first pass at ALAC decoder from David Hammerton; while David's original

decoder works great, this decoder is not completely and seamlessly
integrated yet with FFmpeg

Originally committed as revision 4008 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 970 insertions, 0 deletions

diff --git a/libavcodec/alac.c b/libavcodec/alac.c
new file mode 100644
index 0000000000..0523707381
--- /dev/null
+++ b/libavcodec/alac.c
@@ -0,0 +1,970 @@
+/*
+ * ALAC (Apple Lossless Audio Codec) decoder
+ * Copyright (c) 2005 David Hammerton
+ * All rights reserved.
+ *
+ * This library 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 of the License, or (at your option) any later version.
+ *
+ * This library 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 this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+/**
+ * @file alac.c
+ * ALAC (Apple Lossless Audio Codec) decoder
+ * @author 2005 David Hammerton
+ *
+ * For more information on the ALAC format, visit:
+ *  http://crazney.net/programs/itunes/alac.html
+ *
+ * Note: This decoder expects a 36- (0x24-)byte QuickTime atom to be
+ * passed through the extradata[_size] fields. This atom is tacked onto
+ * the end of an 'alac' stsd atom and has the following format:
+ *  bytes 0-3   atom size (0x24), big-endian
+ *  bytes 4-7   atom type ('alac', not the 'alac' tag from start of stsd)
+ *  bytes 8-35  data bytes needed by decoder
+ */
+
+
+#include "avcodec.h"
+
+#define ALAC_EXTRADATA_SIZE 36
+
+struct alac_file {
+    unsigned char *input_buffer;
+    int input_buffer_index;
+    int input_buffer_size;
+    int input_buffer_bitaccumulator; /* used so we can do arbitary
+                                        bit reads */
+
+    int samplesize;
+    int numchannels;
+    int bytespersample;
+
+
+    /* buffers */
+    int32_t *predicterror_buffer_a;
+    int32_t *predicterror_buffer_b;
+
+    int32_t *outputsamples_buffer_a;
+    int32_t *outputsamples_buffer_b;
+
+
+    /* stuff from setinfo */
+    uint32_t setinfo_max_samples_per_frame; /* 0x1000 = 4096 */    /* max samples per frame? */
+    uint8_t setinfo_7a; /* 0x00 */
+    uint8_t setinfo_sample_size; /* 0x10 */
+    uint8_t setinfo_rice_historymult; /* 0x28 */
+    uint8_t setinfo_rice_initialhistory; /* 0x0a */
+    uint8_t setinfo_rice_kmodifier; /* 0x0e */
+    uint8_t setinfo_7f; /* 0x02 */
+    uint16_t setinfo_80; /* 0x00ff */
+    uint32_t setinfo_82; /* 0x000020e7 */
+    uint32_t setinfo_86; /* 0x00069fe4 */
+    uint32_t setinfo_8a_rate; /* 0x0000ac44 */
+    /* end setinfo stuff */
+};
+
+typedef struct alac_file alac_file;
+
+typedef struct {
+
+    AVCodecContext *avctx;
+    /* init to 0; first frame decode should initialize from extradata and
+     * set this to 1 */
+    int context_initialized;
+
+    alac_file *alac;
+} ALACContext;
+
+static void allocate_buffers(alac_file *alac)
+{
+    alac->predicterror_buffer_a = av_malloc(alac->setinfo_max_samples_per_frame * 4);
+    alac->predicterror_buffer_b = av_malloc(alac->setinfo_max_samples_per_frame * 4);
+
+    alac->outputsamples_buffer_a = av_malloc(alac->setinfo_max_samples_per_frame * 4);
+    alac->outputsamples_buffer_b = av_malloc(alac->setinfo_max_samples_per_frame * 4);
+}
+
+void alac_set_info(alac_file *alac, char *inputbuffer)
+{
+  char *ptr = inputbuffer;
+
+    ptr += 4; /* size */
+    ptr += 4; /* alac */
+    ptr += 4; /* 0 ? */
+
+    alac->setinfo_max_samples_per_frame = BE_32(ptr); /* buffer size / 2 ? */
+    ptr += 4;
+    alac->setinfo_7a = *ptr++;
+    alac->setinfo_sample_size = *ptr++;
+    alac->setinfo_rice_historymult = *ptr++;
+    alac->setinfo_rice_initialhistory = *ptr++;
+    alac->setinfo_rice_kmodifier = *ptr++;
+    alac->setinfo_7f = *ptr++;
+    alac->setinfo_80 = BE_16(ptr);
+    ptr += 2;
+    alac->setinfo_82 = BE_32(ptr);
+    ptr += 4;
+    alac->setinfo_86 = BE_32(ptr);
+    ptr += 4;
+    alac->setinfo_8a_rate = BE_32(ptr);
