diff --git a/src/merge.rs b/src/merge.rs
index 472e74f..aaaeda0 100644
--- a/src/merge.rs
+++ b/src/merge.rs
@@ -1,5 +1,6 @@
 use std::io::Result;
 use std::path::{Path, PathBuf};
+use std::process::Command;
 use std::{fs, io};
 
 fn guess_video_path(path: &Path) -> Result<PathBuf> {
@@ -12,7 +13,7 @@ fn guess_video_path(path: &Path) -> Result<PathBuf> {
         }
 
         let size = entry_path.metadata()?.len();
-        if size > largest_size {
+        if size >= largest_size {
             largest_size = size;
             largest_file = entry_path.into();
         }
@@ -21,6 +22,54 @@ fn guess_video_path(path: &Path) -> Result<PathBuf> {
     Ok(largest_file)
 }
 
+fn convert_audio_to_aac(path: &Path) -> Result<()> {
+    let save_path = path.with_extension("aac");
+    let output = Command::new("ffmpeg")
+        .arg("-y")
+        .arg("-hide_banner")
+        .arg("-i").arg(path)
+        .arg("-c").arg("copy")
+        .arg(save_path)
+        .spawn()?.wait_with_output();
+
+    match output {
+        Ok(res) => {
+            if !res.status.success() {
+                return Err(io::Error::new(io::ErrorKind::Other, format!("ffmpeg exited with status {}", res.status)));
+            }
+        }
+        Err(e) => return Err(e)
+    }
+
+    Ok(())
+}
+
+fn merge(video_path: &Path, audio_path: &Path) -> Result<()> {
+    let origin_video_extension = video_path.extension().unwrap().to_str().unwrap();
+    let origin_filename = format!("original.{}", &origin_video_extension);
+    let origin_path = video_path.parent().unwrap().join(origin_filename);
+    fs::rename(video_path, &origin_path)?;
+    let output = Command::new("ffmpeg")
+        .arg("-y")
+        .arg("-hide_banner")
+        .arg("-i").arg(origin_path)
+        .arg("-i").arg(audio_path)
+        .arg("-c").arg("copy")
+        .arg(video_path)
+        .spawn()?.wait_with_output();
+
+    match output {
+        Ok(res) => {
+            if !res.status.success() {
+                return Err(io::Error::new(io::ErrorKind::Other, format!("ffmpeg exited with status {}", res.status)));
+            }
+        }
+        Err(e) => return Err(e)
+    }
+
+    Ok(())
+}
+
 pub fn merge_video_from_path(path: &Path) -> Result<()> {
     let video_path = guess_video_path(path)?;
     let video_name = video_path.file_name().unwrap().to_str().unwrap();
@@ -32,8 +81,6 @@ pub fn merge_video_from_path(path: &Path) -> Result<()> {
         return Err(io::Error::new(io::ErrorKind::NotFound, "Audio file does not exist"));
     }
 
-    println!("Merging video from {:?}", audio_path);
-    println!("Merging video {:?}", video_name);
-
-    Ok(())
+    convert_audio_to_aac(&audio_path).expect("Audio file corrupted.");
+    merge(&video_path, &audio_path)
 }