avcodec: add gif parser

1 files changed, 188 insertions, 0 deletions

diff --git a/libavcodec/gif_parser.c b/libavcodec/gif_parser.c
new file mode 100644
index 0000000..e88338f
--- /dev/null
+++ b/libavcodec/gif_parser.c
@@ -0,0 +1,188 @@
+/*
+ * 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,
+};