# Action to change extension?

**URL:** <https://community.mp3tag.de/t/action-to-change-extension/16661>\
**Category:** Support\
**Created:** [March 5, 2015, 5:19pm UTC](https://community.mp3tag.de/t/action-to-change-extension/16661 "2015-03-05T17:19:02Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![phossler](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/p/278dde/32.png) [@phossler](https://community.mp3tag.de/u/phossler)\
**Post date:** [March 5, 2015, 5:19pm UTC](https://community.mp3tag.de/t/action-to-change-extension/16661/1 "2015-03-05T17:19:02Z")

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Is there an Action that I can use to change the extension of a file?

When I use iTunes to convert an MP3 audio book it gets generated as a M4A file.

I use M4B for AAC audio books and have to use another program to make mass changes before I use MP3TAG

It'd be more convenient to just use MP3TAG

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**Author:** ![ohrenkino](https://community.mp3tag.de/user_avatar/community.mp3tag.de/ohrenkino/32/4843_2.png) [@ohrenkino](https://community.mp3tag.de/u/ohrenkino)\
**Post date:** [March 5, 2015, 5:29pm UTC](https://community.mp3tag.de/t/action-to-change-extension/16661/2 "2015-03-05T17:29:44Z")

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In the default installation, m4b files are already read by Mp3tag.  
If you want to change a filename, you can use the function  
Convert\>Tag-Tag  
for \_FILENAME\_EXT  
enter as format string:  
$replace(%\_filename\_ext%,m4a,m4b)

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**Author:** ![DetlevD](https://community.mp3tag.de/user_avatar/community.mp3tag.de/detlevd/32/123_2.png) [@DetlevD](https://community.mp3tag.de/u/DetlevD)\
**Post date:** [March 5, 2015, 5:40pm UTC](https://community.mp3tag.de/t/action-to-change-extension/16661/3 "2015-03-05T17:40:07Z")

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> [@Paul\_Hossler](#):
>
> Is there an Action that I can use to change the extension of a file? ... M4A ... M4B ...

Use an action "Replace using Regular Expression" ...  
Field: \_FILENAME  
RegExp: ^(.+).m4a$  
Replace: $1.m4b

DD.20150305.1940.CET

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**Author:** ![phossler](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/p/278dde/32.png) [@phossler](https://community.mp3tag.de/u/phossler)\
**Post date:** [March 5, 2015, 9:31pm UTC](https://community.mp3tag.de/t/action-to-change-extension/16661/4 "2015-03-05T21:31:17Z")

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Thanks to both

Appreciate it

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**Author:** ![system](https://community.mp3tag.de/uploads/default/original/2X/c/ce7035d426cb755a7916793326d23b465222a407.png) [@system](https://community.mp3tag.de/u/system)\
**Post date:** [February 9, 2026, 12:25pm UTC](https://community.mp3tag.de/t/action-to-change-extension/16661/5 "2026-02-09T12:25:34Z")

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Closed on February 9, 2026, 12:25pm UTC