(&alac->gb, 8);
309  decorr_left_weight = get_bits(&alac->gb, 8);
310 
311  for (ch = 0; ch < channels; ch++) {
312  prediction_type[ch] = get_bits(&alac->gb, 4);
313  lpc_quant[ch] = get_bits(&alac->gb, 4);
314  rice_history_mult[ch] = get_bits(&alac->gb, 3);
315  lpc_order[ch] = get_bits(&alac->gb, 5);
316 
317  if (lpc_order[ch] >= alac->max_samples_per_frame)
318  return AVERROR_INVALIDDATA;
319 
320  /* read the predictor table */
321  for (i = lpc_order[ch] - 1; i >= 0; i--)
322  lpc_coefs[ch][i] = get_sbits(&alac->gb, 16);
323  }
324 
325  if (alac->extra_bits) {
326  for (i = 0; i < alac->nb_samples; i++) {
327  for (ch = 0; ch < channels; ch++)
328  alac->extra_bits_buffer[ch][i] = get_bits(&alac->gb, alac->extra_bits);
329  }
330  }
331  for (ch = 0; ch < channels; ch++) {
332  rice_decompress(alac, alac->predict_error_buffer[ch],
333  alac->nb_samples, bps,
334  rice_history_mult[ch] * alac->rice_history_mult / 4);
335 
336  /* adaptive FIR filter */
337  if (prediction_type[ch] == 15) {
338  /* Prediction type 15 runs the adaptive FIR twice.
339  * The first pass uses the special-case coef_num = 31, while
340  * the second pass uses the coefs from the bitstream.
341  *
342  * However, this prediction type is not currently used by the
343  * reference encoder.
344  */
346  alac->predict_error_buffer[ch],
347  alac->nb_samples, bps, NULL, 31, 0);
348  } else if (prediction_type[ch] > 0) {
349  av_log(avctx, AV_LOG_WARNING, "unknown prediction type: %i\n",
350  prediction_type[ch]);
351  }
353  alac->output_samples_buffer[ch], alac->nb_samples,
354  bps, lpc_coefs[ch], lpc_order[ch], lpc_quant[ch]);
355  }
356  } else {
357  /* not compressed, easy case */
358  for (i = 0; i < alac->nb_samples; i++) {
359  for (ch = 0; ch < channels; ch++) {
360  alac->output_samples_buffer[ch][i] =
361  get_sbits_long(&alac->gb, alac->sample_size);
362  }
363  }
364  alac->extra_bits = 0;
365  decorr_shift = 0;
366  decorr_left_weight = 0;
367  }
368 
369  if (channels == 2 && decorr_left_weight) {
371  decorr_shift, decorr_left_weight);
372  }
373 
374  if (alac->extra_bits) {
376  alac->extra_bits, channels, alac->nb_samples);
377  }
378 
379  switch(alac->sample_size) {
380  case 16: {
381  for (ch = 0; ch < channels; ch++) {
382  int16_t *outbuffer = (int16_t *)frame->extended_data[ch_index + ch];
383  for (i = 0; i < alac->nb_samples; i++)
384  *outbuffer++ = alac->output_samples_buffer[ch][i];
385  }}
386  break;
387  case 24: {
388  for (ch = 0; ch < channels; ch++) {
389  for (i = 0; i < alac->nb_samples; i++)
390  alac->output_samples_buffer[ch][i] <<= 8;
391  }}
392  break;
393  }
394 
395  return 0;
396 }
397 
398 static int alac_decode_frame(AVCodecContext *avctx, void *data,
399  int *got_frame_ptr, AVPacket *avpkt)
400 {
401  ALACContext *alac = avctx->priv_data;
402  AVFrame *frame = data;
403  enum AlacRawDataBlockType element;
404  int channels;
405  int ch, ret, got_end;
406 
407  init_get_bits(&alac->gb, avpkt->data, avpkt->size * 8);
408 
409  got_end = 0;
410  alac->nb_samples = 0;
411  ch = 0;
412  while (get_bits_left(&alac->gb) >= 3) {
413  element = get_bits(&alac->gb, 3);
414  if (element == TYPE_END) {
415  got_end = 1;
416  break;
417  }
418  if (element > TYPE_CPE && element != TYPE_LFE) {
419  av_log(avctx, AV_LOG_ERROR, "syntax element unsupported: %d", element);
420  return AVERROR_PATCHWELCOME;
421  }
422 
423  channels = (element == TYPE_CPE) ? 2 : 1;
424  if (ch + channels > alac->channels ||
425  ff_alac_channel_layout_offsets[alac->channels - 1][ch] + channels > alac->channels) {
426  av_log(avctx, AV_LOG_ERROR, "invalid element channel count\n");
427  return AVERROR_INVALIDDATA;
428  }
429 
430  ret = decode_element(avctx, frame,
432  channels);
433  if (ret < 0 && get_bits_left(&alac->gb))
434  return ret;
435 
436  ch += channels;
437  }
438  if (!got_end) {
439  av_log(avctx, AV_LOG_ERROR, "no end tag found. incomplete packet.\n");
