shorten.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

/*
 * 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.c
 * Shorten decoder
 * @author Jeff Muizelaar
 *
 */

#define DEBUG
#include <limits.h>
#include "avcodec.h"
#include "bitstream.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_S16HL 3
#define TYPE_S16LH 5

#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

#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;
    int channels;

    int32_t *decoded[MAX_CHANNELS];
    int32_t *offset[MAX_CHANNELS];
    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;
} ShortenContext;

static int shorten_decode_init(AVCodecContext * avctx)
{
    ShortenContext *s = avctx->priv_data;
    s->avctx = avctx;

    return 0;
}

static int allocate_buffers(ShortenContext *s)
{
    int i, chan;
    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 -1;
        }
        if(s->blocksize + s->nwrap >= UINT_MAX/sizeof(int32_t) || s->blocksize + s->nwrap <= (unsigned)s->nwrap){
            av_log(s->avctx, AV_LOG_ERROR, "s->blocksize + s->nwrap too large\n");
            return -1;
        }

        s->offset[chan] = av_realloc(s->offset[chan], sizeof(int32_t)*FFMAX(1, s->nmean));

        s->decoded[chan] = av_realloc(s->decoded[chan], sizeof(int32_t)*(s->blocksize + s->nwrap));
        for (i=0; i<s->nwrap; i++)
            s->decoded[chan][i] = 0;
        s->decoded[chan] += s->nwrap;
    }
    return 0;
}


static inline unsigned int get_uint(ShortenContext *s, int k)
{
    if (s->version != 0)
        k = get_ur_golomb_shorten(&s->gb, ULONGSIZE);
    return get_ur_golomb_shorten(&s->gb, k);
}


static void fix_bitshift(ShortenContext *s, int32_t *buffer)
{
    int i;

    if (s->bitshift != 0)
        for (i = 0; i < s->blocksize; i++)
            buffer[s->nwrap + i] <<= s->bitshift;
}


static void 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_S16HL:
        case TYPE_S16LH:
            mean = 0;
            break;
        default:
            av_log(s->avctx, AV_LOG_ERROR, "unknown audio type");
            abort();
    }

    for (chan = 0; chan < s->channels; chan++)
        for (i = 0; i < nblock; i++)
            s->offset[chan][i] = mean;
}

static inline int get_le32(GetBitContext *gb)
{
    return bswap_32(get_bits_long(gb, 32));
}

static inline short get_le16(GetBitContext *gb)
{
    return bswap_16(get_bits_long(gb, 16));
}

static int decode_wave_header(AVCodecContext *avctx, uint8_t *header, int header_size)
{
    GetBitContext hb;
    int len;
    int chunk_size;
    short wave_format;

    init_get_bits(&hb, header, header_size*8);
    if (get_le32(&hb) != MKTAG('R','I','F','F')) {
        av_log(avctx, AV_LOG_ERROR, "missing RIFF tag\n");
        return -1;
    }

    chunk_size = get_le32(&hb);

    if (get_le32(&hb) != MKTAG('W','A','V','E')) {
        av_log(avctx, AV_LOG_ERROR, "missing WAVE tag\n");
        return -1;
    }

    while (get_le32(&hb) != MKTAG('f','m','t',' ')) {
        len = get_le32(&hb);
        skip_bits(&hb, 8*len);
    }
    len = get_le32(&hb);

    if (len < 16) {
        av_log(avctx, AV_LOG_ERROR, "fmt chunk was too short\n");
        return -1;
    }

    wave_format = get_le16(&hb);

    switch (wave_format) {
        case WAVE_FORMAT_PCM:
            break;
        default:
            av_log(avctx, AV_LOG_ERROR, "unsupported wave format\n");
            return -1;
    }

    avctx->channels = get_le16(&hb);
    avctx->sample_rate = get_le32(&hb);
    avctx->bit_rate = get_le32(&hb) * 8;
    avctx->block_align = get_le16(&hb);
    avctx->bits_per_sample = get_le16(&hb);

    if (avctx->bits_per_sample != 16) {
        av_log(avctx, AV_LOG_ERROR, "unsupported number of bits per sample\n");
        return -1;
    }

    len -= 16;
    if (len > 0)
        av_log(avctx, AV_LOG_INFO, "%d header bytes unparsed\n", len);

    return 0;
}

static int16_t * interleave_buffer(int16_t *samples, int nchan, int blocksize, int32_t **buffer) {
    int i, chan;
    for (i=0; i<blocksize; i++)
        for (chan=0; chan < nchan; chan++)
            *samples++ = FFMIN(buffer[chan][i], 32768);
    return samples;
}

static void decode_subframe_lpc(ShortenContext *s, int channel, int residual_size, int pred_order)
{
    int sum, i, j;
    int coeffs[pred_order];

    for (i=0; i<pred_order; i++)
        coeffs[i] = get_sr_golomb_shorten(&s->gb, LPCQUANT);

    for (i=0; i < s->blocksize; i++) {
        sum = s->lpcqoffset;
        for (j=0; j<pred_order; j++)
            sum += coeffs[j] * s->decoded[channel][i-j-1];
        s->decoded[channel][i] = get_sr_golomb_shorten(&s->gb, residual_size) + (sum >> LPCQUANT);
    }
}