# M4B file cannot be opened for editng **URL:** \ **Category:** Support\ **Created:** [January 19, 2021, 8:33pm UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661 "2021-01-19T20:33:38Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![idealbrandon](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/i/7feea3/32.png) [@idealbrandon](https://community.mp3tag.de/u/idealbrandon)\ **Post date:** [January 19, 2021, 8:33pm UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661/1 "2021-01-19T20:33:38Z")
I've scoured the forums here for hours and can't find a way to fix this. I have around 400 audiobooks in M4B format, converted using AudioBookBuilder on a mac. I've never had any issues with these files, except with MP3tag. With every.single.file I have tried, if I try to edit tags, I get the `[filename] cannot be opened for writing` error. If I pull these same files over to EZ Meta Tag Editor, change something about the meta and save it there, I am now able to edit the file in MP3Tag. This is not a file ownership issue. I've used some of the tools (mp3val, foobar) that I've seen linked, but they either can't read M4B files or report no issues. Any help is much appreciated. ---
**Author:** ![Florian](https://community.mp3tag.de/user_avatar/community.mp3tag.de/florian/32/5759_2.png) [@Florian](https://community.mp3tag.de/u/Florian)\ **Post date:** [January 19, 2021, 8:46pm UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661/2 "2021-01-19T20:46:48Z")
Hello and welcome! > [@idealbrandon](#): > > I am now able to edit the file in MP3Tag That's interesting. Can you share (privately) one of the files before editing them in another program? ---
**Author:** ![idealbrandon](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/i/7feea3/32.png) [@idealbrandon](https://community.mp3tag.de/u/idealbrandon)\ **Post date:** [January 19, 2021, 9:27pm UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661/3 "2021-01-19T21:27:52Z")
What is the easiest way for me to privately send you a link? ---
**Author:** ![Florian](https://community.mp3tag.de/user_avatar/community.mp3tag.de/florian/32/5759_2.png) [@Florian](https://community.mp3tag.de/u/Florian)\ **Post date:** [January 20, 2021, 5:26am UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661/4 "2021-01-20T05:26:34Z")
If you have Google Drive, DropBox, OneDrive, ... you can upload it there and send me the direct link via PM or [email](https://www.mp3tag.de/en/contact.html). If it's below \< 10MB you can also send it directly. Thanks! ---
**Author:** ![Florian](https://community.mp3tag.de/user_avatar/community.mp3tag.de/florian/32/5759_2.png) [@Florian](https://community.mp3tag.de/u/Florian)\ **Post date:** [January 23, 2021, 5:36pm UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661/5 "2021-01-23T17:36:02Z")
Thanks for the example file! I was able to reproduce the issue and after a long debugging session identified the root cause to be the `mdat` atom actually being 8 bytes smaller than reported in the atom header. This might sound gibberish but simply means, that the file was wrongly encoded. In such cases, I'm not trying to make any assumptions (which could actually lead to data loss), but simply stop and report an error. I wanted to contact the developer to describe the issue and noticed in the changelog, that the issue is apparently already fixed with Audiobook Builder 2.1.2: > Zaps a potenial ‘mdat’ atom length issue. Can you check if you're using this version, and if not, update and verify that the files are working? If you still encounter issues with files built by Audiobook Builder 2.1.2, please send me another example file to analyze the issue. ---
**Author:** ![idealbrandon](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/i/7feea3/32.png) [@idealbrandon](https://community.mp3tag.de/u/idealbrandon)\ **Post date:** [February 5, 2021, 5:23pm UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661/6 "2021-02-05T17:23:02Z")
Hello Florian. I was finally able to test this and can confirm that things are working properly. Thanks for your help ---
**Author:** ![system](https://community.mp3tag.de/uploads/default/original/2X/c/ce7035d426cb755a7916793326d23b465222a407.png) [@system](https://community.mp3tag.de/u/system)\ **Post date:** [March 7, 2021, 5:23pm UTC](https://community.mp3tag.de/t/m4b-file-cannot-be-opened-for-editng/51661/7 "2021-03-07T17:23:32Z")
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