diff --git a/src/const.lisp b/src/const.lisp
index ddb2aa8..08eb7dc 100644
--- a/src/const.lisp
+++ b/src/const.lisp
@@ -25,7 +25,7 @@
     ("yuv444p10le" . "ProRes 4444")
     ("yuva420p"    . "HAP Alpha")
     ("yuv420p"     . "H.264 Default")
-    ;; 必要に応じて拡張
+    ;; Extend as needed
     ))
 
 (defparameter +allowed-input-extensions+
@@ -33,6 +33,3 @@
 
 (defparameter +gif-scale+ "640:-1")
 
-(defparameter +flip-filters+
-  '(("hflip" . "hflip")
-    ("vflip" . "vflip")))
diff --git a/src/ffmpeg.lisp b/src/ffmpeg.lisp
index 77c83b9..2cb881d 100644
--- a/src/ffmpeg.lisp
+++ b/src/ffmpeg.lisp
@@ -4,14 +4,13 @@
   "Validate output path before ffmpeg execution"
   (let* ((output-pathname (pathname output))
          (output-dir (uiop:pathname-directory-pathname output-pathname)))
-    ;; ディレクトリ存在確認
-    ;; 相対パスの場合はカレントディレクトリからの解決を行う
+    ;; Check directory existence (resolve relative paths from current directory)
     (unless (uiop:directory-exists-p output-dir)
       (format t "~a Output directory does not exist: ~a~%" 
               (log-tag "error") (namestring output-dir))
       (uiop:quit 1))
     
-    ;; 出力ファイル名の基本チェック
+    ;; Basic output filename validation
     (let ((filename (file-namestring output-pathname)))
       (when (string= filename "")
         (format t "~a Invalid output filename: ~a~%" 
@@ -24,14 +23,14 @@
     (let ((file-size (with-open-file (stream output :direction :input 
                                              :if-does-not-exist nil)
                        (when stream (file-length stream)))))
-      ;; 0バイトまたは非常に小さいファイル（ヘッダーのみ等）は削除
+      ;; Delete empty or very small files (header-only, etc.)
       (when (and file-size (< file-size 1024))
         (delete-file output)
         (format t "~a Cleaned up incomplete output file: ~a~%" 
                 (log-tag "info") output)))))
 
 (defun run-cmd (cmd output dry-run)
-  ;; Phase 1: 事前検証
+  ;; Pre-execution validation
   (validate-output-path output)
   
   (when (probe-file output)
@@ -44,11 +43,11 @@
         (format t "~a Command: ~{~a ~}~%" (log-tag "dry-run") cmd))
       (progn
         (format t "~a Running: ~{~a ~}~%" (log-tag "info") cmd)
-        ;; Phase 1: 実行前後でのクリーンアップ対応準備
+        ;; Error handling with cleanup
         (handler-case
             (uiop:run-program cmd :output t :error-output t)
           (error (e)
-            ;; 簡易的なエラー処理（Phase 2で本格化）
+            ;; Basic error handling (to be enhanced later)
             (cleanup-partial-output output)
             (error e))))))
 
@@ -116,7 +115,7 @@
          (width (getf first-video-info :width))
          (height (getf first-video-info :height)))
     
-    ;; defensive check
+    ;; Ensure video metadata is valid
     (unless (and fps width height)
       (format t "~a Failed to retrieve fps/width/height from ~a~%" (log-tag "error") (car files))
       (format t "~a Check if the file is a valid video with proper metadata.~%" (log-tag "error"))
@@ -148,27 +147,27 @@
          (filters '())
          (cmd (list "ffmpeg" "-y")))
 
-    ;; ループ再生（inputより先に無いといけないらしい）
+    ;; Loop playback (must come before input argument)
     (when repeat
       (setf cmd (append cmd 
         (list "-stream_loop" (format nil "~a" (1- repeat))))))
 
     (setf cmd (append cmd (list "-i" input)))
 
-    ;; 解像度（縦：横）
+    ;; Resolution scaling
     (when scale
       (destructuring-bind (w . h) scale
         (push (format nil "scale=~A:~A" w h) filters)))
 
-    ;; 逆再生
+    ;; Reverse playback
     (when rev
       (push "reverse" filters))
     
-    ;; 速度変更
+    ;; Speed adjustment
     (when speed
       (push (format nil "setpts=PTS/~a" speed) filters))
     
