How to Resolve Discord Error 50138 File Type Mismatch on Audio Upload

When you try to upload an audio file to Discord, you may see a pop-up error message that reads Error 50138 File Type Mismatch. This error occurs because Discord checks the file extension against the actual file signature and rejects the upload when they do not match. The problem is most common with audio files that have been renamed, converted incorrectly, or downloaded from sources that strip or alter the file header. This article explains the technical reason behind the mismatch and provides step-by-step methods to fix the file so you can successfully upload it to any Discord channel.

Why Discord Shows Error 50138 for Audio Files

Discord uses a security check called magic number detection to verify file types. Every audio file format has a unique byte sequence at the beginning of the file, known as the file signature or magic number. For example, an MP3 file starts with the bytes FF FB or 49 44 33 for ID3 tags. A WAV file starts with 52 49 46 46 (RIFF). When you upload a file, Discord reads these first bytes and compares them to the file extension. If the extension says .mp3 but the signature is that of a WAV file, Discord refuses the upload and returns error 50138.

This mismatch usually happens in three scenarios:

Renamed File Extensions

A user or a script changes the file extension from .wav to .mp3 without converting the actual audio data. The file header still identifies it as a WAV, but the extension claims it is an MP3.

Corrupted or Incomplete Downloads

When an audio file is downloaded from a web page or a messaging app, the download may truncate the file header or wrap it in an incorrect container. The resulting file has a valid extension but a broken signature.

Conversion Tools That Preserve the Wrong Container

Some online converters change the extension but leave the original container structure intact. The file plays correctly in a media player because the player ignores the extension and reads the container, but Discord rejects it.

Steps to Fix Error 50138 by Re-encoding the Audio File

The only reliable fix is to re-encode the file so that the file signature matches the extension. Below are two methods using free software: FFmpeg for a command-line approach and Audacity for a graphical approach.

Method 1: Re-encode with FFmpeg

1. Download and install FFmpeg
   Go to ffmpeg.org and download the Windows build. Extract the zip file to a folder such as C:\ffmpeg. Add the bin folder to your system PATH environment variable so you can run FFmpeg from any Command Prompt window.
2. Open Command Prompt
   Press Windows + R, type cmd, and press Enter. Navigate to the folder containing your audio file using the cd command. For example, cd C:\Users\YourName\Downloads.
3. Run the FFmpeg re-encode command
   Type the following command and press Enter:
   ffmpeg -i inputfile.mp3 -c:a libmp3lame -q:a 2 outputfile.mp3
   Replace inputfile.mp3 with the name of your problematic file. Replace outputfile.mp3 with a new filename. The -c:a libmp3lame flag forces re-encoding to MP3 using the LAME encoder. The -q:a 2 flag sets the quality to approximately 192 kbps, which is fine for Discord.
4. Upload the new file to Discord
   Open Discord, go to any channel, and drag the new outputfile.mp3 into the message box. The upload should proceed without error 50138.

Method 2: Re-encode with Audacity

Audacity is a free audio editor that works well for users who prefer a graphical interface.

1. Download and install Audacity
   Go to audacityteam.org and install the latest version for Windows. Also install the FFmpeg library for Audacity if prompted, as it enables MP3 export.
2. Open the problematic audio file
   Launch Audacity. Go to File > Open and select the file that causes error 50138. Audacity will read the actual audio data regardless of the file extension.
3. Export as a new MP3 file
   Go to File > Export > Export as MP3. Choose a new filename and a destination folder. In the Export Audio dialog, set the Quality to 192 kbps or 256 kbps. Click Save.
4. Upload the new file to Discord
   Drag the exported MP3 file into a Discord channel. The error should no longer appear.

If Discord Still Shows Error 50138 After Re-encoding

If the error persists, the file may have a deeper corruption or an unusual container structure. Try the following additional checks.

File Size Exceeds Discord Upload Limit

Discord free users have an upload limit of 8 MB per file. If your re-encoded file is larger than 8 MB, Discord may reject it with a different error, but some clients show error 50138 as a generic failure. Go to File Properties in Windows File Explorer and check the file size. If it exceeds the limit, reduce the bitrate during re-encoding. In FFmpeg, use -q:a 6 for approximately 128 kbps. In Audacity, choose 128 kbps during export.

File Has an Unsupported Codec

Discord supports common audio codecs: MP3, AAC, WAV, FLAC, and Ogg Vorbis. If your file uses a codec like ALAC or Opus in a non-standard container, Discord may reject it. Re-encode to MP3 or AAC using the methods above.

Antivirus or Security Software Blocks Upload

Some antivirus programs scan files during upload and may temporarily lock the file, causing Discord to read a partial header. Temporarily disable your real-time protection and try the upload again. If it works, add Discord to your antivirus exclusion list.

Discord Audio File Formats: Supported vs Unsupported

Format	Supported by Discord	Typical File Signature
MP3	Yes	FF FB or 49 44 33
WAV	Yes	52 49 46 46
FLAC	Yes	66 4C 61 43
Ogg Vorbis	Yes	4F 67 67 53
AAC in M4A	Yes	00 00 00 20 66 74 79 70 4D 34 41
WMA	No	30 26 B2 75
AIFF	No	46 4F 52 4D

Conclusion

Discord error 50138 is caused by a mismatch between the file extension and the internal file signature. You can fix it by re-encoding the audio file using FFmpeg or Audacity, which creates a new file with matching signature and extension. After re-encoding, check the file size against Discord’s upload limit and ensure the codec is one of the supported formats. For future uploads, always convert audio files with a proper converter rather than simply renaming the extension.