2 * ALAC (Apple Lossless Audio Codec) decoder
3 * Copyright (c) 2005 David Hammerton
5 * This file is part of FFmpeg.
7 * FFmpeg 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
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14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 * ALAC (Apple Lossless Audio Codec) decoder
25 * @author 2005 David Hammerton
27 * For more information on the ALAC format, visit:
28 * http://crazney.net/programs/itunes/alac.html
30 * Note: This decoder expects a 36- (0x24-)byte QuickTime atom to be
31 * passed through the extradata[_size] fields. This atom is tacked onto
32 * the end of an 'alac' stsd atom and has the following format:
33 * bytes 0-3 atom size (0x24), big-endian
34 * bytes 4-7 atom type ('alac', not the 'alac' tag from start of stsd)
35 * bytes 8-35 data bytes needed by decoder
41 * 32bit max sample per frame
45 * 8bit initial history
49 * 32bit max coded frame size
56 #include "bitstream.h"
57 #include "bytestream.h"
59 #define ALAC_EXTRADATA_SIZE 36
60 #define MAX_CHANNELS 2
64 AVCodecContext *avctx;
66 /* init to 0; first frame decode should initialize from extradata and
68 int context_initialized;
75 int32_t *predicterror_buffer[MAX_CHANNELS];
77 int32_t *outputsamples_buffer[MAX_CHANNELS];
79 /* stuff from setinfo */
80 uint32_t setinfo_max_samples_per_frame; /* 0x1000 = 4096 */ /* max samples per frame? */
81 uint8_t setinfo_7a; /* 0x00 */
82 uint8_t setinfo_sample_size; /* 0x10 */
83 uint8_t setinfo_rice_historymult; /* 0x28 */
84 uint8_t setinfo_rice_initialhistory; /* 0x0a */
85 uint8_t setinfo_rice_kmodifier; /* 0x0e */
86 uint8_t setinfo_7f; /* 0x02 */
87 uint16_t setinfo_80; /* 0x00ff */
88 uint32_t setinfo_82; /* 0x000020e7 */ /* max sample size?? */
89 uint32_t setinfo_86; /* 0x00069fe4 */ /* bit rate (average)?? */
90 uint32_t setinfo_8a_rate; /* 0x0000ac44 */
91 /* end setinfo stuff */
95 static void allocate_buffers(ALACContext *alac)
98 for (chan = 0; chan < MAX_CHANNELS; chan++) {
99 alac->predicterror_buffer[chan] =
100 av_malloc(alac->setinfo_max_samples_per_frame * 4);
102 alac->outputsamples_buffer[chan] =
103 av_malloc(alac->setinfo_max_samples_per_frame * 4);
107 static int alac_set_info(ALACContext *alac)
109 unsigned char *ptr = alac->avctx->extradata;
115 if(AV_RB32(ptr) >= UINT_MAX/4){
116 av_log(alac->avctx, AV_LOG_ERROR, "setinfo_max_samples_per_frame too large\n");
120 /* buffer size / 2 ? */
121 alac->setinfo_max_samples_per_frame = bytestream_get_be32(&ptr);
122 alac->setinfo_7a = *ptr++;
123 alac->setinfo_sample_size = *ptr++;
124 alac->setinfo_rice_historymult = *ptr++;
125 alac->setinfo_rice_initialhistory = *ptr++;
126 alac->setinfo_rice_kmodifier = *ptr++;
128 alac->setinfo_7f = *ptr++;
129 alac->setinfo_80 = bytestream_get_be16(&ptr);
130 /* max coded frame size */
131 alac->setinfo_82 = bytestream_get_be32(&ptr);
133 alac->setinfo_86 = bytestream_get_be32(&ptr);
135 alac->setinfo_8a_rate = bytestream_get_be32(&ptr);
137 allocate_buffers(alac);
142 static inline int count_leading_zeros(int32_t input)
144 return 31-av_log2(input);
147 static void bastardized_rice_decompress(ALACContext *alac,
148 int32_t *output_buffer,
150 int readsamplesize, /* arg_10 */
151 int rice_initialhistory, /* arg424->b */
