avfilter/vf_v360: add fixed pixel padding options

doc/filters.texi

@@ -17961,6 +17961,12 @@ No padding.
 
 Default value is @b{@samp{0}}.
 
+@item fin_pad
+@item fout_pad
+Set fixed padding for the input/output cubemap. Values in pixels.
+
+Default value is @b{@samp{0}}. If greater than zero it overrides other padding options.
+
 @item in_forder
 @item out_forder
 Set order of faces for the input/output cubemap. Choose one direction for each position.

libavfilter/v360.h

@@ -114,6 +114,7 @@ typedef struct V360Context {
     int in_stereo, out_stereo;
 
     float in_pad, out_pad;
+    int fin_pad, fout_pad;
 
     float yaw, pitch, roll;
 
@@ -129,6 +130,9 @@ typedef struct V360Context {
     float input_mirror_modifier[2];
     float output_mirror_modifier[3];
 
+    int in_width, in_height;
+    int out_width, out_height;
+
     int pr_width[4], pr_height[4];
 
     int in_offset_w[4], in_offset_h[4];