+    ptr += 4;
+
+    allocate_buffers(alac);
+}
+
+/* stream reading */
+
+/* supports reading 1 to 16 bits, in big endian format */
+static uint32_t readbits_16(alac_file *alac, int bits)
+{
+    uint32_t result;
+    int new_accumulator;
+
+    if (alac->input_buffer_index + 2 >= alac->input_buffer_size) {
+        av_log(NULL, AV_LOG_INFO, "alac: input buffer went out of bounds (%d >= %d)\n",
+            alac->input_buffer_index + 2, alac->input_buffer_size);
+        exit (0);
+    }
+    result = (alac->input_buffer[alac->input_buffer_index + 0] << 16) |
+             (alac->input_buffer[alac->input_buffer_index + 1] << 8) |
+             (alac->input_buffer[alac->input_buffer_index + 2]);
+
+    /* shift left by the number of bits we've already read,
+     * so that the top 'n' bits of the 24 bits we read will
+     * be the return bits */
+    result = result << alac->input_buffer_bitaccumulator;
+
+    result = result & 0x00ffffff;
+
+    /* and then only want the top 'n' bits from that, where
+     * n is 'bits' */
+    result = result >> (24 - bits);
+
+    new_accumulator = (alac->input_buffer_bitaccumulator + bits);
+
+    /* increase the buffer pointer if we've read over n bytes. */
+    alac->input_buffer_index += (new_accumulator >> 3);
+
+    /* and the remainder goes back into the bit accumulator */
+    alac->input_buffer_bitaccumulator = (new_accumulator & 7);
+
+    return result;
+}
+
+/* supports reading 1 to 32 bits, in big endian format */
+static uint32_t readbits(alac_file *alac, int bits)
+{
+    int32_t result = 0;
+
+    if (bits > 16) {
+        bits -= 16;
+        result = readbits_16(alac, 16) << bits;
+    }
+
+    result |= readbits_16(alac, bits);
+
+    return result;
+}
+
+/* reads a single bit */
+static int readbit(alac_file *alac)
+{
+    int result;
+    int new_accumulator;
+
+    if (alac->input_buffer_index >= alac->input_buffer_size) {
+        av_log(NULL, AV_LOG_INFO, "alac: input buffer went out of bounds (%d >= %d)\n",
+            alac->input_buffer_index + 2, alac->input_buffer_size);
+        exit (0);
+    }
+
+    result = alac->input_buffer[alac->input_buffer_index];
+
+    result = result << alac->input_buffer_bitaccumulator;
+
+    result = result >> 7 & 1;
+
+    new_accumulator = (alac->input_buffer_bitaccumulator + 1);
+
+    alac->input_buffer_index += (new_accumulator / 8);
+
+    alac->input_buffer_bitaccumulator = (new_accumulator % 8);
+
+    return result;
+}
+
+static void unreadbits(alac_file *alac, int bits)
+{
+    int new_accumulator = (alac->input_buffer_bitaccumulator - bits);
+
+    alac->input_buffer_index += (new_accumulator >> 3);
+
+    alac->input_buffer_bitaccumulator = (new_accumulator & 7);
+    if (alac->input_buffer_bitaccumulator < 0)
+        alac->input_buffer_bitaccumulator *= -1;
+}
+
+/* hideously inefficient. could use a bitmask search,
+ * alternatively bsr on x86,
+ */
+static int count_leading_zeros(int32_t input)
+{
+    int i = 0;
+    while (!(0x80000000 & input) && i < 32) {
+        i++;
+        input = input << 1;
+    }
+    return i;
+}
+
+void bastardized_rice_decompress(alac_file *alac,
+                                 int32_t *output_buffer,
+                                 int output_size,
+                                 int readsamplesize, /* arg_10 */
+                                 int rice_initialhistory, /* arg424->b */
+                                 int rice_kmodifier, /* arg424->d */
+                                 int rice_historymult, /* arg424->c */
+                                 int rice_kmodifier_mask /* arg424->e */
+        )
+{
+    int output_count;
+    unsigned int history = rice_initialhistory;
+    int sign_modifier = 0;
+
+    for (output_count = 0; output_count < output_size; output_count++) {
+        int32_t x = 0;
+        int32_t x_modified;
+        int32_t final_val;
+
+        /* read x - number of 1s before 0 represent the rice */
