diff --git a/src/cmd/rec.rs b/src/cmd/rec.rs
index 027d62f..377e075 100644
--- a/src/cmd/rec.rs
+++ b/src/cmd/rec.rs
@@ -1,4 +1,3 @@
-use crate::format;
 use crate::format::{asciicast, raw};
 use crate::locale;
 use crate::pty;
@@ -89,7 +88,7 @@ impl Cli {
             .truncate(overwrite)
             .open(&self.filename)?;
 
-        let writer: Box<dyn format::Writer + Send> = if self.raw {
+        let writer: Box<dyn recorder::EventWriter + Send> = if self.raw {
             Box::new(raw::Writer::new(file))
         } else {
             let time_offset = if append {
@@ -105,10 +104,12 @@ impl Cli {
             writer,
             append,
             self.stdin,
-            self.idle_time_limit,
-            self.command.clone(),
-            self.title,
-            capture_env(&self.env),
+            recorder::Metadata {
+                idle_time_limit: self.idle_time_limit,
+                command: self.command.clone(),
+                title: self.title,
+                env: capture_env(&self.env),
+            },
         );
 
         let exec_command = build_exec_command(self.command);
diff --git a/src/format.rs b/src/format.rs
index c971b69..cd7f37c 100644
--- a/src/format.rs
+++ b/src/format.rs
@@ -1,20 +1,2 @@
 pub mod asciicast;
 pub mod raw;
-use std::{collections::HashMap, io};
-
-pub trait Writer {
-    fn header(&mut self, header: &Header) -> io::Result<()>;
-    fn output(&mut self, time: u64, data: &[u8]) -> io::Result<()>;
-    fn input(&mut self, time: u64, data: &[u8]) -> io::Result<()>;
-    fn resize(&mut self, time: u64, size: (u16, u16)) -> io::Result<()>;
-}
-
-pub struct Header {
-    pub cols: u16,
-    pub rows: u16,
-    pub timestamp: Option<u64>,
-    pub idle_time_limit: Option<f64>,
-    pub command: Option<String>,
-    pub title: Option<String>,
-    pub env: HashMap<String, String>,
-}
diff --git a/src/format/asciicast.rs b/src/format/asciicast.rs
index 2ec29c8..471c6c1 100644
--- a/src/format/asciicast.rs
+++ b/src/format/asciicast.rs
@@ -1,3 +1,4 @@
+use crate::recorder;
 use anyhow::Result;
 use serde::{Deserialize, Deserializer};
 use std::collections::HashMap;
@@ -63,12 +64,16 @@ where
     }
 }
 
-impl<W> super::Writer for Writer<W>
+impl<W> recorder::EventWriter for Writer<W>
 where
     W: Write,
 {
-    fn header(&mut self, header: &super::Header) -> io::Result<()> {
-        self.write_header(&header.into())
+    fn start(&mut self, header: &recorder::Header, append: bool) -> io::Result<()> {
+        if append {
+            Ok(())
+        } else {
+            self.write_header(&header.into())
+        }
     }
 
     fn output(&mut self, time: u64, data: &[u8]) -> io::Result<()> {
@@ -267,7 +272,7 @@ fn format_time(time: u64) -> String {
     format!("{}.{:0>6}", time / 1_000_000, time % 1_000_000)
 }
 
-impl From<&Header> for super::Header {
+impl From<&Header> for recorder::Header {
     fn from(header: &Header) -> Self {
         Self {
             cols: header.width,
@@ -281,8 +286,8 @@ impl From<&Header> for super::Header {
     }
 }
 
-impl From<&super::Header> for Header {
-    fn from(header: &super::Header) -> Self {
+impl From<&recorder::Header> for Header {
+    fn from(header: &recorder::Header) -> Self {
         Self {
             width: header.cols,
             height: header.rows,
diff --git a/src/format/raw.rs b/src/format/raw.rs
index 48ca011..77cf1a0 100644
--- a/src/format/raw.rs
+++ b/src/format/raw.rs
@@ -1,3 +1,4 @@
+use crate::recorder;
 use std::io::{self, Write};
 
