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FFmpeg/libavcodec/mss4.c

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/*
* 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 "get_bits.h"
#include "internal.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;
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 *got_frame,
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;
}
if ((ret = ff_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) {
*got_frame = 1;
if ((ret = av_frame_ref(data, c->pic)) < 0)
return ret;
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;
}
if ((ret = av_frame_ref(data, c->pic)) < 0)
return ret;
*got_frame = 1;
return buf_size;
}
static av_cold int mss4_decode_end(AVCodecContext *avctx)
{
MSS4Context * const c = avctx->priv_data;
int i;
av_frame_free(&c->pic);
for (i = 0; i < 3; i++)
av_freep(&c->prev_dc[i]);
mss4_free_vlcs(c);
return 0;
}
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);
}
}
c->pic = av_frame_alloc();
if (!c->pic) {
mss4_decode_end(avctx);
return AVERROR(ENOMEM);
}
avctx->pix_fmt = AV_PIX_FMT_YUV444P;
return 0;
}
AVCodec ff_mts2_decoder = {
.name = "mts2",
.long_name = NULL_IF_CONFIG_SMALL("MS Expression Encoder Screen"),
.type = AVMEDIA_TYPE_VIDEO,
.id = AV_CODEC_ID_MTS2,
.priv_data_size = sizeof(MSS4Context),
.init = mss4_decode_init,
.close = mss4_decode_end,
.decode = mss4_decode_frame,
.capabilities = CODEC_CAP_DR1,
};