shorten.c

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/*
 * Shorten decoder
 * Copyright (c) 2005 Jeff Muizelaar
 *
 * 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
 * Shorten decoder
 * @author Jeff Muizelaar
 */
 
#include <limits.h>
#include "avcodec.h"
#include "bswapdsp.h"
#include "bytestream.h"
#include "codec_internal.h"
#include "decode.h"
#include "get_bits.h"
#include "golomb.h"
 
#define MAX_CHANNELS 8
#define MAX_BLOCKSIZE 65535
 
#define OUT_BUFFER_SIZE 16384
 
#define ULONGSIZE 2
 
#define WAVE_FORMAT_PCM 0x0001
 
#define DEFAULT_BLOCK_SIZE 256
 
#define TYPESIZE 4
#define CHANSIZE 0
#define LPCQSIZE 2
#define ENERGYSIZE 3
#define BITSHIFTSIZE 2
 
#define TYPE_S8    1
#define TYPE_U8    2
#define TYPE_S16HL 3
#define TYPE_U16HL 4
#define TYPE_S16LH 5
#define TYPE_U16LH 6
 
#define NWRAP 3
#define NSKIPSIZE 1
 
#define LPCQUANT 5
#define V2LPCQOFFSET (1 << LPCQUANT)
 
#define FNSIZE 2
#define FN_DIFF0        0
#define FN_DIFF1        1
#define FN_DIFF2        2
#define FN_DIFF3        3
#define FN_QUIT         4
#define FN_BLOCKSIZE    5
#define FN_BITSHIFT     6
#define FN_QLPC         7
#define FN_ZERO         8
#define FN_VERBATIM     9
 
/** indicates if the FN_* command is audio or non-audio */
static const uint8_t is_audio_command[10] = { 1, 1, 1, 1, 0, 0, 0, 1, 1, 0 };
 
#define VERBATIM_CKSIZE_SIZE 5
#define VERBATIM_BYTE_SIZE 8
#define CANONICAL_HEADER_SIZE 44
 
typedef struct ShortenContext {
    AVCodecContext *avctx;
    GetBitContext gb;
 
    int min_framesize, max_framesize;
    unsigned channels;
 
    int32_t *decoded[MAX_CHANNELS];
    int32_t *decoded_base[MAX_CHANNELS];
    int32_t *offset[MAX_CHANNELS];
    int *coeffs;
    uint8_t *bitstream;
    int bitstream_size;
    int bitstream_index;
    unsigned int allocated_bitstream_size;
    int header_size;
    uint8_t header[OUT_BUFFER_SIZE];
    int version;
    int cur_chan;
    int bitshift;
    int nmean;
    int internal_ftype;
    int nwrap;
    int blocksize;
    int bitindex;
    int32_t lpcqoffset;
    int got_header;
    int got_quit_command;
    int swap;
    BswapDSPContext bdsp;
} ShortenContext;
 
static av_cold int shorten_decode_init(AVCodecContext *avctx)
{
    ShortenContext *s = avctx->priv_data;
    s->avctx          = avctx;
 
    ff_bswapdsp_init(&s->bdsp);
 
    return 0;
}
 
static int allocate_buffers(ShortenContext *s)
{
    int i, chan, err;
 
    for (chan = 0; chan < s->channels; chan++) {
        if (FFMAX(1, s->nmean) >= UINT_MAX / sizeof(int32_t)) {
            av_log(s->avctx, AV_LOG_ERROR, "nmean too large\n");
            return AVERROR_INVALIDDATA;
        }
        if (s->blocksize + (uint64_t)s->nwrap >= UINT_MAX / sizeof(int32_t)) {
            av_log(s->avctx, AV_LOG_ERROR,
                   "s->blocksize + s->nwrap too large\n");
            return AVERROR_INVALIDDATA;
        }
 
        if ((err = av_reallocp_array(&s->offset[chan],
                               sizeof(int32_t),
                               FFMAX(1, s->nmean))) < 0)
            return err;
 
        if ((err = av_reallocp_array(&s->decoded_base[chan], (s->blocksize + s->nwrap),
                               sizeof(s->decoded_base[0][0]))) < 0)
            return err;
        for (i = 0; i < s->nwrap; i++)
            s->decoded_base[chan][i] = 0;
        s->decoded[chan] = s->decoded_base[chan] + s->nwrap;
    }
 