-    ;; フリップ操作
+    ;; Video flipping
     (when hflip
       (push "hflip" filters))
     
@@ -179,13 +178,12 @@
       (push "format=gray" filters))
 
     (when filters
-      ;; OK: -vf "scale=1920:1080,reverse"
-      ;; NG: -vf "reverse,scale=1920:1080"
+      ;; Filter order matters: scale before effects like reverse
       (let* ((filters-str (format nil "~{~a~^,~}" (reverse filters)))
               (vf-arg (list "-vf" filters-str)))
         (setf cmd (append cmd vf-arg))))
 
-    ;; コーデック
+    ;; Video codec settings
     (when codec-info
       (let ((encoder (getf codec-info :encoder))
             (pix-fmt (getf codec-info :pix_fmt)))
@@ -193,15 +191,15 @@
         (when pix-fmt
           (setf cmd (append cmd (list "-pix_fmt" pix-fmt))))))
 
-    ;; ミュート
+    ;; Audio removal
     (when mute
       (setf cmd (append cmd (list "-an"))))
 
-    ;; フレームレート
+    ;; Frame rate
     (when fps
       (setf cmd (append cmd (list "-r" (format nil "~a" fps)))))
 
-    ;; 出力ファイル名
+    ;; Add output filename
     (setf cmd (append cmd (list output))) cmd))
 
 (defun encoder-available-p (name)
diff --git a/src/help.lisp b/src/help.lisp
index 8940587..70b532e 100644
--- a/src/help.lisp
+++ b/src/help.lisp
@@ -5,13 +5,13 @@
   (format t "~%visp - minimal ffmpeg wrapper written in Common Lisp~%~%")
   (format t "=================================================~%")
 
-  ;; Usageセクション
+  ;; Usage section
   (format t "Usage:~%")
   (format t "  visp --input <file> [options]    ;; Normal mode~%")
   (format t "  visp --merge <file1> <file2> ... ;; Merge multiple mp4 files into one~%")
   (format t "  visp --gif <file>                ;; Convert a single video to GIF~%~%")
 
-  ;; Normal mode options
+  ;; Options for normal mode
   (format t "Normal mode options:~%")
   (format t "  --input <file>        Input video file or directory (required)~%")
   (format t "                        - If a directory is specified, all video files in it will be processed in batch.~%")
@@ -32,7 +32,7 @@
   (format t "  --dry-run             Show ffmpeg command without executing~%")
   (format t "  --help                Show this help message~%~%")
 
-  ;; Merge mode explanation
+  ;; Merge mode details
   (format t "Merge mode (exclusive):~%")
   (format t "  --merge <file1> <file2> ...~%")
   (format t "    Merge multiple .mp4 videos into one output file.~%")
@@ -44,7 +44,7 @@
   (format t "    - Other options cannot be combined with --merge (except --output and --dry-run)~%")
   (format t "    - However, --dry-run can be combined to preview the ffmpeg command~%~%")
 
-  ;; GIF mode explanation
+  ;; GIF mode details
   (format t "GIF mode (exclusive):~%")
   (format t "  --gif <file>~%")
   (format t "    Convert video to GIF animation.~%")
diff --git a/src/log.lisp b/src/log.lisp
index 45de8f9..07d337a 100644
--- a/src/log.lisp
+++ b/src/log.lisp
@@ -5,8 +5,8 @@
 
 (defun log-tag (type)
   (cond
-    ((string= type "info")     (colorize "[INFO]" "34;1"))    ; 青
-    ((string= type "dry-run")  (colorize "[DRY-RUN]" "33;1")) ; 黄
-    ((string= type "warn")     (colorize "[WARN]" "35;1"))    ; 紫
-    ((string= type "error")    (colorize "[ERROR]" "31;1"))   ; 赤
-    (t type)))  ; fallback
+    ((string= type "info")     (colorize "[INFO]" "34;1"))
+    ((string= type "dry-run")  (colorize "[DRY-RUN]" "33;1"))
+    ((string= type "warn")     (colorize "[WARN]" "35;1"))
+    ((string= type "error")    (colorize "[ERROR]" "31;1"))
+    (t type)))
diff --git a/src/main.lisp b/src/main.lisp
index 97bd135..5f1054a 100644
--- a/src/main.lisp
+++ b/src/main.lisp
@@ -5,7 +5,7 @@
     (format t "~a ffmpeg not found in your system. Please install ffmpeg first.~%" (log-tag "error"))
     (uiop:quit 1))
 
