Add support for NTSC drop-frame timecode.

src/lib/time.c

@@ -88,6 +88,24 @@ lumiera_build_time_fps (float fps, uint frames, uint secs, uint mins, uint hours
   return time;
 }
 
+gavl_time_t
+lumiera_build_time_ntsc_drop (uint frames, uint secs, uint mins, uint hours)
+{
+  REQUIRE (mins < 60);
+  REQUIRE (secs < 60);
+  REQUIRE (frames < 30);
+  REQUIRE_IF (secs == 0 && mins % 10, frames >= 2, "non-existent frame in NTSC drop-frame");
+
+  int total_mins = 60 * hours + mins;
+  int total_frames  = 108000 * hours
+                    + 1800 * mins
+                    + 30 * secs
+                    + frames
+                    - 2 * (total_mins - total_mins / 10);
+
+  return (total_frames / 29.97f) * 1000 * GAVL_TIME_SCALE_MS;
+}
+
 int
 lumiera_time_hours (gavl_time_t time)
 {
@@ -125,3 +143,44 @@ lumiera_time_frame_count (gavl_time_t time, float fps)
 
   return roundf((time / GAVL_TIME_SCALE_MS / 1000.0f) * fps);
 }
+
+/**
+ * This function is used in the NTSC drop-frame functions to avoid code
+ * repetition.
+ * @return the frame number for given time
+ */
+static int
+ntsc_drop_get_frame_number (gavl_time_t time)
+{
+  int frame = lumiera_time_frame_count (time, NTSC_DROP_FRAME_FPS);
+
+  int d = frame / 17982; // 17982 = 600 * 29.97
+  int m = frame % 17982; // 17982 = 600 * 29.97
+
+  return frame + 18*d + 2*((m - 2) / 1798); // 1798 = 60 * 29.97
+}
+
+int
+lumiera_time_ntsc_drop_frames (gavl_time_t time)
+{
+  return ntsc_drop_get_frame_number(time) % 30;
+}
+
+int
+lumiera_time_ntsc_drop_seconds (gavl_time_t time)
+{
+  return ntsc_drop_get_frame_number(time) / 30 % 60;
+}
+
+int
+lumiera_time_ntsc_drop_minutes (gavl_time_t time)
+{
+  return ntsc_drop_get_frame_number(time) / 30 / 60 % 60;
+}
+
+int
+lumiera_time_ntsc_drop_hours (gavl_time_t time)
+{
+  return ntsc_drop_get_frame_number(time) / 30 / 60 / 60 % 24;
+}
+

src/lib/time.h

@@ -25,6 +25,8 @@
 #include <inttypes.h>
 #include <gavl/gavl.h>
 
+#define NTSC_DROP_FRAME_FPS 29.97
+
 /**
  * Formats a time in a safeclib tmpbuf in HH:MM:SS:mmm format.
  * @param size maximal length for the string
@@ -55,6 +57,18 @@ lumiera_build_time (long millis, uint secs, uint mins, uint hours);
 gavl_time_t
 lumiera_build_time_fps (float fps, uint frames, uint secs, uint mins, uint hours);
 
+/**
+ * Builds a time value by summing up the given components.
+ * The components are interpreted as a NTSC drop-frame timecode.
+ * @param frames number of frames
+ * @param secs number of seconds
+ * @param mins number of minutes
+ * @param hours number of hours
+ * You must take care not to specify time codes that are illegal NTSC drop-frame times.
+ */
+gavl_time_t
+lumiera_build_time_ntsc_drop (uint frames, uint secs, uint mins, uint hours);
+
 /**
  * Get the hour part of given time.
  * @param time the time value to use
@@ -99,4 +113,32 @@ lumiera_time_frames (gavl_time_t time, float fps);
 int
 lumiera_time_frame_count (gavl_time_t time, float fps);
 
