avfilter: Make enabled/disabled state available as a field of the AVFilterContext

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/avfilter.c

@@ -993,7 +993,9 @@ static int ff_filter_frame_framed(AVFilterLink *link, AVFrame *frame)
         dstctx->var_values[VAR_N] = link->frame_count;
         dstctx->var_values[VAR_T] = pts == AV_NOPTS_VALUE ? NAN : pts * av_q2d(link->time_base);
         dstctx->var_values[VAR_POS] = pos == -1 ? NAN : pos;
-        if (!av_expr_eval(dstctx->enable, dstctx->var_values, NULL))
+
+        dstctx->is_disabled = !av_expr_eval(dstctx->enable, dstctx->var_values, NULL);
+        if (dstctx->is_disabled)
             filter_frame = dst->passthrough_filter_frame ? dst->passthrough_filter_frame
                                                          : default_filter_frame;
     }

libavfilter/avfilter.h

@@ -570,6 +570,7 @@ struct AVFilterContext {
     char *enable_str;               ///< enable expression string
     void *enable;                   ///< parsed expression (AVExpr*)
     double *var_values;             ///< variable values for the enable expression
+    int is_disabled;                ///< the enabled state from the last expression evaluation
 };
 
 /**