diff --git a/doc/ffmpeginfo.txt b/doc/ffmpeginfo.txt
index 2d21748..0058b3b 100644
--- a/doc/ffmpeginfo.txt
+++ b/doc/ffmpeginfo.txt
@@ -4,4 +4,7 @@ ffmpeg -i demo.mp4 -c copy -f flv -vcodec h264 -acodec aac demo_flv.flv
 
 ffmpeg -f dshow -i video="USB2.0 PC CAMERA" -t 60 -c copy -f h264 -vcodec h264 jt1078.264
 
+ffmpeg -i demo.264 -vcodec copy -f mp4 -movflags frag_keyframe+empty_moov fragmented_demo.mp4
+
+
 chrome://media-internals/
\ No newline at end of file
diff --git a/doc/video/fragmented_demo.mp4 b/doc/video/fragmented_demo.mp4
new file mode 100644
index 0000000..698bd28
Binary files /dev/null and b/doc/video/fragmented_demo.mp4 differ
diff --git a/src/JT1078.FMp4/Boxs/SampleToGroupBox.cs b/src/JT1078.FMp4/Boxs/SampleToGroupBox.cs
index 2f47f72..1bc501c 100644
--- a/src/JT1078.FMp4/Boxs/SampleToGroupBox.cs
+++ b/src/JT1078.FMp4/Boxs/SampleToGroupBox.cs
@@ -32,7 +32,24 @@ namespace JT1078.FMp4
 
         public void ToBuffer(ref FMp4MessagePackWriter writer)
         {
-            //todo:sbgp
+            writer.WriteUInt32(GroupingType);
+            if (Version == 1)
+            {
+                writer.WriteUInt32(GroupingTypeParameter);
+            }
+            if(SampleToGroupInfos!=null && SampleToGroupInfos.Count > 0)
+            {
+                writer.WriteUInt32((uint)SampleToGroupInfos.Count);
+                foreach(var item in SampleToGroupInfos)
+                {
+                    writer.WriteUInt32(item.SampleCount);
+                    writer.WriteUInt32(item.GroupDescriptionIndex);
+                }
+            }
+            else
+            {
+                writer.WriteUInt32(0);
+            }
         }
 
         public class SampleToGroupInfo
diff --git a/src/JT1078.FMp4/Boxs/SubSampleInformationBox.cs b/src/JT1078.FMp4/Boxs/SubSampleInformationBox.cs
index 942b1f4..47e4814 100644
--- a/src/JT1078.FMp4/Boxs/SubSampleInformationBox.cs
+++ b/src/JT1078.FMp4/Boxs/SubSampleInformationBox.cs
@@ -26,7 +26,39 @@ namespace JT1078.FMp4
 
         public void ToBuffer(ref FMp4MessagePackWriter writer)
         {
-            //todo:subs
+            if(SubSampleInformations!=null && SubSampleInformations.Count > 0)
+            {
+                foreach(var item in SubSampleInformations)
+                {
+                    writer.WriteUInt32(item.SampleDelta);
+                    if (item.InnerSubSampleInformations != null && item.InnerSubSampleInformations.Count > 0)
+                    {
+                        writer.WriteUInt16((ushort)item.InnerSubSampleInformations.Count);
+                        foreach(var subItem in item.InnerSubSampleInformations)
+                        {
+                            if (Version == 1)
+                            {
+                                writer.WriteUInt32(subItem.SubsampleSize);
+                            }
+                            else
+                            {
+                                writer.WriteUInt16((ushort)subItem.SubsampleSize);
+                            }
+                            writer.WriteByte(subItem.SubsamplePriority);
+                            writer.WriteByte(subItem.Discardable);
+                            writer.WriteUInt32(subItem.Reserved);
+                        }
+                    }
+                    else
+                    {
+                        writer.WriteUInt16(0);
+                    }
+                }
+            }
+            else
+            {
+                writer.WriteUInt32((uint)SubSampleInformations.Count);
+            }
         }
 
         public class SubSampleInformation
@@ -39,10 +71,10 @@ namespace JT1078.FMp4
             public class InnerSubSampleInformation
             {
                 /// <summary>
-                /// version == 1
+                /// version == 1 uint32
+                /// version != 1 uint16
                 /// </summary>
-                public uint SubsampleSizeLarge { get; set; }
-                public ushort SubsampleSize { get; set; }
+                public uint SubsampleSize { get; set; }
                 public byte SubsamplePriority { get; set; }
                 public byte Discardable { get; set; }
                 public uint Reserved { get; set; }
diff --git a/src/JT1078.FMp4/FMp4Box.cs b/src/JT1078.FMp4/FMp4Box.cs
index 1de854f..b910171 100644
--- a/src/JT1078.FMp4/FMp4Box.cs
+++ b/src/JT1078.FMp4/FMp4Box.cs
@@ -40,7 +40,6 @@ namespace JT1078.FMp4
                     item.MediaDataBox.ToBuffer(ref writer);
                 }
             }
-
         }
     }
 }
diff --git a/src/JT1078.FMp4/JT1078.FMp4.xml b/src/JT1078.FMp4/JT1078.FMp4.xml
index fad6173..8126534 100644
--- a/src/JT1078.FMp4/JT1078.FMp4.xml
+++ b/src/JT1078.FMp4/JT1078.FMp4.xml
@@ -678,9 +678,10 @@
             <param name="version"></param>
             <param name="flags"></param>
         </member>
-        <member name="P:JT1078.FMp4.SubSampleInformationBox.SubSampleInformation.InnerSubSampleInformation.SubsampleSizeLarge">
+        <member name="P:JT1078.FMp4.SubSampleInformationBox.SubSampleInformation.InnerSubSampleInformation.SubsampleSize">
             <summary>
-            version == 1
+            version == 1 uint32
+            version != 1 uint16
             </summary>
         </member>
         <member name="P:JT1078.FMp4.SubsegmentIndexBox.SubsegmentIndexInfos">
diff --git a/src/JT1078.FMp4/Samples/AVC1SampleEntry.cs b/src/JT1078.FMp4/Samples/AVC1SampleEntry.cs
index e00ec60..f556c4c 100644
--- a/src/JT1078.FMp4/Samples/AVC1SampleEntry.cs
+++ b/src/JT1078.FMp4/Samples/AVC1SampleEntry.cs
@@ -36,6 +36,7 @@ namespace JT1078.FMp4.Samples
             }
             End(ref writer);
         }
-        //todo:public MPEG4ExtensionDescriptorsBox MPEG4BitRateBox { get; set; }
+
+        //public MPEG4ExtensionDescriptorsBox MPEG4BitRateBox { get; set; }
     }
 }