diff --git a/include/villas/format.hpp b/include/villas/format.hpp
index 31af72165..f313e2e8a 100644
--- a/include/villas/format.hpp
+++ b/include/villas/format.hpp
@@ -55,12 +55,16 @@ public:
 
   virtual void start() {}
 
+  virtual void reset() {}
+
   virtual void parse(json_t *json);
 
   virtual int print(FILE *f, const struct Sample *const smps[], unsigned cnt);
 
   virtual int scan(FILE *f, struct Sample *const smps[], unsigned cnt);
 
+  virtual void printMetadata(FILE *f, json_t *json) {}
+
   /* Print \p cnt samples from \p smps into buffer \p buf of length \p len.
    *
    * @param buf[out]	The buffer which should be filled with serialized data.
diff --git a/include/villas/formats/line.hpp b/include/villas/formats/line.hpp
index f4b1c0aeb..eb05e13f8 100644
--- a/include/villas/formats/line.hpp
+++ b/include/villas/formats/line.hpp
@@ -38,6 +38,10 @@ public:
     header_printed = true;
   }
 
+  virtual void reset() { header_printed = false; }
+
+  virtual void printMetadata(FILE *f, json_t *json);
+
   virtual int sprint(char *buf, size_t len, size_t *wbytes,
                      const struct Sample *const smps[], unsigned cnt);
   virtual int sscan(const char *buf, size_t len, size_t *rbytes,
diff --git a/lib/formats/column.cpp b/lib/formats/column.cpp
index f3318754f..4bf854645 100644
--- a/lib/formats/column.cpp
+++ b/lib/formats/column.cpp
@@ -137,7 +137,7 @@ void ColumnLineFormat::header(FILE *f, const SignalList::Ptr sigs) {
     return;
 
   if (comment)
-    fprintf(f, "%c", comment);
+    fprintf(f, "%c ", comment);
 
   if (flags & (int)SampleFlags::HAS_TS_ORIGIN)
     fprintf(f, "secs%cnsecs%c", separator, separator);
diff --git a/lib/formats/line.cpp b/lib/formats/line.cpp
index 07fb20115..1e15715a8 100644
--- a/lib/formats/line.cpp
+++ b/lib/formats/line.cpp
@@ -163,3 +163,7 @@ void LineFormat::parse(json_t *json) {
 
   Format::parse(json);
 }
+
+void LineFormat::printMetadata(FILE *f, json_t *json) {
+  fprintf(f, "# %s\n", json_dumps(json, 0));
+}