2 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
3 * Copyright (c) 2012 Konstantin Shishkov
5 * This file is part of Libav.
7 * Libav is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * Libav is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with Libav; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
31 typedef struct MSS1Context {
37 static void arith_normalise(ArithCoder *c)
40 if (c->high >= 0x8000) {
41 if (c->low < 0x8000) {
42 if (c->low >= 0x4000 && c->high < 0xC000) {
59 c->value |= get_bits1(c->gbc.gb);
65 static int arith_get_bits(ArithCoder *c, int bits)
67 int range = c->high - c->low + 1;
68 int val = (((c->value - c->low + 1) << bits) - 1) / range;
69 int prob = range * val;
71 c->high = ((prob + range) >> bits) + c->low - 1;
72 c->low += prob >> bits;
79 static int arith_get_number(ArithCoder *c, int mod_val)
81 int range = c->high - c->low + 1;
82 int val = ((c->value - c->low + 1) * mod_val - 1) / range;
83 int prob = range * val;
85 c->high = (prob + range) / mod_val + c->low - 1;
86 c->low += prob / mod_val;
93 static int arith_get_prob(ArithCoder *c, int16_t *probs)
95 int range = c->high - c->low + 1;
96 int val = ((c->value - c->low + 1) * probs[0] - 1) / range;
99 while (probs[sym] > val)
102 c->high = range * probs[sym - 1] / probs[0] + c->low - 1;
103 c->low += range * probs[sym] / probs[0];
108 ARITH_GET_MODEL_SYM()
110 static void arith_init(ArithCoder *c, GetBitContext *gb)
114 c->value = get_bits(gb, 16);
116 c->get_model_sym = arith_get_model_sym;
117 c->get_number = arith_get_number;
120 static int decode_pal(MSS12Context *ctx, ArithCoder *acoder)
122 int i, ncol, r, g, b;
123 uint32_t *pal = ctx->pal + 256 - ctx->free_colours;
125 if (!ctx->free_colours)
128 ncol = arith_get_number(acoder, ctx->free_colours + 1);
129 for (i = 0; i < ncol; i++) {
130 r = arith_get_bits(acoder, 8);
131 g = arith_get_bits(acoder, 8);
132 b = arith_get_bits(acoder, 8);
133 *pal++ = (r << 16) | (g << 8) | b;
139 static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
142 const uint8_t *buf = avpkt->data;
143 int buf_size = avpkt->size;
144 MSS1Context *ctx = avctx->priv_data;
145 MSS12Context *c = &ctx->ctx;
151 init_get_bits(&gb, buf, buf_size * 8);
152 arith_init(&acoder, &gb);
154 if ((ret = ff_reget_buffer(avctx, &ctx->pic)) < 0) {
155 av_log(avctx, AV_LOG_ERROR, "reget_buffer() failed\n");
159 c->pal_pic = ctx->pic.data[0] + ctx->pic.linesize[0] * (avctx->height - 1);
160 c->pal_stride = -ctx->pic.linesize[0];
161 c->keyframe = !arith_get_bit(&acoder);
164 ff_mss12_slicecontext_reset(&ctx->sc);
165 pal_changed = decode_pal(c, &acoder);
166 ctx->pic.key_frame = 1;
167 ctx->pic.pict_type = AV_PICTURE_TYPE_I;
170 return AVERROR_INVALIDDATA;
171 ctx->pic.key_frame = 0;
172 ctx->pic.pict_type = AV_PICTURE_TYPE_P;
174 c->corrupted = ff_mss12_decode_rect(&ctx->sc, &acoder, 0, 0,
175 avctx->width, avctx->height);
177 return AVERROR_INVALIDDATA;
178 memcpy(ctx->pic.data[1], c->pal, AVPALETTE_SIZE);
179 ctx->pic.palette_has_changed = pal_changed;
181 if ((ret = av_frame_ref(data, &ctx->pic)) < 0)
186 /* always report that the buffer was completely consumed */
190 static av_cold int mss1_decode_init(AVCodecContext *avctx)
192 MSS1Context * const c = avctx->priv_data;
195 c->ctx.avctx = avctx;
196 avctx->coded_frame = &c->pic;
198 ret = ff_mss12_decode_init(&c->ctx, 0, &c->sc, NULL);
200 avctx->pix_fmt = AV_PIX_FMT_PAL8;
205 static av_cold int mss1_decode_end(AVCodecContext *avctx)
207 MSS1Context * const ctx = avctx->priv_data;
209 av_frame_unref(&ctx->pic);
210 ff_mss12_decode_end(&ctx->ctx);
215 AVCodec ff_mss1_decoder = {
217 .type = AVMEDIA_TYPE_VIDEO,
218 .id = AV_CODEC_ID_MSS1,
219 .priv_data_size = sizeof(MSS1Context),
220 .init = mss1_decode_init,
221 .close = mss1_decode_end,
222 .decode = mss1_decode_frame,
223 .capabilities = CODEC_CAP_DR1,
224 .long_name = NULL_IF_CONFIG_SMALL("MS Screen 1"),