Add MPEG-4 Audio Lossless Coding (ALS) decoder.

Patch by Thilo Borgmann, thilo D borgmann A googlemail

Originally committed as revision 20517 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 997 insertions, 0 deletions

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
new file mode 100644
index 0000000000..47b708faf9
--- /dev/null
+++ b/libavcodec/alsdec.c
@@ -0,0 +1,997 @@
+/*
+ * MPEG-4 ALS decoder
+ * Copyright (c) 2009 Thilo Borgmann <thilo.borgmann _at_ googlemail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file libavcodec/alsdec.c
+ * MPEG-4 ALS decoder
+ * @author Thilo Borgmann <thilo.borgmann _at_ googlemail.com>
+ */
+
+
+//#define DEBUG
+
+
+#include "avcodec.h"
+#include "get_bits.h"
+#include "unary.h"
+#include "mpeg4audio.h"
+#include "bytestream.h"
+
+#include "als_data.h"
+
+enum RA_Flag {
+    RA_FLAG_NONE,
+    RA_FLAG_FRAMES,
+    RA_FLAG_HEADER
+};
+
+
+typedef struct {
+    uint32_t samples;         ///< number of samples, 0xFFFFFFFF if unknown
+    int resolution;           ///< 000 = 8-bit; 001 = 16-bit; 010 = 24-bit; 011 = 32-bit
+    int floating;             ///< 1 = IEEE 32-bit floating-point, 0 = integer
+    int frame_length;         ///< frame length for each frame (last frame may differ)
+    int ra_distance;          ///< distance between RA frames (in frames, 0...255)
+    enum RA_Flag ra_flag;     ///< indicates where the size of ra units is stored
+    int adapt_order;          ///< adaptive order: 1 = on, 0 = off
+    int coef_table;           ///< table index of Rice code parameters
+    int long_term_prediction; ///< long term prediction (LTP): 1 = on, 0 = off
+    int max_order;            ///< maximum prediction order (0..1023)
+    int block_switching;      ///< number of block switching levels
+    int bgmc;                 ///< "Block Gilbert-Moore Code": 1 = on, 0 = off (Rice coding only)
+    int sb_part;              ///< sub-block partition
+    int joint_stereo;         ///< joint stereo: 1 = on, 0 = off
+    int mc_coding;            ///< extended inter-channel coding (multi channel coding): 1 = on, 0 = off
+    int chan_config;          ///< indicates that a chan_config_info field is present
+    int chan_sort;            ///< channel rearrangement: 1 = on, 0 = off
+    int rlslms;               ///< use "Recursive Least Square-Least Mean Square" predictor: 1 = on, 0 = off
+    int chan_config_info;     ///< mapping of channels to loudspeaker locations. Unused until setting channel configuration is implemented.
+    int *chan_pos;            ///< original channel positions
+    uint32_t header_size;     ///< header size of original audio file in bytes, provided for debugging
+    uint32_t trailer_size;    ///< trailer size of original audio file in bytes, provided for debugging
+} ALSSpecificConfig;
+
+
+typedef struct {
+    AVCodecContext *avctx;
+    ALSSpecificConfig sconf;
+    GetBitContext gb;
+    unsigned int cur_frame_length;  ///< length of the current frame to decode
+    unsigned int frame_id;          ///< the frame ID / number of the current frame
+    unsigned int js_switch;         ///< if true, joint-stereo decoding is enforced
+    unsigned int num_blocks;        ///< number of blocks used in the current frame
+    int32_t *quant_cof;             ///< quantized parcor coefficients
+    int32_t *lpc_cof;               ///< coefficients of the direct form prediction filter
+    int32_t *prev_raw_samples;      ///< contains unshifted raw samples from the previous block
+    int32_t **raw_samples;          ///< decoded raw samples for each channel
+    int32_t *raw_buffer;            ///< contains all decoded raw samples including carryover samples
+} ALSDecContext;
+
+
+static av_cold void dprint_specific_config(ALSDecContext *ctx)
+{
+#ifdef DEBUG
+    AVCodecContext *avctx    = ctx->avctx;
+    ALSSpecificConfig *sconf = &ctx->sconf;
+
+    dprintf(avctx, "resolution = %i\n",           sconf->resolution);
+    dprintf(avctx, "floating = %i\n",             sconf->floating);
+    dprintf(avctx, "frame_length = %i\n",         sconf->frame_length);
+    dprintf(avctx, "ra_distance = %i\n",          sconf->ra_distance);
+    dprintf(avctx, "ra_flag = %i\n",              sconf->ra_flag);
+    dprintf(avctx, "adapt_order = %i\n",          sconf->adapt_order);
+    dprintf(avctx, "coef_table = %i\n",           sconf->coef_table);
+    dprintf(avctx, "long_term_prediction = %i\n", sconf->long_term_prediction);
+    dprintf(avctx, "max_order = %i\n",            sconf->max_order);
+    dprintf(avctx, "block_switching = %i\n",      sconf->block_switching);
+    dprintf(avctx, "bgmc = %i\n",                 sconf->bgmc);
+    dprintf(avctx, "sb_part = %i\n",              sconf->sb_part);
+    dprintf(avctx, "joint_stereo = %i\n",         sconf->joint_stereo);
+    dprintf(avctx, "mc_coding = %i\n",            sconf->mc_coding);
+    dprintf(avctx, "chan_config = %i\n",          sconf->chan_config);
+    dprintf(avctx, "chan_sort = %i\n",            sconf->chan_sort);
+    dprintf(avctx, "RLSLMS = %i\n",               sconf->rlslms);
+    dprintf(avctx, "chan_config_info = %i\n",     sconf->chan_config_info);
+    dprintf(avctx, "header_size = %i\n",          sconf->header_size);
+    dprintf(avctx, "trailer_size = %i\n",         sconf->trailer_size);
+#endif
+}
+
+
+/** Reads an ALSSpecificConfig from a buffer into the output struct.
