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/*
* GIF parser
* Copyright (c) 2018 Paul B Mahol
*
* 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
*/
/**
* @file
* GIF parser
*/
#include "libavutil/avassert.h"
#include "libavutil/bswap.h"
#include "libavutil/common.h"
#include "gif.h"
#include "parser.h"
typedef enum GIFParseStates {
GIF_HEADER = 1,
GIF_EXTENSION,
GIF_EXTENSION_BLOCK,
GIF_IMAGE,
GIF_IMAGE_BLOCK,
} gif_states;
typedef struct GIFParseContext {
ParseContext pc;
unsigned found_sig;
int found_start;
int found_end;
int index;
int state;
int gct_flag;
int gct_size;
int block_size;
int etype;
int delay;
} GIFParseContext;
static int gif_find_frame_end(GIFParseContext *g, const uint8_t *buf,
int buf_size, void *logctx)
{
int index, next = END_NOT_FOUND;
for (index = 0; index < buf_size; index++) {
if (!g->state) {
if (!memcmp(buf + index, gif87a_sig, 6) ||
!memcmp(buf + index, gif89a_sig, 6)) {
g->state = GIF_HEADER;
g->found_sig++;
} else if (buf[index] == GIF_EXTENSION_INTRODUCER) {
g->state = GIF_EXTENSION;
g->found_start = 1;
} else if (buf[index] == GIF_IMAGE_SEPARATOR) {
g->state = GIF_IMAGE;
} else if (buf[index] == GIF_TRAILER) {
g->state = 0;
g->found_end = 1;
g->found_sig = 0;
} else {
g->found_sig = 0;
}
}
if (g->state == GIF_HEADER) {
if (g->index == 10) {
g->gct_flag = !!(buf[index] & 0x80);
g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
}
if (g->index >= 12 + g->gct_flag * g->gct_size) {
g->state = 0;
g->index = 0;
g->gct_flag = 0;
g->gct_size = 0;
continue;
}
g->index++;
} else if (g->state == GIF_EXTENSION) {
if (g->found_start && g->found_end && g->found_sig) {
next = index;
g->found_start = 0;
g->found_end = 0;
g->index = 0;
g->gct_flag = 0;
g->gct_size = 0;
g->state = 0;
break;
}
if (g->index == 1) {
g->etype = buf[index];
}
if (g->index >= 2) {
g->block_size = buf[index];
g->index = 0;
g->state = GIF_EXTENSION_BLOCK;
continue;
}
g->index++;
} else if (g->state == GIF_IMAGE_BLOCK) {
if (!g->index)
g->block_size = buf[index];
if (g->index >= g->block_size) {
g->index = 0;
if (!g->block_size) {
g->state = 0;
g->found_end = 1;
}
continue;
}
g->index++;
} else if (g->state == GIF_EXTENSION_BLOCK) {
if (g->etype == GIF_GCE_EXT_LABEL) {
if (g->index == 0)
g->delay = 0;
if (g->index >= 1 && g->index <= 2) {
g->delay |= buf[index] << (8 * (g->index - 1));
}
}
if (g->index >= g->block_size) {
g->block_size = buf[index];
g->index = 0;
if (!g->block_size)
g->state = 0;
continue;
}
g->index++;
} else if (g->state == GIF_IMAGE) {
if (g->index == 8) {
g->gct_flag = !!(buf[index] & 0x80);
g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
}
if (g->index >= 10 + g->gct_flag * g->gct_size) {
g->state = GIF_IMAGE_BLOCK;
g->index = 0;
g->gct_flag = 0;
g->gct_size = 0;
continue;
}
g->index++;
}
}
return next;
}
static int gif_parse(AVCodecParserContext *s, AVCodecContext *avctx,
const uint8_t **poutbuf, int *poutbuf_size,
const uint8_t *buf, int buf_size)
{
GIFParseContext *g = s->priv_data;
int next;
next = gif_find_frame_end(g, buf, buf_size, avctx);
if (ff_combine_frame(&g->pc, next, &buf, &buf_size) < 0) {
*poutbuf = NULL;
*poutbuf_size = 0;
return buf_size;
}
s->duration = g->delay;
*poutbuf = buf;
*poutbuf_size = buf_size;
return next;
}
AVCodecParser ff_gif_parser = {
.codec_ids = { AV_CODEC_ID_GIF },
.priv_data_size = sizeof(GIFParseContext),
.parser_parse = gif_parse,
.parser_close = ff_parse_close,
};
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