Go2Webinar decoder

1 files changed, 825 insertions, 0 deletions

diff --git a/libavcodec/g2meet.c b/libavcodec/g2meet.c
new file mode 100644
index 0000000000..72c062c86d
--- /dev/null
+++ b/libavcodec/g2meet.c
@@ -0,0 +1,825 @@
+/*
+ * Go2Webinar 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
+ * Go2Webinar decoder
+ */
+
+#include <zlib.h>
+
+#include "libavutil/intreadwrite.h"
+#include "avcodec.h"
+#include "bytestream.h"
+#include "dsputil.h"
+#include "get_bits.h"
+#include "internal.h"
+#include "mjpeg.h"
+
+enum ChunkType {
+    FRAME_INFO = 0xC8,
+    TILE_DATA,
+    CURSOR_POS,
+    CURSOR_SHAPE,
+    CHUNK_CC,
+    CHUNK_CD
+};
+
+enum Compression {
+    COMPR_EPIC_J_B = 2,
+    COMPR_KEMPF_J_B,
+};
+
+static const uint8_t luma_quant[64] = {
+     8,  6,  5,  8, 12, 20, 26, 31,
+     6,  6,  7, 10, 13, 29, 30, 28,
+     7,  7,  8, 12, 20, 29, 35, 28,
+     7,  9, 11, 15, 26, 44, 40, 31,
+     9, 11, 19, 28, 34, 55, 52, 39,
+    12, 18, 28, 32, 41, 52, 57, 46,
+    25, 32, 39, 44, 52, 61, 60, 51,
+    36, 46, 48, 49, 56, 50, 52, 50
+};
+
+static const uint8_t chroma_quant[64] = {
+     9,  9, 12, 24, 50, 50, 50, 50,
+     9, 11, 13, 33, 50, 50, 50, 50,
+    12, 13, 28, 50, 50, 50, 50, 50,
+    24, 33, 50, 50, 50, 50, 50, 50,
+    50, 50, 50, 50, 50, 50, 50, 50,
+    50, 50, 50, 50, 50, 50, 50, 50,
+    50, 50, 50, 50, 50, 50, 50, 50,
+    50, 50, 50, 50, 50, 50, 50, 50,
+};
+
+typedef struct JPGContext {
+    DSPContext dsp;
+    ScanTable  scantable;
+
+    VLC        dc_vlc[2], ac_vlc[2];
+    int        prev_dc[3];
+    DECLARE_ALIGNED(16, int16_t, block)[6][64];
+
+    uint8_t    *buf;
+} JPGContext;
+
+typedef struct G2MContext {
+    JPGContext jc;
+    int        version;
+
+    int        compression;
+    int        width, height, bpp;
+    int        tile_width, tile_height;
+    int        tiles_x, tiles_y, tile_x, tile_y;
+
+    int        got_header;
+
+    uint8_t    *framebuf;
+    int        framebuf_stride, old_width, old_height;
+
+    uint8_t    *synth_tile, *jpeg_tile;
+    int        tile_stride, old_tile_w, old_tile_h;
+
+    uint8_t    *kempf_buf, *kempf_flags;
+
+    uint8_t    *cursor;
+    int        cursor_stride;
+    int        cursor_fmt;
+    int        cursor_w, cursor_h, cursor_x, cursor_y;
+    int        cursor_hot_x, cursor_hot_y;
+} G2MContext;
+
+static av_cold int build_vlc(VLC *vlc, const uint8_t *bits_table,
+                             const uint8_t *val_table, int nb_codes,
+                             int is_ac)
+{
+    uint8_t  huff_size[256] = { 0 };
+    uint16_t huff_code[256];
+    uint16_t huff_sym[256];
+    int i;
+
+    ff_mjpeg_build_huffman_codes(huff_size, huff_code, bits_table, val_table);
+
+    for (i = 0; i < 256; i++)
+        huff_sym[i] = i + 16 * is_ac;
+
+    if (is_ac)
+        huff_sym[0] = 16 * 256;
+
+    return ff_init_vlc_sparse(vlc, 9, nb_codes, huff_size, 1, 1,
+                              huff_code, 2, 2, huff_sym, 2, 2, 0);
+}
+
+static av_cold int jpg_init(AVCodecContext *avctx, JPGContext *c)
+{
+    int ret;
+
+    ret = build_vlc(&c->dc_vlc[0], avpriv_mjpeg_bits_dc_luminance,
+                    avpriv_mjpeg_val_dc, 12, 0);
+    if (ret)
+        return ret;
+    ret = build_vlc(&c->dc_vlc[1], avpriv_mjpeg_bits_dc_chrominance,