-  ;; 引数がなければコマンドラインから取得
+  ;; Get command line arguments if not provided
   (unless args (setf args (uiop:command-line-arguments)))
   (setf args (clean-args args))
 
@@ -17,7 +17,7 @@
     (dispatch-validation opts)
 
     (cond
-      ;; 1. GIF モード
+      ;; GIF mode
       ((visp-options-gif opts)
        (let* ((input (visp-options-input opts))
               (fps (get-video-fps input)) 
@@ -25,25 +25,25 @@
               (cmd (build-gif-cmd opts output fps)))
          (run-cmd cmd output (visp-options-dry-run opts))))
 
-      ;; 2. 結合モード
+      ;; Merge mode
       ((visp-options-merge-files opts)
        (let* ((output (generate-merge-output-filename opts))
               (cmd (build-merge-cmd opts output)))
          (run-cmd cmd output (visp-options-dry-run opts))))
 
-      ;; 3. バッチモード
+      ;; Batch mode
       ((visp-options-batch-files opts)
        (dolist (file (visp-options-batch-files opts))
-        ;; 出力ファイル名やコマンド生成を通常モードと共通化するため、input を一時的に設定
+         ;; Temporarily set input for each file to reuse normal mode logic
         (setf (visp-options-input opts) file)
-        ;; 出力ファイル名生成
+        ;; Generate output filename in same directory as input
         (let* ((ext (getf (visp-options-codec-info opts) :ext))
-               (filename (generate-output-filename opts ext))         ;; ファイル名だけ
-               (output (output-path-in-same-directory file filename)) ;; ディレクトリと結合してフルパス化
+               (filename (generate-output-filename opts ext))
+               (output (output-path-in-same-directory file filename))
                (cmd (build-cmd opts output)))
           (run-cmd cmd output (visp-options-dry-run opts)))))
 
-      ;; 4. 通常処理
+      ;; Normal mode
       (t
        (let* ((ext (getf (visp-options-codec-info opts) :ext))
               (output (generate-output-filename opts ext))
diff --git a/src/options.lisp b/src/options.lisp
index 45a6f8e..2d21f02 100644
--- a/src/options.lisp
+++ b/src/options.lisp
@@ -9,17 +9,17 @@
   scale
   fps
   repeat
-  half      ;boolean
-  rev       ;boolean
-  mute      ;boolean
-  mono      ;boolean
-  hflip     ;boolean
-  vflip     ;boolean
-  speed     ;float
-  dry-run   ;boolean
+  half
+  rev
+  mute
+  mono
+  hflip
+  vflip
+  speed
+  dry-run
   merge-files
   batch-files
-  gif       ;boolean
+  gif
 )
 
 (defun parse-args-to-options (args)
@@ -79,7 +79,7 @@
                               (incf i))
                     (setf (visp-options-merge-files opts) (nreverse files))))
                  ((string= key "--gif")
-                  ;; --inputが既に設定されている場合はエラー
+                  ;; Error if --input already set
                   (when (visp-options-input opts)
                     (format t "~a Do not use --input with --gif. Use: visp --gif <video-file>~%" 
                             (log-tag "error"))
diff --git a/src/util.lisp b/src/util.lisp
index 1981b60..5ca95d3 100644
--- a/src/util.lisp
+++ b/src/util.lisp
@@ -75,16 +75,16 @@ Accepts integers including -1. Returns NIL on malformed input."
 
 (defun generate-output-filename (opts &optional ext)
   "Generate output filename based on visp-options and optional ext override."
-  ;; --outputが指定されていれば、それを返す
+  ;; Return custom output filename if specified
   (let ((output (visp-options-output opts)))
     (if output
         output
-        ;; 従来通りの自動生成
+        ;; Auto-generate filename based on options
         (let* ((input (visp-options-input opts))
                (base (file-namestring input))
                (dot-pos (position #\. base :from-end t))
                (name (subseq base 0 dot-pos))
-               ;; 拡張子は codec-info の ext 優先、なければ元ファイルの拡張子
+               ;; Use codec extension if available, else original extension
                (ext (or ext (subseq base dot-pos)))
                (res (visp-options-res opts))
                (res-suffix (if res (format nil "_~a" res) ""))
diff --git a/src/validate.lisp b/src/validate.lisp
index e2a0891..0fe0497 100644
--- a/src/validate.lisp
+++ b/src/validate.lisp
@@ -3,23 +3,23 @@
 (defun validate-gif-mode (opts)
   "Validate options for GIF mode: --gif accepts only video files and no other options."
   (let ((input (visp-options-input opts)))
-    ;; 入力ファイルの存在チェック
+    ;; Check if input file exists
     (unless (and input (not (string= input "")))
       (format t "~a --gif mode requires a video file. Use: visp --gif <video-file>~%"
               (log-tag "error"))
       (uiop:quit 1))
 
