MS Expression Encoder Screen decoder

1 files changed, 682 insertions, 0 deletions

diff --git a/libavcodec/mss4.c b/libavcodec/mss4.c
new file mode 100644
index 0000000000..2742d05a5c
--- /dev/null
+++ b/libavcodec/mss4.c
@@ -0,0 +1,682 @@
+/*
+ * Microsoft Screen 4 (aka Microsoft Expression Encoder 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 4 (aka Microsoft Titanium Screen 2,
+ * aka Microsoft Expression Encoder Screen) decoder
+ */
+
+#include "avcodec.h"
+#include "bytestream.h"
+#include "dsputil.h"
+#include "get_bits.h"
+#include "mss34dsp.h"
+#include "unary.h"
+
+#define HEADER_SIZE 8
+
+enum FrameType {
+    INTRA_FRAME = 0,
+    INTER_FRAME,
+    SKIP_FRAME
+};
+
+enum BlockType {
+    SKIP_BLOCK = 0,
+    DCT_BLOCK,
+    IMAGE_BLOCK,
+};
+
+enum CachePos {
+    LEFT = 0,
+    TOP_LEFT,
+    TOP,
+};
+
+static const uint8_t mss4_dc_vlc_lens[2][16] = {
+    { 0, 1, 5, 1, 1, 1, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0 },
+    { 0, 3, 1, 1, 1, 1, 1, 1, 1, 2, 0, 0, 0, 0, 0, 0 }
+};
+
+static const uint8_t mss4_ac_vlc_lens[2][16] = {
+    { 0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 125 },
+    { 0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 119 }
+};
+
+static const uint8_t mss4_ac_vlc_syms[2][162] = {
+  { 0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12,
+    0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,
+    0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xA1, 0x08,
+    0x23, 0x42, 0xB1, 0xC1, 0x15, 0x52, 0xD1, 0xF0,
+    0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0A, 0x16,
+    0x17, 0x18, 0x19, 0x1A, 0x25, 0x26, 0x27, 0x28,
+    0x29, 0x2A, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39,
+    0x3A, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,
+    0x4A, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,
+    0x5A, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
+    0x6A, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,
+    0x7A, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,
+    0x8A, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98,
+    0x99, 0x9A, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7,
+    0xA8, 0xA9, 0xAA, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6,
+    0xB7, 0xB8, 0xB9, 0xBA, 0xC2, 0xC3, 0xC4, 0xC5,
+    0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xD2, 0xD3, 0xD4,
+    0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA, 0xE1, 0xE2,
+    0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA,
+    0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8,
+    0xF9, 0xFA  },
+  { 0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21,
+    0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,
+    0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,
+    0xA1, 0xB1, 0xC1, 0x09, 0x23, 0x33, 0x52, 0xF0,
+    0x15, 0x62, 0x72, 0xD1, 0x0A, 0x16, 0x24, 0x34,
+    0xE1, 0x25, 0xF1, 0x17, 0x18, 0x19, 0x1A, 0x26,
+    0x27, 0x28, 0x29, 0x2A, 0x35, 0x36, 0x37, 0x38,
+    0x39, 0x3A, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
+    0x49, 0x4A, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
+    0x59, 0x5A, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
+    0x69, 0x6A, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
+    0x79, 0x7A, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+    0x88, 0x89, 0x8A, 0x92, 0x93, 0x94, 0x95, 0x96,
+    0x97, 0x98, 0x99, 0x9A, 0xA2, 0xA3, 0xA4, 0xA5,
+    0xA6, 0xA7, 0xA8, 0xA9, 0xAA, 0xB2, 0xB3, 0xB4,
+    0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA, 0xC2, 0xC3,
+    0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xD2,
+    0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA,
