FFmpeg/libavcodec/mss1.c

/*
 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
 * Copyright (c) 2012 Konstantin Shishkov
 *
 * This file is part of Libav.
 *
 * Libav 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.
 *
 * Libav 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 Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
 */

#include "libavutil/intfloat.h"
#include "libavutil/intreadwrite.h"
#include "avcodec.h"
#include "mss12.h"

typedef struct MSS1Context {
    MSS12Context   ctx;
    AVFrame        pic;
} MSS1Context;

static void arith_normalise(ArithCoder *c)
{
    for (;;) {
        if (c->high >= 0x8000) {
            if (c->low < 0x8000) {
                if (c->low >= 0x4000 && c->high < 0xC000) {
                    c->value -= 0x4000;
                    c->low   -= 0x4000;
                    c->high  -= 0x4000;
                } else {
                    return;
                }
            } else {
                c->value -= 0x8000;
                c->low   -= 0x8000;
                c->high  -= 0x8000;
            }
        }
        c->value <<= 1;
        c->low   <<= 1;
        c->high  <<= 1;
        c->high   |= 1;
        c->value  |= get_bits1(c->gb);
    }
}

static int arith_get_bit(ArithCoder *c)
{
    int range = c->high - c->low + 1;
    int bit   = (((c->value - c->low) << 1) + 1) / range;

    if (bit)
        c->low += range >> 1;
    else
        c->high = c->low + (range >> 1) - 1;

    arith_normalise(c);

    return bit;
}

static int arith_get_bits(ArithCoder *c, int bits)
{
    int range = c->high - c->low + 1;
    int val   = (((c->value - c->low + 1) << bits) - 1) / range;
    int prob  = range * val;

    c->high   = ((prob + range) >> bits) + c->low - 1;
    c->low   += prob >> bits;

    arith_normalise(c);

    return val;
}

static int arith_get_number(ArithCoder *c, int mod_val)
{
    int range = c->high - c->low + 1;
    int val   = ((c->value - c->low + 1) * mod_val - 1) / range;
    int prob  = range * val;

    c->high   = (prob + range) / mod_val + c->low - 1;
    c->low   += prob / mod_val;

    arith_normalise(c);

    return val;
}

static int arith_get_prob(ArithCoder *c, int *probs)
{
    int range = c->high - c->low + 1;
    int val   = ((c->value - c->low + 1) * probs[0] - 1) / range;
    int sym   = 1;

    while (probs[sym] > val)
        sym++;

    c->high = range * probs[sym - 1] / probs[0] + c->low - 1;
    c->low += range * probs[sym]     / probs[0];

    return sym;
}

static int arith_get_model_sym(ArithCoder *c, Model *m)
{
    int idx, val;

    idx = arith_get_prob(c, m->cum_prob);

    val = m->idx2sym[idx];
    ff_mss12_model_update(m, idx);

    arith_normalise(c);

    return val;
}

static void arith_init(ArithCoder *c, GetBitContext *gb)
{
    c->low   = 0;
    c->high  = 0xFFFF;
    c->value = get_bits(gb, 16);
    c->gb    = gb;

    c->get_model_sym = arith_get_model_sym;
    c->get_number    = arith_get_number;
}

static int decode_pal(MSS1Context *ctx, ArithCoder *acoder)
{
    int i, ncol, r, g, b;
    uint32_t *pal = ctx->ctx.pal + 256 - ctx->ctx.free_colours;

    if (!ctx->ctx.free_colours)
        return 0;

    ncol = arith_get_number(acoder, ctx->ctx.free_colours + 1);
    for (i = 0; i < ncol; i++) {
        r = arith_get_bits(acoder, 8);
        g = arith_get_bits(acoder, 8);
        b = arith_get_bits(acoder, 8);
        *pal++ = (r << 16) | (g << 8) | b;
    }

    return !!ncol;
}

static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
                             AVPacket *avpkt)
{
    const uint8_t *buf = avpkt->data;
    int buf_size = avpkt->size;
    MSS1Context *c = avctx->priv_data;
    GetBitContext gb;
    ArithCoder acoder;
    int pal_changed = 0;
    int ret;

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

    c->pic.reference    = 3;
    c->pic.buffer_hints = FF_BUFFER_HINTS_VALID | FF_BUFFER_HINTS_PRESERVE |
                          FF_BUFFER_HINTS_REUSABLE;
    if ((ret = avctx->reget_buffer(avctx, &c->pic)) < 0) {
        av_log(avctx, AV_LOG_ERROR, "reget_buffer() failed\n");
        return ret;
    }

    c->ctx.pic_start  = c->pic.data[0] + c->pic.linesize[0] * (avctx->height - 1);
    c->ctx.pic_stride = -c->pic.linesize[0];
    c->ctx.keyframe   = !arith_get_bit(&acoder);
    if (c->ctx.keyframe) {
        ff_mss12_codec_reset(&c->ctx);
        pal_changed      = decode_pal(c, &acoder);
        c->pic.key_frame = 1;
        c->pic.pict_type = AV_PICTURE_TYPE_I;
    } else {
        if (c->ctx.corrupted)
            return AVERROR_INVALIDDATA;
        c->pic.key_frame = 0;
        c->pic.pict_type = AV_PICTURE_TYPE_P;
    }
    c->ctx.corrupted = ff_mss12_decode_rect(&c->ctx, &acoder, 0, 0,
                                            avctx->width, avctx->height);
    if (c->ctx.corrupted)
        return AVERROR_INVALIDDATA;
    memcpy(c->pic.data[1], c->ctx.pal, AVPALETTE_SIZE);
    c->pic.palette_has_changed = pal_changed;

    *data_size = sizeof(AVFrame);
    *(AVFrame*)data = c->pic;

    /* always report that the buffer was completely consumed */
    return buf_size;
}

static av_cold int mss1_decode_init(AVCodecContext *avctx)
{
    MSS1Context * const c = avctx->priv_data;

    c->ctx.avctx       = avctx;
    avctx->coded_frame = &c->pic;

    return ff_mss12_decode_init(avctx, 0);
}

static av_cold int mss1_decode_end(AVCodecContext *avctx)
{
    MSS1Context * const c = avctx->priv_data;

    if (c->pic.data[0])
        avctx->release_buffer(avctx, &c->pic);
    ff_mss12_decode_end(avctx);

    return 0;
}

AVCodec ff_mss1_decoder = {
    .name           = "mss1",
    .type           = AVMEDIA_TYPE_VIDEO,
    .id             = AV_CODEC_ID_MSS1,
    .priv_data_size = sizeof(MSS1Context),
    .init           = mss1_decode_init,
    .close          = mss1_decode_end,
    .decode         = mss1_decode_frame,
    .capabilities   = CODEC_CAP_DR1,
    .long_name      = NULL_IF_CONFIG_SMALL("MS Screen 1"),
};