PeerStreamer

/*

 * Escape 124 Video Decoder

 * Copyright (C) 2008 Eli Friedman (eli.friedman@gmail.com)

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg 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.

 *

 * FFmpeg 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 FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

#include "avcodec.h"

#define ALT_BITSTREAM_READER_LE

#include "get_bits.h"

typedef union MacroBlock {

    uint16_t pixels[4];

    uint32_t pixels32[2];

} MacroBlock;

typedef union SuperBlock {

    uint16_t pixels[64];

    uint32_t pixels32[32];

} SuperBlock;

typedef struct CodeBook {

    unsigned depth;

    unsigned size;

    MacroBlock* blocks;

} CodeBook;

typedef struct Escape124Context {

    AVFrame frame;

    unsigned num_superblocks;

    CodeBook codebooks[3];

} Escape124Context;

static int can_safely_read(GetBitContext* gb, int bits) {

    return get_bits_count(gb) + bits <= gb->size_in_bits;

}

/**

 * Initialize the decoder

 * @param avctx decoder context

 * @return 0 success, negative on error

 */

static av_cold int escape124_decode_init(AVCodecContext *avctx)

{

    Escape124Context *s = avctx->priv_data;

    avctx->pix_fmt = PIX_FMT_RGB555;

    s->num_superblocks = ((unsigned)avctx->width / 8) *

                         ((unsigned)avctx->height / 8);

    return 0;

}

static av_cold int escape124_decode_close(AVCodecContext *avctx)

{

    unsigned i;

    Escape124Context *s = avctx->priv_data;

    for (i = 0; i < 3; i++)

        av_free(s->codebooks[i].blocks);

    if (s->frame.data[0])

        avctx->release_buffer(avctx, &s->frame);

    return 0;

}

static CodeBook unpack_codebook(GetBitContext* gb, unsigned depth,

                                 unsigned size)

{

    unsigned i, j;

    CodeBook cb = { 0 };

    if (!can_safely_read(gb, size * 34))

        return cb;

    if (size >= INT_MAX / sizeof(MacroBlock))

        return cb;

    cb.blocks = av_malloc(size ? size * sizeof(MacroBlock) : 1);

    if (!cb.blocks)

        return cb;

    cb.depth = depth;

    cb.size = size;

    for (i = 0; i < size; i++) {

        unsigned mask_bits = get_bits(gb, 4);

        unsigned color0 = get_bits(gb, 15);

        unsigned color1 = get_bits(gb, 15);

        for (j = 0; j < 4; j++) {

            if (mask_bits & (1 << j))

                cb.blocks[i].pixels[j] = color1;

            else

                cb.blocks[i].pixels[j] = color0;

        }

    }

    return cb;

}

static unsigned decode_skip_count(GetBitContext* gb)

{

    unsigned value;

    // This function reads a maximum of 23 bits,

    // which is within the padding space

    if (!can_safely_read(gb, 1))

        return -1;

    value = get_bits1(gb);

    if (!value)

        return value;

    value += get_bits(gb, 3);

    if (value != (1 + ((1 << 3) - 1)))

        return value;

    value += get_bits(gb, 7);

    if (value != (1 + ((1 << 3) - 1)) + ((1 << 7) - 1))

        return value;

    return value + get_bits(gb, 12);

}

static MacroBlock decode_macroblock(Escape124Context* s, GetBitContext* gb,

                                    int* codebook_index, int superblock_index)

{

    // This function reads a maximum of 22 bits; the callers

    // guard this function appropriately

    unsigned block_index, depth;

    if (get_bits1(gb)) {

        static const char transitions[3][2] = { {2, 1}, {0, 2}, {1, 0} };

        *codebook_index = transitions[*codebook_index][get_bits1(gb)];

    }

    depth = s->codebooks[*codebook_index].depth;

    // depth = 0 means that this shouldn't read any bits;

