alac.c File Reference

#include "avcodec.h"
#include "bitstream.h"
#include "bytestream.h"
#include "unary.h"

Go to the source code of this file.

Data Structures
struct	ALACContext
Defines
#define	ALAC_EXTRADATA_SIZE   36
#define	MAX_CHANNELS   2
Functions
static void	allocate_buffers (ALACContext *alac)
static int	alac_set_info (ALACContext *alac)
static int	decode_scalar (GetBitContext *gb, int k, int limit, int readsamplesize)
static void	bastardized_rice_decompress (ALACContext *alac, int32_t *output_buffer, int output_size, int readsamplesize, int rice_initialhistory, int rice_kmodifier, int rice_historymult, int rice_kmodifier_mask)
static int32_t	extend_sign32 (int32_t val, int bits)
static int	sign_only (int v)
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)
static void	reconstruct_stereo_16 (int32_t *buffer[MAX_CHANNELS], int16_t *buffer_out, int numchannels, int numsamples, uint8_t interlacing_shift, uint8_t interlacing_leftweight)
static int	alac_decode_frame (AVCodecContext *avctx, void *outbuffer, int *outputsize, const uint8_t *inbuffer, int input_buffer_size)
static av_cold int	alac_decode_init (AVCodecContext *avctx)
static av_cold int	alac_decode_close (AVCodecContext *avctx)
Variables
AVCodec	alac_decoder

---

Detailed Description

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

Extradata: 32bit size 32bit tag (=alac) 32bit zero? 32bit max sample per frame 8bit ?? (zero?) 8bit sample size 8bit history mult 8bit initial history 8bit kmodifier 8bit channels? 16bit ?? 32bit max coded frame size 32bit bitrate? 32bit samplerate

Definition in file alac.c.

---

Define Documentation

#define ALAC_EXTRADATA_SIZE   36

Definition at line 60 of file alac.c.

Referenced by alac_decode_frame().

#define MAX_CHANNELS   2

Definition at line 61 of file alac.c.

Referenced by alac_decode_close(), alac_decode_frame(), allocate_buffers(), encode_block(), encode_init(), pcm_decode_frame(), shorten_decode_frame(), and wma_decode_block().

---

Function Documentation

static av_cold int alac_decode_close

(

AVCodecContext *

avctx

)

[static]

Definition at line 601 of file alac.c.

References av_free(), MAX_CHANNELS, ALACContext::outputsamples_buffer, ALACContext::predicterror_buffer, and AVCodecContext::priv_data.

{
    ALACContext *alac = avctx->priv_data;

    int chan;
    for (chan = 0; chan < MAX_CHANNELS; chan++) {
        av_free(alac->predicterror_buffer[chan]);
        av_free(alac->outputsamples_buffer[chan]);
    }

    return 0;
}

static int alac_decode_frame	(	AVCodecContext *	avctx,
		void *	outbuffer,
		int *	outputsize,
		const uint8_t *	inbuffer,
		int	input_buffer_size
	)			[static]

Definition at line 405 of file alac.c.

References ALAC_EXTRADATA_SIZE, alac_set_info(), av_log(), AV_LOG_ERROR, ALACContext::avctx, bastardized_rice_decompress(), ALACContext::bytespersample, ALACContext::context_initialized, extend_sign32(), AVCodecContext::extradata_size, for(), ALACContext::gb, get_bits(), get_bits1(), get_bits_count(), get_bits_long(), init_get_bits(), MAX_CHANNELS, ALACContext::numchannels, ALACContext::outputsamples_buffer, ALACContext::predicterror_buffer, predictor_decompress_fir_adapt(), AVCodecContext::priv_data, reconstruct_stereo_16(), ALACContext::setinfo_max_samples_per_frame, ALACContext::setinfo_rice_historymult, ALACContext::setinfo_rice_initialhistory, ALACContext::setinfo_rice_kmodifier, ALACContext::setinfo_sample_size, and skip_bits().

{
    ALACContext *alac = avctx->priv_data;

    int channels;
    unsigned int outputsamples;
    int hassize;
    int readsamplesize;
    int wasted_bytes;
    int isnotcompressed;
    uint8_t interlacing_shift;
    uint8_t interlacing_leftweight;

    /* short-circuit null buffers */
    if (!inbuffer || !input_buffer_size)
        return input_buffer_size;

