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ffmpeg / libavcodec / gif.c @ cc26bf0d

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/*
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 * GIF encoder.
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 * Copyright (c) 2000 Fabrice Bellard
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 * Copyright (c) 2002 Francois Revol
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 * Copyright (c) 2006 Baptiste Coudurier
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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/*
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 * First version by Francois Revol revol@free.fr
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 *
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 * Features and limitations:
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 * - currently no compression is performed,
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 *   in fact the size of the data is 9/8 the size of the image in 8bpp
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 * - uses only a global standard palette
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 * - tested with IE 5.0, Opera for BeOS, NetPositive (BeOS), and Mozilla (BeOS).
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 *
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 * Reference documents:
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 * http://www.goice.co.jp/member/mo/formats/gif.html
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 * http://astronomy.swin.edu.au/pbourke/dataformats/gif/
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 * http://www.dcs.ed.ac.uk/home/mxr/gfx/2d/GIF89a.txt
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 *
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 * this url claims to have an LZW algorithm not covered by Unisys patent:
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 * http://www.msg.net/utility/whirlgif/gifencod.html
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 * could help reduce the size of the files _a lot_...
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 * some sites mentions an RLE type compression also.
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 */
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#include "avcodec.h"
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#include "bytestream.h"
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/* The GIF format uses reversed order for bitstreams... */
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/* at least they don't use PDP_ENDIAN :) */
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#define BITSTREAM_WRITER_LE
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#include "put_bits.h"
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/* bitstream minipacket size */
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#define GIF_CHUNKS 100
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typedef struct {
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    AVFrame picture;
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} GIFContext;
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/* GIF header */
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static int gif_image_write_header(uint8_t **bytestream,
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                                  int width, int height,
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                                  uint32_t *palette)
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{
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    int i;
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    unsigned int v;
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    bytestream_put_buffer(bytestream, "GIF", 3);
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    bytestream_put_buffer(bytestream, "89a", 3);
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    bytestream_put_le16(bytestream, width);
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    bytestream_put_le16(bytestream, height);
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    bytestream_put_byte(bytestream, 0xf7); /* flags: global clut, 256 entries */
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    bytestream_put_byte(bytestream, 0x1f); /* background color index */
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    bytestream_put_byte(bytestream, 0); /* aspect ratio */
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    /* the global palette */
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    for(i=0;i<256;i++) {
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        v = palette[i];
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        bytestream_put_be24(bytestream, v);
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    }
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    return 0;
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}
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static int gif_image_write_image(uint8_t **bytestream,
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                                 int width, int height,
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                                 const uint8_t *buf, int linesize, int pix_fmt)
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{
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    PutBitContext p;
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    uint8_t buffer[200]; /* 100 * 9 / 8 = 113 */
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    int i, left, w;
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    const uint8_t *ptr;
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    /* image block */
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    bytestream_put_byte(bytestream, 0x2c);
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    bytestream_put_le16(bytestream, 0);
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    bytestream_put_le16(bytestream, 0);
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    bytestream_put_le16(bytestream, width);
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    bytestream_put_le16(bytestream, height);
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    bytestream_put_byte(bytestream, 0x00); /* flags */
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    /* no local clut */
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    bytestream_put_byte(bytestream, 0x08);
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    left= width * height;
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    init_put_bits(&p, buffer, 130);
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/*
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 * the thing here is the bitstream is written as little packets, with a size byte before
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 * but it's still the same bitstream between packets (no flush !)
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 */
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    ptr = buf;
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    w = width;
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    while(left>0) {
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        put_bits(&p, 9, 0x0100); /* clear code */
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        for(i=(left<GIF_CHUNKS)?left:GIF_CHUNKS;i;i--) {
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            put_bits(&p, 9, *ptr++);
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            if (--w == 0) {
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                w = width;
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                buf += linesize;
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                ptr = buf;
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            }
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        }
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        if(left<=GIF_CHUNKS) {
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            put_bits(&p, 9, 0x101); /* end of stream */
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            flush_put_bits(&p);
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        }
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        if(put_bits_ptr(&p) - p.buf > 0) {
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            bytestream_put_byte(bytestream, put_bits_ptr(&p) - p.buf); /* byte count of the packet */
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            bytestream_put_buffer(bytestream, p.buf, put_bits_ptr(&p) - p.buf); /* the actual buffer */
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            p.buf_ptr = p.buf; /* dequeue the bytes off the bitstream */
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        }
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        left-=GIF_CHUNKS;
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    }
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    bytestream_put_byte(bytestream, 0x00); /* end of image block */
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    bytestream_put_byte(bytestream, 0x3b);
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    return 0;
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}
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static av_cold int gif_encode_init(AVCodecContext *avctx)
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{
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    GIFContext *s = avctx->priv_data;
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    avctx->coded_frame = &s->picture;
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    return 0;
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}
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/* better than nothing gif encoder */
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static int gif_encode_frame(AVCodecContext *avctx, unsigned char *outbuf, int buf_size, void *data)
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{
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    GIFContext *s = avctx->priv_data;
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    AVFrame *pict = data;
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    AVFrame *const p = (AVFrame *)&s->picture;
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    uint8_t *outbuf_ptr = outbuf;
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    *p = *pict;
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    p->pict_type = FF_I_TYPE;
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    p->key_frame = 1;
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    gif_image_write_header(&outbuf_ptr, avctx->width, avctx->height, (uint32_t *)pict->data[1]);
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    gif_image_write_image(&outbuf_ptr, avctx->width, avctx->height, pict->data[0], pict->linesize[0], PIX_FMT_PAL8);
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    return outbuf_ptr - outbuf;
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}
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AVCodec gif_encoder = {
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    "gif",
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    CODEC_TYPE_VIDEO,
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    CODEC_ID_GIF,
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    sizeof(GIFContext),
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    gif_encode_init,
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    gif_encode_frame,
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    NULL, //encode_end,
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    .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},
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    .long_name= NULL_IF_CONFIG_SMALL("GIF (Graphics Interchange Format)"),
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};