    // in theory, this is the same as get_bits(gb, 0), but

    // that doesn't actually work.

    block_index = depth ? get_bits(gb, depth) : 0;

    if (*codebook_index == 1) {

        block_index += superblock_index << s->codebooks[1].depth;

    }

    // This condition can occur with invalid bitstreams and

    // *codebook_index == 2

    if (block_index >= s->codebooks[*codebook_index].size)

        return (MacroBlock) { { 0 } };

    return s->codebooks[*codebook_index].blocks[block_index];

}

static void insert_mb_into_sb(SuperBlock* sb, MacroBlock mb, unsigned index) {

   // Formula: ((index / 4) * 16 + (index % 4) * 2) / 2

   uint32_t *dst = sb->pixels32 + index + (index & -4);

   // This technically violates C99 aliasing rules, but it should be safe.

   dst[0] = mb.pixels32[0];

   dst[4] = mb.pixels32[1];

}

static void copy_superblock(uint16_t* dest, unsigned dest_stride,

                            uint16_t* src, unsigned src_stride)

{

    unsigned y;

    if (src)

        for (y = 0; y < 8; y++)

            memcpy(dest + y * dest_stride, src + y * src_stride,

                   sizeof(uint16_t) * 8);

    else

        for (y = 0; y < 8; y++)

            memset(dest + y * dest_stride, 0, sizeof(uint16_t) * 8);

}

static const uint16_t mask_matrix[] = {0x1,   0x2,   0x10,   0x20,

                                       0x4,   0x8,   0x40,   0x80,

                                       0x100, 0x200, 0x1000, 0x2000,

                                       0x400, 0x800, 0x4000, 0x8000};

/**

 * Decode a single frame

 * @param avctx decoder context

 * @param data decoded frame

 * @param data_size size of the decoded frame

 * @param buf input buffer

 * @param buf_size input buffer size

 * @return 0 success, -1 on error

 */

static int escape124_decode_frame(AVCodecContext *avctx,

                                  void *data, int *data_size,

                                  AVPacket *avpkt)

{

    const uint8_t *buf = avpkt->data;

    int buf_size = avpkt->size;

    Escape124Context *s = avctx->priv_data;

    GetBitContext gb;

    unsigned frame_flags, frame_size;

    unsigned i;

    unsigned superblock_index, cb_index = 1,

             superblock_col_index = 0,

             superblocks_per_row = avctx->width / 8, skip = -1;

    uint16_t* old_frame_data, *new_frame_data;

    unsigned old_stride, new_stride;

    AVFrame new_frame = { { 0 } };

    init_get_bits(&gb, buf, buf_size * 8);

    // This call also guards the potential depth reads for the

    // codebook unpacking.

    if (!can_safely_read(&gb, 64))

        return -1;

    frame_flags = get_bits_long(&gb, 32);

    frame_size  = get_bits_long(&gb, 32);

    // Leave last frame unchanged

    // FIXME: Is this necessary?  I haven't seen it in any real samples

    if (!(frame_flags & 0x114) || !(frame_flags & 0x7800000)) {

        av_log(NULL, AV_LOG_DEBUG, "Skipping frame\n");

        *data_size = sizeof(AVFrame);

        *(AVFrame*)data = s->frame;

        return frame_size;

    }

    for (i = 0; i < 3; i++) {

        if (frame_flags & (1 << (17 + i))) {

            unsigned cb_depth, cb_size;

            if (i == 2) {

                // This codebook can be cut off at places other than

                // powers of 2, leaving some of the entries undefined.

                cb_size = get_bits_long(&gb, 20);

                cb_depth = av_log2(cb_size - 1) + 1;

            } else {

                cb_depth = get_bits(&gb, 4);

                if (i == 0) {

                    // This is the most basic codebook: pow(2,depth) entries

                    // for a depth-length key

                    cb_size = 1 << cb_depth;

