filter: add/use a convenience function

I guess this is generally useful for filters which buffer data
internally.

filters/f_utils.c

@@ -251,8 +251,7 @@ static void fixed_aframe_size_process(struct mp_filter *f)
         p->out = NULL;
         p->out_written = 0;
     } else {
-        if (mp_pin_out_request_data(f->ppins[0]))
-            mp_filter_internal_mark_progress(f);
+        mp_pin_out_request_data_next(f->ppins[0]);
     }
 }
 

filters/filter.c

@@ -256,6 +256,12 @@ bool mp_pin_out_request_data(struct mp_pin *p)
     return mp_pin_out_has_data(p);
 }
 
+void mp_pin_out_request_data_next(struct mp_pin *p)
+{
+    if (mp_pin_out_request_data(p))
+        update_filter(p->owner, p->conn->manual_connection);
+}
+
 struct mp_frame mp_pin_out_read(struct mp_pin *p)
 {
     if (!mp_pin_out_request_data(p))

filters/filter.h

@@ -47,6 +47,11 @@ bool mp_pin_in_write(struct mp_pin *p, struct mp_frame frame);
 // buffered in mp_pins goes against this.
 bool mp_pin_out_request_data(struct mp_pin *p);
 
+// Same as mp_pin_out_request_data(), but call the filter's process() function
+// next time even if there is new data. the intention is that the filter reads
+// the data in the next iteration, without checking for the data now.
+void mp_pin_out_request_data_next(struct mp_pin *p);
+
 // Same as mp_pin_out_request_data(), but does not attempt to procure new frames
 // if the return value is false.
 bool mp_pin_out_has_data(struct mp_pin *p);