+                    avpriv_mjpeg_val_dc, 12, 0);
+    if (ret)
+        return ret;
+    ret = build_vlc(&c->ac_vlc[0], avpriv_mjpeg_bits_ac_luminance,
+                    avpriv_mjpeg_val_ac_luminance, 251, 1);
+    if (ret)
+        return ret;
+    ret = build_vlc(&c->ac_vlc[1], avpriv_mjpeg_bits_ac_chrominance,
+                    avpriv_mjpeg_val_ac_chrominance, 251, 1);
+    if (ret)
+        return ret;
+
+    ff_dsputil_init(&c->dsp, avctx);
+    ff_init_scantable(c->dsp.idct_permutation, &c->scantable,
+                      ff_zigzag_direct);
+
+    return 0;
+}
+
+static av_cold void jpg_free_context(JPGContext *ctx)
+{
+    int i;
+
+    for (i = 0; i < 2; i++) {
+        ff_free_vlc(&ctx->dc_vlc[i]);
+        ff_free_vlc(&ctx->ac_vlc[i]);
+    }
+
+    av_freep(&ctx->buf);
+}
+
+static void jpg_unescape(const uint8_t *src, int src_size,
+                         uint8_t *dst, int *dst_size)
+{
+    const uint8_t *src_end = src + src_size;
+    uint8_t *dst_start = dst;
+
+    while (src < src_end) {
+        uint8_t x = *src++;
+
+        *dst++ = x;
+
+        if (x == 0xFF && !*src)
+            src++;
+    }
+    *dst_size = dst - dst_start;
+}
+
+static int jpg_decode_block(JPGContext *c, GetBitContext *gb,
+                            int plane, int16_t *block)
+{
+    int dc, val, pos;
+    const int is_chroma = !!plane;
+    const uint8_t *qmat = is_chroma ? chroma_quant : luma_quant;
+
+    c->dsp.clear_block(block);
+    dc = get_vlc2(gb, c->dc_vlc[is_chroma].table, 9, 3);
+    if (dc < 0)
+        return AVERROR_INVALIDDATA;
+    if (dc)
+        dc = get_xbits(gb, dc);
+    dc = dc * qmat[0] + c->prev_dc[plane];
+    block[0] = dc;
+    c->prev_dc[plane] = dc;
+
+    pos = 0;
+    while (pos < 63) {
+        val = get_vlc2(gb, c->ac_vlc[is_chroma].table, 9, 3);
+        if (val < 0)
+            return AVERROR_INVALIDDATA;
+        pos += val >> 4;
+        val &= 0xF;
+        if (pos > 63)
+            return val ? AVERROR_INVALIDDATA : 0;
+        if (val) {
+            int nbits = val;
+
+            val = get_xbits(gb, nbits);
+            val *= qmat[ff_zigzag_direct[pos]];
+            block[c->scantable.permutated[pos]] = val;
+        }
+    }
+    return 0;
+}
+
+static inline void yuv2rgb(uint8_t *out, int Y, int U, int V)
+{
+    out[0] = av_clip_uint8(Y + (             91881 * V + 32768 >> 16));
+    out[1] = av_clip_uint8(Y + (-22554 * U - 46802 * V + 32768 >> 16));
+    out[2] = av_clip_uint8(Y + (116130 * U             + 32768 >> 16));
+}
+
+static int jpg_decode_data(JPGContext *c, int width, int height,
+                           const uint8_t *src, int src_size,
+                           uint8_t *dst, int dst_stride,
+                           const uint8_t *mask, int mask_stride, int num_mbs,
+                           int swapuv)
+{
+    GetBitContext gb;
+    uint8_t *tmp;
+    int mb_w, mb_h, mb_x, mb_y, i, j;
+    int bx, by;
+    int unesc_size;
+    int ret;
+
+    tmp = av_realloc(c->buf, src_size + FF_INPUT_BUFFER_PADDING_SIZE);
+    if (!tmp)
+        return AVERROR(ENOMEM);
+    c->buf = tmp;
+    jpg_unescape(src, src_size, c->buf, &unesc_size);
+    memset(c->buf + unesc_size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
