[FFmpeg-devel] [PATCH] SIFF demuxer and decoder

[Michael Niedermayer]

Hi

On Fri, Oct 19, 2007 at 11:29:47AM +0300, Kostya wrote:
[...]

> +static int vb_decode_framedata(VBDecContext *c, uint8_t *buf, int offset)
> +{
> +    uint8_t *prev, *cur;
> +    int blk, blocks, t, blk2;
> +    int blocktypes = 0;
> +    int x, y, a, b;
> +    int pattype, pattern;
> +    const int width = c->avctx->width;
> +    uint8_t *pstart = c->prev_frame;
> +    uint8_t *pend = c->prev_frame + width*c->avctx->height;
> +    
> +    prev = c->prev_frame + offset;
> +    cur = c->frame;
> +    
> +    blocks = (c->avctx->width >> 2) * (c->avctx->height >> 2);
> +    blk2 = 0;
> +    for(blk = 0; blk < blocks; blk++){
> +        if(!(blk & 3))
> +            blocktypes = bytestream_get_byte(&buf);
> +        switch(blocktypes & 0xC0){
> +        case 0x00: //skip
> +            for(y = 0; y < 4; y++)
> +                if(check_line(prev + y*width, pstart, pend))
> +                    memcpy(cur + y*width, prev + y*width, 4);
> +                else
> +                    memset(cur + y*width, 0, 4);
> +            break;

it should be enough to check the top-left and bottom-right pixels
the same applies to the other cases


[...]
> +static int siff_probe(AVProbeData *p)
> +{
> +    /* check file header */
> +    if (p->buf[0] == 'S' && p->buf[1] == 'I' &&
> +        p->buf[2] == 'F' && p->buf[3] == 'F')

AV_RL32() == TAG_SIFF or something like that


[...]
> +static int siff_parse_vbv1(AVFormatContext *s, SIFFContext *c, ByteIOContext *pb)
> +{
> +    AVStream *st;
> +    uint32_t tag, size;
> +    int width, height;
> +
> +    tag = get_le32(pb);
> +    if (tag != TAG_VBHD){
> +        av_log(s, AV_LOG_ERROR, "Header chunk is missing\n");
> +        return -1;
> +    }
> +    size = get_be32(pb);
> +    if(size != 32){
> +        av_log(s, AV_LOG_ERROR, "Header chunk size is incorrect\n");
> +        return -1;    
> +    }
> +    if(get_le16(pb) != 1){
> +        av_log(s, AV_LOG_ERROR, "Incorrect header version\n");
> +        return -1;    
> +    }
> +    width = get_le16(pb);
> +    height = get_le16(pb);
> +    url_fskip(pb, 4);
> +    c->frames = get_le16(pb);
> +    if(!c->frames){
> +        av_log(s, AV_LOG_ERROR, "File contains no frames ???\n");
> +        return -1;
> +    }
> +    c->bits = get_le16(pb);
> +    c->rate = get_le16(pb);
> +    c->block_align = c->rate * (c->bits >> 3);
> +
> +    url_fskip(pb, 16); //zeroes
> +
> +    st = av_new_stream(s, 0);
> +    if (!st)
> +        return -1;
> +    st->codec->codec_type = CODEC_TYPE_VIDEO;
> +    st->codec->codec_id   = CODEC_ID_VB;
> +    st->codec->codec_tag  = MKTAG('V', 'B', 'V', '1');
> +    st->codec->width      = width;
> +    st->codec->height     = height;

there are a lot of unneeded intermediate variables here


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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