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mss1.c
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1 /*
2  * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
3  * Copyright (c) 2012 Konstantin Shishkov
4  *
5  * This file is part of FFmpeg.
6  *
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.
11  *
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.
16  *
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
20  */
21 
22 /**
23  * @file
24  * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
25  */
26 
27 #include "avcodec.h"
28 #include "internal.h"
29 #include "mss12.h"
30 
31 typedef struct MSS1Context {
35 } MSS1Context;
36 
38 {
39  for (;;) {
40  if (c->high >= 0x8000) {
41  if (c->low < 0x8000) {
42  if (c->low >= 0x4000 && c->high < 0xC000) {
43  c->value -= 0x4000;
44  c->low -= 0x4000;
45  c->high -= 0x4000;
46  } else {
47  return;
48  }
49  } else {
50  c->value -= 0x8000;
51  c->low -= 0x8000;
52  c->high -= 0x8000;
53  }
54  }
55  c->value <<= 1;
56  c->low <<= 1;
57  c->high <<= 1;
58  c->high |= 1;
59  c->value |= get_bits1(c->gbc.gb);
60  }
61 }
62 
64 
65 static int arith_get_bits(ArithCoder *c, int bits)
66 {
67  int range = c->high - c->low + 1;
68  int val = (((c->value - c->low + 1) << bits) - 1) / range;
69  int prob = range * val;
70 
71  c->high = ((prob + range) >> bits) + c->low - 1;
72  c->low += prob >> bits;
73 
74  arith_normalise(c);
75 
76  return val;
77 }
78 
79 static int arith_get_number(ArithCoder *c, int mod_val)
80 {
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;
84 
85  c->high = (prob + range) / mod_val + c->low - 1;
86  c->low += prob / mod_val;
87 
88  arith_normalise(c);
89 
90  return val;
91 }
92 
93 static int arith_get_prob(ArithCoder *c, int16_t *probs)
94 {
95  int range = c->high - c->low + 1;
96  int val = ((c->value - c->low + 1) * probs[0] - 1) / range;
97  int sym = 1;
98 
99  while (probs[sym] > val)
100  sym++;
101 
102  c->high = range * probs[sym - 1] / probs[0] + c->low - 1;
103  c->low += range * probs[sym] / probs[0];
104 
105  return sym;
106 }
107 
109 
111 {
112  c->low = 0;
113  c->high = 0xFFFF;
114  c->value = get_bits(gb, 16);
115  c->gbc.gb = gb;
116  c->get_model_sym = arith_get_model_sym;
117  c->get_number = arith_get_number;
118 }
119 
120 static int decode_pal(MSS12Context *ctx, ArithCoder *acoder)
121 {
122  int i, ncol, r, g, b;
123  uint32_t *pal = ctx->pal + 256 - ctx->free_colours;
124 
125  if (!ctx->free_colours)
126  return 0;
127 
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++ = (0xFFU << 24) | (r << 16) | (g << 8) | b;
134  }
135 
136  return !!ncol;
137 }
138 
139 static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
140  AVPacket *avpkt)
141 {
142  const uint8_t *buf = avpkt->data;
143  int buf_size = avpkt->size;
144  MSS1Context *ctx = avctx->priv_data;
145  MSS12Context *c = &ctx->ctx;
146  GetBitContext gb;
147  ArithCoder acoder;
148  int pal_changed = 0;
149  int ret;
150 
151  init_get_bits(&gb, buf, buf_size * 8);
152  arith_init(&acoder, &gb);
153 
154  if ((ret = ff_reget_buffer(avctx, &ctx->pic)) < 0)
155  return ret;
156 
157  c->pal_pic = ctx->pic.data[0] + ctx->pic.linesize[0] * (avctx->height - 1);
158  c->pal_stride = -ctx->pic.linesize[0];
159  c->keyframe = !arith_get_bit(&acoder);
160  if (c->keyframe) {
161  c->corrupted = 0;
163  pal_changed = decode_pal(c, &acoder);
164  ctx->pic.key_frame = 1;
166  } else {
167  if (c->corrupted)
168  return AVERROR_INVALIDDATA;
169  ctx->pic.key_frame = 0;
171  }
172  c->corrupted = ff_mss12_decode_rect(&ctx->sc, &acoder, 0, 0,
173  avctx->width, avctx->height);
174  if (c->corrupted)
175  return AVERROR_INVALIDDATA;
176  memcpy(ctx->pic.data[1], c->pal, AVPALETTE_SIZE);
177  ctx->pic.palette_has_changed = pal_changed;
178 
179  if ((ret = av_frame_ref(data, &ctx->pic)) < 0)
180  return ret;
181 
182  *got_frame = 1;
183 
184  /* always report that the buffer was completely consumed */
185  return buf_size;
186 }
187 
189 {
190  MSS1Context * const c = avctx->priv_data;
191  int ret;
192 
193  c->ctx.avctx = avctx;
194 
196 
197  ret = ff_mss12_decode_init(&c->ctx, 0, &c->sc, NULL);
198 
199  avctx->pix_fmt = AV_PIX_FMT_PAL8;
200 
201  return ret;
202 }
203 
205 {
206  MSS1Context * const ctx = avctx->priv_data;
207 
208  av_frame_unref(&ctx->pic);
209  ff_mss12_decode_end(&ctx->ctx);
210 
211  return 0;
212 }
213 
215  .name = "mss1",
216  .type = AVMEDIA_TYPE_VIDEO,
217  .id = AV_CODEC_ID_MSS1,
218  .priv_data_size = sizeof(MSS1Context),
222  .capabilities = CODEC_CAP_DR1,
223  .long_name = NULL_IF_CONFIG_SMALL("MS Screen 1"),
224 };