feat: refactor audio extraction to reusable class

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

@@ -0,0 +1,63 @@
+using FFMpegCore;
+using FFMpegCore.Pipes;
+
+using Channel = FFMpegCore.Enums.Channel;
+
+namespace StreamShorts.Library.Media.Audio;
+
+/// <inheritdoc/>
+public class AudioExtractor : IAudioExtractor
+{
+  public async Task<Stream> ExtractMp3FromMp4Async(Stream video)
+  {
+    if (video is null)
+    {
+      throw new ArgumentNullException(nameof(video), "Video stream cannot be null");
+    }
+
+    if (video.CanRead is false)
+    {
+      throw new ArgumentException("Video stream must be readable", nameof(video));
+    }
+
+    if (video.CanSeek is false)
+    {
+      throw new ArgumentException("Video stream must be seekable", nameof(video));
+    }
+
+    var originalPosition = video.Position;
+
+    try
+    {
+      using 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);
+
+      if (wasExtracted is false)
+      {
+        throw new FailedAudioExtractionException("Failed to extract audio from the video stream.");
+      }
+
+      return mp3Stream;
+    }
+    catch (Exception e) when (e is not FailedAudioExtractionException)
+    {
+      throw new FailedAudioExtractionException("Failed to extract audio", e);
+    }
+    finally
+    {
+      video.Position = originalPosition;
+    }
+  }
+}

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

@@ -0,0 +1,16 @@
+namespace StreamShorts.Library.Media.Audio;
+
+public class FailedAudioExtractionException : Exception
+{
+  public FailedAudioExtractionException() : base()
+  {
+  }
+
+  public FailedAudioExtractionException(string message) : base(message)
+  {
+  }
+
+  public FailedAudioExtractionException(string message, Exception innerException) : base(message, innerException)
+  {
+  }
+}

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

@@ -0,0 +1,19 @@
+namespace StreamShorts.Library.Media.Audio;
+
+/// <summary>
+/// Represents an interface for extracting audio from video streams.
+/// </summary>
+public interface IAudioExtractor
+{
+  /// <summary>
+  /// Extracts MP3 audio from an MP4 video stream.
+  /// </summary>
+  /// <param name="video">The input video stream.</param>
+  /// <returns>A stream containing the extracted MP3 audio.</returns>
+  /// <exception cref="ArgumentNullException">Thrown when the video stream is null.</exception>
+  /// <exception cref="ArgumentException">Thrown when the video stream is not readable.</exception>
+  /// <exception cref="ArgumentException">Thrown when the video stream is not seekable.</exception>
+  /// <exception cref="FailedAudioExtractionException">Thrown when the audio extraction fails.</exception>
+  /// <remarks>The method will preserve the passed video stream's data and position.</remarks>
+  Task<Stream> ExtractMp3FromMp4Async(Stream video);
+}

src/StreamShorts.Library/StreamShorts.Library.csproj

@@ -1,3 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
-
+  <ItemGroup>
+    <PackageReference Include="FFMpegCore" />
+  </ItemGroup>
 </Project>