diff --git a/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Music.kt b/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Music.kt
index 8a8d3b6da..196317c07 100644
--- a/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Music.kt
+++ b/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Music.kt
@@ -125,11 +125,19 @@ internal class Midi2TrackMerger(private var source: Midi2Music) {
     internal fun getMergedMessages(): Midi2Music {
         var l = mutableListOf<Pair<Int,Ump>>()
 
+        var jrTimestampShowedUp = false
+
         for (track in source.tracks) {
             var absTime = 0
             for (mev in track.messages) {
-                if (mev.isJRTimestamp)
+                if (mev.isDeltaClockstamp) {
+                    if (jrTimestampShowedUp)
+                        throw UnsupportedOperationException("The source contains both JR Timestamp and Delta Clockstamp, which is not supported.")
+                    absTime += mev.deltaClockstamp
+                } else if (mev.isJRTimestamp) {
                     absTime += mev.jrTimestamp
+                    jrTimestampShowedUp = true
+                }
                 else
                     l.add(Pair(absTime, mev))
             }
@@ -183,8 +191,13 @@ internal class Midi2TrackMerger(private var source: Midi2Music) {
         while (i < l.size) {
             if (i + 1 < l.size) {
                 val delta = l[i + 1].first - l[i].first
-                if (delta > 0)
-                    l3.add(Ump(UmpFactory.deltaClockstamp(delta)))
+                if (delta > 0) {
+                    if (jrTimestampShowedUp) {
+                        l3.addAll(UmpFactory.jrTimestamps(delta.toLong()).map { Ump(it) })
+                    } else {
+                        l3.add(Ump(UmpFactory.deltaClockstamp(delta)))
+                    }
+                }
                 timeAbs += delta
             }
             l3.add(l[i].second)
@@ -245,9 +258,16 @@ open class Midi2TrackSplitter(private val source: MutableList<Ump>) {
 
     fun split(): Midi2Music {
         var totalDeltaTime = 0
+        var jrTimestampShowedUp = false
         for (e in source) {
-            if (e.isJRTimestamp)
+            if (e.isDeltaClockstamp) {
+                if (jrTimestampShowedUp)
+                    throw UnsupportedOperationException("The source contains both JR Timestamp and Delta Clockstamp, which is not supported.")
+                totalDeltaTime += e.deltaClockstamp
+            } else if (e.isJRTimestamp) {
+                jrTimestampShowedUp = true
                 totalDeltaTime += e.jrTimestamp
+            }
             val id: Int = getTrackId(e)
             getTrack(id).addMessage(totalDeltaTime, e)
         }
diff --git a/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Player.kt b/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Player.kt
index 546ef4515..92bf3461b 100644
--- a/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Player.kt
+++ b/ktmidi/src/commonMain/kotlin/dev/atsushieno/ktmidi/Midi2Player.kt
@@ -13,8 +13,13 @@ internal class Midi2EventLooper(var messages: List<Ump>, private val timer: Midi
     override fun getNextMessage() = messages[eventIdx]
 
     override fun getContextDeltaTimeInSeconds(m: Ump): Double {
-        return if (deltaTimeSpec > 0)
-            if (m.isJRTimestamp) currentTempo.toDouble() / 1_000_000 * m.jrTimestamp / deltaTimeSpec / tempoRatio else 0.0
+        return if (deltaTimeSpec > 0) {
+            if (m.isDeltaClockstamp)
+                currentTempo.toDouble() / 1_000_000 * m.deltaClockstamp / deltaTimeSpec / tempoRatio
+            else if (m.isJRTimestamp)
+                currentTempo.toDouble() / 1_000_000 * m.jrTimestamp / deltaTimeSpec / tempoRatio
+            else 0.0
+        }
         else
             if (m.isJRTimestamp) m.jrTimestamp * 1.0 / 31250 else 0.0
     }
@@ -233,7 +238,12 @@ internal class Midi2SimpleSeekProcessor(ticks: Int) : SeekProcessor<Ump> {
     private var current: Int = 0
 
     override fun filterMessage(message: Ump): SeekFilterResult {
-        current += if(message.isJRTimestamp) message.jrTimestamp else 0
+        current +=
+            if(message.isDeltaClockstamp)
+                message.deltaClockstamp
+            else if(message.isJRTimestamp)
+                message.jrTimestamp
+            else 0
         if (current >= seekTo)
             return SeekFilterResult.PASS_AND_TERMINATE
         when (message.statusCode) {
diff --git a/ktmidi/src/commonTest/kotlin/dev/atsushieno/ktmidi/UmpTranslatorTest.kt b/ktmidi/src/commonTest/kotlin/dev/atsushieno/ktmidi/UmpTranslatorTest.kt
index d2ae8ccdd..b0b06c46c 100644
--- a/ktmidi/src/commonTest/kotlin/dev/atsushieno/ktmidi/UmpTranslatorTest.kt
+++ b/ktmidi/src/commonTest/kotlin/dev/atsushieno/ktmidi/UmpTranslatorTest.kt
@@ -8,14 +8,12 @@ class UmpTranslatorTest {
     @Test
     fun testConvertSingleUmpToMidi1 ()
     {
-        var ump = Ump(0L)
         val dst = MutableList<Byte>(16) { 0 }
-        var size = 0
 
         // MIDI1 Channel Voice Messages
 
-        ump = Ump(UmpFactory.midi1NoteOff(0, 1, 40, 0x70))
-        size = UmpTranslator.translateSingleUmpToMidi1Bytes(dst, ump)
+        var ump = Ump(UmpFactory.midi1NoteOff(0, 1, 40, 0x70))
+        var size = UmpTranslator.translateSingleUmpToMidi1Bytes(dst, ump)
         assertEquals(3,  size)
         assertContentEquals(listOf(0x81, 40, 0x70).map { it.toByte() }, dst.take(size))
 
@@ -92,7 +90,20 @@ class UmpTranslatorTest {
     fun testConvertUmpToMidi1Bytes1() {
         val umps = listOf(
             Ump(0x40904000E0000000),
-            Ump(0x00201000),
+            Ump(0x00401000),
+            Ump(0x4080400000000000),
+        )
+        val dst = MutableList<Byte>(9) { 0 }
+        assertEquals(UmpTranslationResult.OK, UmpTranslator.translateUmpToMidi1Bytes(dst, umps.asSequence()))
+        val expected = listOf(0, 0x90, 0x40, 0x70, 0x80, 0x20, 0x80, 0x40, 0).map { it.toByte() }
+        assertContentEquals(expected, dst)
+    }
+
+    @Test
+    fun testConvertUmpToMidi1Bytes2() {
+        val umps = listOf(
+            Ump(0x40904000E0000000),
+            Ump(0x00201000), // JR Timestamps instead of Delta Clockstamp - still works (we don't have to support it though)
             Ump(0x4080400000000000),
         )
         val dst = MutableList<Byte>(9) { 0 }