+        while (x <= 8 && readbit(alac)) {
+            x++;
+        }
+
+
+        if (x > 8) { /* RICE THRESHOLD */
+          /* use alternative encoding */
+            int32_t value;
+
+            value = readbits(alac, readsamplesize);
+
+            /* mask value to readsamplesize size */
+            if (readsamplesize != 32)
+                value &= (0xffffffff >> (32 - readsamplesize));
+
+            x = value;
+        } else {
+          /* standard rice encoding */
+            int extrabits;
+            int k; /* size of extra bits */
+
+            /* read k, that is bits as is */
+            k = 31 - rice_kmodifier - count_leading_zeros((history >> 9) + 3);
+
+            if (k < 0) 
+                k += rice_kmodifier;
+            else 
+                k = rice_kmodifier;
+
+            if (k != 1) {
+                extrabits = readbits(alac, k);
+
+                /* multiply x by 2^k - 1, as part of their strange algorithm */
+                x = (x << k) - x;
+
+                if (extrabits > 1) {
+                    x += extrabits - 1;
+                } else 
+                    unreadbits(alac, 1);
+            }
+        }
+
+        x_modified = sign_modifier + x;
+        final_val = (x_modified + 1) / 2;
+        if (x_modified & 1) final_val *= -1;
+
+        output_buffer[output_count] = final_val;
+
+        sign_modifier = 0;
+
+        /* now update the history */
+        history += (x_modified * rice_historymult)
+                 - ((history * rice_historymult) >> 9);
+
+        if (x_modified > 0xffff)
+            history = 0xffff;
+
+        /* special case: there may be compressed blocks of 0 */
+        if ((history < 128) && (output_count+1 < output_size)) {
+            int block_size;
+
+            sign_modifier = 1;
+
+            x = 0;
+            while (x <= 8 && readbit(alac)) {
+                x++;
+            }
+
+            if (x > 8) {
+                block_size = readbits(alac, 16);
+                block_size &= 0xffff;
+            } else {
+                int k;
+                int extrabits;
+
+                k = count_leading_zeros(history) + ((history + 16) >> 6 /* / 64 */) - 24;
+
+                extrabits = readbits(alac, k);
+
+                block_size = (((1 << k) - 1) & rice_kmodifier_mask) * x
+                           + extrabits - 1;
+
+                if (extrabits < 2) {
+                    x = 1 - extrabits;
+                    block_size += x;
+                    unreadbits(alac, 1);
+                }
+            }
+
+            if (block_size > 0) {
+                memset(&output_buffer[output_count+1], 0, block_size * 4);
+                output_count += block_size;
+
+            }
+
+            if (block_size > 0xffff)
+                sign_modifier = 0;
+
+            history = 0;
+        }
+    }
+}
+
+#define SIGN_EXTENDED32(val, bits) ((val << (32 - bits)) >> (32 - bits))
+
+#define SIGN_ONLY(v) \
+                     ((v < 0) ? (-1) : \
+                                ((v > 0) ? (1) : \
+                                           (0)))
+
+static void predictor_decompress_fir_adapt(int32_t *error_buffer,
+                                           int32_t *buffer_out,
+                                           int output_size,
+                                           int readsamplesize,
+                                           int16_t *predictor_coef_table,
+                                           int predictor_coef_num,
+                                           int predictor_quantitization)
+{
+    int i;
+
+    /* first sample always copies */
+    *buffer_out = *error_buffer;
+
+    if (!predictor_coef_num) {
+        if (output_size <= 1) return;
+        memcpy(buffer_out+1, error_buffer+1, (output_size-1) * 4);
+        return;
+    }
+
+    if (predictor_coef_num == 0x1f) { /* 11111 - max value of predictor_coef_num */
