diff --git a/src/lib/framerate.h b/src/lib/framerate.h
new file mode 100644
index 000000000..f7f075f91
--- /dev/null
+++ b/src/lib/framerate.h
@@ -0,0 +1,79 @@
+/*
+  framerate.h  -  framerate 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_FRAMERATE_H
+#define CINELERRA_FRAMERATE_H
+
+#include "lib/error.h"
+#include "lib/time.h"
+
+/**
+ * framerates are defined as a rational number
+ * for example NTSC with 29.97fps is {2997, 100}
+ */
+struct cinelerra_framerate_struct
+{
+  unsigned n; //numerator
+  unsigned d; //denominator
+};
+
+typedef struct cinelerra_framerate_struct cinelerra_framerate;
+typedef cinelerra_framerate* CinelerraFramerate;
+
+typedef unsigned long cinelerra_framepos;
+
+/**
+ * Get the frame number of a given time at a given frame rate.
+ * frame indexing starts with 1
+ */
+static inline cinelerra_framepos
+cinelerra_framerate_frame_get_time (const CinelerraFramerate framerate, CinelerraTime time)
+{
+  REQUIRE (framerate);
+  TODO ("if(!time)..");
+  /* we add a magic microsecond for rounding, because of integer truncation frames may be calculated at most 1us earlier,
+     the idea is to compensate odd framerates which fall out off microsecond precision.
+   */
+  return ((time->tv_sec * 1000000ULL + time->tv_usec + /*magic*/1) * framerate->n)/(framerate->d * 1000000ULL) + 1;
+}
+
+/**
+ * Get the start time for a frame.
+ * frame indexing starts with 1
+ */
+static inline CinelerraTime
+cinelerra_framerate_time_get_time_frame (const CinelerraFramerate framerate,
+                                         CinelerraTime time,
+                                         cinelerra_framepos frame)
+{
+  REQUIRE (framerate);
+  REQUIRE (frame>0);
+  TODO ("if(!time)..");
+
+  unsigned long long usec = (frame-1) * (framerate->d * 1000000ULL) / framerate->n;
+
+  time->tv_sec = usec / 1000000;
+  time->tv_usec = usec % 1000000;
+
+  return time;
+}
+
+#endif
diff --git a/src/lib/time.h b/src/lib/time.h
index 78f0854e1..a2dea483b 100644
--- a/src/lib/time.h
+++ b/src/lib/time.h
@@ -1,5 +1,5 @@
 /*
-  time.h  -  Time and frame calculations
+  time.h  -  Time calculations
 
   Copyright (C)         CinelerraCV
     2007,               Christian Thaeter <ct@pipapo.org>
@@ -49,22 +49,6 @@ CINELERRA_ERROR_DECLARE(TIME_NEGATIVE);
 typedef struct timeval cinelerra_time;
 typedef cinelerra_time* CinelerraTime;
 
-/**
- * framerates are defined as a rational number
- * for example NTSC with 29.97fps is {2997, 100}
- */
-struct cinelerra_framerate_struct
-{
-  unsigned numerator;
-  unsigned denominator;
-};
-
-typedef struct cinelerra_framerate_struct cinelerra_framerate;
-typedef cinelerra_framerate* CinelerraFramerate;
-
-typedef unsigned long cinelerra_frame;
-
-
 /**
  * normalize time after operations.
  * used internally
diff --git a/tests/10timefunctions.tests b/tests/10timefunctions.tests
index e2582ddc6..fe4603e0a 100644
--- a/tests/10timefunctions.tests
+++ b/tests/10timefunctions.tests
@@ -44,10 +44,76 @@ END
 PLANNED "overflow"
 PLANNED "underflow"
 
+# frame 1 begins at time 0
+TEST "time to frame NTSC frame 1 begin" ntscframefromtime 0 0 <<END
+out: 1
+END
+
+# and ends at 33365
+TEST "time to frame NTSC frame 1 end" ntscframefromtime 0 33365 <<END
+out: 1
+END
+
+# thus 33366 is start of frame 2
+TEST "time to frame NTSC frame 2 begin" ntscframefromtime 0 33366 <<END
+out: 2
+END
+
+# and 66732 is the end of frame 2
+TEST "time to frame NTSC frame 2 end" ntscframefromtime 0 66732 <<END
+out: 2
+END
+
+# this makes 66733 the start of frame 3
+TEST "time to frame NTSC frame 3 begin" ntscframefromtime 0 66733 <<END
+out: 3
+END
+
+# and 100099 the end of frame 3
+TEST "time to frame NTSC frame 3 end" ntscframefromtime 0 100099 <<END
+out: 3
+END
+
+# and 100100 the start of frame 4
+TEST "time to frame NTSC frame 4 start" ntscframefromtime 0 100100 <<END
+out: 4
+END
+
+# after 1 hour we are at frame 107893
+TEST "time to frame NTSC after 1hour" ntscframefromtime 3600 0 <<END
+out: 107893
+END
+
+# after 200 days we are at frame 517881601
+TEST "time to frame NTSC after 200 days" ntscframefromtime 17280000 0 <<END
+out: 517881601
+END
+
+
+TEST "frame to time NTSC frame 1" ntscframestart 1 <<END
+out: 0 0
+END
+
+TEST "frame to time NTSC frame 2" ntscframestart 2 <<END
+out: 0 33366
+END
+
+TEST "frame to time NTSC frame 3" ntscframestart 3 <<END
+out: 0 66733
+END
+
+TEST "frame to time NTSC frame 4" ntscframestart 4 <<END
+out: 0 100100
+END
+
+TEST "frame to time NTSC 1 hour" ntscframestart 107893 <<END
+out: 3600 0
+END
+
+TEST "frame to time NTSC 200 days" ntscframestart 517881601 <<END
+out: 17280000 0
+END
 
-# the next ones for different common framerates, check corner cases
-PLANNED "time to frame"
-PLANNED "frame to time"
 
 
 # how long are N frames on average (beware of precision!)
diff --git a/tests/time/test-time.c b/tests/time/test-time.c
index 1aaf65abf..6f2021b75 100644
--- a/tests/time/test-time.c
+++ b/tests/time/test-time.c
@@ -23,6 +23,7 @@
 #include <string.h>
 
 #include "lib/time.h"
+#include "lib/frames.h"
 
 
 CINELERRA_ERROR_DEFINE(TEST, "test error");
@@ -30,6 +31,8 @@ CINELERRA_ERROR_DEFINE(TEST, "test error");
 int
 main (int argc, char** argv)
 {
+  NOBUG_INIT;
+
   if (argc == 1)
     return 0;
 
@@ -96,6 +99,26 @@ main (int argc, char** argv)
       printf ("%lu %lu\n", (long)cinelerra_time_sec (&time1), (long)cinelerra_time_usec (&time1));
     }
 
+  if (!strcmp(argv[1], "ntscframefromtime"))
+    {
+      cinelerra_framerate ntsc = {2997, 100};
+      cinelerra_time time;
+
+      cinelerra_time_init (&time, atol (argv[2]), atol (argv[3]));
+
+      printf ("%lu\n", (long)cinelerra_framerate_frame_get_time (&ntsc, &time));
+    }
+
+  if (!strcmp(argv[1], "ntscframestart"))
+    {
+      cinelerra_framerate ntsc = {2997, 100};
+      cinelerra_time time;
+
+      cinelerra_framerate_time_get_time_frame (&ntsc, &time, atol (argv[2]));
+
+      printf ("%lu %lu\n", (long)cinelerra_time_sec(&time), (long)cinelerra_time_usec(&time));
+    }
+
 
   return 0;
 }