C# Web API File supported contentType types for audio

Question

I have a WEB API in dotnet that returns a File

for example

  var fileResult = File(wavAudioBytes, "audio/mpeg");

then return it

 [HttpGet]
 public IActionResult Get()
 {
    
     var fileResult = File(wavAudioBytes, "audio/mpeg");

     return fileResult;
 }

I wanted to know if File contentType if there is a list or built in class that has all the supported list of contentTypes that File supports as its just a string and i don't know which ones it dose or dose not ? Specifically for audio files.

Answer 1

If you're looking to return an audio file in a .NET Web API, the File() method requires a MIME type (Content-Type) as a string. Since .NET doesn't have a built-in method to fetch all valid content types, here’s how you can handle it.

Common MIME Types for Audio Files

.NET allows you to manually specify the MIME type based on the file format. Here are some commonly used types:

MP3 → "audio/mpeg"
 
WAV → "audio/wav"
 
OGG → "audio/ogg"
 
MIDI → "audio/midi"

So, if you’re returning an MP3 file, your API method might look like this:

[HttpGet]
public IActionResult GetAudio()
{
    var fileResult = File(wavAudioBytes, "audio/mpeg"); // For MP3 files
    return fileResult;
}

Handling Different File Types Dynamically

Since .NET doesn’t have a built-in class for all supported MIME types, you can map extensions to MIME types using a dictionary:

var mimeTypes = new Dictionary<string, string>
{
    { ".mp3", "audio/mpeg" },
    { ".wav", "audio/wav" },
    { ".ogg", "audio/ogg" },
    { ".aac", "audio/aac" },
    { ".flac", "audio/flac" }
};
 
string fileExtension = Path.GetExtension(fileName).ToLower();
string contentType = mimeTypes.ContainsKey(fileExtension) ? mimeTypes[fileExtension] : "application/octet-stream";
 
var fileResult = File(wavAudioBytes, contentType);

This way, your API can return different audio formats dynamically without hardcoding the MIME type.

Alternative: Using FileExtensionContentTypeProvider

Instead of maintaining a dictionary, you can use .NET’s built-in FileExtensionContentTypeProvider, which automatically maps file extensions to their correct MIME types:

using Microsoft.AspNetCore.StaticFiles;
 
var provider = new FileExtensionContentTypeProvider();
if (!provider.TryGetContentType(fileName, out string contentType))
{
    contentType = "application/octet-stream"; // Default if not found
}
 
var fileResult = File(wavAudioBytes, contentType);

This is cleaner because it automatically assigns the correct MIME type based on the file extension.

.NET doesn’t have a built-in list of supported MIME types, so you need to specify them manually.

You can hardcode common types or use a dictionary to map file extensions.

The best approach is using FileExtensionContentTypeProvider, which keeps things flexible.