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 "internal.h"
47 #include "lzw.h"
48 
49 /* The GIF format uses reversed order for bitstreams... */
50 /* at least they don't use PDP_ENDIAN :) */
51 #define BITSTREAM_WRITER_LE
52 
53 #include "put_bits.h"
54 
55 typedef struct {
59 } GIFContext;
60 
61 /* GIF header */
63  uint8_t **bytestream, uint32_t *palette)
64 {
65  int i;
66  unsigned int v;
67 
68  bytestream_put_buffer(bytestream, "GIF", 3);
69  bytestream_put_buffer(bytestream, "89a", 3);
70  bytestream_put_le16(bytestream, avctx->width);
71  bytestream_put_le16(bytestream, avctx->height);
72 
73  bytestream_put_byte(bytestream, 0xf7); /* flags: global clut, 256 entries */
74  bytestream_put_byte(bytestream, 0x1f); /* background color index */
75  bytestream_put_byte(bytestream, 0); /* aspect ratio */
76 
77  /* the global palette */
78  for(i=0;i<256;i++) {
79  v = palette[i];
80  bytestream_put_be24(bytestream, v);
81  }
82 
83  return 0;
84 }
85 
87  uint8_t **bytestream, uint8_t *end,
88  const uint8_t *buf, int linesize)
89 {
90  GIFContext *s = avctx->priv_data;
91  int len = 0, height;
92  const uint8_t *ptr;
93  /* image block */
94 
95  bytestream_put_byte(bytestream, 0x2c);
96  bytestream_put_le16(bytestream, 0);
97  bytestream_put_le16(bytestream, 0);
98  bytestream_put_le16(bytestream, avctx->width);
99  bytestream_put_le16(bytestream, avctx->height);
100  bytestream_put_byte(bytestream, 0x00); /* flags */
101  /* no local clut */
102 
103  bytestream_put_byte(bytestream, 0x08);
104 
105  ff_lzw_encode_init(s->lzw, s->buf, avctx->width*avctx->height,
106  12, FF_LZW_GIF, put_bits);
107 
108  ptr = buf;
109  for (height = avctx->height; height--;) {
110  len += ff_lzw_encode(s->lzw, ptr, avctx->width);
111  ptr += linesize;
112  }
114 
115  ptr = s->buf;
116  while (len > 0) {
117  int size = FFMIN(255, len);
118  bytestream_put_byte(bytestream, size);
119  if (end - *bytestream < size)
120  return -1;
121  bytestream_put_buffer(bytestream, ptr, size);
122  ptr += size;
123  len -= size;
124  }
125  bytestream_put_byte(bytestream, 0x00); /* end of image block */
126  bytestream_put_byte(bytestream, 0x3b);
127  return 0;
128 }
129 
131 {
132  GIFContext *s = avctx->priv_data;
133 
134  avctx->coded_frame = &s->picture;
136  if (!s->lzw)
137  return AVERROR(ENOMEM);
138  s->buf = av_malloc(avctx->width*avctx->height*2);
139  if (!s->buf)
140  return AVERROR(ENOMEM);
141  return 0;
142 }
143 
144 /* better than nothing gif encoder */
145 static int gif_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
146  const AVFrame *pict, int *got_packet)
147 {
148  GIFContext *s = avctx->priv_data;
149  AVFrame *const p = &s->picture;
150  uint8_t *outbuf_ptr, *end;
151  int ret;
152 
153  if ((ret = ff_alloc_packet(pkt, avctx->width*avctx->height*7/5 + FF_MIN_BUFFER_SIZE)) < 0) {
154  av_log(avctx, AV_LOG_ERROR, "Error getting output packet.\n");
155  return ret;
156  }
157  outbuf_ptr = pkt->data;
158  end = pkt->data + pkt->size;
159 
160  *p = *pict;
162  p->key_frame = 1;
163  gif_image_write_header(avctx, &outbuf_ptr, (uint32_t *)pict->data[1]);
164  gif_image_write_image(avctx, &outbuf_ptr, end, pict->data[0], pict->linesize[0]);
165 
166  pkt->size = outbuf_ptr - pkt->data;
167  pkt->flags |= AV_PKT_FLAG_KEY;
168  *got_packet = 1;
169 
170  return 0;
171 }
172 
174 {
175  GIFContext *s = avctx->priv_data;
176 
177  av_freep(&s->lzw);
178  av_freep(&s->buf);
179  return 0;
180 }
181 
183  .name = "gif",
184  .type = AVMEDIA_TYPE_VIDEO,
185  .id = AV_CODEC_ID_GIF,
186  .priv_data_size = sizeof(GIFContext),
188  .encode2 = gif_encode_frame,
190  .pix_fmts = (const enum AVPixelFormat[]){
193  },
194  .long_name = NULL_IF_CONFIG_SMALL("GIF (Graphics Interchange Format)"),
195 };