diff --git a/package/android/src/main/java/com/mrousavy/camera/core/ChunkedRecorder.kt b/package/android/src/main/java/com/mrousavy/camera/core/ChunkedRecorder.kt
index 16266fb..9444216 100644
--- a/package/android/src/main/java/com/mrousavy/camera/core/ChunkedRecorder.kt
+++ b/package/android/src/main/java/com/mrousavy/camera/core/ChunkedRecorder.kt
@@ -105,6 +105,12 @@ class ChunkedRecordingManager(private val encoder: MediaCodec, private val outpu
     muxerContext?.finish()
     chunkIndex++
 
+    val format = this.encodedFormat
+    if (format == null) {
+      Log.e(TAG, "Cannot create muxer: encodedFormat is null (onOutputFormatChanged not called yet)")
+      return
+    }
+
     val newFileName = "$chunkIndex.mp4"
     val newOutputFile = File(this.outputDirectory, newFileName)
     Log.i(TAG, "Creating new muxer for file: $newFileName")
@@ -114,7 +120,7 @@ class ChunkedRecordingManager(private val encoder: MediaCodec, private val outpu
     )
     muxer.setOrientationHint(orientationHint)
     muxerContext = MuxerContext(
-        muxer, newOutputFile, chunkIndex, bufferInfo.presentationTimeUs, this.encodedFormat!!, this.callbacks
+        muxer, newOutputFile, chunkIndex, bufferInfo.presentationTimeUs, format, this.callbacks
     )
   }
 
@@ -123,7 +129,8 @@ class ChunkedRecordingManager(private val encoder: MediaCodec, private val outpu
   }
 
   private fun chunkLengthUs(bufferInfo: BufferInfo): Long {
-    return bufferInfo.presentationTimeUs - muxerContext!!.startTimeUs
+    val context = muxerContext ?: return 0L
+    return bufferInfo.presentationTimeUs - context.startTimeUs
   }
 
   fun start() {
@@ -155,7 +162,13 @@ class ChunkedRecordingManager(private val encoder: MediaCodec, private val outpu
       if (muxerContext == null || (atKeyframe(bufferInfo) && chunkLengthUs(bufferInfo) >= targetDurationUs)) {
         this.createNextMuxer(bufferInfo)
       }
-      muxerContext!!.muxer.writeSampleData(muxerContext!!.videoTrack, encodedData, bufferInfo)
+      val context = muxerContext
+      if (context == null) {
+        Log.e(TAG, "Cannot write sample data: muxerContext is null")
+        encoder.releaseOutputBuffer(index, false)
+        return
+      }
+      context.muxer.writeSampleData(context.videoTrack, encodedData, bufferInfo)
       encoder.releaseOutputBuffer(index, false)
     }
   }