    /* initialize from the extradata */
    if (!alac->context_initialized) {
        if (alac->avctx->extradata_size != ALAC_EXTRADATA_SIZE) {
            av_log(avctx, AV_LOG_ERROR, "alac: expected %d extradata bytes\n",
                ALAC_EXTRADATA_SIZE);
            return input_buffer_size;
        }
        if (alac_set_info(alac)) {
            av_log(avctx, AV_LOG_ERROR, "alac: set_info failed\n");
            return input_buffer_size;
        }
        alac->context_initialized = 1;
    }

    init_get_bits(&alac->gb, inbuffer, input_buffer_size * 8);

    channels = get_bits(&alac->gb, 3) + 1;
    if (channels > MAX_CHANNELS) {
        av_log(avctx, AV_LOG_ERROR, "channels > %d not supported\n",
               MAX_CHANNELS);
        return input_buffer_size;
    }

    /* 2^result = something to do with output waiting.
     * perhaps matters if we read > 1 frame in a pass?
     */
    skip_bits(&alac->gb, 4);

    skip_bits(&alac->gb, 12); /* unknown, skip 12 bits */

    /* the output sample size is stored soon */
    hassize = get_bits1(&alac->gb);

    wasted_bytes = get_bits(&alac->gb, 2); /* unknown ? */

    /* whether the frame is compressed */
    isnotcompressed = get_bits1(&alac->gb);

    if (hassize) {
        /* now read the number of samples as a 32bit integer */
        outputsamples = get_bits_long(&alac->gb, 32);
        if(outputsamples > alac->setinfo_max_samples_per_frame){
            av_log(avctx, AV_LOG_ERROR, "outputsamples %d > %d\n", outputsamples, alac->setinfo_max_samples_per_frame);
            return -1;
        }
    } else
        outputsamples = alac->setinfo_max_samples_per_frame;

    if(outputsamples > *outputsize / alac->bytespersample){
        av_log(avctx, AV_LOG_ERROR, "sample buffer too small\n");
        return -1;
    }

    *outputsize = outputsamples * alac->bytespersample;
    readsamplesize = alac->setinfo_sample_size - (wasted_bytes * 8) + channels - 1;

    if (!isnotcompressed) {
        /* so it is compressed */
        int16_t predictor_coef_table[channels][32];
        int predictor_coef_num[channels];
        int prediction_type[channels];
        int prediction_quantitization[channels];
        int ricemodifier[channels];
        int i, chan;

        interlacing_shift = get_bits(&alac->gb, 8);
        interlacing_leftweight = get_bits(&alac->gb, 8);

        for (chan = 0; chan < channels; chan++) {
            prediction_type[chan] = get_bits(&alac->gb, 4);
            prediction_quantitization[chan] = get_bits(&alac->gb, 4);

            ricemodifier[chan] = get_bits(&alac->gb, 3);
            predictor_coef_num[chan] = get_bits(&alac->gb, 5);

            /* read the predictor table */
            for (i = 0; i < predictor_coef_num[chan]; i++)
                predictor_coef_table[chan][i] = (int16_t)get_bits(&alac->gb, 16);
        }

        if (wasted_bytes)
            av_log(avctx, AV_LOG_ERROR, "FIXME: unimplemented, unhandling of wasted_bytes\n");

        for (chan = 0; chan < channels; chan++) {
            bastardized_rice_decompress(alac,
                                        alac->predicterror_buffer[chan],
                                        outputsamples,
                                        readsamplesize,
                                        alac->setinfo_rice_initialhistory,
                                        alac->setinfo_rice_kmodifier,
                                        ricemodifier[chan] * alac->setinfo_rice_historymult / 4,
                                        (1 << alac->setinfo_rice_kmodifier) - 1);

            if (prediction_type[chan] == 0) {
                /* adaptive fir */
                predictor_decompress_fir_adapt(alac->predicterror_buffer[chan],
                                               alac->outputsamples_buffer[chan],
                                               outputsamples,
                                               readsamplesize,
                                               predictor_coef_table[chan],
                                               predictor_coef_num[chan],
                                               prediction_quantitization[chan]);
            } else {
                av_log(avctx, AV_LOG_ERROR, "FIXME: unhandled prediction type: %i\n", prediction_type[chan]);
                /* 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 */
        int i, chan;
        for (i = 0; i < outputsamples; i++)
            for (chan = 0; chan < channels; chan++) {
                int32_t audiobits;

                audiobits = get_bits_long(&alac->gb, alac->setinfo_sample_size);
                audiobits = extend_sign32(audiobits, alac->setinfo_sample_size);

                alac->outputsamples_buffer[chan][i] = audiobits;
            }
        /* wasted_bytes = 0; */
        interlacing_shift = 0;
        interlacing_leftweight = 0;
    }
    if (get_bits(&alac->gb, 3) != 7)
        av_log(avctx, AV_LOG_ERROR, "Error : Wrong End Of Frame\n");

