diff --git a/lib/src/main/java/com/otaliastudios/transcoder/internal/thumbnails/DefaultThumbnailsEngine.kt b/lib/src/main/java/com/otaliastudios/transcoder/internal/thumbnails/DefaultThumbnailsEngine.kt
index f71457d3..123748ac 100644
--- a/lib/src/main/java/com/otaliastudios/transcoder/internal/thumbnails/DefaultThumbnailsEngine.kt
+++ b/lib/src/main/java/com/otaliastudios/transcoder/internal/thumbnails/DefaultThumbnailsEngine.kt
@@ -84,8 +84,8 @@ class DefaultThumbnailsEngine(
         override fun requestKeyFrameTimestamps(): Long {
             return source.requestKeyFrameTimestamps()
         }
-        override fun getKeyFrameTimestampsUs(): ArrayList<Long> {
-            return source.keyFrameTimestampsUs
+        override fun getKeyFrameTimestamps(): ArrayList<Long> {
+            return source.keyFrameTimestamps
         }
 
         override fun isDrained(): Boolean {
@@ -118,13 +118,8 @@ class DefaultThumbnailsEngine(
                 val threshold = stubs.firstOrNull()?.request?.threshold() ?: 0L
                 val nextKeyFrameIndex = source.search(requested)
 
-                val nextKeyFrameUs =
-                    if (nextKeyFrameIndex == -1) Long.MAX_VALUE else source.keyFrameTimestampsUs[nextKeyFrameIndex]
-                val previousKeyFrameUs =
-                    source.keyFrameTimestampsUs[
-                        if (nextKeyFrameIndex > 0)
-                            nextKeyFrameIndex - 1 else (source.keyFrameTimestampsUs.size - 1)
-                    ]
+                val nextKeyFrameUs = source.keyFrameAt(nextKeyFrameIndex) { Long.MAX_VALUE }
+                val previousKeyFrameUs = source.keyFrameAt(nextKeyFrameIndex - 1) { source.lastKeyFrame() }
 
                 log.i(
                     "seek: current ${source.positionUs}," +
@@ -170,18 +165,26 @@ class DefaultThumbnailsEngine(
 
     private lateinit var progress: (Thumbnail) -> Unit
 
+    private fun DataSource.lastKeyFrame(): Long {
+        return keyFrameAt(keyFrameTimestamps.size - 1)
+    }
+
+    private inline fun DataSource.keyFrameAt(index: Int, defaultValue: ((Int)-> Long) = {_ -> -1}): Long {
+        return keyFrameTimestamps.getOrElse(index, defaultValue)
+    }
+
     private fun DataSource.search(timestampUs: Long): Int {
-        if (keyFrameTimestampsUs.isEmpty())
+        if (keyFrameTimestamps.isEmpty())
             requestKeyFrameTimestamps()
 
-        val searchIndex = keyFrameTimestampsUs.binarySearch(timestampUs)
+        val searchIndex = keyFrameTimestamps.binarySearch(timestampUs)
 
         val nextKeyFrameIndex = when {
             searchIndex >= 0 -> searchIndex
             searchIndex < 0 -> {
                 val index = -searchIndex - 1
                 when {
-                    index >= keyFrameTimestampsUs.size -> {
+                    index >= keyFrameTimestamps.size -> {
                         val ts = requestKeyFrameTimestamps()
                         if (ts == -1L) {
                             -1
@@ -189,7 +192,7 @@ class DefaultThumbnailsEngine(
                             search(timestampUs)
                         }
                     }
-                    index < keyFrameTimestampsUs.size -> index
+                    index < keyFrameTimestamps.size -> index
                     else -> {
                         -1 // will never reach here. kotlin is stupid
                     }
diff --git a/lib/src/main/java/com/otaliastudios/transcoder/source/DataSource.java b/lib/src/main/java/com/otaliastudios/transcoder/source/DataSource.java
index c6e2efe7..ab469fec 100644
--- a/lib/src/main/java/com/otaliastudios/transcoder/source/DataSource.java
+++ b/lib/src/main/java/com/otaliastudios/transcoder/source/DataSource.java
@@ -114,9 +114,10 @@ public interface DataSource {
 
