gif.c

来自「ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦」· C语言 代码 · 共 345 行 · 第 1/2 页

    int i;
    unsigned int v;

    bytestream_put_buffer(bytestream, "GIF", 3);
    bytestream_put_buffer(bytestream, "89a", 3);
    bytestream_put_le16(bytestream, width);
    bytestream_put_le16(bytestream, height);

    bytestream_put_byte(bytestream, 0xf7); /* flags: global clut, 256 entries */
    bytestream_put_byte(bytestream, 0x1f); /* background color index */
    bytestream_put_byte(bytestream, 0); /* aspect ratio */

    /* the global palette */
    if (!palette) {
        bytestream_put_buffer(bytestream, (const unsigned char *)gif_clut, 216*3);
        for(i=0;i<((256-216)*3);i++)
            bytestream_put_byte(bytestream, 0);
    } else {
        for(i=0;i<256;i++) {
            v = palette[i];
            bytestream_put_be24(bytestream, v);
        }
    }

        /*        update: this is the 'NETSCAPE EXTENSION' that allows for looped animated gif
                see http://members.aol.com/royalef/gifabout.htm#net-extension

                byte   1       : 33 (hex 0x21) GIF Extension code
                byte   2       : 255 (hex 0xFF) Application Extension Label
                byte   3       : 11 (hex (0x0B) Length of Application Block
                                         (eleven bytes of data to follow)
                bytes  4 to 11 : "NETSCAPE"
                bytes 12 to 14 : "2.0"
                byte  15       : 3 (hex 0x03) Length of Data Sub-Block
                                         (three bytes of data to follow)
                byte  16       : 1 (hex 0x01)
                bytes 17 to 18 : 0 to 65535, an unsigned integer in
                                         lo-hi byte format. This indicate the
                                         number of iterations the loop should
                                         be executed.
                bytes 19       : 0 (hex 0x00) a Data Sub-block Terminator
        */

    /* application extension header */
#ifdef GIF_ADD_APP_HEADER
    if (loop_count >= 0 && loop_count <= 65535) {
        bytestream_put_byte(bytestream, 0x21);
        bytestream_put_byte(bytestream, 0xff);
        bytestream_put_byte(bytestream, 0x0b);
        bytestream_put_buffer(bytestream, "NETSCAPE2.0", 11);  // bytes 4 to 14
        bytestream_put_byte(bytestream, 0x03); // byte 15
        bytestream_put_byte(bytestream, 0x01); // byte 16
        bytestream_put_le16(bytestream, (uint16_t)loop_count);
        bytestream_put_byte(bytestream, 0x00); // byte 19
    }
#endif
    return 0;
}

/* this is maybe slow, but allows for extensions */
static inline unsigned char gif_clut_index(uint8_t r, uint8_t g, uint8_t b)
{
    return ((((r)/47)%6)*6*6+(((g)/47)%6)*6+(((b)/47)%6));
}


static int gif_image_write_image(uint8_t **bytestream,
                                 int x1, int y1, int width, int height,
                                 const uint8_t *buf, int linesize, int pix_fmt)
{
    PutBitContext p;
    uint8_t buffer[200]; /* 100 * 9 / 8 = 113 */
    int i, left, w, v;
    const uint8_t *ptr;
    /* image block */

    bytestream_put_byte(bytestream, 0x2c);
    bytestream_put_le16(bytestream, x1);
    bytestream_put_le16(bytestream, y1);
    bytestream_put_le16(bytestream, width);
    bytestream_put_le16(bytestream, height);
    bytestream_put_byte(bytestream, 0x00); /* flags */
    /* no local clut */

    bytestream_put_byte(bytestream, 0x08);

    left= width * height;

    init_put_bits(&p, buffer, 130);

/*
 * the thing here is the bitstream is written as little packets, with a size byte before
 * but it's still the same bitstream between packets (no flush !)
 */
    ptr = buf;
    w = width;
    while(left>0) {

        gif_put_bits_rev(&p, 9, 0x0100); /* clear code */

        for(i=(left<GIF_CHUNKS)?left:GIF_CHUNKS;i;i--) {
            if (pix_fmt == PIX_FMT_RGB24) {
                v = gif_clut_index(ptr[0], ptr[1], ptr[2]);
                ptr+=3;
            } else {
                v = *ptr++;
            }
            gif_put_bits_rev(&p, 9, v);
            if (--w == 0) {
                w = width;
                buf += linesize;
                ptr = buf;
            }
        }

        if(left<=GIF_CHUNKS) {
            gif_put_bits_rev(&p, 9, 0x101); /* end of stream */
            gif_flush_put_bits_rev(&p);
        }
        if(pbBufPtr(&p) - p.buf > 0) {
            bytestream_put_byte(bytestream, pbBufPtr(&p) - p.buf); /* byte count of the packet */
            bytestream_put_buffer(bytestream, p.buf, pbBufPtr(&p) - p.buf); /* the actual buffer */
            p.buf_ptr = p.buf; /* dequeue the bytes off the bitstream */
        }
        left-=GIF_CHUNKS;
    }
    bytestream_put_byte(bytestream, 0x00); /* end of image block */
    bytestream_put_byte(bytestream, 0x3b);
    return 0;
}

typedef struct {
    int64_t time, file_time;
    uint8_t buffer[100]; /* data chunks */
    AVFrame picture;
} GIFContext;

static int gif_encode_init(AVCodecContext *avctx)
{
    GIFContext *s = avctx->priv_data;

    avctx->coded_frame = &s->picture;
    return 0;
}

/* better than nothing gif encoder */
static int gif_encode_frame(AVCodecContext *avctx, unsigned char *outbuf, int buf_size, void *data)
{
    GIFContext *s = avctx->priv_data;
    AVFrame *pict = data;
    AVFrame *const p = (AVFrame *)&s->picture;
    uint8_t *outbuf_ptr = outbuf;

    *p = *pict;
    p->pict_type = FF_I_TYPE;
    p->key_frame = 1;
    gif_image_write_header(&outbuf_ptr, avctx->width, avctx->height, -1, (uint32_t *)pict->data[1]);
    gif_image_write_image(&outbuf_ptr, 0, 0, avctx->width, avctx->height, pict->data[0], pict->linesize[0], PIX_FMT_PAL8);
    return outbuf_ptr - outbuf;
}

AVCodec gif_encoder = {
    "gif",
    CODEC_TYPE_VIDEO,
    CODEC_ID_GIF,
    sizeof(GIFContext),
    gif_encode_init,
    gif_encode_frame,
    NULL, //encode_end,
    .pix_fmts= (enum PixelFormat[]){PIX_FMT_PAL8, -1},
};