 
-    ;; GIFモード対応拡張子チェック（全動画形式対応）
+    ;; Check supported video file extensions
     (let ((ext (input-extension input)))
       (unless (member ext +allowed-input-extensions+ :test #'string-equal)
         (format t "~a --gif mode supports video files (.mp4, .mov, .flv, .avi, .webm), but got '~a'.~%"
                 (log-tag "error") ext)
         (uiop:quit 1)))
 
-    ;; すべての他オプションを禁止（--dry-runのみ特別に許可）
+    ;; Disallow all other options except --dry-run
     (let ((disallowed-options (list
-                                (visp-options-output opts)   ; --outputオプション禁止  
+                                (visp-options-output opts)
                                 (visp-options-res opts)
                                 (visp-options-codec opts)
                                 (visp-options-scale opts)
@@ -42,7 +42,7 @@
   "Validate options specific to --merge mode."
   (let* ((files (visp-options-merge-files opts)))
 
-    ;; --dry-runと--outputだけは併用を許可する。他はすべて禁止。
+    ;; Only allow --dry-run and --output with --merge
     (when (or (visp-options-input opts)
               (visp-options-res opts)
               (visp-options-codec opts)
@@ -58,27 +58,27 @@
       (format t "~a --merge cannot be combined with other options.~%" (log-tag "error"))
       (uiop:quit 1))
 
-    ;; ファイル数チェック
+    ;; Check minimum file count
     (unless (and files (>= (length files) 2))
       (format t "~a At least two .mp4 files must be specified for --merge.~%" (log-tag "error"))
       (uiop:quit 1))
 
-    ;; 拡張子チェック
+    ;; Check file extensions (merge mode requires .mp4)
     (dolist (file files)
       (unless (string-equal (input-extension file) ".mp4")
         (format t "~a Only .mp4 files are supported for --merge (got: ~a).~%" (log-tag "error") file)
         (uiop:quit 1)))
 
-    ;; ファイル存在確認
+    ;; Check file existence
     (dolist (file files)
       (unless (probe-file file)
         (format t "~a Input file '~a' does not exist.~%" (log-tag "error") file)
         (uiop:quit 1)))
 
-    ;; 動画情報取得
+    ;; Get video metadata
     (let* ((infos (mapcar #'get-video-info files)))
 
-      ;; メタ情報に不備があるファイルを検出（fps / width / height）
+      ;; Detect files with incomplete metadata (fps/width/height)
       (dolist (pair (mapcar #'cons files infos))
         (let ((file (car pair))
               (info (cdr pair)))
@@ -87,21 +87,21 @@
             (format t "~a This file may be corrupted or not a valid video.~%" (log-tag "error"))
             (uiop:quit 1))))
 
-      ;; 音声混在チェック
+      ;; Check for mixed audio/no-audio files
       (let ((has-audio-list (mapcar (lambda (info) (getf info :has-audio)) infos)))
         (unless (or (every #'identity has-audio-list)
                     (every #'not has-audio-list))
           (format t "~a --merge does not support mixing audio and non-audio files.~%" (log-tag "error"))
           (uiop:quit 1)))
 
-      ;; fps混在チェック（warn）
+      ;; Warn about mixed frame rates
       (let ((fps-list (remove-duplicates (mapcar (lambda (info) (getf info :fps)) infos)
                                          :test #'=)))
         (when (> (length fps-list) 1)
           (format t "~a Detected different fps values across files. All will be converted to ~afps.~%"
                   (log-tag "warn") (getf (car infos) :fps))))
 