+    0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9,
+    0xEA, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8,
+    0xF9, 0xFA  }
+};
+
+static const uint8_t vec_len_syms[2][4] = {
+    { 4, 2, 3, 1 },
+    { 4, 1, 2, 3 }
+};
+
+static const uint8_t mss4_vec_entry_vlc_lens[2][16] = {
+    { 0, 2, 2, 3, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
+    { 0, 1, 5, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
+};
+
+static const uint8_t mss4_vec_entry_vlc_syms[2][9] = {
+    { 0, 7, 6, 5, 8, 4, 3, 1, 2 },
+    { 0, 2, 3, 4, 5, 6, 7, 1, 8 }
+};
+
+#define MAX_ENTRIES  162
+
+typedef struct MSS4Context {
+    AVFrame    pic;
+    DSPContext dsp;
+
+    VLC        dc_vlc[2], ac_vlc[2];
+    VLC        vec_entry_vlc[2];
+    int        block[64];
+    uint8_t    imgbuf[3][16 * 16];
+
+    int        quality;
+    uint16_t   quant_mat[2][64];
+
+    int        *prev_dc[3];
+    int        dc_stride[3];
+    int        dc_cache[4][4];
+
+    int        prev_vec[3][4];
+} MSS4Context;
+
+static av_cold int mss4_init_vlc(VLC *vlc, const uint8_t *lens,
+                                 const uint8_t *syms, int num_syms)
+{
+    uint8_t  bits[MAX_ENTRIES];
+    uint16_t codes[MAX_ENTRIES];
+    int i, j;
+    int prefix = 0, max_bits = 0, idx = 0;
+
+    for (i = 0; i < 16; i++) {
+        for (j = 0; j < lens[i]; j++) {
+            bits[idx]  = i + 1;
+            codes[idx] = prefix++;
+            max_bits   = i + 1;
+            idx++;
+        }
+        prefix <<= 1;
+    }
+
+    return ff_init_vlc_sparse(vlc, FFMIN(max_bits, 9), num_syms, bits, 1, 1,
+                              codes, 2, 2, syms, 1, 1, 0);
+}
+
+static av_cold int mss4_init_vlcs(MSS4Context *ctx)
+{
+    int ret, i;
+
+    for (i = 0; i < 2; i++) {
+        ret = mss4_init_vlc(&ctx->dc_vlc[i], mss4_dc_vlc_lens[i], NULL, 12);
+        if (ret)
+            return ret;
+        ret = mss4_init_vlc(&ctx->ac_vlc[i], mss4_ac_vlc_lens[i],
+                            mss4_ac_vlc_syms[i], 162);
+        if (ret)
+            return ret;
+        ret = mss4_init_vlc(&ctx->vec_entry_vlc[i], mss4_vec_entry_vlc_lens[i],
+                            mss4_vec_entry_vlc_syms[i], 9);
+        if (ret)
+            return ret;
+    }
+    return 0;
+}
+
+static av_cold void mss4_free_vlcs(MSS4Context *ctx)
+{
+    int i;
+
+    for (i = 0; i < 2; i++) {
+        ff_free_vlc(&ctx->dc_vlc[i]);
+        ff_free_vlc(&ctx->ac_vlc[i]);
+        ff_free_vlc(&ctx->vec_entry_vlc[i]);
+    }
+}
+
+/* This function returns values in the range
+ * (-range + 1; -range/2] U [range/2; range - 1)
+ * i.e.
+ * nbits = 0 -> 0
+ * nbits = 1 -> -1, 1
+ * nbits = 2 -> -3, -2, 2, 3
+ */
+static av_always_inline int get_coeff_bits(GetBitContext *gb, int nbits)
+{
+    int val;
+
+    if (!nbits)
+        return 0;
+
+    val = get_bits(gb, nbits);
+    if (val < (1 << (nbits - 1)))
+        val -= (1 << nbits) - 1;
+
+    return val;
+}
+
+static inline int get_coeff(GetBitContext *gb, VLC *vlc)
+{
+    int val = get_vlc2(gb, vlc->table, vlc->bits, 2);
+
+    return get_coeff_bits(gb, val);
+}
+
+static int mss4_decode_dct(GetBitContext *gb, VLC *dc_vlc, VLC *ac_vlc,
+                           int *block, int *dc_cache,
+                           int bx, int by, uint16_t *quant_mat)
+{
+    int skip, val, pos = 1, zz_pos, dc;
+
+    memset(block, 0, sizeof(*block) * 64);
+
+    dc = get_coeff(gb, dc_vlc);
+    // DC prediction is the same as in MSS3
+    if (by) {
+        if (bx) {
+            int l, tl, t;
+
+            l  = dc_cache[LEFT];
+            tl = dc_cache[TOP_LEFT];
+            t  = dc_cache[TOP];
+
+            if (FFABS(t - tl) <= FFABS(l - tl))
+                dc += l;
+            else
+                dc += t;