    if ((err = av_reallocp_array(&s->coeffs, s->nwrap, sizeof(*s->coeffs))) < 0)
        return err;
 
    return 0;
}
 
static inline unsigned int get_uint(ShortenContext *s, int k)
{
    if (s->version != 0) {
        k = get_ur_golomb_shorten(&s->gb, ULONGSIZE);
        if (k > 31U)
            return AVERROR_INVALIDDATA;
    }
    return get_ur_golomb_shorten(&s->gb, k);
}
 
static void fix_bitshift(ShortenContext *s, int32_t *buffer)
{
    int i;
 
    if (s->bitshift == 32) {
        for (i = 0; i < s->blocksize; i++)
            buffer[i] = 0;
    } else if (s->bitshift != 0) {
        for (i = 0; i < s->blocksize; i++)
            buffer[i] *= 1U << s->bitshift;
    }
}
 
static int init_offset(ShortenContext *s)
{
    int32_t mean = 0;
    int chan, i;
    int nblock = FFMAX(1, s->nmean);
    /* initialise offset */
    switch (s->internal_ftype) {
    case TYPE_U8:
        s->avctx->sample_fmt = AV_SAMPLE_FMT_U8P;
        mean = 0x80;
        break;
    case TYPE_S16HL:
    case TYPE_S16LH:
        s->avctx->sample_fmt = AV_SAMPLE_FMT_S16P;
        break;
    default:
        av_log(s->avctx, AV_LOG_ERROR, "unknown audio type\n");
        return AVERROR_PATCHWELCOME;
    }
 
    for (chan = 0; chan < s->channels; chan++)
        for (i = 0; i < nblock; i++)
            s->offset[chan][i] = mean;
    return 0;
}
 
static int decode_aiff_header(AVCodecContext *avctx, const uint8_t *header,
                              int header_size)
{
    ShortenContext *s = avctx->priv_data;
    int len, bps, exp;
    GetByteContext gb;
    uint64_t val;
    uint32_t tag;
 
    bytestream2_init(&gb, header, header_size);
 
    if (bytestream2_get_le32(&gb) != MKTAG('F', 'O', 'R', 'M')) {
        av_log(avctx, AV_LOG_ERROR, "missing FORM tag\n");
        return AVERROR_INVALIDDATA;
    }
 
    bytestream2_skip(&gb, 4); /* chunk size */
 
    tag = bytestream2_get_le32(&gb);
    if (tag != MKTAG('A', 'I', 'F', 'F') &&
        tag != MKTAG('A', 'I', 'F', 'C')) {
        av_log(avctx, AV_LOG_ERROR, "missing AIFF tag\n");
        return AVERROR_INVALIDDATA;
    }
 
    while (bytestream2_get_le32(&gb) != MKTAG('C', 'O', 'M', 'M')) {
        len = bytestream2_get_be32(&gb);
        if (len < 0 || bytestream2_get_bytes_left(&gb) < 18LL + len + (len&1)) {
            av_log(avctx, AV_LOG_ERROR, "no COMM chunk found\n");
            return AVERROR_INVALIDDATA;
        }
        bytestream2_skip(&gb, len + (len & 1));
    }
    len = bytestream2_get_be32(&gb);
 
    if (len < 18) {
        av_log(avctx, AV_LOG_ERROR, "COMM chunk was too short\n");
        return AVERROR_INVALIDDATA;
    }
 
    bytestream2_skip(&gb, 6);
    bps = bytestream2_get_be16(&gb);
    avctx->bits_per_coded_sample = bps;
 
    s->swap = tag == MKTAG('A', 'I', 'F', 'C');
 
    if (bps != 16 && bps != 8) {
        av_log(avctx, AV_LOG_ERROR, "unsupported number of bits per sample: %d\n", bps);
        return AVERROR(ENOSYS);
    }
 
    exp = bytestream2_get_be16(&gb) - 16383 - 63;
    val = bytestream2_get_be64(&gb);
    if (exp < -63 || exp > 63) {
        av_log(avctx, AV_LOG_ERROR, "exp %d is out of range\n", exp);
        return AVERROR_INVALIDDATA;
    }
    if (exp >= 0)
        avctx->sample_rate = val << exp;
    else
        avctx->sample_rate = (val + (1ULL<<(-exp-1))) >> -exp;
    len -= 18;
    if (len > 0)
        av_log(avctx, AV_LOG_INFO, "%d header bytes unparsed\n", len);
 
