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
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg 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.
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
26 * @see http://crazney.net/programs/itunes/alac.html
28 * Note: This decoder expects a 36-byte QuickTime atom to be
29 * passed through the extradata[_size] fields. This atom is tacked onto
30 * the end of an 'alac' stsd atom and has the following format:
34 * 32bit tag version (0)
35 * 32bit samples per frame (used when not set explicitly in the frames)
36 * 8bit compatible version (0)
38 * 8bit history mult (40)
39 * 8bit initial history (10)
40 * 8bit rice param limit (14)
43 * 32bit max coded frame size (0 means unknown)
44 * 32bit average bitrate (0 means unknown)
50 #include "libavutil/channel_layout.h"
51 #include "libavutil/opt.h"
54 #include "bytestream.h"
59 #include "alac_data.h"
61 #define ALAC_EXTRADATA_SIZE 36
63 typedef struct ALACContext {
65 AVCodecContext *avctx;
69 int32_t *predict_error_buffer[2];
70 int32_t *output_samples_buffer[2];
71 int32_t *extra_bits_buffer[2];
73 uint32_t max_samples_per_frame;
75 uint8_t rice_history_mult;
76 uint8_t rice_initial_history;
79 int extra_bits; /**< number of extra bits beyond 16-bit */
80 int nb_samples; /**< number of samples in the current frame */
86 static inline unsigned int decode_scalar(GetBitContext *gb, int k, int bps)
88 unsigned int x = get_unary_0_9(gb);
90 if (x > 8) { /* RICE THRESHOLD */
91 /* use alternative encoding */
92 x = get_bits_long(gb, bps);
94 int extrabits = show_bits(gb, k);
96 /* multiply x by 2^k - 1, as part of their strange algorithm */
103 skip_bits(gb, k - 1);
108 static int rice_decompress(ALACContext *alac, int32_t *output_buffer,
109 int nb_samples, int bps, int rice_history_mult)
112 unsigned int history = alac->rice_initial_history;
113 int sign_modifier = 0;
115 for (i = 0; i < nb_samples; i++) {
119 if(get_bits_left(&alac->gb) <= 0)
122 /* calculate rice param and decode next value */
123 k = av_log2((history >> 9) + 3);
124 k = FFMIN(k, alac->rice_limit);
125 x = decode_scalar(&alac->gb, k, bps);
128 output_buffer[i] = (x >> 1) ^ -(x & 1);
130 /* update the history */
134 history += x * rice_history_mult -
135 ((history * rice_history_mult) >> 9);
137 /* special case: there may be compressed blocks of 0 */
138 if ((history < 128) && (i + 1 < nb_samples)) {
141 /* calculate rice param and decode block size */
142 k = 7 - av_log2(history) + ((history + 16) >> 6);
143 k = FFMIN(k, alac->rice_limit);
144 block_size = decode_scalar(&alac->gb, k, 16);
146 if (block_size > 0) {
147 if (block_size >= nb_samples - i) {
148 av_log(alac->avctx, AV_LOG_ERROR,
149 "invalid zero block size of %d %d %d\n", block_size,
151 block_size = nb_samples - i - 1;
153 memset(&output_buffer[i + 1], 0,
154 block_size * sizeof(*output_buffer));
157 if (block_size <= 0xffff)
165 static inline int sign_only(int v)
167 return v ? FFSIGN(v) : 0;
170 static void lpc_prediction(int32_t *error_buffer, int32_t *buffer_out,
