# Action to remove non-BMP characters

**URL:** https://community.mp3tag.de/t/action-to-remove-non-bmp-characters/70119
**Category:** General Discussion
**Created:** [November 11, 2025, 12:48pm UTC](https://community.mp3tag.de/t/action-to-remove-non-bmp-characters/70119 "2025-11-11T12:48:12Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![Verklagekasper](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/v/e99b99/32.png) [@Verklagekasper](https://community.mp3tag.de/u/Verklagekasper)
#### Post date: [November 11, 2025, 12:48pm UTC](https://community.mp3tag.de/t/action-to-remove-non-bmp-characters/70119/1 "2025-11-11T12:48:12Z")

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Hi there,

the media system in my car couldn't read any audio files from a USB stick. Turned out the reason was a few file names that contained Unicode characters outside the "Basic Multilingual Plane" (BMP), U+0000 till U+FFFF. That is, outlandish stuff like emojis: 👁😂...

It took me a while to figure out how to replace such characters using mp3tag, and I want to share the result.

To get rid of non-BMP characters in tags under \*Windows\*, I used the following "Replace with regular expression" action:

Field: \_ALL

Regular expression: [\x{D800}-\x{DBFF}][\x{DC00}-\x{DFFF}]

Replaces matches with: \_

Notice that the pattern doesn't describe non-BMP characters by a range of Unicode code points but rather it decribes what the two subsequent UTF-16 units - the "surrogate pair" - used for such characters look like. I suppose the reason why this (and only this) works is that the regex parser reads strings of wide characters (wchar\_t), and on Windows wchar\_t happens to be a 16 bit word interpreted as a UTF-16 unit.

I suppose that the expression above does \*not\* work on Mac. AFAIK on Mac, the internal encoding would be UTF-32 instead of UTF-16. Which implies that non-BMP characters are actually described by a range of Unicode code points, which makes the pattern simpler:

[\x{10000}-\x{10FFFF}]

But that's just my guess, I have no Mac.

Anyway, once I had all nasty characters replaced in the tags, I generated the file names from the fixed titles, and now my car's media system can play everything again.

Cheers,

Burkhard