    return 0;
}
 
static int decode_wave_header(AVCodecContext *avctx, const uint8_t *header,
                              int header_size)
{
    int len, bps;
    short wave_format;
    GetByteContext gb;
 
    bytestream2_init(&gb, header, header_size);
 
    if (bytestream2_get_le32(&gb) != MKTAG('R', 'I', 'F', 'F')) {
        av_log(avctx, AV_LOG_ERROR, "missing RIFF tag\n");
        return AVERROR_INVALIDDATA;
    }
 
    bytestream2_skip(&gb, 4); /* chunk size */
 
    if (bytestream2_get_le32(&gb) != MKTAG('W', 'A', 'V', 'E')) {
        av_log(avctx, AV_LOG_ERROR, "missing WAVE tag\n");
        return AVERROR_INVALIDDATA;
    }
 
    while (bytestream2_get_le32(&gb) != MKTAG('f', 'm', 't', ' ')) {
        len = bytestream2_get_le32(&gb);
        bytestream2_skip(&gb, len);
        if (len < 0 || bytestream2_get_bytes_left(&gb) < 16) {
            av_log(avctx, AV_LOG_ERROR, "no fmt chunk found\n");
            return AVERROR_INVALIDDATA;
        }
    }
    len = bytestream2_get_le32(&gb);
 
    if (len < 16) {
        av_log(avctx, AV_LOG_ERROR, "fmt chunk was too short\n");
        return AVERROR_INVALIDDATA;
    }
 
    wave_format = bytestream2_get_le16(&gb);
 
    switch (wave_format) {
    case WAVE_FORMAT_PCM:
        break;
    default:
        av_log(avctx, AV_LOG_ERROR, "unsupported wave format\n");
        return AVERROR(ENOSYS);
    }
 
    bytestream2_skip(&gb, 2); // skip channels    (already got from shorten header)
    avctx->sample_rate = bytestream2_get_le32(&gb);
    bytestream2_skip(&gb, 4); // skip bit rate    (represents original uncompressed bit rate)
    bytestream2_skip(&gb, 2); // skip block align (not needed)
    bps = bytestream2_get_le16(&gb);
    avctx->bits_per_coded_sample = bps;
 
    if (bps != 16 && bps != 8) {
        av_log(avctx, AV_LOG_ERROR, "unsupported number of bits per sample: %d\n", bps);
        return AVERROR(ENOSYS);
    }
 
    len -= 16;
    if (len > 0)
        av_log(avctx, AV_LOG_INFO, "%d header bytes unparsed\n", len);
 
    return 0;
}
 
static const int fixed_coeffs[][3] = {
    { 0,  0,  0 },
    { 1,  0,  0 },
    { 2, -1,  0 },
    { 3, -3,  1 }
};
 
static int decode_subframe_lpc(ShortenContext *s, int command, int channel,
                               int residual_size, int32_t coffset)
{
    int pred_order, sum, qshift, init_sum, i, j;
    const int *coeffs;
 
    if (command == FN_QLPC) {
        /* read/validate prediction order */
        pred_order = get_ur_golomb_shorten(&s->gb, LPCQSIZE);
        if ((unsigned)pred_order > s->nwrap) {
            av_log(s->avctx, AV_LOG_ERROR, "invalid pred_order %d\n",
                   pred_order);
            return AVERROR(EINVAL);
        }
        /* read LPC coefficients */
        for (i = 0; i < pred_order; i++)
            s->coeffs[i] = get_sr_golomb_shorten(&s->gb, LPCQUANT);
        coeffs = s->coeffs;
 
        qshift = LPCQUANT;
    } else {
        /* fixed LPC coeffs */
        pred_order = command;
        if (pred_order >= FF_ARRAY_ELEMS(fixed_coeffs)) {
            av_log(s->avctx, AV_LOG_ERROR, "invalid pred_order %d\n",
                   pred_order);
            return AVERROR_INVALIDDATA;
        }
        coeffs     = fixed_coeffs[pred_order];
        qshift     = 0;
    }
 
