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