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Gmane
From: Kostya Shishkov <kostya.shishkov-Re5JQEeQqe8AvxtiuMwx3w <at> public.gmane.org>
Subject: [PATCH] MS Screen 1 decoder
Newsgroups: gmane.comp.video.libav.devel
Date: Saturday 16th June 2012 10:36:16 UTC (over 4 years ago)
---
As a side note, I must say that lavf ASF demuxer outputs wrong data, so for
example eleventh or twelfth frame in
http://samples.ffmpeg.org/V-codecs/MSS1/screen_codec.wmv
is demuxed wrong compared to MPlayer. And of course it causes decoding
errors.

As a second side note, I heard that MSS2 (aka Windows Media Video 9 Screen)
has more features like coding region with WMV9 algorithm and special RLE
modes, arithmetic coder there is also different. So don't expect it soon.
---
 Changelog              |    1 +
 doc/general.texi       |    2 +
 libavcodec/Makefile    |    1 +
 libavcodec/allcodecs.c |    1 +
 libavcodec/avcodec.h   |    1 +
 libavcodec/mss1.c      |  844
++++++++++++++++++++++++++++++++++++++++++++++++
 libavformat/riff.c     |    1 +
 7 files changed, 851 insertions(+), 0 deletions(-)
 create mode 100644 libavcodec/mss1.c

diff --git a/Changelog b/Changelog
index b80ff88..0b6d2e8 100644
--- a/Changelog
+++ b/Changelog
@@ -25,6 +25,7 @@ version :
   be used with -of old.
 - Indeo Audio decoder
 - channelsplit audio filter
+- Microsoft Screen codec decoder
 
 
 version 0.8:
diff --git a/doc/general.texi b/doc/general.texi
index dee8f9e..10e506c 100644
--- a/doc/general.texi
+++ b/doc/general.texi
@@ -520,6 +520,8 @@ following image formats are supported:
 @item LOCO                   @tab     @tab  X
 @item lossless MJPEG         @tab  X  @tab  X
 @item Microsoft RLE          @tab     @tab  X
[email protected] Microsoft Screen       @tab     @tab  X
+    @tab Also known as Windows Media Video V7 Screen.
 @item Microsoft Video 1      @tab     @tab  X
 @item Mimic                  @tab     @tab  X
     @tab Used in MSN Messenger Webcam streams.
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 3bfd78b..6a5a4d6 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -292,6 +292,7 @@ OBJS-$(CONFIG_MSMPEG4V3_ENCODER)       += msmpeg4.o
msmpeg4enc.o msmpeg4data.o \
                                           h263dec.o h263.o ituh263dec.o   
    \
                                           mpeg4videodec.o
 OBJS-$(CONFIG_MSRLE_DECODER)           += msrle.o msrledec.o
+OBJS-$(CONFIG_MSS1_DECODER)            += mss1.o
 OBJS-$(CONFIG_MSVIDEO1_DECODER)        += msvideo1.o
 OBJS-$(CONFIG_MSZH_DECODER)            += lcldec.o
 OBJS-$(CONFIG_MXPEG_DECODER)           += mxpegdec.o mjpegdec.o mjpeg.o
diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
index 01d13d5..50985f6 100644
--- a/libavcodec/allcodecs.c
+++ b/libavcodec/allcodecs.c
@@ -156,6 +156,7 @@ void avcodec_register_all(void)
     REGISTER_ENCDEC  (MSMPEG4V2, msmpeg4v2);
     REGISTER_ENCDEC  (MSMPEG4V3, msmpeg4v3);
     REGISTER_DECODER (MSRLE, msrle);
+    REGISTER_DECODER (MSS1, mss1);
     REGISTER_DECODER (MSVIDEO1, msvideo1);
     REGISTER_DECODER (MSZH, mszh);
     REGISTER_DECODER (MXPEG, mxpeg);
diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 4a07d6d..b56bba0 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -255,6 +255,7 @@ enum CodecID {
     CODEC_ID_CDXL,
     CODEC_ID_XBM,
     CODEC_ID_ZEROCODEC,
+    CODEC_ID_MSS1,
 
     /* various PCM "codecs" */
     CODEC_ID_FIRST_AUDIO = 0x10000,     ///< A dummy id pointing at the
