[x264-devel] Re: A question about "x264_frame_init_lowres"

[Zhe Zheng]

I think this function generate a low resolution version of the current frame
for encoding usage. Not 100 percent sure.

On 1/7/07, 王小静 <wangxiaojing.hnu at gmail.com> wrote:
>
> I'm a newbie of x264,and I  have confused by the x264_frame_init_lowres
> routine in the file  mc.c.
> The routine  is called by x264_encoder_encode when h->frames.b_have_lowresis true.
> I wonder what  does the h-> frames.b_have_lowres stand by and what's the
> function of x264_frame_init_lowres?
> I will be grateful with any reply.Thanks.
> the source of this routine is following:
> void x264_frame_init_lowres( int cpu, x264_frame_t *frame )
> {    // FIXME: tapfilter?
>     const int i_stride = frame->i_stride[0];
>     const int i_stride2 = frame->i_stride_lowres;
>     const int i_width2 = i_stride2 - 64;
>     int x, y, i;
>     for( y = 0; y < frame->i_lines_lowres - 1; y++ )
>     {
>         uint8_t *src0 = &frame->plane[0][2*y*i_stride];
>         uint8_t *src1 = src0+i_stride;
>         uint8_t *src2 = src1+i_stride;
>         uint8_t *dst0 = &frame->lowres[0][y*i_stride2];
>         uint8_t *dsth = &frame->lowres[1][y*i_stride2];
>         uint8_t *dstv = &frame->lowres[2][y*i_stride2];
>         uint8_t *dstc = &frame->lowres[3][y*i_stride2];
>         for( x = 0; x < i_width2 - 1; x++ )
>         {
>             dst0[x] = (src0[2*x  ] + src0[2*x+1] + src1[2*x  ] +
> src1[2*x+1] + 2) >> 2;
>             dsth[x] = (src0[2*x+1] + src0[2*x+2] + src1[2*x+1] +
> src1[2*x+2] + 2) >> 2;
>             dstv[x] = (src1[2*x  ] + src1[2*x+1] + src2[2*x  ] +
> src2[2*x+1] + 2) >> 2;
>             dstc[x] = (src1[2*x+1] + src1[2*x+2] + src2[2*x+1] +
> src2[2*x+2] + 2) >> 2;
>         }
>         dst0[x] = (src0[2*x  ] + src0[2*x+1] + src1[2*x  ] + src1[2*x+1] +
> 2) >> 2;
>         dstv[x] = (src1[2*x  ] + src1[2*x+1] + src2[2*x  ] + src2[2*x+1] +
> 2) >> 2;
>         dsth[x] = (src0[2*x+1] + src1[2*x+1] + 1) >> 1;
>         dstc[x] = (src1[2*x+1] + src2[2*x+1] + 1) >> 1;
>     }
>     for( i = 0; i < 4; i++ )
>         memcpy( &frame->lowres[i][y*i_stride2],
> &frame->lowres[i][(y-1)*i_stride2], i_width2 );
>
>     for( y = 0; y < 16; y++ )
>         for( x = 0; x < 16; x++ )
>             frame->i_cost_est[x][y] = -1;
>
>     x264_frame_expand_border_lowres( frame );
> }
>
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