+    init_get_bits(&gb, c->buf, unesc_size * 8);
+
+    width = FFALIGN(width, 16);
+    mb_w  =  width        >> 4;
+    mb_h  = (height + 15) >> 4;
+
+    if (!num_mbs)
+        num_mbs = mb_w * mb_h;
+
+    for (i = 0; i < 3; i++)
+        c->prev_dc[i] = 1024;
+    bx = by = 0;
+    for (mb_y = 0; mb_y < mb_h; mb_y++) {
+        for (mb_x = 0; mb_x < mb_w; mb_x++) {
+            if (mask && !mask[mb_x]) {
+                bx += 16;
+                continue;
+            }
+            for (j = 0; j < 2; j++) {
+                for (i = 0; i < 2; i++) {
+                    if ((ret = jpg_decode_block(c, &gb, 0,
+                                                c->block[i + j * 2])) != 0)
+                        return ret;
+                    c->dsp.idct(c->block[i + j * 2]);
+                }
+            }
+            for (i = 1; i < 3; i++) {
+                if ((ret = jpg_decode_block(c, &gb, i, c->block[i + 3])) != 0)
+                    return ret;
+                c->dsp.idct(c->block[i + 3]);
+            }
+
+            for (j = 0; j < 16; j++) {
+                uint8_t *out = dst + bx * 3 + (by + j) * dst_stride;
+                for (i = 0; i < 16; i++) {
+                    int Y, U, V;
+
+                    Y = c->block[(j >> 3) * 2 + (i >> 3)][(i & 7) + (j & 7) * 8];
+                    U = c->block[4 ^ swapuv][(i >> 1) + (j >> 1) * 8] - 128;
+                    V = c->block[5 ^ swapuv][(i >> 1) + (j >> 1) * 8] - 128;
+                    yuv2rgb(out + i * 3, Y, U, V);
+                }
+            }
+
+            if (!--num_mbs)
+                return 0;
+            bx += 16;
+        }
+        bx  = 0;
+        by += 16;
+        if (mask)
+            mask += mask_stride;
+    }
+
+    return 0;
+}
+
+static void kempf_restore_buf(const uint8_t *src, int len,
+                              uint8_t *dst, int stride,
+                              const uint8_t *jpeg_tile, int tile_stride,
+                              int width, int height,
+                              const uint8_t *pal, int npal, int tidx)
+{
+    GetBitContext gb;
+    int i, j, nb, col;
+
+    init_get_bits(&gb, src, len * 8);
+
+    if (npal <= 2)       nb = 1;
+    else if (npal <= 4)  nb = 2;
+    else if (npal <= 16) nb = 4;
+    else                 nb = 8;
+
+    for (j = 0; j < height; j++, dst += stride, jpeg_tile += tile_stride) {
+        if (get_bits(&gb, 8))
+            continue;
+        for (i = 0; i < width; i++) {
+            col = get_bits(&gb, nb);
+            if (col != tidx)
+                memcpy(dst + i * 3, pal + col * 3, 3);
+            else
+                memcpy(dst + i * 3, jpeg_tile + i * 3, 3);
+        }
+    }
+}
+
+static int kempf_decode_tile(G2MContext *c, int tile_x, int tile_y,
+                             const uint8_t *src, int src_size)
+{
+    int width, height;
+    int hdr, zsize, npal, tidx = -1, ret;
+    int i, j;
+    const uint8_t *src_end = src + src_size;
+    uint8_t pal[768], transp[3];
+    uLongf dlen = (c->tile_width + 1) * c->tile_height;
+    int sub_type;
+    int nblocks, cblocks, bstride;
+    int bits, bitbuf, coded;
+    uint8_t *dst = c->framebuf + tile_x * c->tile_width * 3 +