    /* subtract offset from previous samples to use in prediction */
    if (command == FN_QLPC && coffset)
        for (i = -pred_order; i < 0; i++)
            s->decoded[channel][i] -= (unsigned)coffset;
 
    /* decode residual and do LPC prediction */
    init_sum = pred_order ? (command == FN_QLPC ? s->lpcqoffset : 0) : coffset;
    for (i = 0; i < s->blocksize; i++) {
        sum = init_sum;
        for (j = 0; j < pred_order; j++)
            sum += coeffs[j] * (unsigned)s->decoded[channel][i - j - 1];
        s->decoded[channel][i] = get_sr_golomb_shorten(&s->gb, residual_size) +
                                 (unsigned)(sum >> qshift);
    }
 
    /* add offset to current samples */
    if (command == FN_QLPC && coffset)
        for (i = 0; i < s->blocksize; i++)
            s->decoded[channel][i] += (unsigned)coffset;
 
    return 0;
}
 
static int read_header(ShortenContext *s)
{
    int i, ret;
    int maxnlpc = 0;
    /* shorten signature */
    if (get_bits_long(&s->gb, 32) != AV_RB32("ajkg")) {
        av_log(s->avctx, AV_LOG_ERROR, "missing shorten magic 'ajkg'\n");
        return AVERROR_INVALIDDATA;
    }
 
    s->lpcqoffset     = 0;
    s->blocksize      = DEFAULT_BLOCK_SIZE;
    s->nmean          = -1;
    s->version        = get_bits(&s->gb, 8);
    s->internal_ftype = get_uint(s, TYPESIZE);
 
    s->channels = get_uint(s, CHANSIZE);
    if (!s->channels) {
        av_log(s->avctx, AV_LOG_ERROR, "No channels reported\n");
        return AVERROR_INVALIDDATA;
    }
    if (s->channels > MAX_CHANNELS) {
        av_log(s->avctx, AV_LOG_ERROR, "too many channels: %d\n", s->channels);
        s->channels = 0;
        return AVERROR_INVALIDDATA;
    }
    if (s->avctx->ch_layout.nb_channels != s->channels) {
        av_channel_layout_uninit(&s->avctx->ch_layout);
        s->avctx->ch_layout.nb_channels = s->channels;
        s->avctx->ch_layout.order       = AV_CHANNEL_ORDER_UNSPEC;
    }
 
    /* get blocksize if version > 0 */
    if (s->version > 0) {
        int skip_bytes;
        unsigned blocksize;
 
        blocksize = get_uint(s, av_log2(DEFAULT_BLOCK_SIZE));
        if (!blocksize || blocksize > MAX_BLOCKSIZE) {
            av_log(s->avctx, AV_LOG_ERROR,
                   "invalid or unsupported block size: %d\n",
                   blocksize);
            return AVERROR(EINVAL);
        }
        s->blocksize = blocksize;
 
        maxnlpc  = get_uint(s, LPCQSIZE);
        if (maxnlpc > 1024U) {
            av_log(s->avctx, AV_LOG_ERROR, "maxnlpc is: %d\n", maxnlpc);
            return AVERROR_INVALIDDATA;
        }
        s->nmean = get_uint(s, 0);
        if (s->nmean > 32768U) {
            av_log(s->avctx, AV_LOG_ERROR, "nmean is: %d\n", s->nmean);
            return AVERROR_INVALIDDATA;
        }
 
        skip_bytes = get_uint(s, NSKIPSIZE);
        if ((unsigned)skip_bytes > FFMAX(get_bits_left(&s->gb), 0)/8) {
            av_log(s->avctx, AV_LOG_ERROR, "invalid skip_bytes: %d\n", skip_bytes);
            return AVERROR_INVALIDDATA;
        }
 
        for (i = 0; i < skip_bytes; i++)
            skip_bits(&s->gb, 8);
    }
    s->nwrap = FFMAX(NWRAP, maxnlpc);
 
    if (s->version > 1)
        s->lpcqoffset = V2LPCQOFFSET;
 
    if (s->avctx->extradata_size > 0)
        goto end;
 
    if (get_ur_golomb_shorten(&s->gb, FNSIZE) != FN_VERBATIM) {
        av_log(s->avctx, AV_LOG_ERROR,
               "missing verbatim section at beginning of stream\n");
        return AVERROR_INVALIDDATA;
    }
 