440  return AVERROR_INVALIDDATA;
441  }
442 
443  if (avpkt->size * 8 - get_bits_count(&alac->gb) > 8) {
444  av_log(avctx, AV_LOG_ERROR, "Error : %d bits left\n",
445  avpkt->size * 8 - get_bits_count(&alac->gb));
446  }
447 
448  *got_frame_ptr = 1;
449 
450  return avpkt->size;
451 }
452 
454 {
455  ALACContext *alac = avctx->priv_data;
456 
457  int ch;
458  for (ch = 0; ch < FFMIN(alac->channels, 2); ch++) {
459  av_freep(&alac->predict_error_buffer[ch]);
460  if (alac->sample_size == 16)
461  av_freep(&alac->output_samples_buffer[ch]);
462  av_freep(&alac->extra_bits_buffer[ch]);
463  }
464 
465  return 0;
466 }
467 
468 static int allocate_buffers(ALACContext *alac)
469 {
470  int ch;
471  int buf_size = alac->max_samples_per_frame * sizeof(int32_t);
472 
473  for (ch = 0; ch < FFMIN(alac->channels, 2); ch++) {
475  buf_size, buf_alloc_fail);
476 
477  if (alac->sample_size == 16) {
479  buf_size, buf_alloc_fail);
480  }
481 
482  FF_ALLOC_OR_GOTO(alac->avctx, alac->extra_bits_buffer[ch],
483  buf_size, buf_alloc_fail);
484  }
485  return 0;
486 buf_alloc_fail:
487  alac_decode_close(alac->avctx);
488  return AVERROR(ENOMEM);
489 }
490 
491 static int alac_set_info(ALACContext *alac)
492 {
493  GetByteContext gb;
494 
495  bytestream2_init(&gb, alac->avctx->extradata,
496  alac->avctx->extradata_size);
497 
498  bytestream2_skipu(&gb, 12); // size:4, alac:4, version:4
499 
500  alac->max_samples_per_frame = bytestream2_get_be32u(&gb);
501  if (!alac->max_samples_per_frame ||
502  alac->max_samples_per_frame > INT_MAX / sizeof(int32_t)) {
503  av_log(alac->avctx, AV_LOG_ERROR, "max samples per frame invalid: %u\n",
504  alac->max_samples_per_frame);
505  return AVERROR_INVALIDDATA;
506  }
507  bytestream2_skipu(&gb, 1); // compatible version
508  alac->sample_size = bytestream2_get_byteu(&gb);
509  alac->rice_history_mult = bytestream2_get_byteu(&gb);
510  alac->rice_initial_history = bytestream2_get_byteu(&gb);
511  alac->rice_limit = bytestream2_get_byteu(&gb);
512  alac->channels = bytestream2_get_byteu(&gb);
513  bytestream2_get_be16u(&gb); // maxRun
514  bytestream2_get_be32u(&gb); // max coded frame size
515  bytestream2_get_be32u(&gb); // average bitrate
516  bytestream2_get_be32u(&gb); // samplerate
517 
518  return 0;
519 }
520 
522 {
523  int ret;
524  ALACContext *alac = avctx->priv_data;
525  alac->avctx = avctx;
526 
527  /* initialize from the extradata */
529  av_log(avctx, AV_LOG_ERROR, "alac: extradata is too small\n");
530  return AVERROR_INVALIDDATA;
531  }
532  if (alac_set_info(alac)) {
533  av_log(avctx, AV_LOG_ERROR, "alac: set_info failed\n");
534  return -1;
535  }
536 
537  switch (alac->sample_size) {
538  case 16: avctx->sample_fmt = AV_SAMPLE_FMT_S16P;
539  break;
540  case 24:
541  case 32: avctx->sample_fmt = AV_SAMPLE_FMT_S32P;
542  break;
543  default: avpriv_request_sample(avctx, "Sample depth %d", alac->sample_size);
544  return AVERROR_PATCHWELCOME;
545  }
546  avctx->bits_per_raw_sample = alac->sample_size;
547 
548  if (alac->channels < 1) {
549  av_log(avctx, AV_LOG_WARNING, "Invalid channel count\n");
550  alac->channels = avctx->channels;
551  } else {
552  if (alac->channels > ALAC_MAX_CHANNELS)
553  alac->channels = avctx->channels;
554  else
555  avctx->channels = alac->channels;
556  }
557  if (avctx->channels > ALAC_MAX_CHANNELS) {
558  av_log(avctx, AV_LOG_ERROR, "Unsupported channel count: %d\n",
559  avctx->channels);
560  return AVERROR_PATCHWELCOME;
561  }
562  avctx->channel_layout = ff_alac_channel_layouts[alac->channels - 1];
563 
564  if ((ret = allocate_buffers(alac)) < 0) {
565  av_log(avctx, AV_LOG_ERROR, "Error allocating buffers\n");
566  return ret;
567  }
568 
569  return 0;
570 }
571 
573  .name = "alac",
574  .long_name = NULL_IF_CONFIG_SMALL("ALAC (Apple Lossless Audio Codec)"),
575  .type = AVMEDIA_TYPE_AUDIO,
576  .id = AV_CODEC_ID_ALAC,
577  .priv_data_size = sizeof(ALACContext),
581  .capabilities = CODEC_CAP_DR1,
582 };