diff --git a/dom/media/MediaData.cpp b/dom/media/MediaData.cpp
index 57f63f969b0a..bbe38650f4c8 100644
--- a/dom/media/MediaData.cpp
+++ b/dom/media/MediaData.cpp
@@ -56,12 +56,10 @@ Span<AudioDataValue> AudioData::Data() const {
   return MakeSpan(GetAdjustedData(), mFrames * mChannels);
 }
 
-bool AudioData::AdjustForStartTime(int64_t aStartTime) {
-  const TimeUnit startTimeOffset =
-      media::TimeUnit::FromMicroseconds(aStartTime);
-  mOriginalTime -= startTimeOffset;
+bool AudioData::AdjustForStartTime(const media::TimeUnit& aStartTime) {
+  mOriginalTime -= aStartTime;
   if (mTrimWindow) {
-    *mTrimWindow -= startTimeOffset;
+    *mTrimWindow -= aStartTime;
   }
   return MediaData::AdjustForStartTime(aStartTime) && mOriginalTime.IsValid();
 }
diff --git a/dom/media/MediaData.h b/dom/media/MediaData.h
index c2775370217a..d908fe67bfd5 100644
--- a/dom/media/MediaData.h
+++ b/dom/media/MediaData.h
@@ -298,8 +298,8 @@ class MediaData {
 
   // Return true if the adjusted time is valid. Caller should handle error when
   // the result is invalid.
-  virtual bool AdjustForStartTime(int64_t aStartTime) {
-    mTime -= media::TimeUnit::FromMicroseconds(aStartTime);
+  virtual bool AdjustForStartTime(const media::TimeUnit& aStartTime) {
+    mTime -= aStartTime;
     return mTime.IsValid();
   }
 
@@ -371,7 +371,7 @@ class AudioData : public MediaData {
 
   // Return true if the adjusted time is valid. Caller should handle error when
   // the result is invalid.
-  bool AdjustForStartTime(int64_t aStartTime) override;
+  bool AdjustForStartTime(const media::TimeUnit& aStartTime) override;
 
   const uint32_t mChannels;
   // The AudioConfig::ChannelLayout map. Channels are ordered as per SMPTE
diff --git a/dom/media/ReaderProxy.cpp b/dom/media/ReaderProxy.cpp
index 5321f3fbe18d..d6788dced6ed 100644
--- a/dom/media/ReaderProxy.cpp
+++ b/dom/media/ReaderProxy.cpp
@@ -43,7 +43,7 @@ RefPtr<ReaderProxy::AudioDataPromise> ReaderProxy::OnAudioDataRequestCompleted(
     RefPtr<AudioData> aAudio) {
   MOZ_ASSERT(mOwnerThread->IsCurrentThreadIn());
 
-  if (aAudio->AdjustForStartTime(StartTime().ToMicroseconds())) {
+  if (aAudio->AdjustForStartTime(StartTime())) {
     return AudioDataPromise::CreateAndResolve(aAudio.forget(), __func__);
   }
   return AudioDataPromise::CreateAndReject(NS_ERROR_DOM_MEDIA_OVERFLOW_ERR,
@@ -76,7 +76,7 @@ RefPtr<ReaderProxy::VideoDataPromise> ReaderProxy::RequestVideoData(
                              ? aTimeThreshold + StartTime()
                              : aTimeThreshold;
 
-  int64_t startTime = StartTime().ToMicroseconds();
+  auto startTime = StartTime();
   return InvokeAsync(mReader->OwnerThread(), mReader.get(), __func__,
                      &MediaFormatReader::RequestVideoData, threshold)
       ->Then(