171 int nb_samples, int bps, int16_t *lpc_coefs,
172 int lpc_order, int lpc_quant)
175 int32_t *pred = buffer_out;
177 /* first sample always copies */
178 *buffer_out = *error_buffer;
184 memcpy(&buffer_out[1], &error_buffer[1],
185 (nb_samples - 1) * sizeof(*buffer_out));
189 if (lpc_order == 31) {
190 /* simple 1st-order prediction */
191 for (i = 1; i < nb_samples; i++) {
192 buffer_out[i] = sign_extend(buffer_out[i - 1] + error_buffer[i],
198 /* read warm-up samples */
199 for (i = 1; i <= lpc_order && i < nb_samples; i++)
200 buffer_out[i] = sign_extend(buffer_out[i - 1] + error_buffer[i], bps);
202 /* NOTE: 4 and 8 are very common cases that could be optimized. */
204 for (; i < nb_samples; i++) {
207 int error_val = error_buffer[i];
212 for (j = 0; j < lpc_order; j++)
213 val += (pred[j] - d) * lpc_coefs[j];
214 val = (val + (1 << (lpc_quant - 1))) >> lpc_quant;
215 val += d + error_val;
216 buffer_out[i] = sign_extend(val, bps);
218 /* adapt LPC coefficients */
219 error_sign = sign_only(error_val);
221 for (j = 0; j < lpc_order && error_val * error_sign > 0; j++) {
224 sign = sign_only(val) * error_sign;
225 lpc_coefs[j] -= sign;
227 error_val -= (val >> lpc_quant) * (j + 1);
233 static void decorrelate_stereo(int32_t *buffer[2], int nb_samples,
234 int decorr_shift, int decorr_left_weight)
238 for (i = 0; i < nb_samples; i++) {
244 a -= (b * decorr_left_weight) >> decorr_shift;
252 static void append_extra_bits(int32_t *buffer[2], int32_t *extra_bits_buffer[2],
253 int extra_bits, int channels, int nb_samples)
257 for (ch = 0; ch < channels; ch++)
258 for (i = 0; i < nb_samples; i++)
259 buffer[ch][i] = (buffer[ch][i] << extra_bits) | extra_bits_buffer[ch][i];
262 static int decode_element(AVCodecContext *avctx, AVFrame *frame, int ch_index,
265 ALACContext *alac = avctx->priv_data;
266 int has_size, bps, is_compressed, decorr_shift, decorr_left_weight, ret;
267 uint32_t output_samples;
270 skip_bits(&alac->gb, 4); /* element instance tag */
271 skip_bits(&alac->gb, 12); /* unused header bits */
273 /* the number of output samples is stored in the frame */
274 has_size = get_bits1(&alac->gb);
276 alac->extra_bits = get_bits(&alac->gb, 2) << 3;
277 bps = alac->sample_size - alac->extra_bits + channels - 1;
279 av_log(avctx, AV_LOG_ERROR, "bps is unsupported: %d\n", bps);
280 return AVERROR_PATCHWELCOME;
283 /* whether the frame is compressed */
284 is_compressed = !get_bits1(&alac->gb);
287 output_samples = get_bits_long(&alac->gb, 32);
289 output_samples = alac->max_samples_per_frame;
290 if (!output_samples || output_samples > alac->max_samples_per_frame) {
291 av_log(avctx, AV_LOG_ERROR, "invalid samples per frame: %"PRIu32"\n",
293 return AVERROR_INVALIDDATA;
295 if (!alac->nb_samples) {
296 ThreadFrame tframe = { .f = frame };
297 /* get output buffer */
298 frame->nb_samples = output_samples;
299 if ((ret = ff_thread_get_buffer(avctx, &tframe, 0)) < 0)
301 } else if (output_samples != alac->nb_samples) {
302 av_log(avctx, AV_LOG_ERROR, "sample count mismatch: %"PRIu32" != %d\n",