start of audio codecs
diff --git a/libavcodec/mss1.c b/libavcodec/mss1.c
new file mode 100644
index 0000000..234756e
--- /dev/null
+++ b/libavcodec/mss1.c
@@ -0,0 +1,844 @@
+/*
+ * 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 "get_bits.h"
+
+enum SplitMode {
+    SPLIT_VERT = 0,
+    SPLIT_HOR,
+    SPLIT_NONE
+};
+
+typedef struct ArithCoder {
+    int low, high, value;
+    GetBitContext *gb;
+} ArithCoder;
+
+#define MODEL_MIN_SYMS 2
+#define MODEL_MAX_SYMS 256
+#define THRESH_ADAPTIVE -1
+#define THRESH_LOW      15
+#define THRESH_HIGH     50
+#define THRESH_KOSTYA 1986
+
+typedef struct Model {
+    int cum_prob[MODEL_MAX_SYMS + 1];
+    int weights[MODEL_MAX_SYMS + 1];
+    int idx2sym[MODEL_MAX_SYMS + 1];
+    int sym2idx[MODEL_MAX_SYMS + 1];
+    int num_syms;
+    int thr_weight, threshold;
+} Model;
+
+static const int sec_order_sizes[4] = { 1, 7, 6, 1 };
+
+typedef struct PixContext {
+    int cache_size, num_syms;
+    uint8_t cache[12];
+    Model cache_model, full_model;
+    Model sec_models[4][8][4];
+} PixContext;
+
+typedef struct MSS1Context {
+    AVCodecContext *avctx;
+    AVFrame        pic;
+    uint8_t        *pic_start;
+    int            pic_stride;
+    uint8_t        *mask;
+    int            mask_linesize;
+    uint32_t       pal[256];
+    int            free_colours;
+    Model          intra_region, inter_region;
+    Model          pivot, edge_mode, split_mode;
+    PixContext     intra_pix_ctx, inter_pix_ctx;
+    int            corrupted;
+} MSS1Context;
+
+static void arith_init(ArithCoder *c, GetBitContext *gb)
+{
+    c->low   = 0;
+    c->high  = 0xFFFF;
+    c->value = get_bits(gb, 16);
+    c->gb    = gb;
+}
+
+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 model_calc_threshold(Model *m)
+{
+    int thr;
+
+    if (m->thr_weight == -1) {
+        thr = 2 * m->weights[m->num_syms] - 1;
+        thr = ((thr >> 1) + 4 * m->cum_prob[0]) / thr;
+    } else {
+        thr = m->num_syms * m->thr_weight;
+    }
+
+    return FFMIN(thr, 0x3FFF);
+}
+
+static void model_reset(Model *m)
+{
+    int i;
+
+    for (i = 0; i <= m->num_syms; i++) {
+        m->weights[i]  = 1;
+        m->cum_prob[i] = m->num_syms - i;
+    }
+    m->weights[0]           = -1;
+    m->idx2sym[0]           = -1;
+    m->sym2idx[m->num_syms] = -1;
+    for (i = 0; i < m->num_syms; i++) {
+        m->sym2idx[i]     = i + 1;
+        m->idx2sym[i + 1] = i;
+    }
+}
+
+static void model_init(Model *m, int num_syms, int thr_weight)
+{
+    m->num_syms   = num_syms;
+    m->thr_weight = thr_weight;
+    m->threshold  = model_calc_threshold(m);
+    model_reset(m);
+}
+
+static void model_rescale_weights(Model *m)
+{
+    int i;
+    int cum_prob;
+
+    if (m->thr_weight == -1)
+        m->threshold = model_calc_threshold(m);
+    while (m->cum_prob[0] > m->threshold) {
+        cum_prob = 0;
+        for (i = m->num_syms; i >= 0; i--) {
+            m->cum_prob[i] = cum_prob;
+            m->weights[i]  = (m->weights[i] + 1) >> 1;
+            cum_prob      += m->weights[i];
+        }
+    }
+}
+
+static void model_update(Model *m, int val)
+{
+    int i;
+
+    if (m->weights[val] == m->weights[val - 1]) {
+        for (i = val; m->weights[i - 1] == m->weights[val]; i--);
+        if (i != val) {
+            int sym1, sym2;
+
+            sym1 = m->idx2sym[val];
+            sym2 = m->idx2sym[i];
+
