fix MTC slave+generator for non integer quarter_frame_duration

e.g. 44.1k [SPS] / 30 [fps] / 4 [MTC-frames per timecode-frame] = 367.5 [samples per MTC-frame]

git-svn-id: svn://localhost/ardour2/branches/3.0@14115 d708f5d6-7413-0410-9779-e7cbd77b26cf

1 files changed, 5 insertions, 3 deletions

diff --git a/libs/ardour/mtc_slave.cc b/libs/ardour/mtc_slave.cc
index b3992598d3..a1005ff953 100644
--- a/libs/ardour/mtc_slave.cc
+++ b/libs/ardour/mtc_slave.cc
@@ -56,6 +56,7 @@ MTC_Slave::MTC_Slave (Session& s, MIDI::Port& p)
 	reset_pending = 0;
 	reset_position = false;
 	mtc_frame = 0;
+	mtc_frame_dll = 0;
 	engine_dll_initstate = 0;
 	busy_guard1 = busy_guard2 = 0;
 
@@ -261,16 +262,16 @@ MTC_Slave::update_mtc_qtr (Parser& /*p*/, int which_qtr, framepos_t now)
 {
 	busy_guard1++;
 	const double qtr_d = quarter_frame_duration;
-	const framepos_t qtr = rint(qtr_d);
 
-	mtc_frame += qtr * transport_direction;
+	mtc_frame_dll += qtr_d * (double) transport_direction;
+	mtc_frame = rint(mtc_frame_dll);
 
 	DEBUG_TRACE (DEBUG::MTC, string_compose ("qtr frame %1 at %2 -> mtc_frame: %3\n", which_qtr, now, mtc_frame));
 
 	double mtc_speed = 0;
 	if (first_mtc_timestamp != 0) {
 		/* update MTC DLL and calculate speed */
-		const double e = mtc_frame - (double(transport_direction) * (double(now) - double(current.timestamp) + t0));
+		const double e = mtc_frame_dll - (double)transport_direction * ((double)now - (double)current.timestamp + t0);
 		t0 = t1;
 		t1 += b * e + e2;
 		e2 += c * e;
@@ -463,6 +464,7 @@ MTC_Slave::update_mtc_time (const byte *msg, bool was_full, framepos_t now)
 			if (first_mtc_timestamp == 0 || current.timestamp == 0) {
 				first_mtc_timestamp = now;
 				init_mtc_dll(mtc_frame, qtr);
+				mtc_frame_dll = mtc_frame;
 			}
 			current.guard1++;
 			current.position = mtc_frame;