+ */
+static av_cold int read_specific_config(ALSDecContext *ctx)
+{
+    GetBitContext gb;
+    uint64_t ht_size;
+    int i, config_offset, crc_enabled;
+    MPEG4AudioConfig m4ac;
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    AVCodecContext *avctx    = ctx->avctx;
+    uint32_t als_id;
+
+    init_get_bits(&gb, avctx->extradata, avctx->extradata_size * 8);
+
+    config_offset = ff_mpeg4audio_get_config(&m4ac, avctx->extradata,
+                                             avctx->extradata_size);
+
+    if (config_offset < 0)
+        return -1;
+
+    skip_bits_long(&gb, config_offset);
+
+    if (get_bits_left(&gb) < (30 << 3))
+        return -1;
+
+    // read the fixed items
+    als_id                      = get_bits_long(&gb, 32);
+    avctx->sample_rate          = m4ac.sample_rate;
+    skip_bits_long(&gb, 32); // sample rate already known
+    sconf->samples              = get_bits_long(&gb, 32);
+    avctx->channels             = m4ac.channels;
+    skip_bits(&gb, 16);      // number of channels already knwon
+    skip_bits(&gb, 3);       // skip file_type
+    sconf->resolution           = get_bits(&gb, 3);
+    sconf->floating             = get_bits1(&gb);
+    skip_bits1(&gb);         // skip msb_first
+    sconf->frame_length         = get_bits(&gb, 16) + 1;
+    sconf->ra_distance          = get_bits(&gb, 8);
+    sconf->ra_flag              = get_bits(&gb, 2);
+    sconf->adapt_order          = get_bits1(&gb);
+    sconf->coef_table           = get_bits(&gb, 2);
+    sconf->long_term_prediction = get_bits1(&gb);
+    sconf->max_order            = get_bits(&gb, 10);
+    sconf->block_switching      = get_bits(&gb, 2);
+    sconf->bgmc                 = get_bits1(&gb);
+    sconf->sb_part              = get_bits1(&gb);
+    sconf->joint_stereo         = get_bits1(&gb);
+    sconf->mc_coding            = get_bits1(&gb);
+    sconf->chan_config          = get_bits1(&gb);
+    sconf->chan_sort            = get_bits1(&gb);
+    crc_enabled                 = get_bits1(&gb);
+    sconf->rlslms               = get_bits1(&gb);
+    skip_bits(&gb, 5);       // skip 5 reserved bits
+    skip_bits1(&gb);         // skip aux_data_enabled
+
+
+    // check for ALSSpecificConfig struct
+    if (als_id != MKBETAG('A','L','S','\0'))
+        return -1;
+
+    ctx->cur_frame_length = sconf->frame_length;
+
+    // allocate quantized parcor coefficient buffer
+    if (!(ctx->quant_cof = av_malloc(sizeof(*ctx->quant_cof) * sconf->max_order)) ||
+        !(ctx->lpc_cof   = av_malloc(sizeof(*ctx->lpc_cof)   * sconf->max_order))) {
+        av_log(avctx, AV_LOG_ERROR, "Allocating buffer memory failed.\n");
+        return AVERROR(ENOMEM);
+    }
+
+    // read channel config
+    if (sconf->chan_config)
+        sconf->chan_config_info = get_bits(&gb, 16);
+    // TODO: use this to set avctx->channel_layout
+
+
+    // read channel sorting
+    if (sconf->chan_sort && avctx->channels > 1) {
+        int chan_pos_bits = av_ceil_log2(avctx->channels);
+        int bits_needed  = avctx->channels * chan_pos_bits + 7;
+        if (get_bits_left(&gb) < bits_needed)
+            return -1;
+
+        if (!(sconf->chan_pos = av_malloc(avctx->channels * sizeof(*sconf->chan_pos))))
+            return AVERROR(ENOMEM);
+
+        for (i = 0; i < avctx->channels; i++)
+            sconf->chan_pos[i] = get_bits(&gb, chan_pos_bits);
+
+        align_get_bits(&gb);
+        // TODO: use this to actually do channel sorting
+    } else {
+        sconf->chan_sort = 0;
+    }
+
+
+    // read fixed header and trailer sizes,
+    // if size = 0xFFFFFFFF then there is no data field!
