video/filter: allow better dataflow

Consider a filter which turns 1 frame into 2 frames (such as an
deinterlacer). Until now, we forced filters to produce all output frames
at once. This was done for simplicity.

Change the filter API such that a filter can produce frames
incrementally.

2 files changed, 20 insertions, 2 deletions

diff --git a/video/filter/vf.c b/video/filter/vf.c
index e76d30ea23..f00e9689c6 100644
--- a/video/filter/vf.c
+++ b/video/filter/vf.c
@@ -379,10 +379,19 @@ void vf_add_output_frame(struct vf_instance *vf, struct mp_image *img)
     }
 }
 
+static bool vf_has_output_frame(struct vf_instance *vf)
+{
+    if (!vf->num_out_queued && vf->filter_out) {
+        if (vf->filter_out(vf) < 0)
+            MP_ERR(vf, "Error filtering frame.\n");
+    }
+    return vf->num_out_queued > 0;
+}
+
 static struct mp_image *vf_dequeue_output_frame(struct vf_instance *vf)
 {
     struct mp_image *res = NULL;
-    if (vf->num_out_queued) {
+    if (vf_has_output_frame(vf)) {
         res = vf->out_queued[0];
         MP_TARRAY_REMOVE_AT(vf->out_queued, vf->num_out_queued, 0);
     }
@@ -445,7 +454,7 @@ int vf_output_frame(struct vf_chain *c, bool eof)
                 if (r < 0)
                     return r;
             }
-            if (cur->num_out_queued)
+            if (vf_has_output_frame(cur))
                 last = cur;
         }
         if (!last)
diff --git a/video/filter/vf.h b/video/filter/vf.h
index 71dcb699c2..6f0985293e 100644
--- a/video/filter/vf.h
+++ b/video/filter/vf.h
@@ -75,6 +75,15 @@ typedef struct vf_instance {
     //          can be used to output delayed or otherwise remaining images.
     int (*filter_ext)(struct vf_instance *vf, struct mp_image *mpi);
 
+    // Produce an output frame. This is called after filter or filter_ext.
+    // You can add 0 or more frames with vf_add_output_frame(). (This allows
+    // distributing the filter load over time -> typically add at most 1 frame.)
+    // If this adds no frame (or is NULL), then the caller assumes that the
+    // filter needs new input.
+    // Return a negative value on error. (No more frames is not an error.)
+    // May be called multiple times, even if the filter gives no output.
+    int (*filter_out)(struct vf_instance *vf);
+
     void (*uninit)(struct vf_instance *vf);
 
     char *label;