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ffmpeg / libavcodec / escape124.c @ 72415b2a

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/*
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 * Escape 124 Video Decoder
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 * Copyright (C) 2008 Eli Friedman (eli.friedman@gmail.com)
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include "avcodec.h"
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#define ALT_BITSTREAM_READER_LE
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#include "get_bits.h"
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typedef union MacroBlock {
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    uint16_t pixels[4];
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    uint32_t pixels32[2];
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} MacroBlock;
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typedef union SuperBlock {
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    uint16_t pixels[64];
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    uint32_t pixels32[32];
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} SuperBlock;
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typedef struct CodeBook {
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    unsigned depth;
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    unsigned size;
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    MacroBlock* blocks;
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} CodeBook;
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typedef struct Escape124Context {
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    AVFrame frame;
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    unsigned num_superblocks;
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    CodeBook codebooks[3];
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} Escape124Context;
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static int can_safely_read(GetBitContext* gb, int bits) {
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    return get_bits_count(gb) + bits <= gb->size_in_bits;
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}
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/**
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 * Initialize the decoder
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 * @param avctx decoder context
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 * @return 0 success, negative on error
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 */
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static av_cold int escape124_decode_init(AVCodecContext *avctx)
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{
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    Escape124Context *s = avctx->priv_data;
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    avctx->pix_fmt = PIX_FMT_RGB555;
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    s->num_superblocks = ((unsigned)avctx->width / 8) *
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                         ((unsigned)avctx->height / 8);
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    return 0;
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}
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static av_cold int escape124_decode_close(AVCodecContext *avctx)
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{
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    unsigned i;
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    Escape124Context *s = avctx->priv_data;
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    for (i = 0; i < 3; i++)
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        av_free(s->codebooks[i].blocks);
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    if (s->frame.data[0])
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        avctx->release_buffer(avctx, &s->frame);
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    return 0;
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}
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static CodeBook unpack_codebook(GetBitContext* gb, unsigned depth,
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                                 unsigned size)
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{
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    unsigned i, j;
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    CodeBook cb = { 0 };
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    if (!can_safely_read(gb, size * 34))
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        return cb;
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    if (size >= INT_MAX / sizeof(MacroBlock))
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        return cb;
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    cb.blocks = av_malloc(size ? size * sizeof(MacroBlock) : 1);
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    if (!cb.blocks)
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        return cb;
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    cb.depth = depth;
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    cb.size = size;
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    for (i = 0; i < size; i++) {
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        unsigned mask_bits = get_bits(gb, 4);
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        unsigned color0 = get_bits(gb, 15);
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        unsigned color1 = get_bits(gb, 15);
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        for (j = 0; j < 4; j++) {
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            if (mask_bits & (1 << j))
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                cb.blocks[i].pixels[j] = color1;
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            else
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                cb.blocks[i].pixels[j] = color0;
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        }
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    }
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    return cb;
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}
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static unsigned decode_skip_count(GetBitContext* gb)
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{
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    unsigned value;
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    // This function reads a maximum of 23 bits,
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    // which is within the padding space
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    if (!can_safely_read(gb, 1))
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        return -1;
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    value = get_bits1(gb);
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    if (!value)
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        return value;
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    value += get_bits(gb, 3);
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    if (value != (1 + ((1 << 3) - 1)))
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        return value;
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    value += get_bits(gb, 7);
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    if (value != (1 + ((1 << 3) - 1)) + ((1 << 7) - 1))
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        return value;
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    return value + get_bits(gb, 12);
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}
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static MacroBlock decode_macroblock(Escape124Context* s, GetBitContext* gb,
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                                    int* codebook_index, int superblock_index)
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{
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    // This function reads a maximum of 22 bits; the callers
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    // guard this function appropriately
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    unsigned block_index, depth;
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    if (get_bits1(gb)) {
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        static const char transitions[3][2] = { {2, 1}, {0, 2}, {1, 0} };
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        *codebook_index = transitions[*codebook_index][get_bits1(gb)];
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    }
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    depth = s->codebooks[*codebook_index].depth;
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    // depth = 0 means that this shouldn't read any bits;
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    // in theory, this is the same as get_bits(gb, 0), but
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    // that doesn't actually work.