+    if (get_bits_left(&gb) < 64)
+        return -1;
+
+    sconf->header_size  = get_bits_long(&gb, 32);
+    sconf->trailer_size = get_bits_long(&gb, 32);
+    if (sconf->header_size  == 0xFFFFFFFF)
+        sconf->header_size  = 0;
+    if (sconf->trailer_size == 0xFFFFFFFF)
+        sconf->trailer_size = 0;
+
+    ht_size = ((int64_t)(sconf->header_size) + (int64_t)(sconf->trailer_size)) << 3;
+
+
+    // skip the header and trailer data
+    if (get_bits_left(&gb) < ht_size)
+        return -1;
+
+    if (ht_size > INT32_MAX)
+        return -1;
+
+    skip_bits_long(&gb, ht_size);
+
+
+    // skip the crc data
+    if (crc_enabled) {
+        if (get_bits_left(&gb) < 32)
+            return -1;
+
+        skip_bits_long(&gb, 32);
+    }
+
+
+    // no need to read the rest of ALSSpecificConfig (ra_unit_size & aux data)
+
+    dprint_specific_config(ctx);
+
+    return 0;
+}
+
+
+/** Checks the ALSSpecificConfig for unsupported features.
+ */
+static int check_specific_config(ALSDecContext *ctx)
+{
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    int error = 0;
+
+    // report unsupported feature and set error value
+    #define MISSING_ERR(cond, str, errval)              \
+    {                                                   \
+        if (cond) {                                     \
+            av_log_missing_feature(ctx->avctx, str, 0); \
+            error = errval;                             \
+        }                                               \
+    }
+
+    MISSING_ERR(sconf->floating,             "Floating point decoding",     -1);
+    MISSING_ERR(sconf->long_term_prediction, "Long-term prediction",        -1);
+    MISSING_ERR(sconf->bgmc,                 "BGMC entropy decoding",       -1);
+    MISSING_ERR(sconf->mc_coding,            "Multi-channel correlation",   -1);
+    MISSING_ERR(sconf->rlslms,               "Adaptive RLS-LMS prediction", -1);
+    MISSING_ERR(sconf->chan_sort,            "Channel sorting",              0);
+
+    return error;
+}
+
+
+/** Parses the bs_info field to extract the block partitioning used in
+ *  block switching mode, refer to ISO/IEC 14496-3, section 11.6.2.
+ */
+static void parse_bs_info(const uint32_t bs_info, unsigned int n,
+                          unsigned int div, unsigned int **div_blocks,
+                          unsigned int *num_blocks)
+{
+    if (n < 31 && ((bs_info << n) & 0x40000000)) {
+        // if the level is valid and the investigated bit n is set
+        // then recursively check both children at bits (2n+1) and (2n+2)
+        n   *= 2;
+        div += 1;
+        parse_bs_info(bs_info, n + 1, div, div_blocks, num_blocks);
+        parse_bs_info(bs_info, n + 2, div, div_blocks, num_blocks);
+    } else {
+        // else the bit is not set or the last level has been reached
+        // (bit implicitly not set)
+        **div_blocks = div;
+        (*div_blocks)++;
+        (*num_blocks)++;
+    }
+}
+
+
+/** Reads and decodes a Rice codeword.
+ */
+static int32_t decode_rice(GetBitContext *gb, unsigned int k)
+{
+    int max = gb->size_in_bits - get_bits_count(gb) - k;
+    int q   = get_unary(gb, 0, max);
+    int r   = k ? get_bits1(gb) : !(q & 1);
+
+    if (k > 1) {
+        q <<= (k - 1);
+        q  += get_bits_long(gb, k - 1);
+    } else if (!k) {
+        q >>= 1;
+    }
+    return r ? q : ~q;
+}
+
+
+/** Converts PARCOR coefficient k to direct filter coefficient.
+ */
+static void parcor_to_lpc(unsigned int k, const int32_t *par, int32_t *cof)
+{
+    int i, j;
+
+    for (i = 0, j = k - 1; i < j; i++, j--) {
+        int tmp1 = ((MUL64(par[k], cof[j]) + (1 << 19)) >> 20);
+        cof[j]  += ((MUL64(par[k], cof[i]) + (1 << 19)) >> 20);
+        cof[i]  += tmp1;
+    }
+    if (i == j)
+        cof[i] += ((MUL64(par[k], cof[j]) + (1 << 19)) >> 20);
+
+    cof[k] = par[k];
+}
+
+
+/** Reads block switching field if necessary and sets actual block sizes.