 pub struct Writer<W> {
@@ -10,9 +11,13 @@ impl<W> Writer<W> {
     }
 }
 
-impl<W: Write> super::Writer for Writer<W> {
-    fn header(&mut self, header: &super::Header) -> io::Result<()> {
-        write!(self.writer, "\x1b[8;{};{}t", header.rows, header.cols)
+impl<W: Write> recorder::EventWriter for Writer<W> {
+    fn start(&mut self, header: &recorder::Header, append: bool) -> io::Result<()> {
+        if append {
+            Ok(())
+        } else {
+            write!(self.writer, "\x1b[8;{};{}t", header.rows, header.cols)
+        }
     }
 
     fn output(&mut self, _time: u64, data: &[u8]) -> io::Result<()> {
diff --git a/src/recorder.rs b/src/recorder.rs
index 7ff0b00..26d24e4 100644
--- a/src/recorder.rs
+++ b/src/recorder.rs
@@ -1,4 +1,3 @@
-use crate::format;
 use crate::pty;
 use std::collections::HashMap;
 use std::io;
@@ -7,19 +6,40 @@ use std::thread;
 use std::time::{Instant, SystemTime, UNIX_EPOCH};
 
 pub struct Recorder {
-    writer: Option<Box<dyn format::Writer + Send>>,
+    writer: Option<Box<dyn EventWriter + Send>>,
     start_time: Instant,
     append: bool,
     record_input: bool,
-    idle_time_limit: Option<f64>,
-    command: Option<String>,
-    title: Option<String>,
-    env: HashMap<String, String>,
+    metadata: Metadata,
     sender: mpsc::Sender<Message>,
     receiver: Option<mpsc::Receiver<Message>>,
     handle: Option<JoinHandle>,
 }
 
+pub trait EventWriter {
+    fn start(&mut self, header: &Header, append: bool) -> io::Result<()>;
+    fn output(&mut self, time: u64, data: &[u8]) -> io::Result<()>;
+    fn input(&mut self, time: u64, data: &[u8]) -> io::Result<()>;
+    fn resize(&mut self, time: u64, size: (u16, u16)) -> io::Result<()>;
+}
+
+pub struct Header {
+    pub cols: u16,
+    pub rows: u16,
+    pub timestamp: Option<u64>,
+    pub idle_time_limit: Option<f64>,
+    pub command: Option<String>,
+    pub title: Option<String>,
+    pub env: HashMap<String, String>,
+}
+
+pub struct Metadata {
+    pub idle_time_limit: Option<f64>,
+    pub command: Option<String>,
+    pub title: Option<String>,
+    pub env: HashMap<String, String>,
+}
+
 enum Message {
     Output(u64, Vec<u8>),
     Input(u64, Vec<u8>),
@@ -30,13 +50,10 @@ struct JoinHandle(Option<thread::JoinHandle<()>>);
 
 impl Recorder {
     pub fn new(
-        writer: Box<dyn format::Writer + Send>,
+        writer: Box<dyn EventWriter + Send>,
         append: bool,
         record_input: bool,
-        idle_time_limit: Option<f64>,
-        command: Option<String>,
-        title: Option<String>,
-        env: HashMap<String, String>,
+        metadata: Metadata,
     ) -> Self {
         let (sender, receiver) = mpsc::channel();
 
@@ -45,10 +62,7 @@ impl Recorder {
             start_time: Instant::now(),
             append,
             record_input,
-            idle_time_limit,
-            command,
-            title,
-            env,
+            metadata,
             sender,
             receiver: Some(receiver),
             handle: None,
@@ -70,19 +84,17 @@ impl pty::Recorder for Recorder {
         let mut writer = self.writer.take().unwrap();
         let receiver = self.receiver.take().unwrap();
 
-        if !self.append {
-            let header = format::Header {
-                cols: size.0,
-                rows: size.1,
-                timestamp: Some(timestamp),
-                idle_time_limit: self.idle_time_limit,
-                command: self.command.clone(),
-                title: self.title.clone(),
-                env: self.env.clone(),
-            };
+        let header = Header {
+            cols: size.0,
+            rows: size.1,
+            timestamp: Some(timestamp),
+            idle_time_limit: self.metadata.idle_time_limit,
+            command: self.metadata.command.clone(),
+            title: self.metadata.title.clone(),
+            env: self.metadata.env.clone(),
+        };
 
-            writer.header(&header)?;
-        }
+        writer.start(&header, self.append)?;
 
         let handle = thread::spawn(move || {
             for msg in receiver {