+        } else {
+            dc += dc_cache[TOP];
+        }
+    } else if (bx) {
+        dc += dc_cache[LEFT];
+    }
+    dc_cache[LEFT] = dc;
+    block[0]       = dc * quant_mat[0];
+
+    while (pos < 64) {
+        val = get_vlc2(gb, ac_vlc->table, 9, 2);
+        if (!val)
+            return 0;
+        if (val == -1)
+            return -1;
+        if (val == 0xF0) {
+            pos += 16;
+            continue;
+        }
+        skip = val >> 4;
+        val  = get_coeff_bits(gb, val & 0xF);
+        pos += skip;
+        if (pos >= 64)
+            return -1;
+
+        zz_pos = ff_zigzag_direct[pos];
+        block[zz_pos] = val * quant_mat[zz_pos];
+        pos++;
+    }
+
+    return pos == 64 ? 0 : -1;
+}
+
+static int mss4_decode_dct_block(MSS4Context *c, GetBitContext *gb,
+                                 uint8_t *dst[3], int mb_x, int mb_y)
+{
+    int i, j, k, ret;
+    uint8_t *out = dst[0];
+
+    for (j = 0; j < 2; j++) {
+        for (i = 0; i < 2; i++) {
+            int xpos = mb_x * 2 + i;
+            c->dc_cache[j][TOP_LEFT] = c->dc_cache[j][TOP];
+            c->dc_cache[j][TOP]      = c->prev_dc[0][mb_x * 2 + i];
+            ret = mss4_decode_dct(gb, c->dc_vlc, c->ac_vlc, c->block,
+                                  c->dc_cache[j],
+                                  xpos, mb_y * 2 + j, c->quant_mat[0]);
+            if (ret)
+                return ret;
+            c->prev_dc[0][mb_x * 2 + i] = c->dc_cache[j][LEFT];
+
+            ff_mss34_dct_put(out + xpos * 8, c->pic.linesize[0],
+                             c->block);
+        }
+        out += 8 * c->pic.linesize[0];
+    }
+
+    for (i = 1; i < 3; i++) {
+        c->dc_cache[i + 1][TOP_LEFT] = c->dc_cache[i + 1][TOP];
+        c->dc_cache[i + 1][TOP]      = c->prev_dc[i][mb_x];
+        ret = mss4_decode_dct(gb, c->dc_vlc + 1, c->ac_vlc + 1,
+                              c->block, c->dc_cache[i + 1], mb_x, mb_y,
+                              c->quant_mat[1]);
+        if (ret)
+            return ret;
+        c->prev_dc[i][mb_x] = c->dc_cache[i + 1][LEFT];
+
+        ff_mss34_dct_put(c->imgbuf[i], 8, c->block);
+        out = dst[i] + mb_x * 16;
+        // Since the DCT block is coded as YUV420 and the whole frame as YUV444,
+        // we need to scale chroma.
+        for (j = 0; j < 16; j++) {
+            for (k = 0; k < 8; k++)
+                AV_WN16A(out + k * 2, c->imgbuf[i][k + (j & ~1) * 4] * 0x101);
+            out += c->pic.linesize[i];
+        }
+    }
+
+    return 0;
+}
+
+static void read_vec_pos(GetBitContext *gb, int *vec_pos, int *sel_flag,
+                         int *sel_len, int *prev)
+{
+    int i, y_flag = 0;
+
+    for (i = 2; i >= 0; i--) {
+        if (!sel_flag[i]) {
+            vec_pos[i] = 0;
+            continue;
+        }
+        if ((!i && !y_flag) || get_bits1(gb)) {
+            if (sel_len[i] > 0) {
+                int pval = prev[i];
+                vec_pos[i] = get_bits(gb, sel_len[i]);
+                if (vec_pos[i] >= pval)
+                    vec_pos[i]++;
+            } else {
+                vec_pos[i] = !prev[i];
+            }
+            y_flag = 1;
+        } else {
+            vec_pos[i] = prev[i];
+        }
+    }
+}
+
+static int get_value_cached(GetBitContext *gb, int vec_pos, uint8_t *vec,
+                            int vec_size, int component, int shift, int *prev)
+{
+    if (vec_pos < vec_size)
+        return vec[vec_pos];
+    if (!get_bits1(gb))
+        return prev[component];
+    prev[component] = get_bits(gb, 8 - shift) << shift;
+    return prev[component];
+}
+
+#define MKVAL(vals)  (vals[0] | (vals[1] << 3) | (vals[2] << 6))
+
+/* Image mode - the hardest to comprehend MSS4 coding mode.