+/**
+ * Get the frame part of given time, using NTSC drop-frame timecode.
+ * @param time the time value to use
+ */
+int
+lumiera_time_ntsc_drop_frames (gavl_time_t time);
+
+/**
+ * Get the second part of given time, using NTSC drop-frame timecode.
+ * @param time the time value to use
+ */
+int
+lumiera_time_ntsc_drop_seconds (gavl_time_t time);
+
+/**
+ * Get the minute part of given time, using NTSC drop-frame timecode.
+ * @param time the time value to use
+ */
+int
+lumiera_time_ntsc_drop_minutes (gavl_time_t time);
+
+/**
+ * Get the hour part of given time, using NTSC drop-frame timecode.
+ * @param time the time value to use
+ */
+int
+lumiera_time_ntsc_drop_hours (gavl_time_t time);
+
 #endif

tests/15time.tests

@@ -7,3 +7,6 @@ END
 
 TEST "frame rate dependent calculations" fps <<END
 END
+
+TEST "ntsc drop-frame calculations" ntsc_drop_frame << END
+END

tests/library/test-time.c

@@ -89,4 +89,85 @@ TEST (fps)
   CHECK (lumiera_time_frame_count (t, FPS+5) == 409498);
 }
 
+/*
+ * 3. NTSC drop-frame calculations.
+ */
+
+TEST (ntsc_drop_frame)
+{
+  // Make sure frame 0 begins at 0
+  gavl_time_t t = lumiera_build_time_ntsc_drop (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);
+
+  // Use some arbitrary value to test with
+  const int FRAMES = 15;
+  const int SECONDS = 20;
+  const int MINUTES = 55;
+  const int HOURS = 3;
+  const float FPS = 24.0;
+
+  t = lumiera_build_time_ntsc_drop (FRAMES, SECONDS, MINUTES, HOURS);
+
+  CHECK (lumiera_time_millis (t)             == 487);
+  CHECK (lumiera_time_seconds (t)            == SECONDS);
+  CHECK (lumiera_time_minutes (t)            == MINUTES);
+  CHECK (lumiera_time_hours (t)              == HOURS);
+
+  // Check standard frame calculations to verify build_time_ntsc_drop
+  CHECK (lumiera_time_frames (t, FPS)        == 11);
+  CHECK (lumiera_time_frames (t, FPS+5)      == 14);
+  CHECK (lumiera_time_frame_count (t, FPS)   == 338892);
+  CHECK (lumiera_time_frame_count (t, FPS+5) == 409494);
+
+  // Frames for NTSC drop
+  CHECK (lumiera_time_ntsc_drop_frames (t)                 == 15);
+  CHECK (lumiera_time_frame_count (t, NTSC_DROP_FRAME_FPS) == 423191);  
+
+  // Make sure we get back the same times.  These tests are perhaps overly exhaustive.
+  int min;
+  int sec;
+  int frame;
+  int hrs;
+  for (hrs = 0; hrs <= 24; hrs += 6)
+    for (min = 0; min <= 59; min += 8)
+      for (sec = 0; sec <= 59; sec += 8)
+        for (frame = 0; frame <= 29; frame++)
+          {
+            // Skip dropped frames
+            if (min % 10 && sec == 0 && frame < 2)
+              continue;
+
+            t = lumiera_build_time_ntsc_drop(frame, sec, min, hrs);
+
+            /* ECHO ("%02d:%02d:%02d.%02d", */
+            /*       lumiera_time_ntsc_drop_hours (t), */
+            /*       lumiera_time_ntsc_drop_minutes (t), */
+            /*       lumiera_time_ntsc_drop_seconds (t), */
+            /*       lumiera_time_ntsc_drop_frames (t)); */
+
+            CHECK (lumiera_time_ntsc_drop_frames (t)  == frame);
+            CHECK (lumiera_time_ntsc_drop_seconds (t) == sec);
+            CHECK (lumiera_time_ntsc_drop_minutes (t) == min);
+            CHECK (lumiera_time_ntsc_drop_hours (t)   == hrs % 24);
+          }
+
+  // Make sure we do not get non-existent frames
+  int i;
+  for (i = 0; i < 59; i++)
+    {
+      int frame = (i % 10 == 0) ? 0 : 2;
+      t = lumiera_build_time_ntsc_drop (frame, 0, i, 0);
+      CHECK (lumiera_time_ntsc_drop_frames (t) == frame);
+    }
+}
+
 TESTS_END