-      ;; 解像度混在チェック（warn）
+      ;; Warn about mixed resolutions
       (let ((size-list (remove-duplicates
                         (mapcar (lambda (info)
                                   (cons (getf info :width) (getf info :height)))
@@ -117,20 +117,20 @@
 (defun validate-input (opts)
   "Check if input file or directory is provided and valid. If directory, collect target files."
   (let ((input (visp-options-input opts)))
-    ;; 入力の有無は必須
+    ;; Input is required
     (unless input
       (format t "Usage: visp --input <filename or directory> [--res 4k] [--mute] ...~%")
       (uiop:quit 1))
 
-    ;; ディレクトリ指定っぽい場合
+    ;; Handle directory input
     (if (uiop:directory-pathname-p input)
         (progn
-          ;; ディレクトリが存在するか
+          ;; Check if directory exists
           (unless (uiop:directory-exists-p input)
             (format t "~a Directory '~a' does not exist.~%" (log-tag "error") input)
             (uiop:quit 1))
 
-          ;; 対象ファイルの取得
+          ;; Get valid video files from directory
           (let ((files (remove-if-not
                          #'(lambda (p)
                              (member (input-extension p) +allowed-input-extensions+ :test #'string-equal))
@@ -139,26 +139,26 @@
               (format t "~a No valid video files found in directory '~a'.~%" (log-tag "error") input)
               (uiop:quit 1))
 
-            ;; batch-files にファイル名 (string 型) を格納
+            ;; Store file paths for batch processing
             (setf (visp-options-batch-files opts) (mapcar #'namestring files))
 
             (format t "~a Batch mode: ~a video file(s) found in directory.~%" (log-tag "info") (length files))))
 
-        ;; ファイル指定の場合
+        ;; Handle single file input
         (progn
-          ;; ファイル存在チェック
+          ;; Check if file exists
           (unless (probe-file input)
             (format t "~a Input file '~a' does not exist.~%" (log-tag "error") input)
             (uiop:quit 1))
 
-          ;; 拡張子チェック
+          ;; Check file extension
           (let ((ext (input-extension input)))
             (unless (member ext +allowed-input-extensions+ :test #'string-equal)
               (format t "~a visp does not support the input file extension '~a'.~%"
                       (log-tag "error") ext)
               (uiop:quit 1)))
 
-            ;; 動画情報の表示
+            ;; Display video information
             (print-video-info (get-video-info input))))))
 
 (defun validate-reverse (opts)
@@ -168,24 +168,24 @@
          (input (visp-options-input opts))
          (ext (input-extension input)))
 
-    ;; --reverse と --loop は併用不可
+    ;; --reverse and --loop cannot be used together
     (when (and rev repeat)
       (format t "~a --loop and --reverse options cannot be used together.~%"
               (log-tag "error"))
       (uiop:quit 1))
 
-    ;; --reverse がサポートする拡張子は限定
+    ;; --reverse only supports specific file extensions
     (when rev
       (unless (member ext '(".mp4" ".mov") :test #'string-equal)
         (format t "~a --reverse option only supports .mov or .mp4 extensions.~%"
                 (log-tag "error"))
         (uiop:quit 1))
 
-      ;; メモリ使用に関する警告
+      ;; Memory usage warning
       (format t "~a --reverse may consume a large amount of memory. Consider using small input files.~%"
               (log-tag "info"))
 
-      ;; reverse時は強制ミュート
+      ;; Force mute when reversing
       (unless (visp-options-mute opts)
         (format t "~a --reverse implies muted audio. Audio will be disabled.~%"
                 (log-tag "info"))
@@ -196,12 +196,12 @@
   (let ((repeat (visp-options-repeat opts)))
     (when repeat
       (let ((repeati (parse-integer repeat :junk-allowed t)))
-        ;; stream_loopの仕様上(repeat >= 1)がマスト
+        ;; stream_loop requires repeat >= 1
         (unless (and (integerp repeati) (>= repeati 1))
           (format t "~a --loop must be an integer >= 1, but got '~a'.~%"
                   (log-tag "error") repeat)
           (uiop:quit 1))
-        ;; repeat は数値に変換して保存
+        ;; Convert and store as integer
         (setf (visp-options-repeat opts) repeati)))))
 
 (defun validate-resolution (opts)
@@ -210,12 +210,12 @@
   (let ((res (visp-options-res opts))
         (half (visp-options-half opts)))
 
-    ;; --res と --half の併用は禁止
+    ;; --res and --half cannot be used together
     (when (and res half)
       (format t "~a --res and --half cannot be used together.~%" (log-tag "error"))
       (uiop:quit 1))
 
