diff --git a/src/mp4box/moov.rs b/src/mp4box/moov.rs
index 872ec7f..cec21c6 100644
--- a/src/mp4box/moov.rs
+++ b/src/mp4box/moov.rs
@@ -140,7 +140,6 @@ impl<W: Write> WriteBox<&mut W> for MoovBox {
         for trak in self.traks.iter() {
             trak.write_box(writer)?;
         }
-
         if let Some(udta) = &self.udta {
             udta.write_box(writer)?;
         }
diff --git a/src/mp4box/mvex.rs b/src/mp4box/mvex.rs
index 8eb0e53..44a4f19 100644
--- a/src/mp4box/mvex.rs
+++ b/src/mp4box/mvex.rs
@@ -7,8 +7,7 @@ use crate::mp4box::{mehd::MehdBox, trex::TrexBox};
 #[derive(Debug, Clone, PartialEq, Eq, Default, Serialize)]
 pub struct MvexBox {
     pub mehd: Option<MehdBox>,
-    // todo: this should be a vec
-    pub trex: TrexBox,
+    pub trex: Vec<TrexBox>,
 }
 
 impl MvexBox {
@@ -17,7 +16,8 @@ impl MvexBox {
     }
 
     pub fn get_size(&self) -> u64 {
-        HEADER_SIZE + self.mehd.as_ref().map(|x| x.box_size()).unwrap_or(0) + self.trex.box_size()
+        let trex_sizes = self.trex.iter().fold(0, |acc, x| acc + x.box_size());
+        HEADER_SIZE + self.mehd.as_ref().map(|x| x.box_size()).unwrap_or(0) + trex_sizes
     }
 }
 
@@ -45,7 +45,7 @@ impl<R: Read + Seek> ReadBox<&mut R> for MvexBox {
         let start = box_start(reader)?;
 
         let mut mehd = None;
-        let mut trex = None;
+        let mut trex: Vec<TrexBox> = Vec::new();
 
         let mut current = reader.stream_position()?;
         let end = start + size;
@@ -64,7 +64,7 @@ impl<R: Read + Seek> ReadBox<&mut R> for MvexBox {
                     mehd = Some(MehdBox::read_box(reader, s)?);
                 }
                 BoxType::TrexBox => {
-                    trex = Some(TrexBox::read_box(reader, s)?);
+                    trex.push(TrexBox::read_box(reader, s)?);
                 }
                 _ => {
                     // XXX warn!()
@@ -75,16 +75,13 @@ impl<R: Read + Seek> ReadBox<&mut R> for MvexBox {
             current = reader.stream_position()?;
         }
 
-        if trex.is_none() {
+        if trex.is_empty() {
             return Err(Error::BoxNotFound(BoxType::TrexBox));
         }
 
         skip_bytes_to(reader, start + size)?;
 
-        Ok(MvexBox {
-            mehd,
-            trex: trex.unwrap(),
-        })
+        Ok(MvexBox { mehd, trex })
     }
 }
 
@@ -96,7 +93,9 @@ impl<W: Write> WriteBox<&mut W> for MvexBox {
         if let Some(mehd) = &self.mehd {
             mehd.write_box(writer)?;
         }
-        self.trex.write_box(writer)?;
+        for trex in self.trex {
+            trex.write_box(writer)?;
+        }
 
         Ok(size)
     }