+            m->idx2sym[val]  = sym2;
+            m->idx2sym[i]    = sym1;
+            m->sym2idx[sym1] = i;
+            m->sym2idx[sym2] = val;
+
+            val = i;
+        }
+    }
+    m->weights[val]++;
+    for (i = val - 1; i >= 0; i--)
+        m->cum_prob[i]++;
+    model_rescale_weights(m);
+}
+
+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];
+    model_update(m, idx);
+
+    arith_normalise(c);
+
+    return val;
+}
+
+static void pixctx_reset(PixContext *ctx)
+{
+    int i, j, k;
+
+    for (i = 0; i < ctx->cache_size; i++)
+        ctx->cache[i] = i;
+
+    model_reset(&ctx->cache_model);
+    model_reset(&ctx->full_model);
+
+    for (i = 0; i < 4; i++)
+        for (j = 0; j < sec_order_sizes[i]; j++)
+            for (k = 0; k < 4; k++)
+                model_reset(&ctx->sec_models[i][j][k]);
+}
+
+static void pixctx_init(PixContext *ctx, int cache_size)
+{
+    int i, j, k;
+
+    ctx->cache_size = cache_size + 4;
+    ctx->num_syms   = cache_size;
+
+    for (i = 0; i < ctx->cache_size; i++)
+        ctx->cache[i] = i;
+
+    model_init(&ctx->cache_model, ctx->num_syms + 1, THRESH_LOW);
+    model_init(&ctx->full_model, 256, THRESH_HIGH);
+
+    for (i = 0; i < 4; i++) {
+        for (j = 0; j < sec_order_sizes[i]; j++) {
+            for (k = 0; k < 4; k++) {
+                model_init(&ctx->sec_models[i][j][k], 2 + i,
+                           i ? THRESH_LOW : THRESH_ADAPTIVE);
+            }
+        }
+    }
+}
+
+static int decode_top_left_pixel(ArithCoder *acoder, PixContext *pctx)
+{
+    int i, val, pix;
+
+    val = arith_get_model_sym(acoder, &pctx->cache_model);
+    if (val < pctx->num_syms) {
+        pix = pctx->cache[val];
+    } else {
+        pix = arith_get_model_sym(acoder, &pctx->full_model);
+        for (i = 0; i < pctx->cache_size - 1; i++)
+            if (pctx->cache[i] == pix)
+                break;
+        val = i;
+    }
+    if (val) {
+        for (i = val; i > 0; i--)
+            pctx->cache[i] = pctx->cache[i - 1];
+        pctx->cache[0] = pix;
+    }
+
+    return pix;
+}
+
+static int decode_pixel(ArithCoder *acoder, PixContext *pctx,
+                        uint8_t *ngb, int num_ngb)
+{
+    int i, val, pix;
+
+    val = arith_get_model_sym(acoder, &pctx->cache_model);
+    if (val < pctx->num_syms) {
+        int idx, j;
+
+
+        idx = 0;
+        for (i = 0; i < pctx->cache_size; i++) {
+            for (j = 0; j < num_ngb; j++)
+                if (pctx->cache[i] == ngb[j])
+                    break;
+            if (j == num_ngb) {
+                if (idx == val)
+                    break;
+                idx++;
+            }
+        }
+        val = FFMIN(i, pctx->cache_size - 1);
+        pix = pctx->cache[val];
+    } else {
+        pix = arith_get_model_sym(acoder, &pctx->full_model);
+        for (i = 0; i < pctx->cache_size - 1; i++)
+            if (pctx->cache[i] == pix)
+                break;
+        val = i;
+    }
+    if (val) {
+        for (i = val; i > 0; i--)
+            pctx->cache[i] = pctx->cache[i - 1];
+        pctx->cache[0] = pix;
+    }
+
+    return pix;
+}
+
+enum ContextDirection {
+    TOP_LEFT = 0,
+    TOP,
+    TOP_RIGHT,
+    LEFT
+};
+
+static int decode_pixel_in_context(ArithCoder *acoder, PixContext *pctx,
+                                   uint8_t *src, int stride, int x, int y,
+                                   int has_right)
+{