    switch(alac->setinfo_sample_size) {
    case 16:
        if (channels == 2) {
            reconstruct_stereo_16(alac->outputsamples_buffer,
                                  (int16_t*)outbuffer,
                                  alac->numchannels,
                                  outputsamples,
                                  interlacing_shift,
                                  interlacing_leftweight);
        } else {
            int i;
            for (i = 0; i < outputsamples; i++) {
                int16_t sample = alac->outputsamples_buffer[0][i];
                ((int16_t*)outbuffer)[i * alac->numchannels] = sample;
            }
        }
        break;
    case 20:
    case 24:
        // It is not clear if there exist any encoder that creates 24 bit ALAC
        // files. iTunes convert 24 bit raw files to 16 bit before encoding.
    case 32:
        av_log(avctx, AV_LOG_ERROR, "FIXME: unimplemented sample size %i\n", alac->setinfo_sample_size);
        break;
    default:
        break;
    }

    if (input_buffer_size * 8 - get_bits_count(&alac->gb) > 8)
        av_log(avctx, AV_LOG_ERROR, "Error : %d bits left\n", input_buffer_size * 8 - get_bits_count(&alac->gb));

    return input_buffer_size;
}

static av_cold int alac_decode_init

(

AVCodecContext *

avctx

)

[static]

Definition at line 589 of file alac.c.

References ALACContext::avctx, AVCodecContext::bits_per_sample, ALACContext::bytespersample, AVCodecContext::channels, ALACContext::context_initialized, ALACContext::numchannels, and AVCodecContext::priv_data.

{
    ALACContext *alac = avctx->priv_data;
    alac->avctx = avctx;
    alac->context_initialized = 0;

    alac->numchannels = alac->avctx->channels;
    alac->bytespersample = (avctx->bits_per_sample / 8) * alac->numchannels;

    return 0;
}

static int alac_set_info

(

ALACContext *

alac

)

[static]

Definition at line 101 of file alac.c.

References allocate_buffers(), av_log(), AV_LOG_ERROR, AV_RB32, ALACContext::avctx, AVCodecContext::extradata, ALACContext::setinfo_max_samples_per_frame, ALACContext::setinfo_rice_historymult, ALACContext::setinfo_rice_initialhistory, ALACContext::setinfo_rice_kmodifier, and ALACContext::setinfo_sample_size.

Referenced by alac_decode_frame().

{
    const unsigned char *ptr = alac->avctx->extradata;

    ptr += 4; /* size */
    ptr += 4; /* alac */
    ptr += 4; /* 0 ? */

    if(AV_RB32(ptr) >= UINT_MAX/4){
        av_log(alac->avctx, AV_LOG_ERROR, "setinfo_max_samples_per_frame too large\n");
        return -1;
    }

    /* buffer size / 2 ? */
    alac->setinfo_max_samples_per_frame = bytestream_get_be32(&ptr);
    ptr++;                          /* ??? */
    alac->setinfo_sample_size           = *ptr++;
    if (alac->setinfo_sample_size > 32) {
        av_log(alac->avctx, AV_LOG_ERROR, "setinfo_sample_size too large\n");
        return -1;
    }
    alac->setinfo_rice_historymult      = *ptr++;
    alac->setinfo_rice_initialhistory   = *ptr++;
    alac->setinfo_rice_kmodifier        = *ptr++;
    ptr++;                         /* channels? */
    bytestream_get_be16(&ptr);      /* ??? */
    bytestream_get_be32(&ptr);      /* max coded frame size */
    bytestream_get_be32(&ptr);      /* bitrate ? */
    bytestream_get_be32(&ptr);      /* samplerate */

    allocate_buffers(alac);

    return 0;
}

static void allocate_buffers

(

ALACContext *

alac

)

[static]

Definition at line 89 of file alac.c.

References av_malloc(), MAX_CHANNELS, ALACContext::outputsamples_buffer, ALACContext::predicterror_buffer, and ALACContext::setinfo_max_samples_per_frame.

Referenced by alac_set_info(), flac_decode_init(), metadata_parse(), and shorten_decode_frame().

{
    int chan;
    for (chan = 0; chan < MAX_CHANNELS; chan++) {
        alac->predicterror_buffer[chan] =
            av_malloc(alac->setinfo_max_samples_per_frame * 4);

        alac->outputsamples_buffer[chan] =
            av_malloc(alac->setinfo_max_samples_per_frame * 4);
    }
}

static void bastardized_rice_decompress	(	ALACContext *	alac,
		int32_t *	output_buffer,
		int	output_size,
		int	readsamplesize,
		int	rice_initialhistory,
		int	rice_kmodifier,
		int	rice_historymult,
		int	rice_kmodifier_mask
	)			[static]

Definition at line 163 of file alac.c.

References av_log(), av_log2(), AV_LOG_ERROR, ALACContext::avctx, decode_scalar(), and ALACContext::gb.

Referenced by alac_decode_frame().