+ *  Also assures that the block sizes of the last frame correspond to the
+ *  actual number of samples.
+ */
+static void get_block_sizes(ALSDecContext *ctx, unsigned int *div_blocks,
+                            uint32_t *bs_info)
+{
+    ALSSpecificConfig *sconf     = &ctx->sconf;
+    GetBitContext *gb            = &ctx->gb;
+    unsigned int *ptr_div_blocks = div_blocks;
+    unsigned int b;
+
+    if (sconf->block_switching) {
+        unsigned int bs_info_len = 1 << (sconf->block_switching + 2);
+        *bs_info = get_bits_long(gb, bs_info_len);
+        *bs_info <<= (32 - bs_info_len);
+    }
+
+    ctx->num_blocks = 0;
+    parse_bs_info(*bs_info, 0, 0, &ptr_div_blocks, &ctx->num_blocks);
+
+    // The last frame may have an overdetermined block structure given in
+    // the bitstream. In that case the defined block structure would need
+    // more samples than available to be consistent.
+    // The block structure is actually used but the block sizes are adapted
+    // to fit the actual number of available samples.
+    // Example: 5 samples, 2nd level block sizes: 2 2 2 2.
+    // This results in the actual block sizes:    2 2 1 0.
+    // This is not specified in 14496-3 but actually done by the reference
+    // codec RM22 revision 2.
+    // This appears to happen in case of an odd number of samples in the last
+    // frame which is actually not allowed by the block length switching part
+    // of 14496-3.
+    // The ALS conformance files feature an odd number of samples in the last
+    // frame.
+
+    for (b = 0; b < ctx->num_blocks; b++)
+        div_blocks[b] = ctx->sconf.frame_length >> div_blocks[b];
+
+    if (ctx->cur_frame_length != ctx->sconf.frame_length) {
+        unsigned int remaining = ctx->cur_frame_length;
+
+        for (b = 0; b < ctx->num_blocks; b++) {
+            if (remaining < div_blocks[b]) {
+                div_blocks[b] = remaining;
+                ctx->num_blocks = b + 1;
+                break;
+            }
+
+            remaining -= div_blocks[b];
+        }
+    }
+}
+
+
+/** Reads the block data for a constant block
+ */
+static void read_const_block(ALSDecContext *ctx, int32_t *raw_samples,
+                             unsigned int block_length, unsigned int *js_blocks)
+{
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    AVCodecContext *avctx    = ctx->avctx;
+    GetBitContext *gb        = &ctx->gb;
+    int32_t const_val        = 0;
+    unsigned int const_block, k;
+
+    const_block  = get_bits1(gb);    // 1 = constant value, 0 = zero block (silence)
+    *js_blocks   = get_bits1(gb);
+
+    // skip 5 reserved bits
+    skip_bits(gb, 5);
+
+    if (const_block) {
+        unsigned int const_val_bits = sconf->floating ? 24 : avctx->bits_per_raw_sample;
+        const_val = get_sbits_long(gb, const_val_bits);
+    }
+
+    // write raw samples into buffer
+    for (k = 0; k < block_length; k++)
+        raw_samples[k] = const_val;
+}
+
+
+/** Reads the block data for a non-constant block
+ */
+static int read_var_block(ALSDecContext *ctx, unsigned int ra_block,
+                          int32_t *raw_samples, unsigned int block_length,
+                          unsigned int *js_blocks, int32_t *raw_other,
+                          unsigned int *shift_lsbs)
+{
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    AVCodecContext *avctx    = ctx->avctx;
+    GetBitContext *gb        = &ctx->gb;
+    unsigned int k;
+    unsigned int s[8];
+    unsigned int sub_blocks, log2_sub_blocks, sb_length;
+    unsigned int opt_order  = 1;
+    int32_t      *quant_cof = ctx->quant_cof;
+    int32_t      *lpc_cof   = ctx->lpc_cof;
+    unsigned int start      = 0;
+    int          smp        = 0;
+    int          sb, store_prev_samples;
+    int64_t      y;
+
+    *js_blocks  = get_bits1(gb);
+
+    // determine the number of subblocks for entropy decoding
+    if (!sconf->bgmc && !sconf->sb_part) {
+        log2_sub_blocks = 0;
+    } else {
+        if (sconf->bgmc && sconf->sb_part)
+            log2_sub_blocks = get_bits(gb, 2);
+        else
+            log2_sub_blocks = 2 * get_bits1(gb);
+    }
+
+    sub_blocks = 1 << log2_sub_blocks;
+
+    // do not continue in case of a damaged stream since
+    // block_length must be evenly divisible by sub_blocks
+    if (block_length & (sub_blocks - 1)) {
+        av_log(avctx, AV_LOG_WARNING,
+               "Block length is not evenly divisible by the number of subblocks.\n");
+        return -1;
+    }
+
+    sb_length = block_length >> log2_sub_blocks;
+
+
+    if (sconf->bgmc) {
+        // TODO: BGMC mode
+    } else {
+        s[0] = get_bits(gb, 4 + (sconf->resolution > 1));
+        for (k = 1; k < sub_blocks; k++)
+            s[k] = s[k - 1] + decode_rice(gb, 0);
+    }
+
+    if (get_bits1(gb))
+        *shift_lsbs = get_bits(gb, 4) + 1;
+
+    store_prev_samples = (*js_blocks && raw_other) || *shift_lsbs;
