| /* |
| * 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, |
| }; |