+                   tile_y * c->tile_height * c->framebuf_stride;
+
+    if (src_size < 2)
+        return AVERROR_INVALIDDATA;
+
+    width  = FFMIN(c->width  - tile_x * c->tile_width,  c->tile_width);
+    height = FFMIN(c->height - tile_y * c->tile_height, c->tile_height);
+
+    hdr = *src++;
+    sub_type = hdr >> 5;
+    if (sub_type == 0) {
+        int j;
+        memcpy(transp, src, 3);
+        src += 3;
+        for (j = 0; j < height; j++, dst += c->framebuf_stride)
+            for (i = 0; i < width; i++)
+                memcpy(dst + i * 3, transp, 3);
+        return 0;
+    } else if (sub_type == 1) {
+        return jpg_decode_data(&c->jc, width, height, src, src_end - src,
+                               dst, c->framebuf_stride, NULL, 0, 0, 0);
+    }
+
+    if (sub_type != 2) {
+        memcpy(transp, src, 3);
+        src += 3;
+    }
+    npal = *src++ + 1;
+    memcpy(pal, src, npal * 3); src += npal * 3;
+    if (sub_type != 2) {
+        for (i = 0; i < npal; i++) {
+            if (!memcmp(pal + i * 3, transp, 3)) {
+               tidx = i;
+               break;
+            }
+        }
+    }
+
+    if (src_end - src < 2)
+        return 0;
+    zsize = (src[0] << 8) | src[1]; src += 2;
+
+    if (src_end - src < zsize)
+        return AVERROR_INVALIDDATA;
+
+    ret = uncompress(c->kempf_buf, &dlen, src, zsize);
+    if (ret)
+        return AVERROR_INVALIDDATA;
+    src += zsize;
+
+    if (sub_type == 2) {
+        kempf_restore_buf(c->kempf_buf, dlen, dst, c->framebuf_stride,
+                          NULL, 0, width, height, pal, npal, tidx);
+        return 0;
+    }
+
+    nblocks = *src++ + 1;
+    cblocks = 0;
+    bstride = FFALIGN(width, 16) >> 4;
+    // blocks are coded LSB and we need normal bitreader for JPEG data
+    bits = 0;
+    for (i = 0; i < (FFALIGN(height, 16) >> 4); i++) {
+        for (j = 0; j < (FFALIGN(width, 16) >> 4); j++) {
+            if (!bits) {
+                bitbuf = *src++;
+                bits   = 8;
+            }
+            coded = bitbuf & 1;
+            bits--;
+            bitbuf >>= 1;
+            cblocks += coded;
+            if (cblocks > nblocks)
+                return AVERROR_INVALIDDATA;
+            c->kempf_flags[j + i * bstride] = coded;
+        }
+    }
+
+    memset(c->jpeg_tile, 0, c->tile_stride * height);
+    jpg_decode_data(&c->jc, width, height, src, src_end - src,
+                    c->jpeg_tile, c->tile_stride,
+                    c->kempf_flags, bstride, nblocks, 0);
+
+    kempf_restore_buf(c->kempf_buf, dlen, dst, c->framebuf_stride,
+                      c->jpeg_tile, c->tile_stride,
+                      width, height, pal, npal, tidx);
+
+    return 0;
+}
+
+static int g2m_init_buffers(G2MContext *c)
+{
+    int aligned_height;
+
+    if (!c->framebuf || c->old_width < c->width || c->height < c->height) {
+        c->framebuf_stride = FFALIGN(c->width * 3, 16);
+        aligned_height     = FFALIGN(c->height,    16);
+        av_free(c->framebuf);
+        c->framebuf = av_mallocz(c->framebuf_stride * aligned_height);
+        if (!c->framebuf)
+            return AVERROR(ENOMEM);
+    }
+    if (!c->synth_tile || !c->jpeg_tile ||
+        c->old_tile_w < c->tile_width ||
+        c->old_tile_h < c->tile_height) {