    s->header_size = get_ur_golomb_shorten(&s->gb, VERBATIM_CKSIZE_SIZE);
    if (s->header_size >= OUT_BUFFER_SIZE ||
        s->header_size < CANONICAL_HEADER_SIZE) {
        av_log(s->avctx, AV_LOG_ERROR, "header is wrong size: %d\n",
               s->header_size);
        return AVERROR_INVALIDDATA;
    }
 
    for (i = 0; i < s->header_size; i++)
        s->header[i] = (char)get_ur_golomb_shorten(&s->gb, VERBATIM_BYTE_SIZE);
 
    if (AV_RL32(s->header) == MKTAG('R','I','F','F')) {
        if ((ret = decode_wave_header(s->avctx, s->header, s->header_size)) < 0)
            return ret;
    } else if (AV_RL32(s->header) == MKTAG('F','O','R','M')) {
        if ((ret = decode_aiff_header(s->avctx, s->header, s->header_size)) < 0)
            return ret;
    } else {
        avpriv_report_missing_feature(s->avctx, "unsupported bit packing %"
                                      PRIX32, AV_RL32(s->header));
        return AVERROR_PATCHWELCOME;
    }
 
end:
 
    if ((ret = allocate_buffers(s)) < 0)
        return ret;
 
    if ((ret = init_offset(s)) < 0)
        return ret;
 
    s->cur_chan = 0;
    s->bitshift = 0;
 
    s->got_header = 1;
 
    return 0;
}
 
static int shorten_decode_frame(AVCodecContext *avctx, AVFrame *frame,
                                int *got_frame_ptr, AVPacket *avpkt)
{
    const uint8_t *buf = avpkt->data;
    int buf_size       = avpkt->size;
    ShortenContext *s  = avctx->priv_data;
    int i, input_buf_size = 0;
    int ret;
 
    /* allocate internal bitstream buffer */
    if (s->max_framesize == 0) {
        void *tmp_ptr;
        s->max_framesize = 8192; // should hopefully be enough for the first header
        tmp_ptr = av_fast_realloc(s->bitstream, &s->allocated_bitstream_size,
                                  s->max_framesize + AV_INPUT_BUFFER_PADDING_SIZE);
        if (!tmp_ptr) {
            s->max_framesize = 0;
            av_log(avctx, AV_LOG_ERROR, "error allocating bitstream buffer\n");
            return AVERROR(ENOMEM);
        }
        memset(tmp_ptr, 0, s->allocated_bitstream_size);
        s->bitstream = tmp_ptr;
    }
 
    /* append current packet data to bitstream buffer */
    buf_size       = FFMIN(buf_size, s->max_framesize - s->bitstream_size);
    input_buf_size = buf_size;
 
    if (s->bitstream_index + s->bitstream_size + buf_size + AV_INPUT_BUFFER_PADDING_SIZE >
        s->allocated_bitstream_size) {
        memmove(s->bitstream, &s->bitstream[s->bitstream_index],
                s->bitstream_size);
        s->bitstream_index = 0;
    }
    if (buf)
        memcpy(&s->bitstream[s->bitstream_index + s->bitstream_size], buf,
               buf_size);
    buf               = &s->bitstream[s->bitstream_index];
    buf_size         += s->bitstream_size;
    s->bitstream_size = buf_size;
 
    /* do not decode until buffer has at least max_framesize bytes or
     * the end of the file has been reached */
    if (buf_size < s->max_framesize && avpkt->data) {
        *got_frame_ptr = 0;
        return input_buf_size;
    }
    /* init and position bitstream reader */
    if ((ret = init_get_bits8(&s->gb, buf, buf_size)) < 0)
        return ret;
    skip_bits(&s->gb, s->bitindex);
 
    /* process header or next subblock */
    if (!s->got_header) {
 
        if ((ret = read_header(s)) < 0)
            return ret;
 
        if (avpkt->size) {
            int max_framesize;
            void *tmp_ptr;
 
            max_framesize = FFMAX(s->max_framesize, s->blocksize * s->channels * 8);
            tmp_ptr = av_fast_realloc(s->bitstream, &s->allocated_bitstream_size,
                                      max_framesize + AV_INPUT_BUFFER_PADDING_SIZE);
            if (!tmp_ptr) {
                av_log(avctx, AV_LOG_ERROR, "error allocating bitstream buffer\n");
                return AVERROR(ENOMEM);
            }
            s->bitstream = tmp_ptr;
            s->max_framesize = max_framesize;
            *got_frame_ptr = 0;
            goto finish_frame;
        }
    }
 
