diff --git a/lib/src/main/java/com/otaliastudios/transcoder/internal/DataSources.kt b/lib/src/main/java/com/otaliastudios/transcoder/internal/DataSources.kt
index 3a4a36c4..1c54868d 100644
--- a/lib/src/main/java/com/otaliastudios/transcoder/internal/DataSources.kt
+++ b/lib/src/main/java/com/otaliastudios/transcoder/internal/DataSources.kt
@@ -62,30 +62,27 @@ class DataSources constructor(
         }
     }
 
-    private fun existsInSources(dataSource: DataSource, sources: List<DataSource>): Boolean {
-        return (sources.find { it.mediaId() == dataSource.mediaId() }) != null
-    }
-
     fun addDataSource(dataSource: DataSource) {
         addVideoDataSource(dataSource)
         addAudioDataSource(dataSource)
     }
 
     fun addVideoDataSource(dataSource: DataSource) {
-        if (existsInSources(dataSource, videoSources)) return
         dataSource.init()
         if (dataSource.getTrackFormat(TrackType.VIDEO) != null && dataSource !in videoSources) {
             videoSources = videoSources + dataSource
         }
     }
+
     fun addAudioDataSource(dataSource: DataSource) {
-        if (existsInSources(dataSource, audioSources)) return
         dataSource.init()
         if (dataSource.getTrackFormat(TrackType.AUDIO) != null) {
             audioSources = audioSources + dataSource
         }
     }
 
+    fun getVideoSources() = videoSources
+
     fun removeDataSource(dataSourceId: String) {
         removeAudioDataSource(dataSourceId)
         removeVideoDataSource(dataSourceId)
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 32b2be69..93544cad 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
@@ -221,7 +221,10 @@ class DefaultThumbnailsEngine(
         return nextKeyFrameIndex
     }
 
-    override  fun addDataSource(dataSource: DataSource) {
+    override fun addDataSource(dataSource: DataSource) {
+        if (dataSources.getVideoSources().find { it.mediaId() == dataSource.mediaId() } != null) {
+            return // dataSource already exists
+        }
         dataSources.addVideoDataSource(dataSource)
         tracks.updateTracksInfo()
         if (tracks.active.has(TrackType.VIDEO)) {