feat: extract audio conversion to separate class and refine audio extraction

src/StreamShorts.Library/Media/Audio/AudioConverter.cs

@@ -0,0 +1,18 @@
+
+using NAudio.Wave;
+
+namespace StreamShorts.Library.Media.Audio;
+
+public class AudioConverter : IAudioConverter
+{
+  public Stream ConvertMp3ToWav16(Stream mp3)
+  {
+    using var reader = new Mp3FileReader(mp3);
+    var outFormat = new WaveFormat(16000, reader.WaveFormat.Channels);
+    using var resampler = new MediaFoundationResampler(reader, outFormat);
+    var waveStream = new MemoryStream();
+    WaveFileWriter.WriteWavFileToStream(waveStream, resampler);
+    waveStream.Position = 0;
+    return waveStream;
+  }
+}

src/StreamShorts.Library/Media/Audio/AudioExtractor.cs

@@ -1,13 +1,19 @@
-using FFMpegCore;
-using FFMpegCore.Pipes;
-
-using Channel = FFMpegCore.Enums.Channel;
-
 namespace StreamShorts.Library.Media.Audio;
 
 /// <inheritdoc/>
 public class AudioExtractor : IAudioExtractor
 {
+  private readonly IFFMpegService _ffmpegService = new FFMpegService();
+
+  public AudioExtractor()
+  {
+  }
+
+  internal AudioExtractor(IFFMpegService ffmpegService)
+  {
+    _ffmpegService = ffmpegService;
+  }
+
   public async Task<Stream> ExtractMp3FromMp4Async(Stream video)
   {
     if (video is null)
@@ -29,26 +35,20 @@ public class AudioExtractor : IAudioExtractor
 
     try
     {
-      using var mp3Stream = new MemoryStream();
+      var mp3Stream = new MemoryStream();
       using var mp4Stream = new MemoryStream();
 
       await video.CopyToAsync(mp4Stream).ConfigureAwait(false);
       mp4Stream.Position = 0;
 
-      var wasExtracted = await FFMpegArguments
-        .FromPipeInput(new StreamPipeSource(mp4Stream))
-        .OutputToPipe(
-          new StreamPipeSink(mp3Stream),
-          o => o.DisableChannel(Channel.Video).ForceFormat("mp3")
-        )
-        .ProcessAsynchronously()
-        .ConfigureAwait(false);
+      var wasExtracted = await _ffmpegService.ExtractAudioFromVideoAsync(mp4Stream, mp3Stream).ConfigureAwait(false);
 
       if (wasExtracted is false)
       {
         throw new FailedAudioExtractionException("Failed to extract audio from the video stream.");
       }
 
+      mp3Stream.Position = 0;
       return mp3Stream;
     }
     catch (Exception e) when (e is not FailedAudioExtractionException)

src/StreamShorts.Library/Media/Audio/IAudioConverter.cs

@@ -0,0 +1,6 @@
+namespace StreamShorts.Library.Media.Audio;
+
+public interface IAudioConverter
+{
+  Stream ConvertMp3ToWav16(Stream mp3);
+}

src/StreamShorts.Library/Media/FFMpegService.cs

@@ -0,0 +1,23 @@
+using System.Diagnostics.CodeAnalysis;
+
+using FFMpegCore;
+using FFMpegCore.Enums;
+using FFMpegCore.Pipes;
+
+namespace StreamShorts.Library.Media;
+
+[ExcludeFromCodeCoverage]
+internal class FFMpegService : IFFMpegService
+{
+  public async Task<bool> ExtractAudioFromVideoAsync(Stream video, Stream audio)
+  {
+    return await FFMpegArguments
+      .FromPipeInput(new StreamPipeSource(video))
+      .OutputToPipe(
+        new StreamPipeSink(audio),
+        static o => o.DisableChannel(Channel.Video).ForceFormat("mp3")
+      )
+      .ProcessAsynchronously()
+      .ConfigureAwait(false);
+  }
+}

src/StreamShorts.Library/Media/IFFMpegService.cs

@@ -0,0 +1,6 @@
+namespace StreamShorts.Library.Media;
+
+internal interface IFFMpegService
+{
+  Task<bool> ExtractAudioFromVideoAsync(Stream video, Stream audio);
+}

src/StreamShorts.Library/StreamShorts.Library.csproj

@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <ItemGroup>
     <PackageReference Include="FFMpegCore" />
+    <PackageReference Include="NAudio" />
   </ItemGroup>
 </Project>