+    uint8_t neighbours[4];
+    uint8_t ref_pix[4];
+    int nlen;
+    int layer = 0, sub;
+    int pix;
+    int i, j;
+
+    if (!y) {
+        memset(neighbours, src[-1], 4);
+    } else {
+        neighbours[TOP] = src[-stride];
+        if (!x) {
+            neighbours[TOP_LEFT] = neighbours[LEFT] = neighbours[TOP];
+        } else {
+            neighbours[TOP_LEFT] = src[-stride - 1];
+            neighbours[    LEFT] = src[-1];
+        }
+        if (has_right)
+            neighbours[TOP_RIGHT] = src[-stride + 1];
+        else
+            neighbours[TOP_RIGHT] = neighbours[TOP];
+    }
+
+    sub = 0;
+    if (x >= 2 && src[-2] == neighbours[LEFT])
+        sub  = 1;
+    if (y >= 2 && src[-2 * stride] == neighbours[TOP])
+        sub |= 2;
+
+    nlen = 1;
+    ref_pix[0] = neighbours[0];
+    for (i = 1; i < 4; i++) {
+        for (j = 0; j < nlen; j++)
+            if (ref_pix[j] == neighbours[i])
+                break;
+        if (j == nlen)
+            ref_pix[nlen++] = neighbours[i];
+    }
+
+    switch (nlen) {
+    case 1:
+    case 4:
+        layer = 0;
+        break;
+    case 2:
+        if (neighbours[TOP] == neighbours[TOP_LEFT]) {
+            if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT])
+                layer = 3;
+            else if (neighbours[LEFT] == neighbours[TOP_LEFT])
+                layer = 2;
+            else
+                layer = 4;
+        } else if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT]) {
+            if (neighbours[LEFT] == neighbours[TOP_LEFT])
+                layer = 1;
+            else
+                layer = 5;
+        } else if (neighbours[LEFT] == neighbours[TOP_LEFT]) {
+            layer = 6;
+        } else {
+            layer = 0;
+        }
+        break;
+    case 3:
+        if (neighbours[TOP] == neighbours[TOP_LEFT])
+            layer = 0;
+        else if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT])
+            layer = 1;
+        else if (neighbours[LEFT] == neighbours[TOP_LEFT])
+            layer = 2;
+        else if (neighbours[TOP_RIGHT] == neighbours[TOP])
+            layer = 3;
+        else if (neighbours[TOP] == neighbours[LEFT])
+            layer = 4;
+        else
+            layer = 5;
+        break;
+    }
+
+    pix = arith_get_model_sym(acoder, &pctx->sec_models[nlen -
1][layer][sub]);
+    if (pix < nlen)
+        return ref_pix[pix];
+    else
+        return decode_pixel(acoder, pctx, ref_pix, nlen);
+}
+
+static int decode_region(MSS1Context *ctx, ArithCoder *acoder, uint8_t
*dst,
+                         int x, int y, int width, int height, int stride,
+                         PixContext *pctx)
+{
+    int i, j;
+
+    dst += x + y * stride;
+
+    dst[0] = decode_top_left_pixel(acoder, pctx);
+    for (j = 0; j < height; j++) {
+        for (i = 0; i < width; i++) {
+            if (!i && !j)
+                continue;
+
+            dst[i] = decode_pixel_in_context(acoder, pctx, dst + i,
stride,
+                                             i, j, width - i - 1);
+        }
+        dst += stride;
+    }
+
+    return 0;
+}
+
+static int decode_region_masked(MSS1Context *ctx, ArithCoder *acoder,
+                                uint8_t *dst, int stride, uint8_t *mask,
+                                int mask_stride, int x, int y,
+                                int width, int height,
+                                PixContext *pctx)
