tdm_error tdm_layer_set_buffer(tdm_layer *layer, tdm_buffer *buffer); // layer has only one buffer
tdm_error tdm_layer_unset_buffer(tdm_layer *layer);
tdm_error tdm_layer_is_usable(tdm_layer *layer, unsigned int *usable);
+tdm_error tdm_layer_set_video_pos(tdm_layer *layer, int zpos);
tdm_capture *tdm_layer_create_capture(tdm_layer *layer, tdm_error *error);