+        c->tile_stride = FFALIGN(c->tile_width * 3, 16);
+        aligned_height = FFALIGN(c->tile_height,    16);
+        av_free(c->synth_tile);
+        av_free(c->jpeg_tile);
+        c->synth_tile  = av_mallocz(c->tile_stride      * aligned_height);
+        c->jpeg_tile   = av_mallocz(c->tile_stride      * aligned_height);
+        c->kempf_buf   = av_mallocz((c->tile_width + 1) * aligned_height
+                                    + FF_INPUT_BUFFER_PADDING_SIZE);
+        c->kempf_flags = av_mallocz( c->tile_width      * aligned_height);
+        if (!c->synth_tile || !c->jpeg_tile ||
+            !c->kempf_buf || !c->kempf_flags)
+            return AVERROR(ENOMEM);
+    }
+
+    return 0;
+}
+
+static int g2m_load_cursor(G2MContext *c, GetByteContext *gb)
+{
+    int i, j, k;
+    uint8_t *dst;
+    uint32_t bits;
+
+    c->cursor_stride = c->cursor_w * 4;
+    c->cursor        = av_realloc(c->cursor, c->cursor_stride * c->cursor_h);
+    if (!c->cursor)
+        return AVERROR(ENOMEM);
+
+    dst = c->cursor;
+    switch (c->cursor_fmt) {
+    case 1: // old monochrome
+        for (j = 0; j < c->cursor_h; j++) {
+            for (i = 0; i < c->cursor_w; i += 32) {
+                bits = bytestream2_get_be32(gb);
+                for (k = 0; k < 32; k++) {
+                    dst[0] = !!(bits & 0x80000000);
+                    dst += 4;
+                    bits <<= 1;
+                }
+            }
+        }
+
+        dst = c->cursor;
+        for (j = 0; j < c->cursor_h; j++) {
+            for (i = 0; i < c->cursor_w; i += 32) {
+                bits = bytestream2_get_be32(gb);
+                for (k = 0; k < 32; k++) {
+                    int mask_bit = !!(bits & 0x80000000);
+                    switch (dst[0] * 2 + mask_bit) {
+                    case 0:
+                        dst[0] = 0xFF; dst[1] = 0x00;
+                        dst[2] = 0x00; dst[3] = 0x00;
+                        break;
+                    case 1:
+                        dst[0] = 0xFF; dst[1] = 0xFF;
+                        dst[2] = 0xFF; dst[3] = 0xFF;
+                        break;
+                    default:
+                        dst[0] = 0x00; dst[1] = 0x00;
+                        dst[2] = 0x00; dst[3] = 0x00;
+                    }
+                    dst += 4;
+                    bits <<= 1;
+                }
+            }
+        }
+        break;
+    case 32: // full colour
+        /* skip monochrome version of the cursor and decode RGBA instead */
+        bytestream2_skip(gb, c->cursor_h * (FFALIGN(c->cursor_w, 32) >> 3));
+        for (j = 0; j < c->cursor_h; j++) {
+            for (i = 0; i < c->cursor_w; i++) {
+                int val = bytestream2_get_be32(gb);
+                *dst++ = val >>  0;
+                *dst++ = val >>  8;
+                *dst++ = val >> 16;
+                *dst++ = val >> 24;
+            }
+        }
+        break;
+    default:
+        return AVERROR_PATCHWELCOME;
+    }
+    return 0;
+}
+
+#define APPLY_ALPHA(src, new, alpha) \
+    src = (src * (256 - alpha) + new * alpha) >> 8
+
+static void g2m_paint_cursor(G2MContext *c, uint8_t *dst, int stride)
+{
+    int i, j;
+    int x, y, w, h;
+    const uint8_t *cursor;
