diff --git a/src/chunk.rs b/src/chunk.rs
new file mode 100644
index 0000000..181bcb2
--- /dev/null
+++ b/src/chunk.rs
@@ -0,0 +1,50 @@
+use std::rc::Rc;
+
+pub enum Chunk {
+    Headers {
+        bytes: Rc<Vec<u8>>
+    },
+    ClusterHead {
+        keyframe: bool,
+        start: u64,
+        end: u64,
+        // space for a Cluster tag and a Timecode tag
+        bytes: [u8;16]
+    },
+    ClusterBody {
+        bytes: Rc<Vec<u8>>
+    }
+}
+
+impl AsRef<[u8]> for Chunk {
+    fn as_ref(&self) -> &[u8] {
+        match self {
+            &Chunk::Headers {ref bytes, ..} => &bytes,
+            &Chunk::ClusterHead {ref bytes, ..} => bytes,
+            &Chunk::ClusterBody {ref bytes, ..} => &bytes
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use chunk::*;
+    use std::io::Cursor;
+    use webm::*;
+
+    #[test]
+    fn enough_space_for_header() {
+        let mut chunk = Chunk::ClusterHead {
+            keyframe: false,
+            start: 0,
+            end: 0,
+            bytes: [0;16]
+        };
+        if let Chunk::ClusterHead {ref mut bytes, ..} = chunk {
+            let mut cursor = Cursor::new(bytes as &mut [u8]);
+            encode_webm_element(&WebmElement::Cluster, &mut cursor).unwrap();
+            encode_webm_element(&WebmElement::Timecode(u64::max_value()), &mut cursor).unwrap();
+        }
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index b20111c..4f689c5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,6 +2,7 @@
 extern crate bytes;
 extern crate futures;
 
+pub mod chunk;
 pub mod ebml;
 mod iterator;
 pub mod timecode_fixer;