-    ;; --res が指定されていれば有効な解像度か確認
+    ;; Validate resolution if specified
     (when res
       (let* ((pair (resolution-from-key res))
              (dims (or (and pair (cdr pair))
@@ -243,12 +243,12 @@
   (let ((fps (visp-options-fps opts)))
     (when fps
       (let ((fpsi (parse-integer fps :junk-allowed t)))
-        ;; fpsは必ず0より大きい整数
+        ;; FPS must be positive integer
         (unless (and (integerp fpsi) (> fpsi 0))
           (format t "~a --fps must be a positive integer, but got '~a'.~%" 
                   (log-tag "error") fps)
           (uiop:quit 1))
-        ;; 明示的に整数に変換して再セット
+        ;; Convert to integer
         (setf (visp-options-fps opts) fpsi)))))
 
 (defun validate-codec (opts)
@@ -256,26 +256,26 @@
   (let* ((key (visp-options-codec opts))
          (codec-info (codec-info-from-key key)))
 
-    ;; 指定された codec が visp の対応リストにない場合
+    ;; Check if codec is supported by visp
     (when (and key (not codec-info))
       (format t "~a visp does not support the codec '~a'.~%" 
               (log-tag "error") key)
       (uiop:quit 1))
 
-    ;; codec はあるが、システムに encoder が存在しない場合
+    ;; Check if encoder is available in system ffmpeg
     (when (and codec-info
                (not (encoder-available-p (getf codec-info :encoder))))
       (format t "~a ffmpeg on this system does not support the encoder '~a'.~%"
               (log-tag "error") (getf codec-info :encoder))
       (uiop:quit 1))
 
-    ;; hapとproresはpix_fmtを指定しないといけない（そしてそれは固定値）
+    ;; Some codecs require specific pixel formats
     (when (getf codec-info :pix_fmt)
       (let* ((fmt (getf codec-info :pix_fmt))
              (label (or (cdr (assoc fmt +pixfmt-name-map+ :test #'string=)) fmt)))
         (format t "~a Using pixel format: ~a (~a)~%" (log-tag "info") label fmt)))
 
-    ;; 成功したら codec-info をオプションに保存
+    ;; Store codec info if validation succeeds
     (setf (visp-options-codec-info opts) codec-info)))
 
 (defun validate-mono (opts)
@@ -291,19 +291,19 @@
   (let ((speed (visp-options-speed opts)))
     (when speed
       (let ((speedf (parse-number speed)))
-        ;; speedは必ず0より大きい数値
+        ;; Speed must be positive number
         (unless (and (numberp speedf) (> speedf 0))
           (format t "~a --speed must be a positive number, but got '~a'.~%" 
                   (log-tag "error") speed)
           (uiop:quit 1))
-        ;; 明示的に数値に変換して再セット
+        ;; Convert to number
         (setf (visp-options-speed opts) speedf)))))
 
 (defun validate-output (opts)
   "Validate the --output option: check if parent directory exists for the given path."
   (let ((output (visp-options-output opts)))
     (when output
-      ;; 出力ファイルのディレクトリが存在するかチェック
+      ;; Check if output directory exists
       (let ((parent-dir (uiop:pathname-directory-pathname (pathname output))))
         (unless (uiop:directory-exists-p parent-dir)
           (format t "~a Output directory '~a' does not exist.~%" 
diff --git a/src/video.lisp b/src/video.lisp
index c1850a5..274871b 100644
--- a/src/video.lisp
+++ b/src/video.lisp
@@ -52,7 +52,7 @@
          (rate (assoc "r_frame_rate" info :test #'string=))
          (duration (assoc "duration" info :test #'string=)))
 
-    ;; 音声情報取得
+    ;; Get audio information
     (let* ((audio-cmd (list "ffprobe" "-v" "error"
                             "-select_streams" "a"
                             "-show_entries" "stream=codec_name"
@@ -60,7 +60,7 @@
                             input))
            (audio-codec (string-trim '(#\Newline)
                                      (uiop:run-program audio-cmd :output :string)))
-           (has-audio (not (string= audio-codec "")))) ; 空なら音声なし
+           (has-audio (not (string= audio-codec "")))) ; Empty string means no audio
       
       `(:width ,(when width (parse-integer (cdr width)))
         :height ,(when height (parse-integer (cdr height)))