+{
+    int i, j;
+
+    dst  += x + y * stride;
+    mask += x + y * mask_stride;
+
+    if (mask[0] != 0xFF)
+        dst[0] = decode_top_left_pixel(acoder, pctx);
+    for (j = 0; j < height; j++) {
+        for (i = 0; i < width; i++) {
+            if (!i && !j || mask[i] != 0xFF)
+                continue;
+
+            dst[i] = decode_pixel_in_context(acoder, pctx, dst + i,
stride,
+                                             i, j, width - i - 1);
+        }
+        dst  += stride;
+        mask += mask_stride;
+    }
+
+    return 0;
+}
+
+static void codec_init(MSS1Context *ctx)
+{
+    model_init(&ctx->intra_region, 2, THRESH_ADAPTIVE);
+    model_init(&ctx->inter_region, 2, THRESH_ADAPTIVE);
+    model_init(&ctx->split_mode,   3, THRESH_HIGH);
+    model_init(&ctx->edge_mode,    2, THRESH_HIGH);
+    model_init(&ctx->pivot,        3, THRESH_LOW);
+    pixctx_init(&ctx->intra_pix_ctx, 8);
+    pixctx_init(&ctx->inter_pix_ctx, 2);
+    ctx->corrupted = 1;
+}
+
+static void codec_reset(MSS1Context *ctx)
+{
+    model_reset(&ctx->intra_region);
+    model_reset(&ctx->inter_region);
+    model_reset(&ctx->split_mode);
+    model_reset(&ctx->edge_mode);
+    model_reset(&ctx->pivot);
+    pixctx_reset(&ctx->intra_pix_ctx);
+    pixctx_reset(&ctx->inter_pix_ctx);
+
+    ctx->corrupted = 0;
+}
+
+static int decode_pal(MSS1Context *ctx, ArithCoder *acoder)
+{
+    int i, ncol, r, g, b;
+    uint32_t *pal = ctx->pal + 256 - ctx->free_colours;
+
+    if (!ctx->free_colours)
+        return 0;
+
+    ncol = arith_get_number(acoder, 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 0;
+}
+
+static int decode_pivot(MSS1Context *ctx, ArithCoder *acoder, int base)
+{
+    int val, inv;
+
+    inv = arith_get_model_sym(acoder, &ctx->edge_mode);
+    val = arith_get_model_sym(acoder, &ctx->pivot) + 1;
+
+    if (val > 2) {
+        if ((base + 1) / 2 - 2 <= 0) {
+            ctx->corrupted = 1;
+            return 0;
+        }
+        val = arith_get_number(acoder, (base + 1) / 2 - 2) + 3;
+    }
+
+    if (val == base) {
+        ctx->corrupted = 1;
+        return 0;
+    }
+
+    return inv ? base - val : val;
+}
+
+static int decode_region_intra(MSS1Context *ctx, ArithCoder *acoder,
+                               int x, int y, int width, int height)
+{
+    int mode;
+
+    mode = arith_get_model_sym(acoder, &ctx->intra_region);
+
+    if (!mode) {
+        int i, pix;
+        int stride = ctx->pic_stride;
+        uint8_t *dst = ctx->pic_start + x + y * stride;
+
+        pix = decode_top_left_pixel(acoder, &ctx->intra_pix_ctx);
+        for (i = 0; i < height; i++, dst += stride)
+            memset(dst, pix, width);
+    } else {
+        return decode_region(ctx, acoder, ctx->pic_start,
+                             x, y, width, height, ctx->pic_stride,
+                             &ctx->intra_pix_ctx);
+    }
+
+    return 0;
+}
+
+static int decode_intra(MSS1Context *ctx, ArithCoder *acoder,
+                        int x, int y, int width, int height)
+{
+    int mode, pivot;
+
+    if (ctx->corrupted)
+        return -1;
+
+    mode = arith_get_model_sym(acoder, &ctx->split_mode);
+
+    switch (mode) {
+    case SPLIT_VERT:
+        pivot = decode_pivot(ctx, acoder, height);
+        if (ctx->corrupted)
+            return -1;
+        if (decode_intra(ctx, acoder, x, y, width, pivot))
+            return -1;