+
+
+    if (!sconf->rlslms) {
+        if (sconf->adapt_order) {
+            int opt_order_length = av_ceil_log2(av_clip((block_length >> 3) - 1,
+                                                2, sconf->max_order + 1));
+            opt_order            = get_bits(gb, opt_order_length);
+        } else {
+            opt_order = sconf->max_order;
+        }
+
+        if (opt_order) {
+            int add_base;
+
+            if (sconf->coef_table == 3) {
+                add_base = 0x7F;
+
+                // read coefficient 0
+                quant_cof[0] = 32 * parcor_scaled_values[get_bits(gb, 7)];
+
+                // read coefficient 1
+                if (opt_order > 1)
+                    quant_cof[1] = -32 * parcor_scaled_values[get_bits(gb, 7)];
+
+                // read coefficients 2 to opt_order
+                for (k = 2; k < opt_order; k++)
+                    quant_cof[k] = get_bits(gb, 7);
+            } else {
+                int k_max;
+                add_base = 1;
+
+                // read coefficient 0 to 19
+                k_max = FFMIN(opt_order, 20);
+                for (k = 0; k < k_max; k++) {
+                    int rice_param = parcor_rice_table[sconf->coef_table][k][1];
+                    int offset     = parcor_rice_table[sconf->coef_table][k][0];
+                    quant_cof[k] = decode_rice(gb, rice_param) + offset;
+                }
+
+                // read coefficients 20 to 126
+                k_max = FFMIN(opt_order, 127);
+                for (; k < k_max; k++)
+                    quant_cof[k] = decode_rice(gb, 2) + (k & 1);
+
+                // read coefficients 127 to opt_order
+                for (; k < opt_order; k++)
+                    quant_cof[k] = decode_rice(gb, 1);
+
+                quant_cof[0] = 32 * parcor_scaled_values[quant_cof[0] + 64];
+
+                if (opt_order > 1)
+                    quant_cof[1] = -32 * parcor_scaled_values[quant_cof[1] + 64];
+            }
+
+            for (k = 2; k < opt_order; k++)
+                quant_cof[k] = (quant_cof[k] << 14) + (add_base << 13);
+        }
+    }
+
+    // TODO: LTP mode
+
+    // read first value and residuals in case of a random access block
+    if (ra_block) {
+        if (opt_order)
+            raw_samples[0] = decode_rice(gb, avctx->bits_per_raw_sample - 4);
+        if (opt_order > 1)
+            raw_samples[1] = decode_rice(gb, s[0] + 3);
+        if (opt_order > 2)
+            raw_samples[2] = decode_rice(gb, s[0] + 1);
+
+        start = FFMIN(opt_order, 3);
+    }
+
+    // read all residuals
+    if (sconf->bgmc) {
+        // TODO: BGMC mode
+    } else {
+        int32_t *current_res = raw_samples + start;
+
+        for (sb = 0; sb < sub_blocks; sb++, start = 0)
+            for (; start < sb_length; start++)
+                *current_res++ = decode_rice(gb, s[sb]);
+     }
+
+    // reconstruct all samples from residuals
+    if (ra_block) {
+        for (smp = 0; smp < opt_order; smp++) {
+            y = 1 << 19;
+
+            for (sb = 0; sb < smp; sb++)
+                y += MUL64(lpc_cof[sb],raw_samples[smp - (sb + 1)]);
+
+            raw_samples[smp] -= y >> 20;
+            parcor_to_lpc(smp, quant_cof, lpc_cof);
+        }
+    } else {
+        for (k = 0; k < opt_order; k++)
+            parcor_to_lpc(k, quant_cof, lpc_cof);
+
+        // store previous samples in case that they have to be altered
+        if (store_prev_samples)
+            memcpy(ctx->prev_raw_samples, raw_samples - sconf->max_order,
+                   sizeof(*ctx->prev_raw_samples) * sconf->max_order);
+
+        // reconstruct difference signal for prediction (joint-stereo)
+        if (*js_blocks && raw_other) {
+            int32_t *left, *right;
+
+            if (raw_other > raw_samples) {          // D = R - L
+                left  = raw_samples;
+                right = raw_other;
+            } else {                                // D = R - L
+                left  = raw_other;
+                right = raw_samples;
+            }
+
+            for (sb = -1; sb >= -sconf->max_order; sb--)
+                raw_samples[sb] = right[sb] - left[sb];
+        }
+
+        // reconstruct shifted signal
+        if (*shift_lsbs)
+            for (sb = -1; sb >= -sconf->max_order; sb--)
+                raw_samples[sb] >>= *shift_lsbs;
+    }
+
+    // reconstruct raw samples
+    for (; smp < block_length; smp++) {
+        y = 1 << 19;
+
+        for (sb = 0; sb < opt_order; sb++)
+            y += MUL64(lpc_cof[sb],raw_samples[smp - (sb + 1)]);
+
+        raw_samples[smp] -= y >> 20;
+    }
+
+    // restore previous samples in case that they have been altered
+    if (store_prev_samples)
+        memcpy(raw_samples - sconf->max_order, ctx->prev_raw_samples,
+               sizeof(*raw_samples) * sconf->max_order);
+
+    return 0;
+}
+
+
+/** Reads the block data.