+      /* second-best case scenario for fir decompression,
+       * error describes a small difference from the previous sample only
+       */
+        if (output_size <= 1) return;
+        for (i = 0; i < output_size - 1; i++) {
+            int32_t prev_value;
+            int32_t error_value;
+
+            prev_value = buffer_out[i];
+            error_value = error_buffer[i+1];
+            buffer_out[i+1] = SIGN_EXTENDED32((prev_value + error_value), readsamplesize);
+        }
+        return;
+    }
+
+    /* read warm-up samples */
+    if (predictor_coef_num > 0) {
+        int i;
+        for (i = 0; i < predictor_coef_num; i++) {
+            int32_t val;
+
+            val = buffer_out[i] + error_buffer[i+1];
+
+            val = SIGN_EXTENDED32(val, readsamplesize);
+
+            buffer_out[i+1] = val;
+        }
+    }
+
+#if 0
+    /* 4 and 8 are very common cases (the only ones i've seen). these
+     * should be unrolled and optimised
+     */
+    if (predictor_coef_num == 4) {
+        /* FIXME: optimised general case */
+        return;
+    }
+
+    if (predictor_coef_table == 8) {
+        /* FIXME: optimised general case */
+        return;
+    }
+#endif
+
+
+    /* general case */
+    if (predictor_coef_num > 0) {
+        for (i = predictor_coef_num + 1;
+             i < output_size;
+             i++) {
+            int j;
+            int sum = 0;
+            int outval;
+            int error_val = error_buffer[i];
+
+            for (j = 0; j < predictor_coef_num; j++) {
+                sum += (buffer_out[predictor_coef_num-j] - buffer_out[0]) *
+                       predictor_coef_table[j];
+            }
+
+            outval = (1 << (predictor_quantitization-1)) + sum;
+            outval = outval >> predictor_quantitization;
+            outval = outval + buffer_out[0] + error_val;
+            outval = SIGN_EXTENDED32(outval, readsamplesize);
+
+            buffer_out[predictor_coef_num+1] = outval;
+
+            if (error_val > 0) {
+                int predictor_num = predictor_coef_num - 1;
+
+                while (predictor_num >= 0 && error_val > 0) {
+                    int val = buffer_out[0] - buffer_out[predictor_coef_num - predictor_num];
+                    int sign = SIGN_ONLY(val);
+
+                    predictor_coef_table[predictor_num] -= sign;
+
+                    val *= sign; /* absolute value */
+
+                    error_val -= ((val >> predictor_quantitization) *
+                                  (predictor_coef_num - predictor_num));
+
+                    predictor_num--;
+                }
+            } else if (error_val < 0) {
+                int predictor_num = predictor_coef_num - 1;
+
+                while (predictor_num >= 0 && error_val < 0) {
+                    int val = buffer_out[0] - buffer_out[predictor_coef_num - predictor_num];
+                    int sign = - SIGN_ONLY(val);
+
+                    predictor_coef_table[predictor_num] -= sign;
+
+                    val *= sign; /* neg value */
+
+                    error_val -= ((val >> predictor_quantitization) *
+                                  (predictor_coef_num - predictor_num));
+
+                    predictor_num--;
+                }
+            }
+
+            buffer_out++;
+        }
+    }
+}
+
+void deinterlace_16(int32_t *buffer_a, int32_t *buffer_b,
+                    int16_t *buffer_out,
+                    int numchannels, int numsamples,
+                    uint8_t interlacing_shift,
+                    uint8_t interlacing_leftweight) {
+
+    int i;
+    if (numsamples <= 0) return;
+
+    /* weighted interlacing */
+    if (interlacing_leftweight) {
+        for (i = 0; i < numsamples; i++) {
+            int32_t difference, midright;
+            int16_t left;
+            int16_t right;
+
+            midright = buffer_a[i];
