libavcodec/gif.c

   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 FFmpeg.
   8  *
   9  * FFmpeg 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  * FFmpeg 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 FFmpeg; 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
  47 /* The GIF format uses reversed order for bitstreams... */
  48 /* at least they don't use PDP_ENDIAN :) */
  49 #define BITSTREAM_WRITER_LE
  50
  51 #include "put_bits.h"
  52
  53 /* bitstream minipacket size */
  54 #define GIF_CHUNKS 100
  55
  56 /* GIF header */
  57 static int gif_image_write_header(uint8_t **bytestream,
  58                                   int width, int height,
  59                                   uint32_t *palette)
  60 {
  61     int i;
  62     unsigned int v;
  63
  64     bytestream_put_buffer(bytestream, "GIF", 3);
  65     bytestream_put_buffer(bytestream, "89a", 3);
  66     bytestream_put_le16(bytestream, width);
  67     bytestream_put_le16(bytestream, height);
  68
  69     bytestream_put_byte(bytestream, 0xf7); /* flags: global clut, 256 entries */
  70     bytestream_put_byte(bytestream, 0x1f); /* background color index */
  71     bytestream_put_byte(bytestream, 0); /* aspect ratio */
  72
  73     /* the global palette */
  74     for(i=0;i<256;i++) {
  75         v = palette[i];
  76         bytestream_put_be24(bytestream, v);
  77     }
  78
  79     return 0;
  80 }
  81
  82 static int gif_image_write_image(uint8_t **bytestream,
  83                                  int x1, int y1, int width, int height,
  84                                  const uint8_t *buf, int linesize, int pix_fmt)
  85 {
  86     PutBitContext p;
  87     uint8_t buffer[200]; /* 100 * 9 / 8 = 113 */
  88     int i, left, w;
  89     const uint8_t *ptr;
  90     /* image block */
  91
  92     bytestream_put_byte(bytestream, 0x2c);
  93     bytestream_put_le16(bytestream, x1);
  94     bytestream_put_le16(bytestream, y1);
  95     bytestream_put_le16(bytestream, width);
  96     bytestream_put_le16(bytestream, height);
  97     bytestream_put_byte(bytestream, 0x00); /* flags */
  98     /* no local clut */
  99
 100     bytestream_put_byte(bytestream, 0x08);
 101
 102     left= width * height;
 103
 104     init_put_bits(&p, buffer, 130);
 105
 106 /*
 107  * the thing here is the bitstream is written as little packets, with a size byte before
 108  * but it's still the same bitstream between packets (no flush !)
 109  */
 110     ptr = buf;
 111     w = width;
 112     while(left>0) {
 113
 114         put_bits(&p, 9, 0x0100); /* clear code */
 115
 116         for(i=(left<GIF_CHUNKS)?left:GIF_CHUNKS;i;i--) {
 117             put_bits(&p, 9, *ptr++);
 118             if (--w == 0) {
 119                 w = width;
 120                 buf += linesize;
 121                 ptr = buf;
 122             }
 123         }
 124
 125         if(left<=GIF_CHUNKS) {
 126             put_bits(&p, 9, 0x101); /* end of stream */
 127             flush_put_bits(&p);
 128         }
 129         if(put_bits_ptr(&p) - p.buf > 0) {
 130             bytestream_put_byte(bytestream, put_bits_ptr(&p) - p.buf); /* byte count of the packet */
 131             bytestream_put_buffer(bytestream, p.buf, put_bits_ptr(&p) - p.buf); /* the actual buffer */
 132             p.buf_ptr = p.buf; /* dequeue the bytes off the bitstream */
 133         }
 134         left-=GIF_CHUNKS;
 135     }
 136     bytestream_put_byte(bytestream, 0x00); /* end of image block */
 137     bytestream_put_byte(bytestream, 0x3b);
 138     return 0;
 139 }
 140
 141 typedef struct {
 142     AVFrame picture;
 143 } GIFContext;
 144
 145 static av_cold int gif_encode_init(AVCodecContext *avctx)
 146 {
 147     GIFContext *s = avctx->priv_data;
 148
 149     avctx->coded_frame = &s->picture;
 150     return 0;
 151 }
 152
 153 /* better than nothing gif encoder */
 154 static int gif_encode_frame(AVCodecContext *avctx, unsigned char *outbuf, int buf_size, void *data)
 155 {
 156     GIFContext *s = avctx->priv_data;
 157     AVFrame *pict = data;
 158     AVFrame *const p = (AVFrame *)&s->picture;
 159     uint8_t *outbuf_ptr = outbuf;
 160
 161     *p = *pict;
 162     p->pict_type = FF_I_TYPE;
 163     p->key_frame = 1;
 164     gif_image_write_header(&outbuf_ptr, avctx->width, avctx->height, (uint32_t *)pict->data[1]);
 165     gif_image_write_image(&outbuf_ptr, 0, 0, avctx->width, avctx->height, pict->data[0], pict->linesize[0], PIX_FMT_PAL8);
 166     return outbuf_ptr - outbuf;
 167 }
 168
 169 AVCodec gif_encoder = {
 170     "gif",
 171     CODEC_TYPE_VIDEO,
 172     CODEC_ID_GIF,
 173     sizeof(GIFContext),
 174     gif_encode_init,
 175     gif_encode_frame,
 176     NULL, //encode_end,
 177     .pix_fmts= (const enum PixelFormat[]){PIX_FMT_RGB8, PIX_FMT_BGR8, PIX_FMT_RGB4_BYTE, PIX_FMT_BGR4_BYTE, PIX_FMT_GRAY8, PIX_FMT_PAL8, PIX_FMT_NONE},
 178     .long_name= NULL_IF_CONFIG_SMALL("GIF (Graphics Interchange Format)"),
 179 };