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    block_index = depth ? get_bits(gb, depth) : 0;
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    if (*codebook_index == 1) {
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        block_index += superblock_index << s->codebooks[1].depth;
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    }
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    // This condition can occur with invalid bitstreams and
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    // *codebook_index == 2
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    if (block_index >= s->codebooks[*codebook_index].size)
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        return (MacroBlock) { { 0 } };
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    return s->codebooks[*codebook_index].blocks[block_index];
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}
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static void insert_mb_into_sb(SuperBlock* sb, MacroBlock mb, unsigned index) {
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   // Formula: ((index / 4) * 16 + (index % 4) * 2) / 2
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   uint32_t *dst = sb->pixels32 + index + (index & -4);
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   // This technically violates C99 aliasing rules, but it should be safe.
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   dst[0] = mb.pixels32[0];
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   dst[4] = mb.pixels32[1];
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}
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static void copy_superblock(uint16_t* dest, unsigned dest_stride,
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                            uint16_t* src, unsigned src_stride)
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{
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    unsigned y;
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    if (src)
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        for (y = 0; y < 8; y++)
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            memcpy(dest + y * dest_stride, src + y * src_stride,
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                   sizeof(uint16_t) * 8);
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    else
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        for (y = 0; y < 8; y++)
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            memset(dest + y * dest_stride, 0, sizeof(uint16_t) * 8);
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}
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static const uint16_t mask_matrix[] = {0x1,   0x2,   0x10,   0x20,
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                                       0x4,   0x8,   0x40,   0x80,
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                                       0x100, 0x200, 0x1000, 0x2000,
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                                       0x400, 0x800, 0x4000, 0x8000};
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/**
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 * Decode a single frame
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 * @param avctx decoder context
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 * @param data decoded frame
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 * @param data_size size of the decoded frame
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 * @param buf input buffer
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 * @param buf_size input buffer size
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 * @return 0 success, -1 on error
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 */
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static int escape124_decode_frame(AVCodecContext *avctx,
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                                  void *data, int *data_size,
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                                  AVPacket *avpkt)
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{
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    const uint8_t *buf = avpkt->data;
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    int buf_size = avpkt->size;
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    Escape124Context *s = avctx->priv_data;
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    GetBitContext gb;
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    unsigned frame_flags, frame_size;
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    unsigned i;
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    unsigned superblock_index, cb_index = 1,
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             superblock_col_index = 0,
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             superblocks_per_row = avctx->width / 8, skip = -1;
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    uint16_t* old_frame_data, *new_frame_data;
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    unsigned old_stride, new_stride;
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    AVFrame new_frame = { { 0 } };
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    init_get_bits(&gb, buf, buf_size * 8);
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    // This call also guards the potential depth reads for the
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    // codebook unpacking.
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    if (!can_safely_read(&gb, 64))
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        return -1;
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    frame_flags = get_bits_long(&gb, 32);
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    frame_size  = get_bits_long(&gb, 32);
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    // Leave last frame unchanged
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    // FIXME: Is this necessary?  I haven't seen it in any real samples
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    if (!(frame_flags & 0x114) || !(frame_flags & 0x7800000)) {
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        av_log(NULL, AV_LOG_DEBUG, "Skipping frame\n");
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        *data_size = sizeof(AVFrame);
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        *(AVFrame*)data = s->frame;
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        return frame_size;
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    }
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    for (i = 0; i < 3; i++) {
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        if (frame_flags & (1 << (17 + i))) {
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            unsigned cb_depth, cb_size;
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            if (i == 2) {
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                // This codebook can be cut off at places other than
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                // powers of 2, leaving some of the entries undefined.