+            difference = buffer_b[i];
+
+
+            right = midright - ((difference * interlacing_leftweight) >> interlacing_shift);
+            left = (midright - ((difference * interlacing_leftweight) >> interlacing_shift))
+                 + difference;
+
+            /* output is always little endian */
+/*
+            if (host_bigendian) {
+                be2me_16(left);
+                be2me_16(right);
+            }
+*/
+
+            buffer_out[i*numchannels] = left;
+            buffer_out[i*numchannels + 1] = right;
+        }
+
+        return;
+    }
+
+    /* otherwise basic interlacing took place */
+    for (i = 0; i < numsamples; i++) {
+        int16_t left, right;
+
+        left = buffer_a[i];
+        right = buffer_b[i];
+
+        /* output is always little endian */
+/*
+        if (host_bigendian) {
+            be2me_16(left);
+            be2me_16(right);
+        }
+*/
+
+        buffer_out[i*numchannels] = left;
+        buffer_out[i*numchannels + 1] = right;
+    }
+}
+
+int decode_frame(ALACContext *s, alac_file *alac,
+                  unsigned char *inbuffer,
+                  int input_buffer_size,
+                  void *outbuffer, int *outputsize){
+
+    int channels;
+    int32_t outputsamples = alac->setinfo_max_samples_per_frame;
+
+    /* initialize from the extradata */
+    if (!s->context_initialized) {
+        if (s->avctx->extradata_size != ALAC_EXTRADATA_SIZE) {
+            av_log(NULL, AV_LOG_ERROR, "alac: expected %d extradata bytes\n", 
+                ALAC_EXTRADATA_SIZE);
+            return input_buffer_size;
+        }
+        alac_set_info(s->alac, s->avctx->extradata);
+        s->context_initialized = 1;
+    }
+    
+
+    /* setup the stream */
+    alac->input_buffer = inbuffer;
+    alac->input_buffer_index = 0;
+    alac->input_buffer_size = input_buffer_size;
+    alac->input_buffer_bitaccumulator = 0;
+
+    channels = readbits(alac, 3);
+
+    *outputsize = outputsamples * alac->bytespersample;
+
+    switch(channels) {
+    case 0: { /* 1 channel */
+        int hassize;
+        int isnotcompressed;
+        int readsamplesize;
+
+        int wasted_bytes;
+        int ricemodifier;
+
+
+        /* 2^result = something to do with output waiting.
+         * perhaps matters if we read > 1 frame in a pass?
+         */
+        readbits(alac, 4);
+
+        readbits(alac, 12); /* unknown, skip 12 bits */
+
+        hassize = readbits(alac, 1); /* the output sample size is stored soon */
+
+        wasted_bytes = readbits(alac, 2); /* unknown ? */
+
+        isnotcompressed = readbits(alac, 1); /* whether the frame is compressed */
+
+        if (hassize) {
+            /* now read the number of samples,
+             * as a 32bit integer */
+            outputsamples = readbits(alac, 32);
+            *outputsize = outputsamples * alac->bytespersample;
+        }
+
+        readsamplesize = alac->setinfo_sample_size - (wasted_bytes * 8);
+
+        if (!isnotcompressed) {
+         /* so it is compressed */
+            int16_t predictor_coef_table[32];
+            int predictor_coef_num;
+            int prediction_type;
+            int prediction_quantitization;
+            int i;
+
+            /* skip 16 bits, not sure what they are. seem to be used in
+             * two channel case */
+            readbits(alac, 8);
+            readbits(alac, 8);
+
+            prediction_type = readbits(alac, 4);
+            prediction_quantitization = readbits(alac, 4);
+
+            ricemodifier = readbits(alac, 3);
+            predictor_coef_num = readbits(alac, 5);
+
+            /* read the predictor table */
+            for (i = 0; i < predictor_coef_num; i++) {
+                predictor_coef_table[i] = (int16_t)readbits(alac, 16);
+            }
+
+            if (wasted_bytes) {
+                /* these bytes seem to have something to do with
+                 * > 2 channel files.
