gif.c
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1 /*
2  * GIF encoder.
3  * Copyright (c) 2000 Fabrice Bellard
4  * Copyright (c) 2002 Francois Revol
5  * Copyright (c) 2006 Baptiste Coudurier
6  *
7  * This file is part of Libav.
8  *
9  * Libav is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU Lesser General Public
11  * License as published by the Free Software Foundation; either
12  * version 2.1 of the License, or (at your option) any later version.
13  *
14  * Libav is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17  * Lesser General Public License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public
20  * License along with Libav; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22  */
23 
24 /*
25  * First version by Francois Revol revol@free.fr
26  *
27  * Features and limitations:
28  * - currently no compression is performed,
29  * in fact the size of the data is 9/8 the size of the image in 8bpp
30  * - uses only a global standard palette
31  * - tested with IE 5.0, Opera for BeOS, NetPositive (BeOS), and Mozilla (BeOS).
32  *
33  * Reference documents:
34  * http://www.goice.co.jp/member/mo/formats/gif.html
35  * http://astronomy.swin.edu.au/pbourke/dataformats/gif/
36  * http://www.dcs.ed.ac.uk/home/mxr/gfx/2d/GIF89a.txt
37  *
38  * this url claims to have an LZW algorithm not covered by Unisys patent:
39  * http://www.msg.net/utility/whirlgif/gifencod.html
40  * could help reduce the size of the files _a lot_...
41  * some sites mentions an RLE type compression also.
42  */
43 
44 #include "avcodec.h"
45 #include "bytestream.h"
46 #include "lzw.h"
47 
48 /* The GIF format uses reversed order for bitstreams... */
49 /* at least they don't use PDP_ENDIAN :) */
50 #define BITSTREAM_WRITER_LE
51 
52 #include "put_bits.h"
53 
54 typedef struct {
57  uint8_t *buf;
58 } GIFContext;
59 
60 /* GIF header */
62  uint8_t **bytestream, uint32_t *palette)
63 {
64  int i;
65  unsigned int v;
66 
67  bytestream_put_buffer(bytestream, "GIF", 3);
68  bytestream_put_buffer(bytestream, "89a", 3);
69  bytestream_put_le16(bytestream, avctx->width);
70  bytestream_put_le16(bytestream, avctx->height);
71 
72  bytestream_put_byte(bytestream, 0xf7); /* flags: global clut, 256 entries */
73  bytestream_put_byte(bytestream, 0x1f); /* background color index */
74  bytestream_put_byte(bytestream, 0); /* aspect ratio */
75 
76  /* the global palette */
77  for(i=0;i<256;i++) {
78  v = palette[i];
79  bytestream_put_be24(bytestream, v);
80  }
81 
82  return 0;
83 }
84 
86  uint8_t **bytestream, uint8_t *end,
87  const uint8_t *buf, int linesize)
88 {
89  GIFContext *s = avctx->priv_data;
90  int len = 0, height;
91  const uint8_t *ptr;
92  /* image block */
93 
94  bytestream_put_byte(bytestream, 0x2c);
95  bytestream_put_le16(bytestream, 0);
96  bytestream_put_le16(bytestream, 0);
97  bytestream_put_le16(bytestream, avctx->width);
98  bytestream_put_le16(bytestream, avctx->height);
99  bytestream_put_byte(bytestream, 0x00); /* flags */
100  /* no local clut */
101 
102  bytestream_put_byte(bytestream, 0x08);
103 
104  ff_lzw_encode_init(s->lzw, s->buf, avctx->width*avctx->height,
105  12, FF_LZW_GIF, put_bits);
106 
107  ptr = buf;
108  for (height = avctx->height; height--;) {
109  len += ff_lzw_encode(s->lzw, ptr, avctx->width);
110  ptr += linesize;
111  }
113 
114  ptr = s->buf;
115  while (len > 0) {
116  int size = FFMIN(255, len);
117  bytestream_put_byte(bytestream, size);
118  if (end - *bytestream < size)
119  return -1;
120  bytestream_put_buffer(bytestream, ptr, size);
121  ptr += size;
122  len -= size;
123  }
124  bytestream_put_byte(bytestream, 0x00); /* end of image block */
125  bytestream_put_byte(bytestream, 0x3b);
126  return 0;
127 }
128 
130 {
131  GIFContext *s = avctx->priv_data;
132 
133  avctx->coded_frame = &s->picture;
135  if (!s->lzw)
136  return AVERROR(ENOMEM);
137  s->buf = av_malloc(avctx->width*avctx->height*2);
138  if (!s->buf)
139  return AVERROR(ENOMEM);
140  return 0;
141 }
142 
143 /* better than nothing gif encoder */
144 static int gif_encode_frame(AVCodecContext *avctx, unsigned char *outbuf, int buf_size, void *data)
145 {
146  GIFContext *s = avctx->priv_data;
147  AVFrame *pict = data;
148  AVFrame *const p = (AVFrame *)&s->picture;
149  uint8_t *outbuf_ptr = outbuf;
150  uint8_t *end = outbuf + buf_size;
151 
152  *p = *pict;
154  p->key_frame = 1;
155  gif_image_write_header(avctx, &outbuf_ptr, (uint32_t *)pict->data[1]);
156  gif_image_write_image(avctx, &outbuf_ptr, end, pict->data[0], pict->linesize[0]);
157  return outbuf_ptr - outbuf;
158 }
159 
161 {
162  GIFContext *s = avctx->priv_data;
163 
164  av_freep(&s->lzw);
165  av_freep(&s->buf);
166  return 0;
167 }
168 
170  .name = "gif",
171  .type = AVMEDIA_TYPE_VIDEO,
172  .id = CODEC_ID_GIF,
173  .priv_data_size = sizeof(GIFContext),
175  .encode = gif_encode_frame,
178  .long_name= NULL_IF_CONFIG_SMALL("GIF (Graphics Interchange Format)"),
179 };