+ */
+static int read_block_data(ALSDecContext *ctx, unsigned int ra_block,
+                           int32_t *raw_samples, unsigned int block_length,
+                           unsigned int *js_blocks, int32_t *raw_other)
+{
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    GetBitContext *gb        = &ctx->gb;
+    unsigned int shift_lsbs  = 0;
+    unsigned int k;
+
+    // read block type flag and read the samples accordingly
+    if (get_bits1(gb)) {
+        if (read_var_block(ctx, ra_block, raw_samples, block_length, js_blocks,
+                           raw_other, &shift_lsbs))
+            return -1;
+    } else {
+        read_const_block(ctx, raw_samples, block_length, js_blocks);
+    }
+
+    // TODO: read RLSLMS extension data
+
+    if (!sconf->mc_coding || ctx->js_switch)
+        align_get_bits(gb);
+
+    if (shift_lsbs)
+        for (k = 0; k < block_length; k++)
+            raw_samples[k] <<= shift_lsbs;
+
+    return 0;
+}
+
+
+/** Computes the number of samples left to decode for the current frame and
+ *  sets these samples to zero.
+ */
+static void zero_remaining(unsigned int b, unsigned int b_max,
+                           const unsigned int *div_blocks, int32_t *buf)
+{
+    unsigned int count = 0;
+
+    while (b < b_max)
+        count += div_blocks[b];
+
+    memset(buf, 0, sizeof(*buf) * count);
+}
+
+
+/** Decodes blocks independently.
+ */
+static int decode_blocks_ind(ALSDecContext *ctx, unsigned int ra_frame,
+                             unsigned int c, const unsigned int *div_blocks,
+                             unsigned int *js_blocks)
+{
+    int32_t *raw_sample;
+    unsigned int b;
+    raw_sample = ctx->raw_samples[c];
+
+    for (b = 0; b < ctx->num_blocks; b++) {
+        if (read_block_data(ctx, ra_frame, raw_sample,
+                            div_blocks[b], &js_blocks[0], NULL)) {
+            // damaged block, write zero for the rest of the frame
+            zero_remaining(b, ctx->num_blocks, div_blocks, raw_sample);
+            return -1;
+        }
+        raw_sample += div_blocks[b];
+        ra_frame    = 0;
+    }
+
+    return 0;
+}
+
+
+/** Decodes blocks dependently.
+ */
+static int decode_blocks(ALSDecContext *ctx, unsigned int ra_frame,
+                         unsigned int c, const unsigned int *div_blocks,
+                         unsigned int *js_blocks)
+{
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    unsigned int offset = 0;
+    int32_t *raw_samples_R;
+    int32_t *raw_samples_L;
+    unsigned int b;
+
+    // decode all blocks
+    for (b = 0; b < ctx->num_blocks; b++) {
+        unsigned int s;
+        raw_samples_L = ctx->raw_samples[c    ] + offset;
+        raw_samples_R = ctx->raw_samples[c + 1] + offset;
+        if (read_block_data(ctx, ra_frame, raw_samples_L, div_blocks[b],
+                            &js_blocks[0], raw_samples_R) ||
+            read_block_data(ctx, ra_frame, raw_samples_R, div_blocks[b],
+                            &js_blocks[1], raw_samples_L)) {
+            // damaged block, write zero for the rest of the frame
+            zero_remaining(b, ctx->num_blocks, div_blocks, raw_samples_L);
+            zero_remaining(b, ctx->num_blocks, div_blocks, raw_samples_R);
+            return -1;
+        }
+
+        // reconstruct joint-stereo blocks
+        if (js_blocks[0]) {
+            if (js_blocks[1])
+                av_log(ctx->avctx, AV_LOG_WARNING, "Invalid channel pair!\n");
+
+            for (s = 0; s < div_blocks[b]; s++)
+                raw_samples_L[s] = raw_samples_R[s] - raw_samples_L[s];
+        } else if (js_blocks[1]) {
+            for (s = 0; s < div_blocks[b]; s++)
+                raw_samples_R[s] = raw_samples_R[s] + raw_samples_L[s];
+        }
+
+        offset  += div_blocks[b];
+        ra_frame = 0;
+    }
+
+    // store carryover raw samples,
+    // the others channel raw samples are stored by the calling function.