+                 */
+                av_log(NULL, AV_LOG_ERROR, "FIXME: unimplemented, unhandling of wasted_bytes\n");
+            }
+
+            bastardized_rice_decompress(alac,
+                                        alac->predicterror_buffer_a,
+                                        outputsamples,
+                                        readsamplesize,
+                                        alac->setinfo_rice_initialhistory,
+                                        alac->setinfo_rice_kmodifier,
+                                        ricemodifier * alac->setinfo_rice_historymult / 4,
+                                        (1 << alac->setinfo_rice_kmodifier) - 1);
+
+            if (prediction_type == 0) {
+              /* adaptive fir */
+                predictor_decompress_fir_adapt(alac->predicterror_buffer_a,
+                                               alac->outputsamples_buffer_a,
+                                               outputsamples,
+                                               readsamplesize,
+                                               predictor_coef_table,
+                                               predictor_coef_num,
+                                               prediction_quantitization);
+            } else {
+                av_log(NULL, AV_LOG_ERROR, "FIXME: unhandled prediction type: %i\n", prediction_type);
+                /* i think the only other prediction type (or perhaps this is just a
+                 * boolean?) runs adaptive fir twice.. like:
+                 * predictor_decompress_fir_adapt(predictor_error, tempout, ...)
+                 * predictor_decompress_fir_adapt(predictor_error, outputsamples ...)
+                 * little strange..
+                 */
+            }
+
+        } else {
+          /* not compressed, easy case */
+            if (readsamplesize <= 16) {
+                int i;
+                for (i = 0; i < outputsamples; i++) {
+                    int32_t audiobits = readbits(alac, readsamplesize);
+
+                    audiobits = SIGN_EXTENDED32(audiobits, readsamplesize);
+
+                    alac->outputsamples_buffer_a[i] = audiobits;
+                }
+            } else {
+                int i;
+                for (i = 0; i < outputsamples; i++) {
+                    int32_t audiobits;
+
+                    audiobits = readbits(alac, 16);
+                    /* special case of sign extension..
+                     * as we'll be ORing the low 16bits into this */
+                    audiobits = audiobits << 16;
+                    audiobits = audiobits >> (32 - readsamplesize);
+
+                    audiobits |= readbits(alac, readsamplesize - 16);
+
+                    alac->outputsamples_buffer_a[i] = audiobits;
+                }
+            }
+            /* wasted_bytes = 0; // unused */
+        }
+
+        switch(alac->setinfo_sample_size) {
+        case 16: {
+            int i;
+            for (i = 0; i < outputsamples; i++) {
+                int16_t sample = alac->outputsamples_buffer_a[i];
+                be2me_16(sample);
+                ((int16_t*)outbuffer)[i * alac->numchannels] = sample;
+            }
+            break;
+        }
+        case 20:
+        case 24:
+        case 32:
+            av_log(NULL, AV_LOG_ERROR, "FIXME: unimplemented sample size %i\n", alac->setinfo_sample_size);
+            break;
+        default:
+            break;
+        }
+        break;
+    }
+    case 1: { /* 2 channels */
+        int hassize;
+        int isnotcompressed;
+        int readsamplesize;
+
+        int wasted_bytes;
+
+        uint8_t interlacing_shift;
+        uint8_t interlacing_leftweight;
+
+        /* 2^result = something to do with output waiting.
+         * perhaps matters if we read > 1 frame in a pass?