    /* if quit command was read previously, don't decode anything */
    if (s->got_quit_command) {
        *got_frame_ptr = 0;
        return avpkt->size;
    }
 
    s->cur_chan = 0;
    while (s->cur_chan < s->channels) {
        unsigned cmd;
        int len;
 
        if (get_bits_left(&s->gb) < 3 + FNSIZE) {
            *got_frame_ptr = 0;
            break;
        }
 
        cmd = get_ur_golomb_shorten(&s->gb, FNSIZE);
 
        if (cmd > FN_VERBATIM) {
            av_log(avctx, AV_LOG_ERROR, "unknown shorten function %d\n", cmd);
            *got_frame_ptr = 0;
            break;
        }
 
        if (!is_audio_command[cmd]) {
            /* process non-audio command */
            switch (cmd) {
            case FN_VERBATIM:
                len = get_ur_golomb_shorten(&s->gb, VERBATIM_CKSIZE_SIZE);
                if (len < 0 || len > get_bits_left(&s->gb)) {
                    av_log(avctx, AV_LOG_ERROR, "verbatim length %d invalid\n",
                           len);
                    return AVERROR_INVALIDDATA;
                }
                while (len--)
                    get_ur_golomb_shorten(&s->gb, VERBATIM_BYTE_SIZE);
                break;
            case FN_BITSHIFT: {
                unsigned bitshift = get_ur_golomb_shorten(&s->gb, BITSHIFTSIZE);
                if (bitshift > 32) {
                    av_log(avctx, AV_LOG_ERROR, "bitshift %d is invalid\n",
                           bitshift);
                    return AVERROR_INVALIDDATA;
                }
                s->bitshift = bitshift;
                break;
            }
            case FN_BLOCKSIZE: {
                unsigned blocksize = get_uint(s, av_log2(s->blocksize));
                if (blocksize > s->blocksize) {
                    avpriv_report_missing_feature(avctx,
                                                  "Increasing block size");
                    return AVERROR_PATCHWELCOME;
                }
                if (!blocksize || blocksize > MAX_BLOCKSIZE) {
                    av_log(avctx, AV_LOG_ERROR, "invalid or unsupported "
                                                "block size: %d\n", blocksize);
                    return AVERROR(EINVAL);
                }
                s->blocksize = blocksize;
                break;
            }
            case FN_QUIT:
                s->got_quit_command = 1;
                break;
            }
            if (cmd == FN_QUIT)
                break;
        } else {
            /* process audio command */
            int residual_size = 0;
            int channel = s->cur_chan;
            int32_t coffset;
 
            /* get Rice code for residual decoding */
            if (cmd != FN_ZERO) {
                residual_size = get_ur_golomb_shorten(&s->gb, ENERGYSIZE);
                /* This is a hack as version 0 differed in the definition
                 * of get_sr_golomb_shorten(). */
                if (s->version == 0)
                    residual_size--;
                if (residual_size > 30U) {
                    av_log(avctx, AV_LOG_ERROR, "residual size unsupportd: %d\n", residual_size);
                    return AVERROR_INVALIDDATA;
                }
            }
 
            /* calculate sample offset using means from previous blocks */
            if (s->nmean == 0)
                coffset = s->offset[channel][0];
            else {
                int32_t sum = (s->version < 2) ? 0 : s->nmean / 2;
                for (i = 0; i < s->nmean; i++)
                    sum += (unsigned)s->offset[channel][i];
                coffset = sum / s->nmean;
                if (s->version >= 2)
                    coffset = s->bitshift == 0 ? coffset : coffset >> s->bitshift - 1 >> 1;
            }
 
            /* decode samples for this channel */
            if (cmd == FN_ZERO) {
                for (i = 0; i < s->blocksize; i++)
                    s->decoded[channel][i] = 0;
            } else {
                if ((ret = decode_subframe_lpc(s, cmd, channel,
                                               residual_size, coffset)) < 0)
                    return ret;
            }
 
