diff --git a/src/JT1078.FMp4.Test/JT1078ToFMp4Box_Test.cs b/src/JT1078.FMp4.Test/JT1078ToFMp4Box_Test.cs
index 745ab81..f9333e7 100644
--- a/src/JT1078.FMp4.Test/JT1078ToFMp4Box_Test.cs
+++ b/src/JT1078.FMp4.Test/JT1078ToFMp4Box_Test.cs
@@ -117,16 +117,12 @@ namespace JT1078.FMp4.Test
             //fragmentBox.MovieFragmentBox.TrackFragmentBox.SampleDependencyTypeBox.SampleDependencyTypes = new List<SampleDependencyTypeBox.SampleDependencyType>();
             //todo:fragmentBox.MovieFragmentBox.TrackFragmentBox.SampleDependencyTypeBox.SampleDependencyTypes
             fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackFragmentBaseMediaDecodeTimeBox = new TrackFragmentBaseMediaDecodeTimeBox();
-            //upperWordBaseMediaDecodeTime = Math.floor(baseMediaDecodeTime / (UINT32_MAX + 1)),
-            //lowerWordBaseMediaDecodeTime = Math.floor(baseMediaDecodeTime % (UINT32_MAX + 1));
             //todo:BaseMediaDecodeTime 
             fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackFragmentBaseMediaDecodeTimeBox.BaseMediaDecodeTime = 0;
             //trun
             fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackRunBox = new TrackRunBox(flags: 0x5);
-            //todo:DataOffset 
             fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackRunBox.DataOffset = 120;
-            //todo:FirstSampleFlags 
-            fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackRunBox.FirstSampleFlags = 33554432;
+            fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackRunBox.FirstSampleFlags = 0;
             fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackRunBox.TrackRunInfos = new List<TrackRunBox.TrackRunInfo>();
             fragmentBox.MovieFragmentBox.TrackFragmentBox.TrackRunBox.TrackRunInfos.Add(new TrackRunBox.TrackRunInfo());
             fragmentBox.MediaDataBox = new MediaDataBox();
diff --git a/src/JT1078.FMp4/Boxs/TrackRunBox.cs b/src/JT1078.FMp4/Boxs/TrackRunBox.cs
index 6d1c0d7..b91dacb 100644
--- a/src/JT1078.FMp4/Boxs/TrackRunBox.cs
+++ b/src/JT1078.FMp4/Boxs/TrackRunBox.cs
@@ -23,6 +23,8 @@ namespace JT1078.FMp4
         public uint SampleCount { get; set; }
         /// <summary>
         /// 可选的
+        /// 用来表示和该moof配套的mdat中实际数据内容距moof开头有多少byte
+        /// 相当于就是 moof.byteLength + mdat.headerSize(8)
         /// </summary>
         public int DataOffset { get; set; }
         /// <summary>
diff --git a/src/JT1078.FMp4/JT1078.FMp4.xml b/src/JT1078.FMp4/JT1078.FMp4.xml
index 6e97545..8a049a0 100644
--- a/src/JT1078.FMp4/JT1078.FMp4.xml
+++ b/src/JT1078.FMp4/JT1078.FMp4.xml
@@ -985,6 +985,8 @@
         <member name="P:JT1078.FMp4.TrackRunBox.DataOffset">
             <summary>
             可选的
+            用来表示和该moof配套的mdat中实际数据内容距moof开头有多少byte
+            相当于就是 moof.byteLength + mdat.headerSize
             </summary>
         </member>
         <member name="P:JT1078.FMp4.TrackRunBox.FirstSampleFlags">