     default long requestKeyFrameTimestamps() { return -1;}
 
-    default ArrayList<Long> getKeyFrameTimestampsUs() {
+    default ArrayList<Long> getKeyFrameTimestamps() {
         return new ArrayList<>();
     }
+
     /**
      * Rewinds this source, moving it to its default state.
      * To be used again, tracks will be selected again.
diff --git a/lib/src/main/java/com/otaliastudios/transcoder/source/DefaultDataSource.java b/lib/src/main/java/com/otaliastudios/transcoder/source/DefaultDataSource.java
index 3faf7422..7e7c1beb 100644
--- a/lib/src/main/java/com/otaliastudios/transcoder/source/DefaultDataSource.java
+++ b/lib/src/main/java/com/otaliastudios/transcoder/source/DefaultDataSource.java
@@ -45,7 +45,7 @@ public abstract class DefaultDataSource implements DataSource {
     private long mDontRenderRangeStart = -1L;
     private long mDontRenderRangeEnd = -1L;
 
-    private final ArrayList<Long> keyFrameTsUs = new ArrayList<>();
+    private final ArrayList<Long> keyFrameTimestamps = new ArrayList<>();
     @Override
     public void initialize() {
         LOG.i("initialize(): initializing...");
@@ -92,8 +92,8 @@ public void initialize() {
     }
 
     @Override
-    public ArrayList<Long> getKeyFrameTimestampsUs() {
-        return keyFrameTsUs;
+    public ArrayList<Long> getKeyFrameTimestamps() {
+        return keyFrameTimestamps;
     }
 
     private Boolean lastKeyFrame = false;
@@ -101,15 +101,15 @@ public ArrayList<Long> getKeyFrameTimestampsUs() {
     public long requestKeyFrameTimestamps() {
 
         if(lastKeyFrame) return  -1L;
-        if(keyFrameTsUs.size() > 0) {
-            mExtractor.seekTo(keyFrameTsUs.get(keyFrameTsUs.size() - 1) + 10001L, MediaExtractor.SEEK_TO_NEXT_SYNC);
+        if(keyFrameTimestamps.size() > 0) {
+            mExtractor.seekTo(keyFrameTimestamps.get(keyFrameTimestamps.size() - 1) + 10001L, MediaExtractor.SEEK_TO_NEXT_SYNC);
         }
 
         long sampleTime = mExtractor.getSampleTime();
 
-        if (sampleTime == -1 || (keyFrameTsUs.size() > 0 && sampleTime == keyFrameTsUs.get(keyFrameTsUs.size() - 1))) {
+        if (sampleTime == -1 || (keyFrameTimestamps.size() > 0 && sampleTime == keyFrameTimestamps.get(keyFrameTimestamps.size() - 1))) {
             lastKeyFrame = true;
-            mExtractor.seekTo(keyFrameTsUs.get(keyFrameTsUs.size() - 1) + 10001L, MediaExtractor.SEEK_TO_PREVIOUS_SYNC);
+            mExtractor.seekTo(keyFrameTimestamps.get(keyFrameTimestamps.size() - 1) + 10001L, MediaExtractor.SEEK_TO_PREVIOUS_SYNC);
             return -1;
         }
         LOG.i("keyFrameStartTime:" + sampleTime);
@@ -119,17 +119,17 @@ public long requestKeyFrameTimestamps() {
         int prefetchCount = 100;
         while (sampleTime >= 0L && sampleTime != lastSampleTime && count < prefetchCount) {
             if ((mExtractor.getSampleFlags() & MediaExtractor.SAMPLE_FLAG_SYNC) > 0) {
-                if (!keyFrameTsUs.isEmpty() && sampleTime <= keyFrameTsUs.get(keyFrameTsUs.size() - 1)) {
-                    Collections.sort(keyFrameTsUs);
+                if (!keyFrameTimestamps.isEmpty() && sampleTime <= keyFrameTimestamps.get(keyFrameTimestamps.size() - 1)) {
+                    Collections.sort(keyFrameTimestamps);
                 }
-                keyFrameTsUs.add(sampleTime);
+                keyFrameTimestamps.add(sampleTime);
             }
             mExtractor.seekTo(sampleTime + 10001L, MediaExtractor.SEEK_TO_NEXT_SYNC);
             lastSampleTime = sampleTime;
             sampleTime = mExtractor.getSampleTime();
             count++;
         }
-        LOG.i("keyFrameStopCount:" + keyFrameTsUs);
+        LOG.i("keyFrameStopCount:" + keyFrameTimestamps);
         return sampleTime;
     }