+         */
+        readbits(alac, 4);
+
+        readbits(alac, 12); /* unknown, skip 12 bits */
+
+        hassize = readbits(alac, 1); /* the output sample size is stored soon */
+
+        wasted_bytes = readbits(alac, 2); /* unknown ? */
+
+        isnotcompressed = readbits(alac, 1); /* whether the frame is compressed */
+
+        if (hassize) {
+            /* now read the number of samples,
+             * as a 32bit integer */
+            outputsamples = readbits(alac, 32);
+            *outputsize = outputsamples * alac->bytespersample;
+        }
+
+        readsamplesize = alac->setinfo_sample_size - (wasted_bytes * 8) + 1;
+
+        if (!isnotcompressed) {
+         /* compressed */
+            int16_t predictor_coef_table_a[32];
+            int predictor_coef_num_a;
+            int prediction_type_a;
+            int prediction_quantitization_a;
+            int ricemodifier_a;
+
+            int16_t predictor_coef_table_b[32];
+            int predictor_coef_num_b;
+            int prediction_type_b;
+            int prediction_quantitization_b;
+            int ricemodifier_b;
+
+            int i;
+
+            interlacing_shift = readbits(alac, 8);
+            interlacing_leftweight = readbits(alac, 8);
+
+            /******** channel 1 ***********/
+            prediction_type_a = readbits(alac, 4);
+            prediction_quantitization_a = readbits(alac, 4);
+
+            ricemodifier_a = readbits(alac, 3);
+            predictor_coef_num_a = readbits(alac, 5);
+
+            /* read the predictor table */
+            for (i = 0; i < predictor_coef_num_a; i++) {
+                predictor_coef_table_a[i] = (int16_t)readbits(alac, 16);
+            }
+
+            /******** channel 2 *********/
+            prediction_type_b = readbits(alac, 4);
+            prediction_quantitization_b = readbits(alac, 4);
+
+            ricemodifier_b = readbits(alac, 3);
+            predictor_coef_num_b = readbits(alac, 5);
+
+            /* read the predictor table */
+            for (i = 0; i < predictor_coef_num_b; i++) {
+                predictor_coef_table_b[i] = (int16_t)readbits(alac, 16);
+            }
+
+            /*********************/
+            if (wasted_bytes) {
+              /* see mono case */
+                av_log(NULL, AV_LOG_ERROR, "FIXME: unimplemented, unhandling of wasted_bytes\n");
+            }
+
+            /* channel 1 */
+            bastardized_rice_decompress(alac,
+                                        alac->predicterror_buffer_a,
+                                        outputsamples,
+                                        readsamplesize,
+                                        alac->setinfo_rice_initialhistory,
+                                        alac->setinfo_rice_kmodifier,
+                                        ricemodifier_a * alac->setinfo_rice_historymult / 4,
+                                        (1 << alac->setinfo_rice_kmodifier) - 1);
+
+            if (prediction_type_a == 0) {
+              /* adaptive fir */
+                predictor_decompress_fir_adapt(alac->predicterror_buffer_a,
+                                               alac->outputsamples_buffer_a,
+                                               outputsamples,
+                                               readsamplesize,
+                                               predictor_coef_table_a,
+                                               predictor_coef_num_a,
+                                               prediction_quantitization_a);
+            } else {
+              /* see mono case */
+                av_log(NULL, AV_LOG_ERROR, "FIXME: unhandled prediction type: %i\n", prediction_type_a);
+            }
+
+            /* channel 2 */
+            bastardized_rice_decompress(alac,
+                                        alac->predicterror_buffer_b,
+                                        outputsamples,
+                                        readsamplesize,
+                                        alac->setinfo_rice_initialhistory,
+                                        alac->setinfo_rice_kmodifier,
+                                        ricemodifier_b * alac->setinfo_rice_historymult / 4,
+                                        (1 << alac->setinfo_rice_kmodifier) - 1);
+
+            if (prediction_type_b == 0) {
+              /* adaptive fir */
+                predictor_decompress_fir_adapt(alac->predicterror_buffer_b,
+                                               alac->outputsamples_buffer_b,
