2 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
3 * Copyright (c) 2012 Konstantin Shishkov
5 * This file is part of FFmpeg.
7 * FFmpeg 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 * FFmpeg 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 FFmpeg; 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
30 typedef struct MSS1Context {
36 static void arith_normalise(ArithCoder *c)
39 if (c->high >= 0x8000) {
40 if (c->low < 0x8000) {
41 if (c->low >= 0x4000 && c->high < 0xC000) {
58 c->value |= get_bits1(c->gbc.gb);
64 static int arith_get_bits(ArithCoder *c, int bits)
66 int range = c->high - c->low + 1;
67 int val = (((c->value - c->low + 1) << bits) - 1) / range;
68 int prob = range * val;
70 c->high = ((prob + range) >> bits) + c->low - 1;
71 c->low += prob >> bits;
78 static int arith_get_number(ArithCoder *c, int mod_val)
80 int range = c->high - c->low + 1;
81 int val = ((c->value - c->low + 1) * mod_val - 1) / range;
82 int prob = range * val;
84 c->high = (prob + range) / mod_val + c->low - 1;
85 c->low += prob / mod_val;
92 static int arith_get_prob(ArithCoder *c, int16_t *probs)
94 int range = c->high - c->low + 1;
95 int val = ((c->value - c->low + 1) * probs[0] - 1) / range;
98 while (probs[sym] > val)
101 c->high = range * probs[sym - 1] / probs[0] + c->low - 1;
102 c->low += range * probs[sym] / probs[0];
107 ARITH_GET_MODEL_SYM()
109 static void arith_init(ArithCoder *c, GetBitContext *gb)
113 c->value = get_bits(gb, 16);
115 c->get_model_sym = arith_get_model_sym;
116 c->get_number = arith_get_number;
119 static int decode_pal(MSS12Context *ctx, ArithCoder *acoder)
121 int i, ncol, r, g, b;
122 uint32_t *pal = ctx->pal + 256 - ctx->free_colours;
124 if (!ctx->free_colours)
127 ncol = arith_get_number(acoder, ctx->free_colours + 1);
128 for (i = 0; i < ncol; i++) {
129 r = arith_get_bits(acoder, 8);
130 g = arith_get_bits(acoder, 8);
131 b = arith_get_bits(acoder, 8);
132 *pal++ = (0xFFU << 24) | (r << 16) | (g << 8) | b;
138 static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
141 const uint8_t *buf = avpkt->data;
142 int buf_size = avpkt->size;
143 MSS1Context *ctx = avctx->priv_data;
144 MSS12Context *c = &ctx->ctx;
150 init_get_bits(&gb, buf, buf_size * 8);
151 arith_init(&acoder, &gb);
153 ctx->pic.reference = 3;
154 ctx->pic.buffer_hints = FF_BUFFER_HINTS_VALID | FF_BUFFER_HINTS_READABLE |
155 FF_BUFFER_HINTS_PRESERVE | FF_BUFFER_HINTS_REUSABLE;
156 if ((ret = avctx->reget_buffer(avctx, &ctx->pic)) < 0) {
157 av_log(avctx, AV_LOG_ERROR, "reget_buffer() failed\n");
161 c->pal_pic = ctx->pic.data[0] + ctx->pic.linesize[0] * (avctx->height - 1);
162 c->pal_stride = -ctx->pic.linesize[0];
163 c->keyframe = !arith_get_bit(&acoder);
166 ff_mss12_slicecontext_reset(&ctx->sc);
167 pal_changed = decode_pal(c, &acoder);
168 ctx->pic.key_frame = 1;
169 ctx->pic.pict_type = AV_PICTURE_TYPE_I;
172 return AVERROR_INVALIDDATA;
173 ctx->pic.key_frame = 0;
174 ctx->pic.pict_type = AV_PICTURE_TYPE_P;
176 c->corrupted = ff_mss12_decode_rect(&ctx->sc, &acoder, 0, 0,
177 avctx->width, avctx->height);
179 return AVERROR_INVALIDDATA;
180 memcpy(ctx->pic.data[1], c->pal, AVPALETTE_SIZE);
181 ctx->pic.palette_has_changed = pal_changed;
184 *(AVFrame*)data = ctx->pic;
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 if (ctx->pic.data[0])
210 avctx->release_buffer(avctx, &ctx->pic);
211 ff_mss12_decode_end(&ctx->ctx);
216 AVCodec ff_mss1_decoder = {
218 .type = AVMEDIA_TYPE_VIDEO,
219 .id = AV_CODEC_ID_MSS1,
220 .priv_data_size = sizeof(MSS1Context),
221 .init = mss1_decode_init,
222 .close = mss1_decode_end,
223 .decode = mss1_decode_frame,
224 .capabilities = CODEC_CAP_DR1,
225 .long_name = NULL_IF_CONFIG_SMALL("MS Screen 1"),