try-fix: https://github.com/mltframework/mlt/issues/1058

src/framework/mlt_field.c

@@ -240,7 +240,17 @@ void mlt_field_close(mlt_field self)
 
 void mlt_field_disconnect_service(mlt_field self, mlt_service service)
 {
-    mlt_service p = mlt_service_producer(service);
+    mlt_service p = NULL;
+    if(mlt_service_filter_type == mlt_service_identify(service))
+    {
+        mlt_filter filter = MLT_FILTER(service);
+        int track = mlt_filter_get_track(filter);
+        p = mlt_service_peek_producer(service, track);
+    }
+    else
+    {
+        p = mlt_service_producer(service);
+    }
     mlt_service c = mlt_service_consumer(service);
     int i;
     switch (mlt_service_identify(c)) {

src/framework/mlt_service.c

@@ -421,6 +421,27 @@ mlt_service mlt_service_producer(mlt_service self)
         return self;
 }
 
+/** Get the N-th connected producer.
+ *
+ * \public \memberof mlt_service_s
+ * \param self a service
+ * \param index which of potentially multiple producers to this service (0 based)
+ * \return the N-th producer
+ */
+
+mlt_service mlt_service_peek_producer(mlt_service self, int index)
+{
+    mlt_service producer = NULL;
+
+    // Get the service base
+    mlt_service_base *base = self->local;
+
+    if (base->in != NULL && index < base->count)
+        producer = base->in[index];
+
+    return producer;
+}
+
 /** Associate a service to a consumer.
  *
  * Overwrites connection to any existing consumer.

src/framework/mlt_service.h

@@ -90,6 +90,7 @@ extern int mlt_service_get_frame(mlt_service self, mlt_frame_ptr frame, int inde
 extern mlt_properties mlt_service_properties(mlt_service self);
 extern mlt_service mlt_service_consumer(mlt_service self);
 extern mlt_service mlt_service_producer(mlt_service self);
+extern mlt_service mlt_service_peek_producer(mlt_service self, int index);
 extern int mlt_service_attach(mlt_service self, mlt_filter filter);
 extern int mlt_service_detach(mlt_service self, mlt_filter filter);
 extern void mlt_service_apply_filters(mlt_service self, mlt_frame frame, int index);