[FFmpeg-devel] [PATCH v1] filter select - avoid 2 times rounding

[Nicolas George]

Ulf Zibis (12019-07-19):
> >From f14142a22d340cba48b3e2352a33026590dec3a5 Mon Sep 17 00:00:00 2001
> From: Ulf Zibis <Ulf.Zibis at CoSoCo.de>
> Date: 19.07.2019, 18:27:51
> 

> avfilter/select: avoid twice rounding

Maybe I a missing something, I see no change in rounding in this code. I
suspect your diagnosis is wrong.

> 
> diff --git a/libavfilter/f_select.c b/libavfilter/f_select.c
> index 1132375..39cc004 100644
> --- a/libavfilter/f_select.c
> +++ b/libavfilter/f_select.c
> @@ -297,6 +297,7 @@
>  
>  #define D2TS(d)  (isnan(d) ? AV_NOPTS_VALUE : (int64_t)(d))
>  #define TS2D(ts) ((ts) == AV_NOPTS_VALUE ? NAN : (double)(ts))

> +#define TS2DT(ts, tb) (TS2D((ts) * (tb).num / (double)(tb).den))

You are multiplying two possibly large integers: it can overflow. I am
not sure if it is really a concern, but it must not be done blindly.

>  
>  static void select_frame(AVFilterContext *ctx, AVFrame *frame)
>  {
> @@ -307,11 +308,11 @@
>      if (isnan(select->var_values[VAR_START_PTS]))
>          select->var_values[VAR_START_PTS] = TS2D(frame->pts);
>      if (isnan(select->var_values[VAR_START_T]))
> -        select->var_values[VAR_START_T] = TS2D(frame->pts) * av_q2d(inlink->time_base);
> +        select->var_values[VAR_START_T] = TS2DT(frame->pts, inlink->time_base);
>  
>      select->var_values[VAR_N  ] = inlink->frame_count_out;
>      select->var_values[VAR_PTS] = TS2D(frame->pts);
> -    select->var_values[VAR_T  ] = TS2D(frame->pts) * av_q2d(inlink->time_base);
> +    select->var_values[VAR_T  ] = TS2DT(frame->pts, inlink->time_base);
>      select->var_values[VAR_POS] = frame->pkt_pos == -1 ? NAN : frame->pkt_pos;
>      select->var_values[VAR_KEY] = frame->key_frame;
>      select->var_values[VAR_CONCATDEC_SELECT] = get_concatdec_select(frame, av_rescale_q(frame->pts, inlink->time_base, AV_TIME_BASE_Q));


Regards,

-- 
  Nicolas George
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