+
+    if (!c->cursor)
+        return;
+
+    x = c->cursor_x - c->cursor_hot_x;
+    y = c->cursor_y - c->cursor_hot_y;
+
+    cursor = c->cursor;
+    w      = c->cursor_w;
+    h      = c->cursor_h;
+
+    if (x + w > c->width)
+        w = c->width - x;
+    if (y + h > c->height)
+        h = c->height - y;
+    if (x < 0) {
+        w      +=  x;
+        cursor += -x * 4;
+    } else {
+        dst    +=  x * 3;
+    }
+    if (y < 0) {
+        h      +=  y;
+        cursor += -y * c->cursor_stride;
+    } else {
+        dst    +=  y * stride;
+    }
+    if (w < 0 || h < 0)
+        return;
+
+    for (j = 0; j < h; j++) {
+        for (i = 0; i < w; i++) {
+            uint8_t alpha = cursor[i * 4];
+            APPLY_ALPHA(dst[i * 3 + 0], cursor[i * 4 + 1], alpha);
+            APPLY_ALPHA(dst[i * 3 + 1], cursor[i * 4 + 2], alpha);
+            APPLY_ALPHA(dst[i * 3 + 2], cursor[i * 4 + 3], alpha);
+        }
+        dst    += stride;
+        cursor += c->cursor_stride;
+    }
+}
+
+static int g2m_decode_frame(AVCodecContext *avctx, void *data,
+                            int *got_picture_ptr, AVPacket *avpkt)
+{
+    const uint8_t *buf = avpkt->data;
+    int buf_size = avpkt->size;
+    G2MContext *c = avctx->priv_data;
+    AVFrame *pic = data;
+    GetByteContext bc, tbc;
+    int magic;
+    int got_header = 0;
+    uint32_t chunk_size, cur_size;
+    int chunk_type;
+    int i;
+    int ret;
+
+    if (buf_size < 12) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Frame should have at least 12 bytes, got %d instead\n",
+               buf_size);
+        return AVERROR_INVALIDDATA;
+    }
+
+    bytestream2_init(&bc, buf, buf_size);
+
+    magic = bytestream2_get_be32(&bc);
+    if ((magic & ~0xF) != MKBETAG('G', '2', 'M', '0') ||
+        (magic & 0xF) < 2 || (magic & 0xF) > 4) {
+        av_log(avctx, AV_LOG_ERROR, "Wrong magic %08X\n", magic);
+        return AVERROR_INVALIDDATA;
+    }
+
+    if ((magic & 0xF) != 4) {
+        av_log(avctx, AV_LOG_ERROR, "G2M2 and G2M3 are not yet supported\n");
+        return AVERROR(ENOSYS);
+    }
+
+    while (bytestream2_get_bytes_left(&bc) > 5) {
+        chunk_size = bytestream2_get_le32(&bc) - 1;
+        chunk_type = bytestream2_get_byte(&bc);
+        if (chunk_size > bytestream2_get_bytes_left(&bc)) {
+            av_log(avctx, AV_LOG_ERROR, "Invalid chunk size %d type %02X\n",
+                   chunk_size, chunk_type);
+            break;
+        }
+        switch (chunk_type) {
+        case FRAME_INFO:
+            c->got_header = 0;
+            if (chunk_size < 21) {
+                av_log(avctx, AV_LOG_ERROR, "Invalid frame info size %d\n",
+                       chunk_size);
+                break;
+            }
+            c->width  = bytestream2_get_be32(&bc);
+            c->height = bytestream2_get_be32(&bc);
+            if (c->width  < 16 || c->width  > avctx->width ||
+                c->height < 16 || c->height > avctx->height) {
+                av_log(avctx, AV_LOG_ERROR,
+                       "Invalid frame dimensions %dx%d\n",
+                       c->width, c->height);
+                c->width = c->height = 0;
+                bytestream2_skip(&bc, bytestream2_get_bytes_left(&bc));