+    memmove(ctx->raw_samples[c] - sconf->max_order,
+            ctx->raw_samples[c] - sconf->max_order + sconf->frame_length,
+            sizeof(*ctx->raw_samples[c]) * sconf->max_order);
+
+    return 0;
+}
+
+
+/** Reads the frame data.
+ */
+static int read_frame_data(ALSDecContext *ctx, unsigned int ra_frame)
+{
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    AVCodecContext *avctx    = ctx->avctx;
+    GetBitContext *gb = &ctx->gb;
+    unsigned int div_blocks[32];                ///< block sizes.
+    unsigned int c;
+    unsigned int js_blocks[2];
+
+    uint32_t bs_info = 0;
+
+    // skip the size of the ra unit if present in the frame
+    if (sconf->ra_flag == RA_FLAG_FRAMES && ra_frame)
+        skip_bits_long(gb, 32);
+
+    if (sconf->mc_coding && sconf->joint_stereo) {
+        ctx->js_switch = get_bits1(gb);
+        align_get_bits(gb);
+    }
+
+    if (!sconf->mc_coding || ctx->js_switch) {
+        int independent_bs = !sconf->joint_stereo;
+
+        for (c = 0; c < avctx->channels; c++) {
+            js_blocks[0] = 0;
+            js_blocks[1] = 0;
+
+            get_block_sizes(ctx, div_blocks, &bs_info);
+
+            // if joint_stereo and block_switching is set, independent decoding
+            // is signaled via the first bit of bs_info
+            if (sconf->joint_stereo && sconf->block_switching)
+                if (bs_info >> 31)
+                    independent_bs = 2;
+
+            // if this is the last channel, it has to be decoded independently
+            if (c == avctx->channels - 1)
+                independent_bs = 1;
+
+            if (independent_bs) {
+                if (decode_blocks_ind(ctx, ra_frame, c, div_blocks, js_blocks))
+                    return -1;
+
+                independent_bs--;
+            } else {
+                if (decode_blocks(ctx, ra_frame, c, div_blocks, js_blocks))
+                    return -1;
+
+                c++;
+            }
+
+            // store carryover raw samples
+            memmove(ctx->raw_samples[c] - sconf->max_order,
+                    ctx->raw_samples[c] - sconf->max_order + sconf->frame_length,
+                    sizeof(*ctx->raw_samples[c]) * sconf->max_order);
+        }
+    } else { // multi-channel coding
+        get_block_sizes(ctx, div_blocks, &bs_info);
+
+        // TODO: multi channel coding might use a temporary buffer instead as
+        //       the actual channel is not known when read_block-data is called
+        if (decode_blocks_ind(ctx, ra_frame, 0, div_blocks, js_blocks))
+            return -1;
+        // TODO: read_channel_data
+    }
+
+    // TODO: read_diff_float_data
+
+    return 0;
+}
+
+
+/** Decodes an ALS frame.
+ */
+static int decode_frame(AVCodecContext *avctx,
+                        void *data, int *data_size,
+                        AVPacket *avpkt)
+{
+    ALSDecContext *ctx       = avctx->priv_data;
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    const uint8_t *buffer    = avpkt->data;
+    int buffer_size          = avpkt->size;
+    int invalid_frame, size;
+    unsigned int c, sample, ra_frame, bytes_read, shift;
+
+    init_get_bits(&ctx->gb, buffer, buffer_size * 8);
+
+    // In the case that the distance between random access frames is set to zero
+    // (sconf->ra_distance == 0) no frame is treated as a random access frame.
+    // For the first frame, if prediction is used, all samples used from the
+    // previous frame are assumed to be zero.
