diff --git a/src/lib/time.h b/src/lib/time.h
new file mode 100644
index 000000000..421736860
--- /dev/null
+++ b/src/lib/time.h
@@ -0,0 +1,191 @@
+/*
+  time.h  -  Time and frame calculations
+
+  Copyright (C)         CinelerraCV
+    2007,               Christian Thaeter <ct@pipapo.org>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#ifndef CINELERRA_TIME_H
+#define CINELERRA_TIME_H
+
+#include <sys/time.h>
+#include <time.h>
+
+#include "error.h"
+
+/*
+  this time functions are small macro like wrapers, they are all inlined for performance reasons
+  time is passed around as pointers, this pointer must never be NULL
+
+  timehandling is a delicate business, be careful of precision errors accumulating, TODO explain how to use time
+
+*/
+
+/* over or underflow (tried to make a movie which has negative length? or more than some hundreds days?) */
+CINELERRA_ERROR_DECLARE(TIME_RANGE);
+
+/*
+  Note: we measure time starting from zero,
+  time never becomes negative
+  (I didnt checked if the time types are signed)
+*/
+typedef struct timeval cinelerra_time;
+typedef cinelerra_time* CinelerraTime;
+
+/**
+ * framerates are defined as a rational number and a base time (usually 1sec (do we need this?))
+ * for example NTSC with 29.97fps is {2997, 100, {1, 0}}
+ */
+struct cinelerra_framerate_struct
+{
+  unsigned numerator;
+  unsigned denominator;
+  cinelerra_time base;
+};
+
+typedef struct cinelerra_framerate_struct cinelerra_framerate;
+typedef cinelerra_framerate CinelerraFramerate;
+
+typedef unsigned long cinelerra_frame;
+
+
+
+
+/** set a time value to zero.
+ */
+inline CinelerraTime
+cinelerra_time_clear (CinelerraTime time)
+{
+  REQUIRE (time);
+  time->tv_sec = 0;
+  time->tv_usec = 0;
+  return time;
+}
+
+/** get current time.
+ */
+inline CinelerraTime
+cinelerra_time_current (CinelerraTime time)
+{
+  REQUIRE (time);
+  /* gettime should never ever fail in a correct program */
+  if (gettimeofday (time, 0))
+    CINELERRA_DIE;
+
+  return time;
+}
+
+/** init from floating point representation.
+ */
+inline CinelerraTime
+cinelerra_time_set_double (CinelerraTime time, double fp)
+{
+  REQUIRE (time);
+  REQUIRE (fp >= 0.0);
+
+  time->tv_sec = fp;
+  time->tv_usec = (fp - time->tv_sec) * 1000000.0;
+  return time;
+}
+
+/** convert to floating point repesentation.
+ */
+inline double
+cinelerra_time_double_get (CinelerraTime time)
+{
+  REQUIRE (time);
+  double fp;
+
+  fp = time->tv_sec;
+  fp += time->tv_usec / 1000000.0;
+  return fp;
+}
+
+
+
+/** convert from floating point repesentation.
+ */
+inline CinelerraTime
+cinelerra_time_set_double (CinelerraTime time, double fp)
+{
+  REQUIRE (time);
+  REQUIRE (fp >= 0.0);
+
+  time->tv_sec = fp;
+  time->tv_usec = (fp - time->tv_sec) * 1000000.0;
+  return time;
+}
+
+/* internal function */
+inline void
+cinelerra_time_normalize (CinelerraTime time)
+{
+  if (time->tv_usec >= 1000000)
+    {
+      time->tv_sec += (time->tv_usec / 1000000);
+      time->tv_usec = (time->tv_usec % 1000000);
+    }
+}
+
+/** copy time
+ */
+inline CinelerraTime
+cinelerra_time_copy (CinelerraTime dest, const CinelerraTime src)
+{
+  REQUIRE (dest);
+  REQUIRE (src);
+  dest->tv_sec = src->tv_sec;
+  dest->tv_usec = src->tv_usec;
+  return time;
+}
+
+/** add time.
+ */
+inline CinelerraTime
+cinelerra_time_add (CinelerraTime dest, const CinelerraTime to_add)
+{
+  REQUIRE (dest);
+  REQUIRE (to_add);
+  REQUIRE (dest->tv_sec + to_add->tv_sec > dest->tv_sec, "time overflow");
+  TODO ("handling overflow as error?");
+
+  dest->tv_sec += to_add->tv_sec;
+  time->tv_usec += to_add->tv_usec;
+
+  cinelerra_time_normalize (dest);
+  return dest;
+}
+
+/** substact time.
+ */
+inline CinelerraTime
+cinelerra_time_sub (CinelerraTime dest, const CinelerraTime to_sub)
+{
+  REQUIRE (dest);
+  REQUIRE (to_sub);
+  REQUIRE (dest->tv_sec - to_sub->tv_sec < dest->tv_sec, "time underflow");
+  TODO ("handling underflow as error?");
+
+  dest->tv_sec -= to_sub->tv_sec;
+  time->tv_usec -= to_sub->tv_usec;
+
+  cinelerra_time_normalize (dest);
+  return dest;
+}
+
+
+#endif
diff --git a/tests/10timefunctions.tests b/tests/10timefunctions.tests
index 764d91fd8..dd08aca5f 100644
--- a/tests/10timefunctions.tests
+++ b/tests/10timefunctions.tests
@@ -1,9 +1,32 @@
 
-TESTING "Time functions"
+TESTING "Time functions" ./test_time
 
-PLANNED "get time"
-PLANNED "add time, normalized"
-PLANNED "substract time, normalized"
+TEST "time to float" tofloat 15 500000 <<END
+out: 15.5
+END
+
+PLANNED "float to time" fromfloat 33.6666666661 <<END
+out: 33 666667
+END
+
+PLANNED "from rational" fromrational 4 3 <<END
+out: 1 333333
+END
+
+PLANNED "get time" gettime <<END
+return: 0
+END
+
+PLANNED "add time, normalized" add 1234567890 123456789 <<END
+out: 13580 24679
+END
+
+PLANNED "substract time, normalized" sub 1234567890 123456789 <<END
+out: 11111 11101
+END
+
+PLANNED "overflow"
+PLANNED "underflow"
 
 
 # the next ones for different common framerates, check corner cases