+                                               outputsamples,
+                                               readsamplesize,
+                                               predictor_coef_table_b,
+                                               predictor_coef_num_b,
+                                               prediction_quantitization_b);
+            } else {
+                av_log(NULL, AV_LOG_ERROR, "FIXME: unhandled prediction type: %i\n", prediction_type_b);
+            }
+        } else { 
+         /* not compressed, easy case */
+            if (alac->setinfo_sample_size <= 16) {
+                int i;
+                for (i = 0; i < outputsamples; i++) {
+                    int32_t audiobits_a, audiobits_b;
+
+                    audiobits_a = readbits(alac, alac->setinfo_sample_size);
+                    audiobits_b = readbits(alac, alac->setinfo_sample_size);
+
+                    audiobits_a = SIGN_EXTENDED32(audiobits_a, alac->setinfo_sample_size);
+                    audiobits_b = SIGN_EXTENDED32(audiobits_b, alac->setinfo_sample_size);
+
+                    alac->outputsamples_buffer_a[i] = audiobits_a;
+                    alac->outputsamples_buffer_b[i] = audiobits_b;
+                }
+            } else {
+                int i;
+                for (i = 0; i < outputsamples; i++) {
+                    int32_t audiobits_a, audiobits_b;
+
+                    audiobits_a = readbits(alac, 16);
+                    audiobits_a = audiobits_a << 16;
+                    audiobits_a = audiobits_a >> (32 - alac->setinfo_sample_size);
+                    audiobits_a |= readbits(alac, alac->setinfo_sample_size - 16);
+
+                    audiobits_b = readbits(alac, 16);
+                    audiobits_b = audiobits_b << 16;
+                    audiobits_b = audiobits_b >> (32 - alac->setinfo_sample_size);
+                    audiobits_b |= readbits(alac, alac->setinfo_sample_size - 16);
+
+                    alac->outputsamples_buffer_a[i] = audiobits_a;
+                    alac->outputsamples_buffer_b[i] = audiobits_b;
+                }
+            }
+            /* wasted_bytes = 0; */
+            interlacing_shift = 0;
+            interlacing_leftweight = 0;
+        }
+
+        switch(alac->setinfo_sample_size) {
+        case 16: {
+            deinterlace_16(alac->outputsamples_buffer_a,
+                           alac->outputsamples_buffer_b,
+                           (int16_t*)outbuffer,
+                           alac->numchannels,
+                           outputsamples,
+                           interlacing_shift,
+                           interlacing_leftweight);
+            break;
+        }
+        case 20:
+        case 24:
+        case 32:
+            av_log(NULL, AV_LOG_ERROR, "FIXME: unimplemented sample size %i\n", alac->setinfo_sample_size);
+            break;
+        default:
+            break;
+        }
+
+        break;
+    }
+    }
+
+av_log(NULL, AV_LOG_INFO, "buf size = %d, consumed %d\n",
+  input_buffer_size, alac->input_buffer_index);
+
+    /* avoid infinite loop: if decoder consumed 0 bytes; report all bytes
+     * consumed */
+//    if (alac->input_buffer_index)
+//        return alac->input_buffer_index;
+//    else
+        return input_buffer_size;
+}
+
+static int alac_decode_init(AVCodecContext * avctx)
+{
+    ALACContext *s = avctx->priv_data;
+    s->avctx = avctx;
+    s->context_initialized = 0;
+
+    s->alac = av_malloc(sizeof(alac_file));
+
+    s->alac->samplesize = s->avctx->bits_per_sample;
+    s->alac->numchannels = s->avctx->channels;
+    s->alac->bytespersample = (s->alac->samplesize / 8) * s->alac->numchannels;
+
+    return 0;
+}
+
+static int alac_decode_frame(AVCodecContext *avctx,
+                             void *data, int *data_size,
+                             uint8_t *buf, int buf_size)
+{
+    ALACContext *s = avctx->priv_data;
+    int bytes_consumed = buf_size;
+
+    if (buf)
+        bytes_consumed = decode_frame(s, s->alac, buf, buf_size, 
+            data, data_size);
+
+    return bytes_consumed;
+}
+
+static int alac_decode_close(AVCodecContext *avctx)
+{
+    ALACContext *s = avctx->priv_data;
+
+    av_free(s->alac->predicterror_buffer_a);
+    av_free(s->alac->predicterror_buffer_b);
+
+    av_free(s->alac->outputsamples_buffer_a);
+    av_free(s->alac->outputsamples_buffer_b);
+
+    return 0;
+}
+
+AVCodec alac_decoder = {
+    "alac",
+    CODEC_TYPE_AUDIO,
+    CODEC_ID_ALAC,
+    sizeof(ALACContext),
+    alac_decode_init,
+    NULL,
+    alac_decode_close,
+    alac_decode_frame,
+};