diff --git a/TODO.txt b/TODO.txt
index 02786ca..fa1b668 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -1,5 +1,6 @@
 =========== GENERAL ==============
 
+- add time slow down setting
 - the horizon on background seems too low? maybe add setting to shift it a bit?
 - add argc/argv to gameInit? could be used to quickly start maps, verify
   replays etc.
diff --git a/racing.h b/racing.h
index 8bd4ef5..7381d83 100644
--- a/racing.h
+++ b/racing.h
@@ -1,5 +1,22 @@
 /**
-  racing module: implements the racing physics and logic.
+  Racing module: implements the racing physics and logic as well as replays and
+  other related things.
+
+  Some comments:
+  - Replays are internally stored as follows: the replay consists of 16 bit
+    words representing changes in input at specific frame. In lowest 4 bits the
+    new input state is recorded, the remaining 12 bits record physics frame
+    offset against the previous input change. If the 12 bits don't suffice
+    because the offset is too big (input didn't change for more than 2^12
+    frames), there must simply be inserted an extra word that just copies the
+    current input state.
+  - Replay text format: first there is hexadeciaml hash of the map (exactly 8
+    characters), then the name of the map follows immediately, then the
+    character ';', then the replay data, i.e. the sries of 16 bit words in
+    hexadecimal. The blocks (but nothing else) may be preceeded or followed by
+    blank characters. All hexadecimal letters must be lowercase. The word
+    00000000 may optinally be used to terminate the replay, the rest of the
+    string will be ignored.
 */
 
 #ifndef _LCR_RACING_H
@@ -86,6 +103,12 @@ struct
   uint8_t carNotOKCount;
 } LCR_racing;
 
+struct
+{
+  uint16_t eventCount;
+  uint16_t events[LCR_SETTING_REPLAY_MAX_SIZE]; 
+} LCR_currentReplay;
+
 /**
   Gets times of the run in milliseconds.
 */
diff --git a/settings.h b/settings.h
index 62ed9a9..d14b282 100644
--- a/settings.h
+++ b/settings.h
@@ -193,4 +193,10 @@
   #define LCR_SETTING_MAP_CHUNK_RELOAD_INTERVAL 16
 #endif
 
+#ifndef LCR_SETTING_REPLAY_MAX_SIZE
+  /** Says the maximum size of a replay (in replay events). The value 0 will
+    turn replays off completely. */
+  #define LCR_SETTING_REPLAY_MAX_SIZE 256
+#endif
+
 #endif // guard