How to Mount Subtitles for Blu-ray Movie Files

🛠 Tools and Programming
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This article was converted by SimpRead; the original source is www.zhihu.com.

The BD original disc format wasn’t specified.

If it’s a complete BDMV folder, locate the corresponding MPLS file for the main feature video inside the PLAYLIST subfolder; name your subtitle file identically to that MPLS file (e.g., if the MPLS file is 00001.mpls, name your subtitle 00001.sup). For convenience, you may create a shortcut to the MPLS file.

If instead you only have standalone M2TS video files, simply attach external subtitles directly—or remux them together with subtitles into a single MKV container. If you prefer the BDMV folder structure, you can also use tsMuxerGUI to convert M2TS files back into a full BDMV folder layout (though this is usually unnecessary).

If you’re working with physical Blu-ray discs or ISO disc images, just copy out the entire disc contents and follow the steps above.

For Blu-ray collectors, the ultimate archival format is the BDMV folder paired with DIY externally attached PGS subtitles (.sup), delivering the purest possible experience.

Let’s emphasize this: Simply place your DIY subtitle file in the same folder as the target MPLS file — no extra manipulation required. Avoid modifying or altering any files within the original BDMV folder structure; doing so compromises authenticity. If you must modify something, remuxing into MKV is simpler and more reliable.

For typical home theater setups, remuxing into MKV format is convenient for TV playback. However, on PCs or projectors, where playback restrictions are minimal, preserving the native BDMV folder structure is preferable — not only does it allow access to bonus features (e.g., behind-the-scenes material), but it also retains the authentic “feel” of an original Blu-ray disc.

Hope this helps!

Update (July 1, 2022): Clarifying proper external subtitle attachment — some users may still be unclear about correct implementation, leading to unrecognized subtitles in media players.

Also included below is a brief overview of common subtitle formats and their characteristics.

Common subtitle filename conventions:

  • Movie Name.[ASS](https://zhida.zhihu.com/search?content_id=475077835&content_type=Answer&match_order=1&q=ass&zd_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJ6aGlkYV9zZXJ2ZXIiLCJleHAiOjE3NzEwMzY4NjAsInEiOiJhc3MiLCJ6aGlkYV9zb3VyY2UiOiJlbnRpdHkiLCJjb250ZW50X2lkIjo0NzUwNzc4MzUsImNvbnRlbnRfdHlwZSI6IkFuc3dlciIsIm1hdGNoX29yZGVyIjoxLCJ6ZF90b2tlbiI6bnVsbH0.K4c_651v6x87_fM2FWRrT7CYFj97rkcdUpI2YOSI3Rk&zhida_source=entity) — Most widely used text-based subtitle format
  • Movie Name.[SRT](https://zhida.zhihu.com/search?content_id=475077835&content_type=Answer&match_order=1&q=srt&zd_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJ6aGlkYV9zZXJ2ZXIiLCJleHAiOjE3NzEwMzY4NjAsInEiOiJzcnQiLCJ6aGlkYV9zb3VyY2UiOiJlbnRpdHkiLCJjb250ZW50X2lkIjo0NzUwNzc4MzUsImNvbnRlbnRfdHlwZSI6IkFuc3dlciIsIm1hdGNoX29yZGVyIjoxLCJ6ZF90b2tlbiI6bnVsbH0.24bM0Ixre36kAWYwxcOZWjPf-8Mv2-bkWALvTrV3p_A&zhida_source=entity) — Most basic text-based subtitle format
  • Movie Name.[SSA](https://zhida.zhihu.com/search?content_id=475077835&content_type=Answer&match_order=1&q=ssa&zd_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJ6aGlkYV9zZXJ2ZXIiLCJleHAiOjE3NzEwMzY4NjAsInEiOiJzc2EiLCJ6aGlkYV9zb3VyY2UiOiJlbnRpdHkiLCJjb250ZW50X2lkIjo0NzUwNzc4MzUsImNvbnRlbnRfdHlwZSI6IkFuc3dlciIsIm1hdGNoX29yZGVyIjoxLCJ6ZF90b2tlbiI6bnVsbH0.OW3L8AunrkzGgMG30DDicAWtBD8vGh7P5BiddjjLvB4&zhida_source=entity) — Rarely used today; largely superseded by ASS
  • Movie Name.SUB — Graphical subtitle format commonly used on DVD original discs (typically embedded within the video stream)
  • Movie Name.SUP — Graphical subtitle format (i.e., PGS subtitles), standard for Blu-ray original discs

