diff --git a/examples/mp4info.rs b/examples/mp4info.rs
index 69bb3d6..a263777 100644
--- a/examples/mp4info.rs
+++ b/examples/mp4info.rs
@@ -130,7 +130,7 @@ fn subtitle_info(track: &Mp4Track) -> Result<String> {
             track.box_type()?,
         ))
     } else {
-        Ok("subtitle test".to_string())
+        Err(Error::InvalidData("tx3g box not found"))
     }
 }
 
diff --git a/src/track.rs b/src/track.rs
index 8e65def..4644533 100644
--- a/src/track.rs
+++ b/src/track.rs
@@ -17,6 +17,7 @@ use crate::mp4box::{
     stsc::StscEntry,
     stss::StssBox,
     stts::SttsEntry,
+    tx3g::Tx3gBox,
     vmhd::VmhdBox,
 };
 use crate::*;
@@ -509,7 +510,10 @@ impl Mp4TrackWriter {
                 let mp4a = Mp4aBox::new(aac_config);
                 trak.mdia.minf.stbl.stsd.mp4a = Some(mp4a);
             }
-            MediaConfig::TtxtConfig(ref _ttxt_config) => {}
+            MediaConfig::TtxtConfig(ref _ttxt_config) => {
+                let tx3g = Tx3gBox::default();
+                trak.mdia.minf.stbl.stsd.tx3g = Some(tx3g);
+            }
         }
         Ok(Mp4TrackWriter {
             trak,