diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index ed81d9a5b..56dff6cef 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -29,5 +29,6 @@ libcin3_a_SOURCES = \
 noinst_HEADERS += \
 	$(libcin3_a_srcdir)/plugin.h \
 	$(libcin3_a_srcdir)/error.h \
-	$(libcin3_a_srcdir)/time.h
+	$(libcin3_a_srcdir)/time.h \
+	$(libcin3_a_srcdir)/framerate.h
 
diff --git a/src/lib/framerate.h b/src/lib/framerate.h
index f7f075f91..ef3561f87 100644
--- a/src/lib/framerate.h
+++ b/src/lib/framerate.h
@@ -27,7 +27,7 @@
 
 /**
  * framerates are defined as a rational number
- * for example NTSC with 29.97fps is {2997, 100}
+ * for example NTSC with 30000/1001fps
  */
 struct cinelerra_framerate_struct
 {
@@ -68,7 +68,7 @@ cinelerra_framerate_time_get_time_frame (const CinelerraFramerate framerate,
   REQUIRE (frame>0);
   TODO ("if(!time)..");
 
-  unsigned long long usec = (frame-1) * (framerate->d * 1000000ULL) / framerate->n;
+  unsigned long long usec = ((frame-1) * framerate->d * 1000000ULL - (/*magic*/frame>1?1:0)) / framerate->n;
 
   time->tv_sec = usec / 1000000;
   time->tv_usec = usec % 1000000;
diff --git a/tests/10timefunctions.tests b/tests/10timefunctions.tests
index fe4603e0a..835e1a918 100644
--- a/tests/10timefunctions.tests
+++ b/tests/10timefunctions.tests
@@ -69,16 +69,6 @@ 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
@@ -86,7 +76,7 @@ END
 
 # after 200 days we are at frame 517881601
 TEST "time to frame NTSC after 200 days" ntscframefromtime 17280000 0 <<END
-out: 517881601
+out: 517882118
 END
 
 
@@ -98,24 +88,40 @@ 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
+TEST "frame->time->frame conversion 2" ntscframecheck 2 <<END
+out: frame 2 1
 END
 
-TEST "frame to time NTSC frame 4" ntscframestart 4 <<END
-out: 0 100100
+TEST "frame->time->frame conversion 3" ntscframecheck 3 <<END
+out: frame 3 2
+END
+TEST "frame->time->frame conversion 4" ntscframecheck 4 <<END
+out: frame 4 3
+END
+TEST "frame->time->frame conversion 5" ntscframecheck 5 <<END
+out: frame 5 4
+END
+TEST "frame->time->frame conversion 6" ntscframecheck 6 <<END
+out: frame 6 5
+END
+TEST "frame->time->frame conversion 7" ntscframecheck 7 <<END
+out: frame 7 6
+END
+TEST "frame->time->frame conversion 8" ntscframecheck 8 <<END
+out: frame 8 7
+END
+TEST "frame->time->frame conversion 9" ntscframecheck 9 <<END
+out: frame 9 8
 END
 
-TEST "frame to time NTSC 1 hour" ntscframestart 107893 <<END
-out: 3600 0
+TEST "frame->time->frame conversion 100000" ntscframecheck 100000 <<END
+out: frame 100000 99999
 END
 
-TEST "frame to time NTSC 200 days" ntscframestart 517881601 <<END
-out: 17280000 0
+TEST "frame->time->frame conversion 999999" ntscframecheck 999999 <<END
+out: frame 999999 999998
 END
 
-
-
 # how long are N frames on average (beware of precision!)
 PLANNED "frame duration"
 
diff --git a/tests/time/test-time.c b/tests/time/test-time.c
index 6f2021b75..6bbc84833 100644
--- a/tests/time/test-time.c
+++ b/tests/time/test-time.c
@@ -23,7 +23,7 @@
 #include <string.h>
 
 #include "lib/time.h"
-#include "lib/frames.h"
+#include "lib/framerate.h"
 
 
 CINELERRA_ERROR_DEFINE(TEST, "test error");
@@ -101,7 +101,7 @@ main (int argc, char** argv)
 
   if (!strcmp(argv[1], "ntscframefromtime"))
     {
-      cinelerra_framerate ntsc = {2997, 100};
+      cinelerra_framerate ntsc = {30000, 1001};
       cinelerra_time time;
 
       cinelerra_time_init (&time, atol (argv[2]), atol (argv[3]));
@@ -111,7 +111,7 @@ main (int argc, char** argv)
 
   if (!strcmp(argv[1], "ntscframestart"))
     {
-      cinelerra_framerate ntsc = {2997, 100};
+      cinelerra_framerate ntsc = {30000, 1001};
       cinelerra_time time;
 
       cinelerra_framerate_time_get_time_frame (&ntsc, &time, atol (argv[2]));
@@ -119,6 +119,28 @@ main (int argc, char** argv)
       printf ("%lu %lu\n", (long)cinelerra_time_sec(&time), (long)cinelerra_time_usec(&time));
     }
 
+  if (!strcmp(argv[1], "ntscframecheck"))
+    {
+      cinelerra_framerate ntsc = {30000, 1001};
+      cinelerra_time time1;
+      cinelerra_time time2;
+      cinelerra_framepos frame;
+
+      cinelerra_framepos frame1;
+      cinelerra_framepos frame2;
+
+      frame = atol (argv[2]);
+
+
+      cinelerra_framerate_time_get_time_frame (&ntsc, &time1, frame);
+      printf("frame %lu ", frame1 = cinelerra_framerate_frame_get_time (&ntsc, &time1));
+
+      cinelerra_time_init (&time2, 0, 1);
+      cinelerra_time_sub (&time1, &time2);
+      printf("%lu\n", frame2 = cinelerra_framerate_frame_get_time (&ntsc, &time1));
+
+      ENSURE (frame1 == frame2+1);
+    }
 
   return 0;
 }