                } else {

                    // This codebook varies per superblock

                    // FIXME: I don't think this handles integer overflow

                    // properly

                    cb_size = s->num_superblocks << cb_depth;

                }

            }

            av_free(s->codebooks[i].blocks);

            s->codebooks[i] = unpack_codebook(&gb, cb_depth, cb_size);

            if (!s->codebooks[i].blocks)

                return -1;

        }

    }

    new_frame.reference = 3;

    if (avctx->get_buffer(avctx, &new_frame)) {

        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");

        return -1;

    }

    new_frame_data = (uint16_t*)new_frame.data[0];

    new_stride = new_frame.linesize[0] / 2;

    old_frame_data = (uint16_t*)s->frame.data[0];

    old_stride = s->frame.linesize[0] / 2;

    for (superblock_index = 0; superblock_index < s->num_superblocks;

         superblock_index++) {

        MacroBlock mb;

        SuperBlock sb;

        unsigned multi_mask = 0;

        if (skip == -1) {

            // Note that this call will make us skip the rest of the blocks

            // if the frame prematurely ends

            skip = decode_skip_count(&gb);

        }

        if (skip) {

            copy_superblock(new_frame_data, new_stride,

                            old_frame_data, old_stride);

        } else {

            copy_superblock(sb.pixels, 8,

                            old_frame_data, old_stride);

            while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {

                unsigned mask;

                mb = decode_macroblock(s, &gb, &cb_index, superblock_index);

                mask = get_bits(&gb, 16);

                multi_mask |= mask;

                for (i = 0; i < 16; i++) {

                    if (mask & mask_matrix[i]) {

                        insert_mb_into_sb(&sb, mb, i);

                    }

                }

            }

            if (can_safely_read(&gb, 1) && !get_bits1(&gb)) {

                unsigned inv_mask = get_bits(&gb, 4);

                for (i = 0; i < 4; i++) {

                    if (inv_mask & (1 << i)) {

                        multi_mask ^= 0xF << i*4;

                    } else {

                        multi_mask ^= get_bits(&gb, 4) << i*4;

                    }

                }

                for (i = 0; i < 16; i++) {

                    if (multi_mask & mask_matrix[i]) {

                        if (!can_safely_read(&gb, 1))

                            break;

                        mb = decode_macroblock(s, &gb, &cb_index,

                                               superblock_index);

                        insert_mb_into_sb(&sb, mb, i);

                    }

                }

            } else if (frame_flags & (1 << 16)) {

                while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {

                    mb = decode_macroblock(s, &gb, &cb_index, superblock_index);

                    insert_mb_into_sb(&sb, mb, get_bits(&gb, 4));

                }

            }

            copy_superblock(new_frame_data, new_stride, sb.pixels, 8);

        }

        superblock_col_index++;

        new_frame_data += 8;

        if (old_frame_data)

            old_frame_data += 8;

        if (superblock_col_index == superblocks_per_row) {

            new_frame_data += new_stride * 8 - superblocks_per_row * 8;

            if (old_frame_data)

                old_frame_data += old_stride * 8 - superblocks_per_row * 8;

            superblock_col_index = 0;

        }

        skip--;

    }

    av_log(NULL, AV_LOG_DEBUG,

           "Escape sizes: %i, %i, %i\n",

           frame_size, buf_size, get_bits_count(&gb) / 8);

    if (s->frame.data[0])

        avctx->release_buffer(avctx, &s->frame);

    *(AVFrame*)data = s->frame = new_frame;

    *data_size = sizeof(AVFrame);

    return frame_size;

}

AVCodec escape124_decoder = {

    "escape124",

    CODEC_TYPE_VIDEO,

    CODEC_ID_ESCAPE124,

    sizeof(Escape124Context),

    escape124_decode_init,

    NULL,

    escape124_decode_close,

    escape124_decode_frame,

    CODEC_CAP_DR1,

    .long_name = NULL_IF_CONFIG_SMALL("Escape 124"),

};