+            }
+            if (c->width != avctx->width || c->height != avctx->height)
+                avcodec_set_dimensions(avctx, c->width, c->height);
+            c->compression = bytestream2_get_be32(&bc);
+            if (c->compression != 2 && c->compression != 3) {
+                av_log(avctx, AV_LOG_ERROR,
+                       "Unknown compression method %d\n",
+                       c->compression);
+                return AVERROR_PATCHWELCOME;
+            }
+            c->tile_width  = bytestream2_get_be32(&bc);
+            c->tile_height = bytestream2_get_be32(&bc);
+            if (!c->tile_width || !c->tile_height) {
+                av_log(avctx, AV_LOG_ERROR,
+                       "Invalid tile dimensions %dx%d\n",
+                       c->tile_width, c->tile_height);
+                return AVERROR_INVALIDDATA;
+            }
+            c->tiles_x = (c->width  + c->tile_width  - 1) / c->tile_width;
+            c->tiles_y = (c->height + c->tile_height - 1) / c->tile_height;
+            c->bpp = bytestream2_get_byte(&bc);
+            chunk_size -= 21;
+            bytestream2_skip(&bc, chunk_size);
+            if (g2m_init_buffers(c))
+                return AVERROR(ENOMEM);
+            got_header = 1;
+            break;
+        case TILE_DATA:
+            if (!c->tiles_x || !c->tiles_y) {
+                av_log(avctx, AV_LOG_WARNING,
+                       "No frame header - skipping tile\n");
+                bytestream2_skip(&bc, bytestream2_get_bytes_left(&bc));
+                break;
+            }
+            if (chunk_size < 2) {
+                av_log(avctx, AV_LOG_ERROR, "Invalid tile data size %d\n",
+                       chunk_size);
+                break;
+            }
+            c->tile_x = bytestream2_get_byte(&bc);
+            c->tile_y = bytestream2_get_byte(&bc);
+            if (c->tile_x >= c->tiles_x || c->tile_y >= c->tiles_y) {
+                av_log(avctx, AV_LOG_ERROR,
+                       "Invalid tile pos %d,%d (in %dx%d grid)\n",
+                       c->tile_x, c->tile_y, c->tiles_x, c->tiles_y);
+                break;
+            }
+            chunk_size -= 2;
+            ret = 0;
+            switch (c->compression) {
+            case COMPR_EPIC_J_B:
+                av_log(avctx, AV_LOG_ERROR,
+                       "ePIC j-b compression is not implemented yet\n");
+                return AVERROR(ENOSYS);
+            case COMPR_KEMPF_J_B:
+                ret = kempf_decode_tile(c, c->tile_x, c->tile_y,
+                                        buf + bytestream2_tell(&bc),
+                                        chunk_size);
+                break;
+            }
+            if (ret && c->framebuf)
+                av_log(avctx, AV_LOG_ERROR, "Error decoding tile %d,%d\n",
+                       c->tile_x, c->tile_y);
+            bytestream2_skip(&bc, chunk_size);
+            break;
+        case CURSOR_POS:
+            if (chunk_size < 5) {
+                av_log(avctx, AV_LOG_ERROR, "Invalid cursor pos size %d\n",
+                       chunk_size);
+                break;
+            }
+            c->cursor_x = bytestream2_get_be16(&bc);
+            c->cursor_y = bytestream2_get_be16(&bc);