152 int rice_kmodifier, /* arg424->d */
153 int rice_historymult, /* arg424->c */
154 int rice_kmodifier_mask /* arg424->e */
158 unsigned int history = rice_initialhistory;
159 int sign_modifier = 0;
161 for (output_count = 0; output_count < output_size; output_count++) {
166 /* read x - number of 1s before 0 represent the rice */
167 while (x <= 8 && get_bits1(&alac->gb)) {
171 if (x > 8) { /* RICE THRESHOLD */
172 /* use alternative encoding */
175 value = get_bits(&alac->gb, readsamplesize);
177 /* mask value to readsamplesize size */
178 if (readsamplesize != 32)
179 value &= (0xffffffff >> (32 - readsamplesize));
183 /* standard rice encoding */
185 int k; /* size of extra bits */
187 /* read k, that is bits as is */
188 k = 31 - rice_kmodifier - count_leading_zeros((history >> 9) + 3);
196 extrabits = show_bits(&alac->gb, k);
198 /* multiply x by 2^k - 1, as part of their strange algorithm */
203 skip_bits(&alac->gb, k);
205 skip_bits(&alac->gb, k - 1);
209 x_modified = sign_modifier + x;
210 final_val = (x_modified + 1) / 2;
211 if (x_modified & 1) final_val *= -1;
213 output_buffer[output_count] = final_val;
217 /* now update the history */
218 history += x_modified * rice_historymult
219 - ((history * rice_historymult) >> 9);
221 if (x_modified > 0xffff)
224 /* special case: there may be compressed blocks of 0 */
225 if ((history < 128) && (output_count+1 < output_size)) {
231 while (x <= 8 && get_bits1(&alac->gb)) {
236 block_size = get_bits(&alac->gb, 16);
237 block_size &= 0xffff;
242 k = count_leading_zeros(history) + ((history + 16) >> 6 /* / 64 */) - 24;
244 extrabits = show_bits(&alac->gb, k);
246 block_size = (((1 << k) - 1) & rice_kmodifier_mask) * x
252 skip_bits(&alac->gb, k - 1);
254 skip_bits(&alac->gb, k);
258 if (block_size > 0) {
259 memset(&output_buffer[output_count+1], 0, block_size * 4);
260 output_count += block_size;
263 if (block_size > 0xffff)
271 static inline int32_t extend_sign32(int32_t val, int bits)
273 return (val << (32 - bits)) >> (32 - bits);
276 static inline int sign_only(int v)
278 return v ? FFSIGN(v) : 0;
281 static void predictor_decompress_fir_adapt(int32_t *error_buffer,
285 int16_t *predictor_coef_table,
286 int predictor_coef_num,
287 int predictor_quantitization)
291 /* first sample always copies */
292 *buffer_out = *error_buffer;
294 if (!predictor_coef_num) {
295 if (output_size <= 1)
298 memcpy(buffer_out+1, error_buffer+1, (output_size-1) * 4);
302 if (predictor_coef_num == 0x1f) { /* 11111 - max value of predictor_coef_num */
303 /* second-best case scenario for fir decompression,
304 * error describes a small difference from the previous sample only
306 if (output_size <= 1)
308 for (i = 0; i < output_size - 1; i++) {
312 prev_value = buffer_out[i];
313 error_value = error_buffer[i+1];
315 extend_sign32((prev_value + error_value), readsamplesize);
320 /* read warm-up samples */
321 if (predictor_coef_num > 0)
322 for (i = 0; i < predictor_coef_num; i++) {
325 val = buffer_out[i] + error_buffer[i+1];
326 val = extend_sign32(val, readsamplesize);
327 buffer_out[i+1] = val;
331 /* 4 and 8 are very common cases (the only ones i've seen). these
332 * should be unrolled and optimised
