diff --git a/src/lib/time.c b/src/lib/time.c
index 3748d7e8d..337456db3 100644
--- a/src/lib/time.c
+++ b/src/lib/time.c
@@ -22,6 +22,7 @@
 #include <nobug.h>
 #include "lib/time.h"
 #include "lib/tmpbuf.h"
+#include <math.h>
 
 /* GAVL_TIME_SCALE is the correct factor or dividend when using gavl_time_t for
  * units of whole seconds from gavl_time_t.  Since we want to use milliseconds,
@@ -58,8 +59,12 @@ lumiera_tmpbuf_print_time (gavl_time_t time)
 }
 
 gavl_time_t
-lumiera_build_time(long millis, uint secs, uint mins, uint hours)
+lumiera_build_time (long millis, uint secs, uint mins, uint hours)
 {
+  REQUIRE (millis >= 0 && millis <= 999);
+  REQUIRE (mins < 60);
+  REQUIRE (secs < 60);
+
   gavl_time_t time = millis
                    + 1000 * secs
                    + 1000 * 60 * mins
@@ -68,39 +73,55 @@ lumiera_build_time(long millis, uint secs, uint mins, uint hours)
   return time;
 }
 
+gavl_time_t
+lumiera_build_time_fps (float fps, uint frames, uint secs, uint mins, uint hours)
+{
+  REQUIRE (mins < 60);
+  REQUIRE (secs < 60);
+  REQUIRE (frames < fps);
+
+  gavl_time_t time = frames * (1000.0 / fps)
+                   + 1000 * secs
+                   + 1000 * 60 * mins
+                   + 1000 * 60 * 60 * hours;
+  time *= GAVL_TIME_SCALE_MS;
+  return time;
+}
+
 int
-lumiera_time_hours(gavl_time_t time)
+lumiera_time_hours (gavl_time_t time)
 {
   return time / GAVL_TIME_SCALE_MS / 1000 / 60 / 60;
 }
 
 int
-lumiera_time_minutes(gavl_time_t time)
+lumiera_time_minutes (gavl_time_t time)
 {
   return (time / GAVL_TIME_SCALE_MS / 1000 / 60) % 60;
 }
 
 int
-lumiera_time_seconds(gavl_time_t time)
+lumiera_time_seconds (gavl_time_t time)
 {
   return (time / GAVL_TIME_SCALE_MS / 1000) % 60;
 }
 
 int
-lumiera_time_millis(gavl_time_t time)
+lumiera_time_millis (gavl_time_t time)
 {
   return (time / GAVL_TIME_SCALE_MS) % 1000;
 }
 
 int
-lumiera_time_frames(gavl_time_t time, float fps)
+lumiera_time_frames (gavl_time_t time, float fps)
 {
   return (fps * (lumiera_time_millis(time))) / 1000;
 }
 
 int
-lumiera_time_frame_count(gavl_time_t time, float fps)
+lumiera_time_frame_count (gavl_time_t time, float fps)
 {
-  int ms = (time / GAVL_TIME_SCALE_MS);
-  return fps * ms / 1000;
+  REQUIRE (fps > 0);
+
+  return roundf((time / GAVL_TIME_SCALE_MS / 1000.0f) * fps);
 }
diff --git a/src/lib/time.h b/src/lib/time.h
index 4a3812238..df7b1dfb0 100644
--- a/src/lib/time.h
+++ b/src/lib/time.h
@@ -36,43 +36,67 @@ lumiera_tmpbuf_print_time (gavl_time_t time);
 
 /**
  * Builds a time value by summing up the given components.
+ * @param millis number of milliseconds
+ * @param secs number of seconds
+ * @param mins number of minutes
+ * @param hours number of hours
  */
 gavl_time_t
 lumiera_build_time (long millis, uint secs, uint mins, uint hours);
 
 /**
- * Get the hour part of given time.
+ * Builds a time value by summing up the given components.
+ * @param fps the frame rate to be used
+ * @param frames number of frames
+ * @param secs number of seconds
+ * @param mins number of minutes
+ * @param hours number of hours
  */
-int lumiera_time_hours(gavl_time_t time);
+gavl_time_t
+lumiera_build_time_fps (float fps, uint frames, uint secs, uint mins, uint hours);
+
+/**
+ * Get the hour part of given time.
+ * @param time the time value to use
+ */
+int
+lumiera_time_hours (gavl_time_t time);
 
 /**
  * Get the minute part of given time.
+ * @param time the time value to use
  */
-int lumiera_time_minutes(gavl_time_t time);
+int
+lumiera_time_minutes (gavl_time_t time);
 
 /**
  * Get the seconds part of given time.
+ * @param time the time value to use
  */
-int lumiera_time_seconds(gavl_time_t time);
+int
+lumiera_time_seconds (gavl_time_t time);
 
 /**
  * Get the milliseconds part of given time.
+ * @param time the time value to use
  */
-int lumiera_time_millis(gavl_time_t time);
+int
+lumiera_time_millis (gavl_time_t time);
 
 /**
- * Get the frame part of given time, using the given number of frames.
- * @param gavl_time_t the time we are interested in converting
- * @param fps Frame rate (float for now, but should be a rational)
+ * Get the frame part of given time, using the given fps.
+ * @param time the time value to use
+ * @param fps frame rate (float for now, but should be a rational)
  */
-int lumiera_time_frames(gavl_time_t time, float fps);
+int
+lumiera_time_frames (gavl_time_t time, float fps);
 