+            bytestream2_skip(&bc, chunk_size - 4);
+            break;
+        case CURSOR_SHAPE:
+            if (chunk_size < 8) {
+                av_log(avctx, AV_LOG_ERROR, "Invalid cursor data size %d\n",
+                       chunk_size);
+                break;
+            }
+            bytestream2_init(&tbc, buf + bytestream2_tell(&bc),
+                             chunk_size - 4);
+            cur_size        = bytestream2_get_be32(&tbc);
+            c->cursor_w     = bytestream2_get_byte(&tbc);
+            c->cursor_h     = bytestream2_get_byte(&tbc);
+            c->cursor_hot_x = bytestream2_get_byte(&tbc);
+            c->cursor_hot_y = bytestream2_get_byte(&tbc);
+            c->cursor_fmt   = bytestream2_get_byte(&tbc);
+            if (cur_size >= chunk_size ||
+                c->cursor_w * c->cursor_h / 4 > cur_size) {
+                av_log(avctx, AV_LOG_ERROR, "Invalid cursor data size %d\n",
+                       chunk_size);
+                break;
+            }
+            g2m_load_cursor(c, &tbc);
+            bytestream2_skip(&bc, chunk_size);
+            break;
+        case CHUNK_CC:
+        case CHUNK_CD:
+            bytestream2_skip(&bc, chunk_size);
+            break;
+        default:
+            av_log(avctx, AV_LOG_WARNING, "Skipping chunk type %02X\n",
+                   chunk_type);
+            bytestream2_skip(&bc, chunk_size);
+        }
+    }
+    if (got_header)
+        c->got_header = 1;
+
+    if (c->width && c->height) {
+        if ((ret = ff_get_buffer(avctx, pic, 0)) < 0) {
+            av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
+            return ret;
+        }
+
+        pic->key_frame = got_header;
+        pic->pict_type = got_header ? AV_PICTURE_TYPE_I : AV_PICTURE_TYPE_P;
+
+        for (i = 0; i < avctx->height; i++)
+            memcpy(pic->data[0] + i * pic->linesize[0],
+                   c->framebuf  + i * c->framebuf_stride,
+                   c->width * 3);
+        g2m_paint_cursor(c, pic->data[0], pic->linesize[0]);
+
+        *got_picture_ptr = 1;
+    }
+
+    return buf_size;
+}
+
+static av_cold int g2m_decode_init(AVCodecContext *avctx)
+{
+    G2MContext * const c = avctx->priv_data;
+    int ret;
+
+    if ((ret = jpg_init(avctx, &c->jc)) != 0) {
+        av_log(avctx, AV_LOG_ERROR, "Cannot initialise VLCs\n");
+        jpg_free_context(&c->jc);
+        return AVERROR(ENOMEM);
+    }
+
+    avctx->pix_fmt     = PIX_FMT_RGB24;
+
+    return 0;
+}
+
+static av_cold int g2m_decode_end(AVCodecContext *avctx)
+{
+    G2MContext * const c = avctx->priv_data;
+
+    jpg_free_context(&c->jc);
+
+    av_freep(&c->kempf_buf);
+    av_freep(&c->kempf_flags);
+    av_freep(&c->synth_tile);
+    av_freep(&c->jpeg_tile);
+    av_freep(&c->cursor);
+    av_freep(&c->framebuf);
+
+    return 0;
+}
+
+AVCodec ff_g2m_decoder = {
+    .name           = "g2m",
+    .long_name      = NULL_IF_CONFIG_SMALL("Go2Meeting"),
+    .type           = AVMEDIA_TYPE_VIDEO,
+    .id             = AV_CODEC_ID_G2M,
+    .priv_data_size = sizeof(G2MContext),
+    .init           = g2m_decode_init,
+    .close          = g2m_decode_end,
+    .decode         = g2m_decode_frame,
+    .capabilities   = CODEC_CAP_DR1,
+};