[x264-devel] Why number of forward reference frames is limited to 2?

[BugMaster]

On Mon, 29 Sep 2014 11:57:00 +0200, dj alek wrote:
>  
> Hi!
>  Does anyone know the reason of hardcoded limit of RefPicList1 size?:
>   - b_ref_reorder[2];
>   - sps->vui.i_num_reorder_frames = param->i_bframe_pyramid ? 2 : param->i_bframe ? 1 : 0;
>   - h->frames.i_max_ref1 = X264_MIN(
> h->sps->vui.i_num_reorder_frames, h->param.i_frame_reference );
>   - etc
>  Is the increase in size will not improve the encoding quality? I
> mean, eg, redistribution of parameter i_frame_reference = 10 to
> num_ref_l0 = 5 & num_ref_l1 = 5 instead of the current num_ref_l0 =
> 8 & num_ref_l1 = 2 (to use 5 forward + 5 backward frames for
> reference rather than 2 forward + 8 backward)?  
>   

There is no reason to set RefPicList1 size large because you will have
at max 2 futures frames when using [one level] B-pyramid so there are
nothing to put there more than this 2 frames.