You uploaded an audio file to a lesson. It plays fine on your Mac or iPhone. Then a student on Android or Windows tells you it shows 0:00 and will not play.
The file is not broken. The label on it is wrong.
This guide shows you how to spot the problem and re-export your audio so it plays for every student on every device.
Who runs into this
You record audio in Voice Memos, GarageBand, or another Apple tool
You rename the file to .mp3 before uploading
Your file plays on Apple devices but fails on Android and Windows
Why your audio fails on Android and Windows
Think of an audio file as a box with a label.
The label is the file extension, like .mp3 or .m4a
The contents are the actual audio inside the box
Apple tools like Voice Memos save audio in M4A format. When you rename that file to .mp3, you change the label but not the contents. The box still holds M4A audio. The label now says MP3.
Apple devices ignore the mismatch and play the file anyway. Android and Windows do not. They open the box, see the label does not match the contents, and refuse to play.
Your students on Android often see the file download and relabel itself as .m4a. That is their device correcting the wrong label you gave it.
Important: Renaming an audio file does not convert it. You have to re-export the audio to change what is actually inside the box.
How to fix audio that won't play
Use this when you have a file that fails on Android or Windows. You will re-export it to create a clean file.
Fix it on a Mac
Find the original recording in Finder
Right-click the file, choose Rename, and change the extension from .mp3 to .m4a
Open the file in QuickTime Player
Go to File > Export As > Audio Only
Save the new file
Upload the exported .m4a file to your lesson
Fix it on Windows
Download and install VLC media player from videolan.org
Open VLC, go to Media > Convert / Save
Click Add, select your audio file, then click Convert / Save
Under Profile, choose Audio - MP3
Set a destination file ending in .mp3, then click Start
Upload the converted file to your lesson
Both methods rebuild the audio so the label matches the contents. Android and Windows then accept the file and play it.
Tip: Keep the re-exported file. Do not rename it back to a different extension. That would reintroduce the mismatch and break playback again.
How to check a file before you upload it
You can verify any audio file before it ever reaches a lesson. This catches the problem early. The file extension alone tells you nothing about what is inside.
Check on a Mac
Open Terminal on your Mac
Type file followed by a space
Drag your audio file directly into the Terminal window to paste its path
Press Return
Read the result against this table:
Extension | Inspection result | Status |
.mp3 | MPEG ADTS, layer III | Clean. Safe to upload. |
.mp3 | ISO Media, Apple iTunes ALAC/AAC-LC (.M4A) Audio | Broken. Re-export before upload. |
.m4a | ISO Media, Apple iTunes ALAC/AAC-LC (.M4A) Audio | Clean. Safe to upload. |
Check on Windows
Windows has no built-in command for this. Use VLC media player to read the real format.
Download and install VLC media player from videolan.org
Open VLC, go to Media > Open File, and select your audio file
Press Ctrl+J, or go to Tools > Codec Information
Read the Codec field
Read the result against this table:
Codec field shows | What it means | Status |
MPEG Audio layer 1/2/3 (mpga) | Genuine MP3 | Clean. Safe to upload. |
MPEG AAC Audio (mp4a) | File is actually AAC/M4A | Broken. Re-export before upload. |
The rule is the same on both systems. The label and the contents have to match. An MP3 file should report MP3 audio inside. An M4A file should report AAC audio inside.
FAQs
Why does my audio play on my Mac but not for my students?
Why does my audio play on my Mac but not for my students?
Apple software is relaxed about format mismatches and plays the file regardless. Android and Windows check that the file extension matches the audio inside. When it does not, they reject the file.
Can I just rename the file from .mp3 to .m4a?
Can I just rename the file from .mp3 to .m4a?
Renaming alone is not enough to guarantee a clean file. Re-export the audio with QuickTime on a Mac or VLC on Windows. That rebuilds the file with a matching label and contents so every platform accepts it.
Which tools cause this problem?
Which tools cause this problem?
Voice Memos, GarageBand, and similar Apple apps save audio as AAC inside an M4A file by default. The problem starts the moment you change that file to .mp3 without re-exporting it.
My file shows 0:00. Does that mean it is corrupted?
My file shows 0:00. Does that mean it is corrupted?
No. The audio is intact. Teachable cannot read the duration because the file label does not match the format inside. Re-export the file and the duration displays correctly.
How do I avoid this for future uploads?
How do I avoid this for future uploads?
Check each audio file before you upload it. Use Terminal on a Mac or VLC on Windows. Only upload files where the extension matches the contents. This takes seconds and prevents student complaints later.