{
    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;
        int32_t x_modified;
        int32_t final_val;

        /* standard rice encoding */
        int k; /* size of extra bits */

        /* read k, that is bits as is */
        k = av_log2((history >> 9) + 3);
        x= decode_scalar(&alac->gb, k, rice_kmodifier, readsamplesize);

        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 k;
            unsigned int block_size;

            sign_modifier = 1;

            k = 7 - av_log2(history) + ((history + 16) >> 6 /* / 64 */);

            block_size= decode_scalar(&alac->gb, k, rice_kmodifier, 16);

            if (block_size > 0) {
                if(block_size >= output_size - output_count){
                    av_log(alac->avctx, AV_LOG_ERROR, "invalid zero block size of %d %d %d\n", block_size, output_size, output_count);
                    block_size= output_size - output_count - 1;
                }
                memset(&output_buffer[output_count+1], 0, block_size * 4);
                output_count += block_size;
            }

            if (block_size > 0xffff)
                sign_modifier = 0;

            history = 0;
        }
    }
}

static int decode_scalar	(	GetBitContext *	gb,
		int	k,
		int	limit,
		int	readsamplesize
	)			[inline, static]

Definition at line 136 of file alac.c.

References get_bits(), get_unary_0_9(), show_bits(), and skip_bits().

Referenced by bastardized_rice_decompress().

                                                                                        {
    /* read x - number of 1s before 0 represent the rice */
    int x = get_unary_0_9(gb);

    if (x > 8) { /* RICE THRESHOLD */
        /* use alternative encoding */
        x = get_bits(gb, readsamplesize);
    } else {
        if (k >= limit)
            k = limit;

        if (k != 1) {
            int extrabits = show_bits(gb, k);

            /* multiply x by 2^k - 1, as part of their strange algorithm */
            x = (x << k) - x;

            if (extrabits > 1) {
                x += extrabits - 1;
                skip_bits(gb, k);
            } else
                skip_bits(gb, k - 1);
        }
    }
    return x;
}

static int32_t extend_sign32	(	int32_t	val,
		int	bits
	)			[inline, static]

Definition at line 232 of file alac.c.

Referenced by alac_decode_frame(), and predictor_decompress_fir_adapt().

{
    return (val << (32 - bits)) >> (32 - bits);
}

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
	)			[static]

Definition at line 242 of file alac.c.

References extend_sign32(), and sign_only().

Referenced by alac_decode_frame().

{
    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] =
                extend_sign32((prev_value + error_value), readsamplesize);
        }
        return;
    }

    /* read warm-up samples */
    if (predictor_coef_num > 0)
        for (i = 0; i < predictor_coef_num; i++) {
            int32_t val;

            val = buffer_out[i] + error_buffer[i+1];
            val = extend_sign32(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 optimized
     */
    if (predictor_coef_num == 4) {
        /* FIXME: optimized general case */
        return;
    }

    if (predictor_coef_table == 8) {
        /* FIXME: optimized 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 = extend_sign32(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++;
        }
    }
}

static void reconstruct_stereo_16	(	int32_t *	buffer[MAX_CHANNELS],
		int16_t *	buffer_out,
		int	numchannels,
		int	numsamples,
		uint8_t	interlacing_shift,
		uint8_t	interlacing_leftweight
	)			[static]

Definition at line 365 of file alac.c.

Referenced by alac_decode_frame().

{
    int i;
    if (numsamples <= 0)
        return;

    /* weighted interlacing */
    if (interlacing_leftweight) {
        for (i = 0; i < numsamples; i++) {
            int32_t a, b;

            a = buffer[0][i];
            b = buffer[1][i];

            a -= (b * interlacing_leftweight) >> interlacing_shift;
            b += a;

            buffer_out[i*numchannels] = b;
            buffer_out[i*numchannels + 1] = a;
        }

        return;
    }

    /* otherwise basic interlacing took place */
    for (i = 0; i < numsamples; i++) {
        int16_t left, right;

        left = buffer[0][i];
        right = buffer[1][i];

        buffer_out[i*numchannels] = left;
        buffer_out[i*numchannels + 1] = right;
    }
}

static int sign_only

(

int

v

)

[inline, static]

Definition at line 237 of file alac.c.

References FFSIGN.

Referenced by predictor_decompress_fir_adapt().

{
    return v ? FFSIGN(v) : 0;
}

---

Variable Documentation

AVCodec alac_decoder

Initial value:

 {
    "alac",
    CODEC_TYPE_AUDIO,
    CODEC_ID_ALAC,
    sizeof(ALACContext),
    alac_decode_init,
    NULL,
    alac_decode_close,
    alac_decode_frame,
    .long_name = NULL_IF_CONFIG_SMALL("ALAC (Apple Lossless Audio Codec)"),
}

Definition at line 614 of file alac.c.

---