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                cb_size = get_bits_long(&gb, 20);
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                cb_depth = av_log2(cb_size - 1) + 1;
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            } else {
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                cb_depth = get_bits(&gb, 4);
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                if (i == 0) {
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                    // This is the most basic codebook: pow(2,depth) entries
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                    // for a depth-length key
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                    cb_size = 1 << cb_depth;
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                } else {
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                    // This codebook varies per superblock
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                    // FIXME: I don't think this handles integer overflow
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                    // properly
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                    cb_size = s->num_superblocks << cb_depth;
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                }
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            }
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            av_free(s->codebooks[i].blocks);
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            s->codebooks[i] = unpack_codebook(&gb, cb_depth, cb_size);
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            if (!s->codebooks[i].blocks)
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                return -1;
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        }
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    }
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    new_frame.reference = 3;
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    if (avctx->get_buffer(avctx, &new_frame)) {
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        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
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        return -1;
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    }
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    new_frame_data = (uint16_t*)new_frame.data[0];
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    new_stride = new_frame.linesize[0] / 2;
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    old_frame_data = (uint16_t*)s->frame.data[0];
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    old_stride = s->frame.linesize[0] / 2;
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    for (superblock_index = 0; superblock_index < s->num_superblocks;
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         superblock_index++) {
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        MacroBlock mb;
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        SuperBlock sb;
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        unsigned multi_mask = 0;
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        if (skip == -1) {
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            // Note that this call will make us skip the rest of the blocks
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            // if the frame prematurely ends
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            skip = decode_skip_count(&gb);
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        }
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        if (skip) {
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            copy_superblock(new_frame_data, new_stride,
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                            old_frame_data, old_stride);
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        } else {
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            copy_superblock(sb.pixels, 8,
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                            old_frame_data, old_stride);
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            while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
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                unsigned mask;
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                mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
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                mask = get_bits(&gb, 16);
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                multi_mask |= mask;
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                for (i = 0; i < 16; i++) {
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                    if (mask & mask_matrix[i]) {
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                        insert_mb_into_sb(&sb, mb, i);
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                    }
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                }
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            }
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            if (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
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                unsigned inv_mask = get_bits(&gb, 4);
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                for (i = 0; i < 4; i++) {
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                    if (inv_mask & (1 << i)) {
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                        multi_mask ^= 0xF << i*4;
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                    } else {
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                        multi_mask ^= get_bits(&gb, 4) << i*4;
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                    }
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                }
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                for (i = 0; i < 16; i++) {
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                    if (multi_mask & mask_matrix[i]) {
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                        if (!can_safely_read(&gb, 1))
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                            break;
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                        mb = decode_macroblock(s, &gb, &cb_index,
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                                               superblock_index);
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                        insert_mb_into_sb(&sb, mb, i);
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                    }
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                }
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            } else if (frame_flags & (1 << 16)) {
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                while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
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                    mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
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                    insert_mb_into_sb(&sb, mb, get_bits(&gb, 4));
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                }
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            }
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            copy_superblock(new_frame_data, new_stride, sb.pixels, 8);
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        }
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        superblock_col_index++;
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        new_frame_data += 8;
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        if (old_frame_data)
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            old_frame_data += 8;
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        if (superblock_col_index == superblocks_per_row) {
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            new_frame_data += new_stride * 8 - superblocks_per_row * 8;
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            if (old_frame_data)
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                old_frame_data += old_stride * 8 - superblocks_per_row * 8;
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            superblock_col_index = 0;
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        }
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        skip--;
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    }
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    av_log(NULL, AV_LOG_DEBUG,
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           "Escape sizes: %i, %i, %i\n",
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           frame_size, buf_size, get_bits_count(&gb) / 8);
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    if (s->frame.data[0])
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        avctx->release_buffer(avctx, &s->frame);
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    *(AVFrame*)data = s->frame = new_frame;
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    *data_size = sizeof(AVFrame);
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    return frame_size;
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}
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AVCodec escape124_decoder = {
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    "escape124",
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    AVMEDIA_TYPE_VIDEO,
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    CODEC_ID_ESCAPE124,
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    sizeof(Escape124Context),
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    escape124_decode_init,
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    NULL,
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    escape124_decode_close,
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    escape124_decode_frame,
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    CODEC_CAP_DR1,
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    .long_name = NULL_IF_CONFIG_SMALL("Escape 124"),
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};
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