+        if (decode_intra(ctx, acoder, x, y + pivot, width, height -
pivot))
+            return -1;
+        break;
+    case SPLIT_HOR:
+        pivot = decode_pivot(ctx, acoder, width);
+        if (ctx->corrupted)
+            return -1;
+        if (decode_intra(ctx, acoder, x, y, pivot, height))
+            return -1;
+        if (decode_intra(ctx, acoder, x + pivot, y, width - pivot,
height))
+            return -1;
+        break;
+    case SPLIT_NONE:
+        return decode_region_intra(ctx, acoder, x, y, width, height);
+    default:
+        return -1;
+    }
+
+    return 0;
+}
+
+static int decode_region_inter(MSS1Context *ctx, ArithCoder *acoder,
+                               int x, int y, int width, int height)
+{
+    int mode;
+
+    mode = arith_get_model_sym(acoder, &ctx->inter_region);
+
+    if (!mode) {
+        mode = decode_top_left_pixel(acoder, &ctx->inter_pix_ctx);
+        if (mode != 0xFF) {
+            return 0;
+        } else {
+            return decode_region_intra(ctx, acoder, x, y, width, height);
+        }
+    } else {
+        if (decode_region(ctx, acoder, ctx->mask,
+                          x, y, width, height, ctx->mask_linesize,
+                          &ctx->inter_pix_ctx) < 0)
+            return -1;
+        return decode_region_masked(ctx, acoder, ctx->pic_start,
+                                    -ctx->pic.linesize[0], ctx->mask,
+                                    ctx->mask_linesize,
+                                    x, y, width, height,
+                                    &ctx->intra_pix_ctx);
+    }
+
+    return 0;
+}
+
+static int decode_inter(MSS1Context *ctx, ArithCoder *acoder,
+                        int x, int y, int width, int height)
+{
+    int mode, pivot;
+
+    if (ctx->corrupted)
+        return -1;
+
+    mode = arith_get_model_sym(acoder, &ctx->split_mode);
+
+    switch (mode) {
+    case SPLIT_VERT:
+        pivot = decode_pivot(ctx, acoder, height);
+        if (decode_inter(ctx, acoder, x, y, width, pivot))
+            return -1;
+        if (decode_inter(ctx, acoder, x, y + pivot, width, height -
pivot))
+            return -1;
+        break;
+    case SPLIT_HOR:
+        pivot = decode_pivot(ctx, acoder, width);
+        if (decode_inter(ctx, acoder, x, y, pivot, height))
+            return -1;
+        if (decode_inter(ctx, acoder, x + pivot, y, width - pivot,
height))
+            return -1;
+        break;
+    case SPLIT_NONE:
+        return decode_region_inter(ctx, acoder, x, y, width, height);
+    default:
+        return -1;
+    }
+
+    return 0;
+}
+
+static int 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->pic_start  = c->pic.data[0] + c->pic.linesize[0] * (avctx->height -
1);
+    c->pic_stride = -c->pic.linesize[0];
+    if (!arith_get_bit(&acoder)) {
+        codec_reset(c);
+        pal_changed = decode_pal(c, &acoder);
+        c->corrupted = decode_intra(c, &acoder, 0, 0, avctx->width,
avctx->height);
+        c->pic.key_frame = 1;
+        c->pic.pict_type = AV_PICTURE_TYPE_I;
+    } else {
+        if (c->corrupted)
+            return AVERROR_INVALIDDATA;
+        c->corrupted = decode_inter(c, &acoder, 0, 0, avctx->width,
avctx->height);
+        c->pic.key_frame = 0;
+        c->pic.pict_type = AV_PICTURE_TYPE_P;
+    }
+    if (c->corrupted)
+        return AVERROR_INVALIDDATA;
+    memcpy(c->pic.data[1], c->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 decode_init(AVCodecContext *avctx)