+    ra_frame = sconf->ra_distance && !(ctx->frame_id % sconf->ra_distance);
+
+    // the last frame to decode might have a different length
+    if (sconf->samples != 0xFFFFFFFF)
+        ctx->cur_frame_length = FFMIN(sconf->samples - ctx->frame_id * (uint64_t) sconf->frame_length,
+                                      sconf->frame_length);
+    else
+        ctx->cur_frame_length = sconf->frame_length;
+
+    // decode the frame data
+    if ((invalid_frame = read_frame_data(ctx, ra_frame) < 0))
+        av_log(ctx->avctx, AV_LOG_WARNING,
+               "Reading frame data failed. Skipping RA unit.\n");
+
+    ctx->frame_id++;
+
+    // check for size of decoded data
+    size = ctx->cur_frame_length * avctx->channels *
+           (av_get_bits_per_sample_format(avctx->sample_fmt) >> 3);
+
+    if (size > *data_size) {
+        av_log(avctx, AV_LOG_ERROR, "Decoded data exceeds buffer size.\n");
+        return -1;
+    }
+
+    *data_size = size;
+
+    // transform decoded frame into output format
+    #define INTERLEAVE_OUTPUT(bps)                                 \
+    {                                                              \
+        int##bps##_t *dest = (int##bps##_t*) data;                 \
+        shift = bps - ctx->avctx->bits_per_raw_sample;             \
+        for (sample = 0; sample < ctx->cur_frame_length; sample++) \
+            for (c = 0; c < avctx->channels; c++)                  \
+                *dest++ = ctx->raw_samples[c][sample] << shift;    \
+    }
+
+    if (ctx->avctx->bits_per_raw_sample <= 16) {
+        INTERLEAVE_OUTPUT(16)
+    } else {
+        INTERLEAVE_OUTPUT(32)
+    }
+
+    bytes_read = invalid_frame ? buffer_size :
+                                 (get_bits_count(&ctx->gb) + 7) >> 3;
+
+    return bytes_read;
+}
+
+
+/** Uninitializes the ALS decoder.
+ */
+static av_cold int decode_end(AVCodecContext *avctx)
+{
+    ALSDecContext *ctx = avctx->priv_data;
+
+    av_freep(&ctx->sconf.chan_pos);
+
+    av_freep(&ctx->quant_cof);
+    av_freep(&ctx->lpc_cof);
+    av_freep(&ctx->prev_raw_samples);
+    av_freep(&ctx->raw_samples);
+    av_freep(&ctx->raw_buffer);
+
+    return 0;
+}
+
+
+/** Initializes the ALS decoder.
+ */
+static av_cold int decode_init(AVCodecContext *avctx)
+{
+    unsigned int c;
+    unsigned int channel_size;
+    ALSDecContext *ctx = avctx->priv_data;
+    ALSSpecificConfig *sconf = &ctx->sconf;
+    ctx->avctx = avctx;
+
+    if (!avctx->extradata) {
+        av_log(avctx, AV_LOG_ERROR, "Missing required ALS extradata.\n");
+        return -1;
+    }
+
+    if (read_specific_config(ctx)) {
+        av_log(avctx, AV_LOG_ERROR, "Reading ALSSpecificConfig failed.\n");
+        decode_end(avctx);
+        return -1;
+    }
+
+    if (check_specific_config(ctx)) {
+        decode_end(avctx);
+        return -1;
+    }
+
+    if (sconf->floating) {
+        avctx->sample_fmt          = SAMPLE_FMT_FLT;
+        avctx->bits_per_raw_sample = 32;
+    } else {
+        avctx->sample_fmt          = sconf->resolution > 1
+                                     ? SAMPLE_FMT_S32 : SAMPLE_FMT_S16;
+        avctx->bits_per_raw_sample = (sconf->resolution + 1) * 8;
+    }
+
+    avctx->frame_size = sconf->frame_length;
+    channel_size      = sconf->frame_length + sconf->max_order;
+
+    ctx->prev_raw_samples = av_malloc (sizeof(*ctx->prev_raw_samples) * sconf->max_order);
+    ctx->raw_buffer       = av_mallocz(sizeof(*ctx->     raw_buffer)  * avctx->channels * channel_size);
+    ctx->raw_samples      = av_malloc (sizeof(*ctx->     raw_samples) * avctx->channels);
+
+    // allocate previous raw sample buffer
+    if (!ctx->prev_raw_samples || !ctx->raw_buffer|| !ctx->raw_samples) {
+        av_log(avctx, AV_LOG_ERROR, "Allocating buffer memory failed.\n");
+        decode_end(avctx);
+        return AVERROR(ENOMEM);
+    }
+
+    // assign raw samples buffers
+    ctx->raw_samples[0] = ctx->raw_buffer + sconf->max_order;
+    for (c = 1; c < avctx->channels; c++)
+        ctx->raw_samples[c] = ctx->raw_samples[c - 1] + channel_size;
+
+    return 0;
+}
+
+
+/** Flushes (resets) the frame ID after seeking.
+ */
+static av_cold void flush(AVCodecContext *avctx)
+{
+    ALSDecContext *ctx = avctx->priv_data;
+
+    ctx->frame_id = 0;
+}
+
+
+AVCodec als_decoder = {
+    "als",
+    CODEC_TYPE_AUDIO,
+    CODEC_ID_MP4ALS,
+    sizeof(ALSDecContext),
+    decode_init,
+    NULL,
+    decode_end,
+    decode_frame,
+    .flush = flush,
+    .capabilities = CODEC_CAP_SUBFRAMES,
+    .long_name = NULL_IF_CONFIG_SMALL("MPEG-4 Audio Lossless Coding (ALS)"),
+};
+