+ *
+ * In this mode all three 16x16 blocks are coded together with a method
+ * remotely similar to the methods employed in MSS1-MSS3.
+ * The idea is that every component has a vector of 1-4 most common symbols
+ * and an escape mode for reading new value from the bitstream. Decoding
+ * consists of retrieving pixel values from the vector or reading new ones
+ * from the bitstream; depending on flags read from the bitstream, these vector
+ * positions can be updated or reused from the state of the previous line
+ * or previous pixel.
+ */
+static int mss4_decode_image_block(MSS4Context *ctx, GetBitContext *gb,
+                                   uint8_t *picdst[3], int mb_x, int mb_y)
+{
+    uint8_t vec[3][4];
+    int     vec_len[3];
+    int     sel_len[3], sel_flag[3];
+    int     i, j, k, mode, split;
+    int     prev_vec1 = 0, prev_split = 0;
+    int     vals[3] = { 0 };
+    int     prev_pix[3] = { 0 };
+    int     prev_mode[16] = { 0 };
+    uint8_t *dst[3];
+
+    const int val_shift = ctx->quality == 100 ? 0 : 2;
+
+    for (i = 0; i < 3; i++)
+        dst[i] = ctx->imgbuf[i];
+
+    for (i = 0; i < 3; i++) {
+        vec_len[i] = vec_len_syms[!!i][get_unary(gb, 0, 3)];
+        for (j = 0; j < vec_len[i]; j++) {
+            vec[i][j]  = get_coeff(gb, &ctx->vec_entry_vlc[!!i]);
+            vec[i][j] += ctx->prev_vec[i][j];
+            ctx->prev_vec[i][j] = vec[i][j];
+        }
+        sel_flag[i] = vec_len[i] > 1;
+        sel_len[i]  = vec_len[i] > 2 ? vec_len[i] - 2 : 0;
+    }
+
+    for (j = 0; j < 16; j++) {
+        if (get_bits1(gb)) {
+            split = 0;
+            if (get_bits1(gb)) {
+                prev_mode[0] = 0;
+                vals[0] = vals[1] = vals[2] = 0;
+                mode = 2;
+            } else {
+                mode = get_bits1(gb);
+                if (mode)
+                    split = get_bits(gb, 4);
+            }
+            for (i = 0; i < 16; i++) {
+                if (mode <= 1) {
+                    vals[0] =  prev_mode[i]       & 7;
+                    vals[1] = (prev_mode[i] >> 3) & 7;
+                    vals[2] =  prev_mode[i] >> 6;
+                    if (mode == 1 && i == split) {
+                        read_vec_pos(gb, vals, sel_flag, sel_len, vals);
+                    }
+                } else if (mode == 2) {
+                    if (get_bits1(gb))
+                        read_vec_pos(gb, vals, sel_flag, sel_len, vals);
+                }
+                for (k = 0; k < 3; k++)
+                    *dst[k]++ = get_value_cached(gb, vals[k], vec[k],
+                                                 vec_len[k], k,
+                                                 val_shift, prev_pix);
+                prev_mode[i] = MKVAL(vals);
+            }
+        } else {
+            if (get_bits1(gb)) {
+                split = get_bits(gb, 4);
+                if (split >= prev_split)
+                    split++;
+                prev_split = split;
+            } else {
+                split = prev_split;
+            }
+            if (split) {
+                vals[0] =  prev_mode[0]       & 7;
+                vals[1] = (prev_mode[0] >> 3) & 7;
+                vals[2] =  prev_mode[0] >> 6;
+                for (i = 0; i < 3; i++) {
+                    for (k = 0; k < split; k++) {
+                        *dst[i]++ = get_value_cached(gb, vals[i], vec[i],
+                                                     vec_len[i], i, val_shift,
+                                                     prev_pix);