334 if (predictor_coef_num == 4) {
335 /* FIXME: optimised general case */
339 if (predictor_coef_table == 8) {
340 /* FIXME: optimised general case */
346 if (predictor_coef_num > 0) {
347 for (i = predictor_coef_num + 1; i < output_size; i++) {
351 int error_val = error_buffer[i];
353 for (j = 0; j < predictor_coef_num; j++) {
354 sum += (buffer_out[predictor_coef_num-j] - buffer_out[0]) *
355 predictor_coef_table[j];
358 outval = (1 << (predictor_quantitization-1)) + sum;
359 outval = outval >> predictor_quantitization;
360 outval = outval + buffer_out[0] + error_val;
361 outval = extend_sign32(outval, readsamplesize);
363 buffer_out[predictor_coef_num+1] = outval;
366 int predictor_num = predictor_coef_num - 1;
368 while (predictor_num >= 0 && error_val > 0) {
369 int val = buffer_out[0] - buffer_out[predictor_coef_num - predictor_num];
370 int sign = sign_only(val);
372 predictor_coef_table[predictor_num] -= sign;
374 val *= sign; /* absolute value */
376 error_val -= ((val >> predictor_quantitization) *
377 (predictor_coef_num - predictor_num));
381 } else if (error_val < 0) {
382 int predictor_num = predictor_coef_num - 1;
384 while (predictor_num >= 0 && error_val < 0) {
385 int val = buffer_out[0] - buffer_out[predictor_coef_num - predictor_num];
386 int sign = - sign_only(val);
388 predictor_coef_table[predictor_num] -= sign;
390 val *= sign; /* neg value */
392 error_val -= ((val >> predictor_quantitization) *
393 (predictor_coef_num - predictor_num));
404 static void reconstruct_stereo_16(int32_t *buffer[MAX_CHANNELS],
406 int numchannels, int numsamples,
407 uint8_t interlacing_shift,
408 uint8_t interlacing_leftweight)
414 /* weighted interlacing */
415 if (interlacing_leftweight) {
416 for (i = 0; i < numsamples; i++) {
422 a -= (b * interlacing_leftweight) >> interlacing_shift;
425 buffer_out[i*numchannels] = b;
426 buffer_out[i*numchannels + 1] = a;
432 /* otherwise basic interlacing took place */
433 for (i = 0; i < numsamples; i++) {
437 right = buffer[1][i];
439 buffer_out[i*numchannels] = left;
440 buffer_out[i*numchannels + 1] = right;
444 static int alac_decode_frame(AVCodecContext *avctx,
445 void *outbuffer, int *outputsize,
446 uint8_t *inbuffer, int input_buffer_size)
448 ALACContext *alac = avctx->priv_data;
451 int32_t outputsamples;
456 uint8_t interlacing_shift;
457 uint8_t interlacing_leftweight;
459 /* short-circuit null buffers */
460 if (!inbuffer || !input_buffer_size)
461 return input_buffer_size;
463 /* initialize from the extradata */
464 if (!alac->context_initialized) {
465 if (alac->avctx->extradata_size != ALAC_EXTRADATA_SIZE) {
466 av_log(avctx, AV_LOG_ERROR, "alac: expected %d extradata bytes\n",
467 ALAC_EXTRADATA_SIZE);
468 return input_buffer_size;
470 if (alac_set_info(alac)) {
471 av_log(avctx, AV_LOG_ERROR, "alac: set_info failed\n");
472 return input_buffer_size;
474 alac->context_initialized = 1;
477 init_get_bits(&alac->gb, inbuffer, input_buffer_size * 8);
479 channels = get_bits(&alac->gb, 3) + 1;
480 if (channels > MAX_CHANNELS) {
481 av_log(avctx, AV_LOG_ERROR, "channels > %d not supported\n",
483 return input_buffer_size;
486 /* 2^result = something to do with output waiting.
487 * perhaps matters if we read > 1 frame in a pass?
