feat: enable processing of large video files over 2GB

Update audio extraction to use file-based streaming
instead of in-memory buffers to support processing
video files larger than 2GB.

**Changes:**
- Modified `IAudioExtractor.ExtractMp3FromMp4Async()`
  to accept an output audio stream parameter instead
  of creating a MemoryStream internally
- Updated `AudioExtractor` to write directly to the
  provided audio stream, eliminating the need to load
  entire video into memory
- Enhanced `FFMpegService` to detect FileStream inputs
  and use direct file-to-file processing when possible,
  falling back to pipe-based streaming for other stream types
- Refactored `DefaultCommand` to create output directory
  and audio file stream before extraction, enabling direct
  file-based audio extraction
- Updated all unit and integration tests to accommodate the
  new audio stream parameter

This change prevents `OutOfMemoryException` errors when processing
large video files by streaming data directly to disk rather than
buffering in memory. Additionally, it removes the possibility of
overflowing the 2GB size limit that `MemoryStream` has, which
would result in `IOException` errors when trying to write or
copy to it.

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

@@ -25,7 +25,7 @@ public sealed class AudioExtractor : IAudioExtractor
     _videoService = videoService ?? throw new ArgumentNullException(nameof(videoService), $"{nameof(videoService)} cannot be null");
   }
 
-  public async Task<Stream> ExtractMp3FromMp4Async(Stream video)
+  public async Task<Stream> ExtractMp3FromMp4Async(Stream video, Stream audio)
   {
     if (video is null)
     {
@@ -42,25 +42,29 @@ public sealed class AudioExtractor : IAudioExtractor
       throw new ArgumentException("Video stream must be seekable", nameof(video));
     }
 
+    if (audio is null)
+    {
+      throw new ArgumentNullException(nameof(audio), "Audio stream cannot be null");
+    }
+
+    if (audio.CanWrite is false)
+    {
+      throw new ArgumentException("Audio stream must be writable", nameof(audio));
+    }
+
     var originalPosition = video.Position;
 
     try
     {
-      var mp3Stream = new MemoryStream();
-      using var mp4Stream = new MemoryStream();
-
-      await video.CopyToAsync(mp4Stream).ConfigureAwait(false);
-      mp4Stream.Position = 0;
-
-      var wasExtracted = await _videoService.ExtractAudioFromVideoAsync(mp4Stream, mp3Stream).ConfigureAwait(false);
+      var wasExtracted = await _videoService.ExtractAudioFromVideoAsync(video, audio).ConfigureAwait(false);
 
       if (wasExtracted is false)
       {
         throw new FailedAudioExtractionException("Failed to extract audio from the video stream.");
       }
 
-      mp3Stream.Position = 0;
-      return mp3Stream;
+      audio.Position = 0;
+      return audio;
     }
     catch (Exception e) when (e is not FailedAudioExtractionException)
     {

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

@@ -9,11 +9,14 @@ public interface IAudioExtractor
   /// Extracts MP3 audio from an MP4 video stream.
   /// </summary>
   /// <param name="video">The input video stream.</param>
+  /// <param name="audio">The output audio stream where the extracted MP3 will be written.</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="ArgumentNullException">Thrown when the audio stream is null.</exception>
+  /// <exception cref="ArgumentException">Thrown when the audio stream is not writable.</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);
+  Task<Stream> ExtractMp3FromMp4Async(Stream video, Stream audio);
 }

src/StreamShorts.Library/Media/FFMpegService.cs

@@ -12,14 +12,17 @@ internal sealed class FFMpegService : IVideoService
 {
   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);
+    var inputArguments = video is FileStream videoFileStream
+      ? FFMpegArguments.FromFileInput(videoFileStream.Name)
+      : FFMpegArguments.FromPipeInput(new StreamPipeSource(video));
+
+    Action<FFMpegArgumentOptions> arguments = static o => o.DisableChannel(Channel.Video).ForceFormat("mp3");
+
+    var processor = audio is FileStream audioFileStream
+      ? inputArguments.OutputToFile(audioFileStream.Name, addArguments: arguments)
+      : inputArguments.OutputToPipe(new StreamPipeSink(audio), addArguments: arguments);
+    
+    return await processor.ProcessAsynchronously().ConfigureAwait(false);
   }
 
   public async Task CreateClipFromVideoAsync(