303 output_samples, alac->nb_samples);
304 return AVERROR_INVALIDDATA;
306 alac->nb_samples = output_samples;
307 if (alac->direct_output) {
308 for (ch = 0; ch < channels; ch++)
309 alac->output_samples_buffer[ch] = (int32_t *)frame->extended_data[ch_index + ch];
313 int16_t lpc_coefs[2][32];
315 int prediction_type[2];
317 int rice_history_mult[2];
319 if (!alac->rice_limit) {
320 avpriv_request_sample(alac->avctx,
321 "Compression with rice limit 0");
322 return AVERROR(ENOSYS);
325 decorr_shift = get_bits(&alac->gb, 8);
326 decorr_left_weight = get_bits(&alac->gb, 8);
328 for (ch = 0; ch < channels; ch++) {
329 prediction_type[ch] = get_bits(&alac->gb, 4);
330 lpc_quant[ch] = get_bits(&alac->gb, 4);
331 rice_history_mult[ch] = get_bits(&alac->gb, 3);
332 lpc_order[ch] = get_bits(&alac->gb, 5);
334 if (lpc_order[ch] >= alac->max_samples_per_frame)
335 return AVERROR_INVALIDDATA;
337 /* read the predictor table */
338 for (i = lpc_order[ch] - 1; i >= 0; i--)
339 lpc_coefs[ch][i] = get_sbits(&alac->gb, 16);
342 if (alac->extra_bits) {
343 for (i = 0; i < alac->nb_samples; i++) {
344 if(get_bits_left(&alac->gb) <= 0)
346 for (ch = 0; ch < channels; ch++)
347 alac->extra_bits_buffer[ch][i] = get_bits(&alac->gb, alac->extra_bits);
350 for (ch = 0; ch < channels; ch++) {
351 int ret=rice_decompress(alac, alac->predict_error_buffer[ch],
352 alac->nb_samples, bps,
353 rice_history_mult[ch] * alac->rice_history_mult / 4);
357 /* adaptive FIR filter */
358 if (prediction_type[ch] == 15) {
359 /* Prediction type 15 runs the adaptive FIR twice.
360 * The first pass uses the special-case coef_num = 31, while
361 * the second pass uses the coefs from the bitstream.
363 * However, this prediction type is not currently used by the
366 lpc_prediction(alac->predict_error_buffer[ch],
367 alac->predict_error_buffer[ch],
368 alac->nb_samples, bps, NULL, 31, 0);
369 } else if (prediction_type[ch] > 0) {
370 av_log(avctx, AV_LOG_WARNING, "unknown prediction type: %i\n",
371 prediction_type[ch]);
373 lpc_prediction(alac->predict_error_buffer[ch],
374 alac->output_samples_buffer[ch], alac->nb_samples,
375 bps, lpc_coefs[ch], lpc_order[ch], lpc_quant[ch]);
378 /* not compressed, easy case */
379 for (i = 0; i < alac->nb_samples; i++) {
380 if(get_bits_left(&alac->gb) <= 0)
382 for (ch = 0; ch < channels; ch++) {
383 alac->output_samples_buffer[ch][i] =
384 get_sbits_long(&alac->gb, alac->sample_size);
387 alac->extra_bits = 0;
389 decorr_left_weight = 0;
392 if (alac->extra_bits && alac->extra_bit_bug) {
393 append_extra_bits(alac->output_samples_buffer, alac->extra_bits_buffer,
394 alac->extra_bits, channels, alac->nb_samples);
397 if (channels == 2 && decorr_left_weight) {
398 decorrelate_stereo(alac->output_samples_buffer, alac->nb_samples,
399 decorr_shift, decorr_left_weight);
402 if (alac->extra_bits && !alac->extra_bit_bug) {
403 append_extra_bits(alac->output_samples_buffer, alac->extra_bits_buffer,
404 alac->extra_bits, channels, alac->nb_samples);
407 switch(alac->sample_size) {
409 for (ch = 0; ch < channels; ch++) {
