replay_gain: fall back to track gain if album gain is unavailable

NEWS

@@ -72,6 +72,7 @@ ver 0.16 (20??/??/??)
   - automatically convert to 16 bit samples
 * replay gain:
   - reimplemented as a filter plugin
+  - fall back to track gain if album gain is unavailable
 * log unused/unknown block parameters
 * removed the deprecated "error_file" option
 * save state when stopped

src/filter/replay_gain_filter_plugin.c

@@ -184,9 +184,10 @@ replay_gain_filter_set_info(struct filter *_filter,
 	struct replay_gain_filter *filter =
 		(struct replay_gain_filter *)_filter;
 
-	if (info != NULL)
+	if (info != NULL) {
 		filter->info = *info;
-	else
+		replay_gain_info_complete(&filter->info);
+	} else
 		replay_gain_info_init(&filter->info);
 
 	replay_gain_filter_update(filter);

src/replay_gain_info.c

@@ -35,3 +35,11 @@ replay_gain_tuple_scale(const struct replay_gain_tuple *tuple, float preamp)
 
 	return scale;
 }
+
+void
+replay_gain_info_complete(struct replay_gain_info *info)
+{
+	if (!replay_gain_tuple_defined(&info->tuples[REPLAY_GAIN_ALBUM]))
+		info->tuples[REPLAY_GAIN_ALBUM] =
+			info->tuples[REPLAY_GAIN_TRACK];
+}

src/replay_gain_info.h

@@ -63,4 +63,11 @@ replay_gain_tuple_defined(const struct replay_gain_tuple *tuple)
 float
 replay_gain_tuple_scale(const struct replay_gain_tuple *tuple, float preamp);
 
+/**
+ * Attempt to auto-complete missing data.  In particular, if album
+ * information is missing, track gain is used.
+ */
+void
+replay_gain_info_complete(struct replay_gain_info *info);
+
 #endif