 /**
- * Get the frame count for the given time.
- * @param gavl_time_t the time we are interested in converting
- * @param fps Frame rate (float for now, but should be a rational)
+ * Get the frame count for the given time, using the given fps.
+ * @param time the time value to use
+ * @param fps frame rate (float for now, but should be a rational)
  */
-int lumiera_time_frame_count(gavl_time_t time, float fps);
+int
+lumiera_time_frame_count (gavl_time_t time, float fps);
 
 #endif
-
diff --git a/tests/15time.tests b/tests/15time.tests
index 0cb57ddcc..30ae5515c 100644
--- a/tests/15time.tests
+++ b/tests/15time.tests
@@ -4,3 +4,6 @@ TEST "basic functionality" basic <<END
 err: ECHO: .*: 00:00:00.000
 err: ECHO: .*: 03:55:20.700
 END
+
+TEST "frame rate dependent calculations" fps <<END
+END
diff --git a/tests/library/test-time.c b/tests/library/test-time.c
index fc0f4f343..6bb0d6c74 100644
--- a/tests/library/test-time.c
+++ b/tests/library/test-time.c
@@ -28,6 +28,7 @@ typedef unsigned int uint;
 
 TESTS_BEGIN
 
+const int FRAMES = 15;
 const int MILLIS = 700;
 const int SECONDS = 20;
 const int MINUTES = 55;
@@ -38,35 +39,54 @@ const float FPS = 24.0;
  * 1. Basic functionality
  */
 
-TEST (basic) {
+TEST (basic)
+{
   // Zero
-  gavl_time_t t = lumiera_build_time(0,0,0,0);
+  gavl_time_t t = lumiera_build_time (0,0,0,0);
 
-  CHECK ((gavl_time_t) t                    == 0);
-  CHECK (lumiera_time_millis(t)             == 0);
-  CHECK (lumiera_time_seconds(t)            == 0);
-  CHECK (lumiera_time_minutes(t)            == 0);
-  CHECK (lumiera_time_hours(t)              == 0);
-  CHECK (lumiera_time_frames(t, FPS)        == 0);
-  CHECK (lumiera_time_frames(t, FPS+5)      == 0);
-  CHECK (lumiera_time_frame_count(t, FPS)   == 0);
-  CHECK (lumiera_time_frame_count(t, FPS+5) == 0);
+  CHECK ((gavl_time_t) t                     == 0);
+  CHECK (lumiera_time_millis (t)             == 0);
+  CHECK (lumiera_time_seconds (t)            == 0);
+  CHECK (lumiera_time_minutes (t)            == 0);
+  CHECK (lumiera_time_hours (t)              == 0);
+  CHECK (lumiera_time_frames (t, FPS)        == 0);
+  CHECK (lumiera_time_frames (t, FPS+5)      == 0);
+  CHECK (lumiera_time_frame_count (t, FPS)   == 0);
+  CHECK (lumiera_time_frame_count (t, FPS+5) == 0);
 
-  ECHO ("%s", lumiera_tmpbuf_print_time(t));
+  ECHO ("%s", lumiera_tmpbuf_print_time (t));
 
   // Non-zero
-  t = lumiera_build_time(MILLIS, SECONDS, MINUTES, HOURS);
+  t = lumiera_build_time (MILLIS, SECONDS, MINUTES, HOURS);
 
-  CHECK (lumiera_time_millis(t)             == MILLIS);
-  CHECK (lumiera_time_seconds(t)            == SECONDS);
-  CHECK (lumiera_time_minutes(t)            == MINUTES);
-  CHECK (lumiera_time_hours(t)              == HOURS);
-  CHECK (lumiera_time_frames(t, FPS)        == (int)((FPS * MILLIS) / 1000));
-  CHECK (lumiera_time_frames(t, FPS+5)      == (int)(((FPS+5) * MILLIS) / 1000));
-  CHECK (lumiera_time_frame_count(t, FPS)   == 338896);
-  CHECK (lumiera_time_frame_count(t, FPS+5) == 409500);
+  CHECK (lumiera_time_millis (t)             == MILLIS);
+  CHECK (lumiera_time_seconds (t)            == SECONDS);
+  CHECK (lumiera_time_minutes (t)            == MINUTES);
+  CHECK (lumiera_time_hours (t)              == HOURS);
+  CHECK (lumiera_time_frames (t, FPS)        == (int)((FPS * MILLIS) / 1000));
+  CHECK (lumiera_time_frames (t, FPS+5)      == (int)(((FPS+5) * MILLIS) / 1000));
+  CHECK (lumiera_time_frame_count (t, FPS)   == 338897);
+  CHECK (lumiera_time_frame_count (t, FPS+5) == 409500);
 
-  ECHO ("%s", lumiera_tmpbuf_print_time(t));
+  ECHO ("%s", lumiera_tmpbuf_print_time (t));
+}
+
+/*
+ * 2. Frame rate dependent calculations.
+ */
+
+TEST (fps)
+{
+  gavl_time_t t = lumiera_build_time_fps (FPS, FRAMES, SECONDS, MINUTES, HOURS);
+
+  CHECK (lumiera_time_millis (t)             == (int)(FRAMES * (1000.0 / FPS)));
+  CHECK (lumiera_time_seconds (t)            == SECONDS);
+  CHECK (lumiera_time_minutes (t)            == MINUTES);
+  CHECK (lumiera_time_hours (t)              == HOURS);
+  CHECK (lumiera_time_frames (t, FPS)        == FRAMES);
+  CHECK (lumiera_time_frames (t, FPS+5)      == (int)(((FPS+5) * 625) / 1000));
+  CHECK (lumiera_time_frame_count (t, FPS)   == 338895);
+  CHECK (lumiera_time_frame_count (t, FPS+5) == 409498);
 }
 
 TESTS_END