Difference Between Text-Based and Graphical Subtitles:

Text-based subtitles (e.g., ASS/SRT/SSA) can be opened and edited directly in subtitle editors — allowing modification of both text content and timing. Graphical subtitles (e.g., SUB/SUP), by contrast, are image-based streams — they cannot be edited directly and require OCR recognition and conversion into text-based formats before editing.

How to Correctly Attach External Subtitles

Three Key Rules:

  1. Identify precisely which file you click to initiate playback.
  2. Name your subtitle file identically to that playback-initiating file.
  3. Ensure the subtitle file resides in the same folder as the playback-initiating file.

That’s all.

Beginner-Friendly Explanation:

Typically, video files such as .mp4, .mkv, .ts, or .m2ts start playing immediately when clicked. For these files:

Example:

  • Video filename: Iron Man.mkv
  • Corresponding external subtitle filename: Iron Man.ass

In short: Under normal circumstances, the base part of the subtitle filename must match the base part of the video filename exactly. Both files must reside in the same folder.

Within your media player, the attached subtitle will appear as .ass.

To add descriptive language tags (e.g., indicating language or type), you may append identifiers before the extension:

Example: Iron Man.chs.ass
→ Within the player, this appears as chs.ass

Logic: As long as the prefix matches the video filename, followed by a dot (.), the player will recognize it. After the dot, you may specify the subtitle format (e.g., .ass, .sup) or add optional descriptors like chs (Chinese Simplified), eng (English), etc., then end with the appropriate extension.

Full filename example: Iron Man.chs.ass
Player display: chs.ass

Special Note on Attaching Subtitles to Blu-ray Original Discs:

Blu-ray original discs contain “playlist” files with the .mpls extension located in the BDMV/PLAYLIST/ subfolder. Open the PLAYLIST folder — you’ll see multiple .mpls files. These small files (usually ~1 KB each) act as pointers directing the player to actual video content stored in the STREAM/ folder as .m2ts files — the latter being the true primary video assets.

Among those .mpls files, some launch special features (e.g., behind-the-scenes footage), others play previews or trailers; only one or a few correspond to the main movie. You need to identify the correct one:

  • In Chinese releases: typically 00001.mpls
  • In North American releases: often 00100.mpls or 00001.mpls
  • In German releases: frequently 00800.mpls

Some follow patterns; others don’t — if uncertain, test sequentially (preferably starting with round-numbered files). Once identified, rename your subtitle file to match that .mpls filename exactly.

Example: If 00100.mpls launches the main film, name your subtitle 00100.sup. When you open 00100.mpls, playback will correctly route to its associated .m2ts file and load the matching .sup subtitle.

Some users prefer opening .m2ts files directly to play Blu-ray content — in that case, simply name your subtitle to match the corresponding .m2ts filename (e.g., 00001.m2ts → 00001.sup).

Crucial Reminder: Your subtitle file must reside in the same folder as the file you click to begin playback.

  • If launching via .mpls: Place subtitle in the PLAYLIST folder alongside the .mpls file.
  • If launching via .m2ts: Place subtitle in the STREAM folder alongside the .m2ts file.

This guide is as thorough as possible — surely no one could remain confused after reading this.

Watching movies should be fun — and yes, tinkering is part of the joy. I tinker — therefore, I am happy.