489 skip_bits(&alac->gb, 4);
491 skip_bits(&alac->gb, 12); /* unknown, skip 12 bits */
493 /* the output sample size is stored soon */
494 hassize = get_bits1(&alac->gb);
496 wasted_bytes = get_bits(&alac->gb, 2); /* unknown ? */
498 /* whether the frame is compressed */
499 isnotcompressed = get_bits1(&alac->gb);
502 /* now read the number of samples as a 32bit integer */
503 outputsamples = get_bits(&alac->gb, 32);
505 outputsamples = alac->setinfo_max_samples_per_frame;
507 *outputsize = outputsamples * alac->bytespersample;
508 readsamplesize = alac->setinfo_sample_size - (wasted_bytes * 8) + channels - 1;
510 if (!isnotcompressed) {
511 /* so it is compressed */
512 int16_t predictor_coef_table[channels][32];
513 int predictor_coef_num[channels];
514 int prediction_type[channels];
515 int prediction_quantitization[channels];
516 int ricemodifier[channels];
519 interlacing_shift = get_bits(&alac->gb, 8);
520 interlacing_leftweight = get_bits(&alac->gb, 8);
522 for (chan = 0; chan < channels; chan++) {
523 prediction_type[chan] = get_bits(&alac->gb, 4);
524 prediction_quantitization[chan] = get_bits(&alac->gb, 4);
526 ricemodifier[chan] = get_bits(&alac->gb, 3);
527 predictor_coef_num[chan] = get_bits(&alac->gb, 5);
529 /* read the predictor table */
530 for (i = 0; i < predictor_coef_num[chan]; i++)
531 predictor_coef_table[chan][i] = (int16_t)get_bits(&alac->gb, 16);
535 av_log(avctx, AV_LOG_ERROR, "FIXME: unimplemented, unhandling of wasted_bytes\n");
537 for (chan = 0; chan < channels; chan++) {
538 bastardized_rice_decompress(alac,
539 alac->predicterror_buffer[chan],
542 alac->setinfo_rice_initialhistory,
543 alac->setinfo_rice_kmodifier,
544 ricemodifier[chan] * alac->setinfo_rice_historymult / 4,
545 (1 << alac->setinfo_rice_kmodifier) - 1);
547 if (prediction_type[chan] == 0) {
549 predictor_decompress_fir_adapt(alac->predicterror_buffer[chan],
550 alac->outputsamples_buffer[chan],
553 predictor_coef_table[chan],
554 predictor_coef_num[chan],
555 prediction_quantitization[chan]);
557 av_log(avctx, AV_LOG_ERROR, "FIXME: unhandled prediction type: %i\n", prediction_type[chan]);
558 /* I think the only other prediction type (or perhaps this is
559 * just a boolean?) runs adaptive fir twice.. like:
560 * predictor_decompress_fir_adapt(predictor_error, tempout, ...)
561 * predictor_decompress_fir_adapt(predictor_error, outputsamples ...)
567 /* not compressed, easy case */
568 if (alac->setinfo_sample_size <= 16) {
570 for (chan = 0; chan < channels; chan++)
571 for (i = 0; i < outputsamples; i++) {
574 audiobits = get_bits(&alac->gb, alac->setinfo_sample_size);
575 audiobits = extend_sign32(audiobits, readsamplesize);
577 alac->outputsamples_buffer[chan][i] = audiobits;
581 for (chan = 0; chan < channels; chan++)
582 for (i = 0; i < outputsamples; i++) {
585 audiobits = get_bits(&alac->gb, 16);
586 /* special case of sign extension..
587 * as we'll be ORing the low 16bits into this */
588 audiobits = audiobits << 16;
589 audiobits = audiobits >> (32 - alac->setinfo_sample_size);
590 audiobits |= get_bits(&alac->gb, alac->setinfo_sample_size - 16);
592 alac->outputsamples_buffer[chan][i] = audiobits;
595 /* wasted_bytes = 0; */
596 interlacing_shift = 0;
597 interlacing_leftweight = 0;
600 switch(alac->setinfo_sample_size) {
603 reconstruct_stereo_16(alac->outputsamples_buffer,
608 interlacing_leftweight);
611 for (i = 0; i < outputsamples; i++) {
612 int16_t sample = alac->outputsamples_buffer[0][i];
613 ((int16_t*)outbuffer)[i * alac->numchannels] = sample;
619 // It is not clear if there exist any encoder that creates 24 bit ALAC
620 // files. iTunes convert 24 bit raw files to 16 bit before encoding.
622 av_log(avctx, AV_LOG_ERROR, "FIXME: unimplemented sample size %i\n", alac->setinfo_sample_size);
628 return input_buffer_size;
631 static int alac_decode_init(AVCodecContext * avctx)
633 ALACContext *alac = avctx->priv_data;
635 alac->context_initialized = 0;
637 alac->samplesize = alac->avctx->bits_per_sample;
638 alac->numchannels = alac->avctx->channels;
639 alac->bytespersample = (alac->samplesize / 8) * alac->numchannels;
644 static int alac_decode_close(AVCodecContext *avctx)
646 ALACContext *alac = avctx->priv_data;
649 for (chan = 0; chan < MAX_CHANNELS; chan++) {
650 av_free(alac->predicterror_buffer[chan]);
651 av_free(alac->outputsamples_buffer[chan]);
657 AVCodec alac_decoder = {