            /* update means with info from the current block */
            if (s->nmean > 0) {
                int64_t sum = (s->version < 2) ? 0 : s->blocksize / 2;
                for (i = 0; i < s->blocksize; i++)
                    sum += s->decoded[channel][i];
 
                for (i = 1; i < s->nmean; i++)
                    s->offset[channel][i - 1] = s->offset[channel][i];
 
                if (s->version < 2)
                    s->offset[channel][s->nmean - 1] = sum / s->blocksize;
                else
                    s->offset[channel][s->nmean - 1] = s->bitshift == 32 ? 0 : (sum / s->blocksize) * (1LL << s->bitshift);
            }
 
            /* copy wrap samples for use with next block */
            for (i = -s->nwrap; i < 0; i++)
                s->decoded[channel][i] = s->decoded[channel][i + s->blocksize];
 
            /* shift samples to add in unused zero bits which were removed
             * during encoding */
            fix_bitshift(s, s->decoded[channel]);
 
            /* if this is the last channel in the block, output the samples */
            s->cur_chan++;
            if (s->cur_chan == s->channels) {
                uint8_t *samples_u8;
                int16_t *samples_s16;
                int chan;
 
                /* get output buffer */
                frame->nb_samples = s->blocksize;
                if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
                    return ret;
 
                for (chan = 0; chan < s->channels; chan++) {
                    samples_u8  = ((uint8_t **)frame->extended_data)[chan];
                    samples_s16 = ((int16_t **)frame->extended_data)[chan];
                    for (i = 0; i < s->blocksize; i++) {
                        switch (s->internal_ftype) {
                        case TYPE_U8:
                            *samples_u8++ = av_clip_uint8(s->decoded[chan][i]);
                            break;
                        case TYPE_S16HL:
                        case TYPE_S16LH:
                            *samples_s16++ = av_clip_int16(s->decoded[chan][i]);
                            break;
                        }
                    }
                    if (s->swap && s->internal_ftype != TYPE_U8)
                        s->bdsp.bswap16_buf(((uint16_t **)frame->extended_data)[chan],
                                            ((uint16_t **)frame->extended_data)[chan],
                                            s->blocksize);
 
                }
 
                *got_frame_ptr = 1;
            }
        }
    }
    if (s->cur_chan < s->channels)
        *got_frame_ptr = 0;
 
finish_frame:
    s->bitindex = get_bits_count(&s->gb) - 8 * (get_bits_count(&s->gb) / 8);
    i           = get_bits_count(&s->gb) / 8;
    if (i > buf_size) {
        av_log(s->avctx, AV_LOG_ERROR, "overread: %d\n", i - buf_size);
        s->bitstream_size  = 0;
        s->bitstream_index = 0;
        return AVERROR_INVALIDDATA;
    }
    if (s->bitstream_size) {
        s->bitstream_index += i;
        s->bitstream_size  -= i;
        return input_buf_size;
    } else
        return i;
}
 
static av_cold int shorten_decode_close(AVCodecContext *avctx)
{
    ShortenContext *s = avctx->priv_data;
    int i;
 
    for (i = 0; i < s->channels; i++) {
        s->decoded[i] = NULL;
        av_freep(&s->decoded_base[i]);
        av_freep(&s->offset[i]);
    }
    av_freep(&s->bitstream);
    av_freep(&s->coeffs);
 
    return 0;
}
 
const FFCodec ff_shorten_decoder = {
    .p.name         = "shorten",
    CODEC_LONG_NAME("Shorten"),
    .p.type         = AVMEDIA_TYPE_AUDIO,
    .p.id           = AV_CODEC_ID_SHORTEN,
    .priv_data_size = sizeof(ShortenContext),
    .init           = shorten_decode_init,
    .close          = shorten_decode_close,
    FF_CODEC_DECODE_CB(shorten_decode_frame),
    .p.capabilities = AV_CODEC_CAP_CHANNEL_CONF |
                      AV_CODEC_CAP_DELAY |
                      AV_CODEC_CAP_DR1 |
                      AV_CODEC_CAP_SUBFRAMES ,
    .p.sample_fmts  = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_S16P,
                                                      AV_SAMPLE_FMT_U8P,
                                                      AV_SAMPLE_FMT_NONE },
};