+                        prev_mode[k] = MKVAL(vals);
+                    }
+                }
+            }
+
+            if (split != 16) {
+                vals[0] =  prev_vec1       & 7;
+                vals[1] = (prev_vec1 >> 3) & 7;
+                vals[2] =  prev_vec1 >> 6;
+                if (get_bits1(gb)) {
+                    read_vec_pos(gb, vals, sel_flag, sel_len, vals);
+                    prev_vec1 = MKVAL(vals);
+                }
+                for (i = 0; i < 3; i++) {
+                    for (k = 0; k < 16 - split; k++) {
+                        *dst[i]++ = get_value_cached(gb, vals[i], vec[i],
+                                                     vec_len[i], i, val_shift,
+                                                     prev_pix);
+                        prev_mode[split + k] = MKVAL(vals);
+                    }
+                }
+            }
+        }
+    }
+
+    for (i = 0; i < 3; i++)
+        for (j = 0; j < 16; j++)
+            memcpy(picdst[i] + mb_x * 16 + j * ctx->pic.linesize[i],
+                   ctx->imgbuf[i] + j * 16, 16);
+
+    return 0;
+}
+
+static inline void mss4_update_dc_cache(MSS4Context *c, int mb_x)
+{
+    int i;
+
+    c->dc_cache[0][TOP]  = c->prev_dc[0][mb_x * 2 + 1];
+    c->dc_cache[0][LEFT] = 0;
+    c->dc_cache[1][TOP]  = 0;
+    c->dc_cache[1][LEFT] = 0;
+
+    for (i = 0; i < 2; i++)
+        c->prev_dc[0][mb_x * 2 + i] = 0;
+
+    for (i = 1; i < 3; i++) {
+        c->dc_cache[i + 1][TOP]  = c->prev_dc[i][mb_x];
+        c->dc_cache[i + 1][LEFT] = 0;
+        c->prev_dc[i][mb_x]      = 0;
+    }
+}
+
+static int mss4_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
+                             AVPacket *avpkt)
+{
+    const uint8_t *buf = avpkt->data;
+    int buf_size = avpkt->size;
+    MSS4Context *c = avctx->priv_data;
+    GetBitContext gb;
+    GetByteContext bc;
+    uint8_t *dst[3];
+    int width, height, quality, frame_type;
+    int x, y, i, mb_width, mb_height, blk_type;
+    int ret;
+
+    if (buf_size < HEADER_SIZE) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Frame should have at least %d bytes, got %d instead\n",
+               HEADER_SIZE, buf_size);
+        return AVERROR_INVALIDDATA;
+    }
+
+    bytestream2_init(&bc, buf, buf_size);
+    width      = bytestream2_get_be16(&bc);
+    height     = bytestream2_get_be16(&bc);
+    bytestream2_skip(&bc, 2);
+    quality    = bytestream2_get_byte(&bc);
+    frame_type = bytestream2_get_byte(&bc);
+
+    if (width > avctx->width ||
+        height != avctx->height) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid frame dimensions %dx%d\n",
+               width, height);
+        return AVERROR_INVALIDDATA;
+    }
+    if (quality < 1 || quality > 100) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid quality setting %d\n", quality);
+        return AVERROR_INVALIDDATA;
+    }
+    if ((frame_type & ~3) || frame_type == 3) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid frame type %d\n", frame_type);
+        return AVERROR_INVALIDDATA;
+    }
+
+    if (frame_type != SKIP_FRAME && !bytestream2_get_bytes_left(&bc)) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Empty frame found but it is not a skip frame.\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    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.key_frame = (frame_type == INTRA_FRAME);
+    c->pic.pict_type = (frame_type == INTRA_FRAME) ? AV_PICTURE_TYPE_I
+                                                   : AV_PICTURE_TYPE_P;
+    if (frame_type == SKIP_FRAME) {