+{
+    MSS1Context * const c = avctx->priv_data;
+    int i;
+
+    c->avctx = avctx;
+
+    if (avctx->extradata_size < 52 + 256 * 3) {
+        av_log(avctx, AV_LOG_ERROR, "Insufficient extradata size %d\n",
+               avctx->extradata_size);
+        return AVERROR_INVALIDDATA;
+    }
+
+    if (AV_RB32(avctx->extradata) < avctx->extradata_size) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Insufficient extradata size: expected %d got %d\n",
+               AV_RB32(avctx->extradata),
+               avctx->extradata_size);
+        return AVERROR_INVALIDDATA;
+    }
+
+    av_log(avctx, AV_LOG_DEBUG, "Encoder version %d.%d\n",
+           AV_RB32(avctx->extradata + 4), AV_RB32(avctx->extradata + 8));
+    c->free_colours     = AV_RB32(avctx->extradata + 48);
+    av_log(avctx, AV_LOG_DEBUG, "%d free colour(s)\n", c->free_colours);
+    avctx->coded_width  = AV_RB32(avctx->extradata + 20);
+    avctx->coded_height = AV_RB32(avctx->extradata + 24);
+
+    av_log(avctx, AV_LOG_DEBUG, "Display dimensions %dx%d\n",
+           AV_RB32(avctx->extradata + 12), AV_RB32(avctx->extradata +
16));
+    av_log(avctx, AV_LOG_DEBUG, "Coded dimensions %dx%d\n",
+           avctx->coded_width, avctx->coded_height);
+    av_log(avctx, AV_LOG_DEBUG, "%g frames per second\n",
+           av_int2float(AV_RB32(avctx->extradata + 28)));
+    av_log(avctx, AV_LOG_DEBUG, "Bitrate %d bps\n",
+           AV_RB32(avctx->extradata + 32));
+    av_log(avctx, AV_LOG_DEBUG, "Max. lead time %g ms\n",
+           av_int2float(AV_RB32(avctx->extradata + 36)));
+    av_log(avctx, AV_LOG_DEBUG, "Max. lag time %g ms\n",
+           av_int2float(AV_RB32(avctx->extradata + 40)));
+    av_log(avctx, AV_LOG_DEBUG, "Max. seek time %g ms\n",
+           av_int2float(AV_RB32(avctx->extradata + 44)));
+
+    for (i = 0; i < 256; i++)
+        c->pal[i] = AV_RB24(avctx->extradata + 52 + i * 3);
+
+    avctx->pix_fmt = PIX_FMT_PAL8;
+
+    c->mask_linesize = FFALIGN(avctx->coded_width, 16);
+    c->mask = av_malloc(c->mask_linesize * avctx->coded_height);
+    if (!c->mask) {
+        av_log(avctx, AV_LOG_ERROR, "Cannot allocate mask plane\n");
+        return AVERROR(ENOMEM);
+    }
+
+    avctx->coded_frame = &c->pic;
+
+    codec_init(c);
+
+    return 0;
+}
+
+static av_cold int decode_end(AVCodecContext *avctx)
+{
+    MSS1Context * const c = avctx->priv_data;
+
+    if (c->pic.data[0])
+        avctx->release_buffer(avctx, &c->pic);
+    av_freep(&c->mask);
+
+    return 0;
+}
+
+AVCodec ff_mss1_decoder = {
+    .name           = "mss1",
+    .type           = AVMEDIA_TYPE_VIDEO,
+    .id             = CODEC_ID_MSS1,
+    .priv_data_size = sizeof(MSS1Context),
+    .init           = decode_init,
+    .close          = decode_end,
+    .decode         = decode_frame,
+    .capabilities   = CODEC_CAP_DR1,
+    .long_name      = NULL_IF_CONFIG_SMALL("MS Screen 1"),
+};
diff --git a/libavformat/riff.c b/libavformat/riff.c
index 922a863..efab704 100644
--- a/libavformat/riff.c
+++ b/libavformat/riff.c
@@ -284,6 +284,7 @@ const AVCodecTag ff_codec_bmp_tags[] = {
     { CODEC_ID_VBLE,         MKTAG('V', 'B', 'L', 'E') },
     { CODEC_ID_DXTORY,       MKTAG('x', 't', 'o', 'r') },
     { CODEC_ID_ZEROCODEC,    MKTAG('Z', 'E', 'C', 'O') },
+    { CODEC_ID_MSS1,         MKTAG('M', 'S', 'S', '1') },
     { CODEC_ID_NONE,         0 }
 };
 
-- 
1.7.0.4
 
CD: 760ms