PeerStreamer

/*

 * RTJpeg decoding functions

 * Copyright (c) 2006 Reimar Doeffinger

 *

 * 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

 */

#include "libavutil/common.h"

#include "get_bits.h"

#include "dsputil.h"

#include "rtjpeg.h"

#define PUT_COEFF(c) \

    i = scan[coeff--]; \

    block[i] = (c) * quant[i];

//! aligns the bitstream to the give power of two

#define ALIGN(a) \

    n = (-get_bits_count(gb)) & (a - 1); \

    if (n) {skip_bits(gb, n);}

/**

 * \brief read one block from stream

 * \param gb contains stream data

 * \param block where data is written to

 * \param scan array containing the mapping stream address -> block position

 * \param quant quantization factors

 *

 * Note: GetBitContext is used to make the code simpler, since all data is

 * aligned this could be done faster in a different way, e.g. as it is done

 * in MPlayer libmpcodecs/native/rtjpegn.c.

 */

static inline int get_block(GetBitContext *gb, DCTELEM *block, const uint8_t *scan,

                            const uint32_t *quant) {

    int coeff, i, n;

    int8_t ac;

    uint8_t dc = get_bits(gb, 8);

    // block not coded

    if (dc == 255)

       return 0;

    // number of non-zero coefficients

    coeff = get_bits(gb, 6);

    // normally we would only need to clear the (63 - coeff) last values,

    // but since we do not know where they are we just clear the whole block

    memset(block, 0, 64 * sizeof(DCTELEM));

    // 2 bits per coefficient

    while (coeff) {

        ac = get_sbits(gb, 2);

        if (ac == -2)

            break; // continue with more bits

        PUT_COEFF(ac);

    }

    // 4 bits per coefficient

    ALIGN(4);

    while (coeff) {

        ac = get_sbits(gb, 4);

        if (ac == -8)

            break; // continue with more bits

        PUT_COEFF(ac);

    }

    // 8 bits per coefficient

    ALIGN(8);

    while (coeff) {

        ac = get_sbits(gb, 8);

        PUT_COEFF(ac);

    }

    PUT_COEFF(dc);

    return 1;

}

/**

 * \brief decode one rtjpeg YUV420 frame

 * \param c context, must be initialized via rtjpeg_decode_init

 * \param f AVFrame to place decoded frame into. If parts of the frame

 *          are not coded they are left unchanged, so consider initializing it

 * \param buf buffer containing input data

 * \param buf_size length of input data in bytes

 * \return number of bytes consumed from the input buffer

 */

int rtjpeg_decode_frame_yuv420(RTJpegContext *c, AVFrame *f,

                               const uint8_t *buf, int buf_size) {

    DECLARE_ALIGNED_16(DCTELEM, block[64]);

    GetBitContext gb;

    int w = c->w / 16, h = c->h / 16;

    int x, y;

    uint8_t *y1 = f->data[0], *y2 = f->data[0] + 8 * f->linesize[0];

    uint8_t *u = f->data[1], *v = f->data[2];

    init_get_bits(&gb, buf, buf_size * 8);

    for (y = 0; y < h; y++) {

        for (x = 0; x < w; x++) {

            if (get_block(&gb, block, c->scan, c->lquant))

                c->dsp->idct_put(y1, f->linesize[0], block);

            y1 += 8;

            if (get_block(&gb, block, c->scan, c->lquant))

                c->dsp->idct_put(y1, f->linesize[0], block);

            y1 += 8;

            if (get_block(&gb, block, c->scan, c->lquant))

                c->dsp->idct_put(y2, f->linesize[0], block);

            y2 += 8;

            if (get_block(&gb, block, c->scan, c->lquant))

                c->dsp->idct_put(y2, f->linesize[0], block);

            y2 += 8;

            if (get_block(&gb, block, c->scan, c->cquant))

                c->dsp->idct_put(u, f->linesize[1], block);

            u += 8;

            if (get_block(&gb, block, c->scan, c->cquant))

                c->dsp->idct_put(v, f->linesize[2], block);

            v += 8;

        }

        y1 += 2 * 8 * (f->linesize[0] - w);

        y2 += 2 * 8 * (f->linesize[0] - w);

        u += 8 * (f->linesize[1] - w);

        v += 8 * (f->linesize[2] - w);

    }

    return get_bits_count(&gb) / 8;

}

/**

 * \brief initialize an RTJpegContext, may be called multiple times

 * \param c context to initialize

 * \param dsp specifies the idct to use for decoding

 * \param width width of image, will be rounded down to the nearest multiple

 *              of 16 for decoding

 * \param height height of image, will be rounded down to the nearest multiple

 *              of 16 for decoding

 * \param lquant luma quantization table to use

 * \param cquant chroma quantization table to use

 */

void rtjpeg_decode_init(RTJpegContext *c, DSPContext *dsp,

                        int width, int height,

                        const uint32_t *lquant, const uint32_t *cquant) {

    int i;

    c->dsp = dsp;

    for (i = 0; i < 64; i++) {

        int z = ff_zigzag_direct[i];

        int p = c->dsp->idct_permutation[i];

        z = ((z << 3) | (z >> 3)) & 63; // rtjpeg uses a transposed variant

        // permute the scan and quantization tables for the chosen idct

        c->scan[i] = c->dsp->idct_permutation[z];

        c->lquant[p] = lquant[i];

        c->cquant[p] = cquant[i];

    }

    c->w = width;

    c->h = height;

}