410 int16_t *outbuffer = (int16_t *)frame->extended_data[ch_index + ch];
411 for (i = 0; i < alac->nb_samples; i++)
412 *outbuffer++ = alac->output_samples_buffer[ch][i];
416 for (ch = 0; ch < channels; ch++) {
417 for (i = 0; i < alac->nb_samples; i++)
418 alac->output_samples_buffer[ch][i] <<= 8;
426 static int alac_decode_frame(AVCodecContext *avctx, void *data,
427 int *got_frame_ptr, AVPacket *avpkt)
429 ALACContext *alac = avctx->priv_data;
430 AVFrame *frame = data;
431 enum AlacRawDataBlockType element;
433 int ch, ret, got_end;
435 if ((ret = init_get_bits8(&alac->gb, avpkt->data, avpkt->size)) < 0)
439 alac->nb_samples = 0;
441 while (get_bits_left(&alac->gb) >= 3) {
442 element = get_bits(&alac->gb, 3);
443 if (element == TYPE_END) {
447 if (element > TYPE_CPE && element != TYPE_LFE) {
448 av_log(avctx, AV_LOG_ERROR, "syntax element unsupported: %d\n", element);
449 return AVERROR_PATCHWELCOME;
452 channels = (element == TYPE_CPE) ? 2 : 1;
453 if (ch + channels > alac->channels ||
454 ff_alac_channel_layout_offsets[alac->channels - 1][ch] + channels > alac->channels) {
455 av_log(avctx, AV_LOG_ERROR, "invalid element channel count\n");
456 return AVERROR_INVALIDDATA;
459 ret = decode_element(avctx, frame,
460 ff_alac_channel_layout_offsets[alac->channels - 1][ch],
462 if (ret < 0 && get_bits_left(&alac->gb))
468 av_log(avctx, AV_LOG_ERROR, "no end tag found. incomplete packet.\n");
469 return AVERROR_INVALIDDATA;
472 if (avpkt->size * 8 - get_bits_count(&alac->gb) > 8) {
473 av_log(avctx, AV_LOG_ERROR, "Error : %d bits left\n",
474 avpkt->size * 8 - get_bits_count(&alac->gb));
477 if (alac->channels == ch)
480 av_log(avctx, AV_LOG_WARNING, "Failed to decode all channels\n");
485 static av_cold int alac_decode_close(AVCodecContext *avctx)
487 ALACContext *alac = avctx->priv_data;
490 for (ch = 0; ch < FFMIN(alac->channels, 2); ch++) {
491 av_freep(&alac->predict_error_buffer[ch]);
492 if (!alac->direct_output)
493 av_freep(&alac->output_samples_buffer[ch]);
494 av_freep(&alac->extra_bits_buffer[ch]);
500 static int allocate_buffers(ALACContext *alac)
503 int buf_size = alac->max_samples_per_frame * sizeof(int32_t);
505 for (ch = 0; ch < 2; ch++) {
506 alac->predict_error_buffer[ch] = NULL;
507 alac->output_samples_buffer[ch] = NULL;
508 alac->extra_bits_buffer[ch] = NULL;
511 for (ch = 0; ch < FFMIN(alac->channels, 2); ch++) {
512 FF_ALLOC_OR_GOTO(alac->avctx, alac->predict_error_buffer[ch],
513 buf_size, buf_alloc_fail);
515 alac->direct_output = alac->sample_size > 16;
516 if (!alac->direct_output) {
517 FF_ALLOC_OR_GOTO(alac->avctx, alac->output_samples_buffer[ch],
518 buf_size, buf_alloc_fail);
521 FF_ALLOC_OR_GOTO(alac->avctx, alac->extra_bits_buffer[ch],
522 buf_size, buf_alloc_fail);
526 alac_decode_close(alac->avctx);
527 return AVERROR(ENOMEM);
530 static int alac_set_info(ALACContext *alac)
534 bytestream2_init(&gb, alac->avctx->extradata,
535 alac->avctx->extradata_size);
537 bytestream2_skipu(&gb, 12); // size:4, alac:4, version:4
539 alac->max_samples_per_frame = bytestream2_get_be32u(&gb);