+        *data_size = sizeof(AVFrame);
+        *(AVFrame*)data = c->pic;
+
+        return buf_size;
+    }
+
+    if (c->quality != quality) {
+        c->quality = quality;
+        for (i = 0; i < 2; i++)
+            ff_mss34_gen_quant_mat(c->quant_mat[i], quality, !i);
+    }
+
+    init_get_bits(&gb, buf + HEADER_SIZE, (buf_size - HEADER_SIZE) * 8);
+
+    mb_width  = FFALIGN(width,  16) >> 4;
+    mb_height = FFALIGN(height, 16) >> 4;
+    dst[0] = c->pic.data[0];
+    dst[1] = c->pic.data[1];
+    dst[2] = c->pic.data[2];
+
+    memset(c->prev_vec, 0, sizeof(c->prev_vec));
+    for (y = 0; y < mb_height; y++) {
+        memset(c->dc_cache, 0, sizeof(c->dc_cache));
+        for (x = 0; x < mb_width; x++) {
+            blk_type = decode012(&gb);
+            switch (blk_type) {
+            case DCT_BLOCK:
+                if (mss4_decode_dct_block(c, &gb, dst, x, y) < 0) {
+                    av_log(avctx, AV_LOG_ERROR,
+                           "Error decoding DCT block %d,%d\n",
+                           x, y);
+                    return AVERROR_INVALIDDATA;
+                }
+                break;
+            case IMAGE_BLOCK:
+                if (mss4_decode_image_block(c, &gb, dst, x, y) < 0) {
+                    av_log(avctx, AV_LOG_ERROR,
+                           "Error decoding VQ block %d,%d\n",
+                           x, y);
+                    return AVERROR_INVALIDDATA;
+                }
+                break;
+            case SKIP_BLOCK:
+                if (frame_type == INTRA_FRAME) {
+                    av_log(avctx, AV_LOG_ERROR, "Skip block in intra frame\n");
+                    return AVERROR_INVALIDDATA;
+                }
+                break;
+            }
+            if (blk_type != DCT_BLOCK)
+                mss4_update_dc_cache(c, x);
+        }
+        dst[0] += c->pic.linesize[0] * 16;
+        dst[1] += c->pic.linesize[1] * 16;
+        dst[2] += c->pic.linesize[2] * 16;
+    }
+
+    *data_size = sizeof(AVFrame);
+    *(AVFrame*)data = c->pic;
+
+    return buf_size;
+}
+
+static av_cold int mss4_decode_init(AVCodecContext *avctx)
+{
+    MSS4Context * const c = avctx->priv_data;
+    int i;
+
+    if (mss4_init_vlcs(c)) {
+        av_log(avctx, AV_LOG_ERROR, "Cannot initialise VLCs\n");
+        mss4_free_vlcs(c);
+        return AVERROR(ENOMEM);
+    }
+    for (i = 0; i < 3; i++) {
+        c->dc_stride[i] = FFALIGN(avctx->width, 16) >> (2 + !!i);
+        c->prev_dc[i]   = av_malloc(sizeof(**c->prev_dc) * c->dc_stride[i]);
+        if (!c->prev_dc[i]) {
+            av_log(avctx, AV_LOG_ERROR, "Cannot allocate buffer\n");
+            mss4_free_vlcs(c);
+            return AVERROR(ENOMEM);
+        }
+    }
+
+    avctx->pix_fmt     = PIX_FMT_YUV444P;
+    avctx->coded_frame = &c->pic;
+
+    return 0;
+}
+
+static av_cold int mss4_decode_end(AVCodecContext *avctx)
+{
+    MSS4Context * const c = avctx->priv_data;
+    int i;
+
+    if (c->pic.data[0])
+        avctx->release_buffer(avctx, &c->pic);
+    for (i = 0; i < 3; i++)
+        av_freep(&c->prev_dc[i]);
+    mss4_free_vlcs(c);
+
+    return 0;
+}
+
+AVCodec ff_mts2_decoder = {
+    .name           = "mts2",
+    .type           = AVMEDIA_TYPE_VIDEO,
+    .id             = CODEC_ID_MTS2,
+    .priv_data_size = sizeof(MSS4Context),
+    .init           = mss4_decode_init,
+    .close          = mss4_decode_end,
+    .decode         = mss4_decode_frame,
+    .capabilities   = CODEC_CAP_DR1,
+    .long_name      = NULL_IF_CONFIG_SMALL("MS Expression Encoder Screen"),
+};