vf_crop: keepaspect support

libavfilter/vf_crop.c

@@ -74,6 +74,9 @@ typedef struct {
     int  w;             ///< width of the cropped area
     int  h;             ///< height of the cropped area
 
+    AVRational out_sar; ///< output sample aspect ratio
+    int keep_aspect;    ///< keep display aspect ratio when cropping
+
     int max_step[4];    ///< max pixel step for each plane, expressed as a number of bytes
     int hsub, vsub;     ///< chroma subsampling
     char x_expr[256], y_expr[256], ow_expr[256], oh_expr[256];
@@ -124,7 +127,7 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
     av_strlcpy(crop->y_expr, "(in_h-out_h)/2", sizeof(crop->y_expr));
 
     if (args)
-        sscanf(args, "%255[^:]:%255[^:]:%255[^:]:%255[^:]", crop->ow_expr, crop->oh_expr, crop->x_expr, crop->y_expr);
+        sscanf(args, "%255[^:]:%255[^:]:%255[^:]:%255[^:]:%d", crop->ow_expr, crop->oh_expr, crop->x_expr, crop->y_expr, &crop->keep_aspect);
 
     return 0;
 }
@@ -210,6 +213,14 @@ static int config_input(AVFilterLink *link)
                              NULL, NULL, NULL, NULL, 0, ctx)) < 0)
         return AVERROR(EINVAL);
 
+    if (crop->keep_aspect) {
+        AVRational dar = av_mul_q(link->sample_aspect_ratio,
+                                  (AVRational){ link->w, link->h });
+        av_reduce(&crop->out_sar.num, &crop->out_sar.den,
+                  dar.num * crop->h, dar.den * crop->w, INT_MAX);
+    } else
+        crop->out_sar = link->sample_aspect_ratio;
+
     av_log(ctx, AV_LOG_INFO, "w:%d h:%d -> w:%d h:%d\n",
            link->w, link->h, crop->w, crop->h);
 
@@ -239,6 +250,7 @@ static int config_output(AVFilterLink *link)
 
     link->w = crop->w;
     link->h = crop->h;
+    link->sample_aspect_ratio = crop->out_sar;
 
     return 0;
 }