540 if (!alac->max_samples_per_frame ||
541 alac->max_samples_per_frame > INT_MAX / sizeof(int32_t)) {
542 av_log(alac->avctx, AV_LOG_ERROR,
543 "max samples per frame invalid: %"PRIu32"\n",
544 alac->max_samples_per_frame);
545 return AVERROR_INVALIDDATA;
547 bytestream2_skipu(&gb, 1); // compatible version
548 alac->sample_size = bytestream2_get_byteu(&gb);
549 alac->rice_history_mult = bytestream2_get_byteu(&gb);
550 alac->rice_initial_history = bytestream2_get_byteu(&gb);
551 alac->rice_limit = bytestream2_get_byteu(&gb);
552 alac->channels = bytestream2_get_byteu(&gb);
553 bytestream2_get_be16u(&gb); // maxRun
554 bytestream2_get_be32u(&gb); // max coded frame size
555 bytestream2_get_be32u(&gb); // average bitrate
556 bytestream2_get_be32u(&gb); // samplerate
561 static av_cold int alac_decode_init(AVCodecContext * avctx)
564 ALACContext *alac = avctx->priv_data;
567 /* initialize from the extradata */
568 if (alac->avctx->extradata_size < ALAC_EXTRADATA_SIZE) {
569 av_log(avctx, AV_LOG_ERROR, "extradata is too small\n");
570 return AVERROR_INVALIDDATA;
572 if (alac_set_info(alac)) {
573 av_log(avctx, AV_LOG_ERROR, "set_info failed\n");
577 switch (alac->sample_size) {
578 case 16: avctx->sample_fmt = AV_SAMPLE_FMT_S16P;
581 case 32: avctx->sample_fmt = AV_SAMPLE_FMT_S32P;
583 default: avpriv_request_sample(avctx, "Sample depth %d", alac->sample_size);
584 return AVERROR_PATCHWELCOME;
586 avctx->bits_per_raw_sample = alac->sample_size;
588 if (alac->channels < 1) {
589 av_log(avctx, AV_LOG_WARNING, "Invalid channel count\n");
590 alac->channels = avctx->channels;
592 if (alac->channels > ALAC_MAX_CHANNELS)
593 alac->channels = avctx->channels;
595 avctx->channels = alac->channels;
597 if (avctx->channels > ALAC_MAX_CHANNELS || avctx->channels <= 0 ) {
598 av_log(avctx, AV_LOG_ERROR, "Unsupported channel count: %d\n",
600 return AVERROR_PATCHWELCOME;
602 avctx->channel_layout = ff_alac_channel_layouts[alac->channels - 1];
604 if ((ret = allocate_buffers(alac)) < 0) {
605 av_log(avctx, AV_LOG_ERROR, "Error allocating buffers\n");
612 static int init_thread_copy(AVCodecContext *avctx)
614 ALACContext *alac = avctx->priv_data;
616 return allocate_buffers(alac);
619 static const AVOption options[] = {
620 { "extra_bits_bug", "Force non-standard decoding process",
621 offsetof(ALACContext, extra_bit_bug), AV_OPT_TYPE_INT, { .i64 = 0 },
622 0, 1, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_DECODING_PARAM },
626 static const AVClass alac_class = {
627 .class_name = "alac",
628 .item_name = av_default_item_name,
630 .version = LIBAVUTIL_VERSION_INT,
633 AVCodec ff_alac_decoder = {
635 .long_name = NULL_IF_CONFIG_SMALL("ALAC (Apple Lossless Audio Codec)"),
636 .type = AVMEDIA_TYPE_AUDIO,
637 .id = AV_CODEC_ID_ALAC,
638 .priv_data_size = sizeof(ALACContext),
639 .init = alac_decode_init,
640 .close = alac_decode_close,
641 .decode = alac_decode_frame,
642 .init_thread_copy = ONLY_IF_THREADS_ENABLED(init_thread_copy),
643 .capabilities = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS,
644 .priv_class = &alac_class