Introduce the ability to split a video's original audio without encoding

This commit introduces the "raw" encoding mechanism, which does nothing
except split the source audio into separate tracks without any encoding
whatsoever. This option is perfect for those who prefer to simply split
the audio into separate files in the original format.

To use, simply use '--format raw' as the parameter.

README.md

@@ -27,6 +27,7 @@ This project allows you to transform long YouTube album videos into properly cur
 - Embedded cover art, using thumbnails derived from the provided video, or using an existing image
 - Batch processing of multiple album videos from YouTube or local videos
 - Song information can be read from a file, or from a YouTube video's chapters/timeline
+- Optional lossless splitting of the video's original audio, without any re-encoding whatsoever
 
 ## Album Records
 
@@ -68,6 +69,10 @@ First, create the records file as described above. Once you're done, invoke the
     # encoding of choice (default is mp3)
     --format flac \
 
+    # losslessly split the original audio
+    # no metadata or re-encoding is applied
+    --format raw \
+
     # mass fill with optional metadata
     --genre "OP/ED/IN/IM" \
     --artist "Various" --artist "Artists" \
@@ -82,7 +87,7 @@ Once you're ready, continue with the program and it will start curating the vide
 
 | Parameter         | Description                                                                              |
 | ----------------- | ---------------------------------------------------------------------------------------- |
-| `--format=VALUE`  | audio encoding format; supported values: `mp3`, `flac`, `vorbis`, `opus`                 |
+| `--format=VALUE`  | audio encoding format; supported values: `mp3`, `flac`, `vorbis`, `opus`, `raw`          |
 | `--album=VALUE`   | path to album record file(s) (see above); multiple `--album 'abc.txt' --album 'xyz.txt'` |
 | `--artist=VALUE`  | album artist(s) to assign to the tracks' metadata; multiple: `--artist 'a' --artist 'b'` |
 | `--genre=VALUE`   | genre to assign to the tracks' metadata                                                  |

doc/encoding.md

@@ -10,3 +10,6 @@ The encoding process creates an audio file of a [track](./track.md) using the ch
 | FLAC       | `flac`     |
 | Ogg Vorbis | `oggenc`   |
 | Ogg Opus   | `opusenc`  |
+| RAW^0      | `ffmpeg`   |
+
+^0 = RAW refers to lossless splitting of the video's original audio stream into separate tracks, without any re-encoding whatsoever. Everything described above gets skipped when using this encoding "format".

src/Albums/Album.cs

@@ -21,7 +21,7 @@
 using System.Linq;
 using System.Text.Json.Serialization;
 using System.Xml.Serialization;
-using Gunloader.Programs;
+using Gunloader.Encoders;
 using Gunloader.Serialisation;
 using static System.Guid;
 using static System.IO.Path;
@@ -63,16 +63,18 @@ public DirectoryInfo Target /* normalised album title // guid on empty album */
 
     public void Encode(Toolkit toolkit)
     {
+      var output  = new FileInfo(NewGuid().ToString());
+      var extract = toolkit.Encoder is RAW;
       var video = Source.Contains("http")
-        ? toolkit.YTDL.Download(Source, new FileInfo(NewGuid().ToString()))
+        ? toolkit.YTDL.Download(Source, output, extract)
         : new FileInfo(Source);
 
       if (!Target.Exists)
         Target.Create();
 
       foreach (var track in Tracks)
       {
-        var encoded = track.Encode(toolkit, new FileInfo(Source));
+        var encoded = track.Encode(toolkit, video);
         var final   = Combine(Target.FullName, $"{track.Number}. {track.Normalised}{encoded.Extension}");
 
         encoded.MoveTo(final);

src/Encoders/RAW.cs

@@ -0,0 +1,52 @@
+/**
+ * Copyright (C) 2021 Miris Wisdom
+ * 
+ * This file is part of Gunloader.
+ * 
+ * Gunloader is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2.
+ * 
+ * Gunloader is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with Gunloader.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+using System.Diagnostics;
+using System.IO;
+using static System.Diagnostics.Process;
+using static System.IO.Path;
+
+namespace Gunloader.Encoders
+{
+  public class RAW : Encoder
+  {
+    public string Program { get; set; } = "ffmpeg";
+
+    public override FileInfo Encode(Track track, FileInfo audio = null, FileInfo cover = null)
+    {
+      audio ??= new FileInfo(track.Number + ".wav");
+      var output = $"{GetFileNameWithoutExtension(track.Number)}{audio.Extension}";
+
+      /**
+       * Split input audio into separate files of the same type, without any form of re-encoding.
+       */
+
+      Start(new ProcessStartInfo
+      {
+        FileName = Program,
+        Arguments = $"-ss {track.Start} "                                                  +
+                    $"{(string.IsNullOrWhiteSpace(track.End) ? "" : $"-to {track.End}")} " +
+                    $"-i {audio.Name} "                                                    +
+                    "-c:a copy "                                                           +
+                    $"{output}"
+      })?.WaitForExit();
+
+      return new FileInfo(output);
+    }
+  }
+}

src/Program.Args.cs

@@ -79,6 +79,12 @@ public static partial class Program
               Toolkit.Encoder      = new Opus();
               Toolkit.FFmpeg.Lossy = true;
               break;
+            case "raw":
+            case "original":
+            case "no-encode":
+              Toolkit.Encoder      = new RAW();
+              Toolkit.FFmpeg.Lossy = false;
+              break;
             default:
               WriteLine("Unknown format provided!");
               Exit(2);

src/Programs/YTDL.cs

@@ -28,13 +28,14 @@ public class YTDL
   {
     public string Program { get; set; } = "youtube-dl";
 
-    public FileInfo Download(string download, FileInfo output)
+    public FileInfo Download(string download, FileInfo output, bool extract = false)
     {
       Start(new ProcessStartInfo
       {
         FileName = Program,
-        Arguments = $"{download} " +
-                    $"--output {output.Name}"
+        Arguments = $"{download} "                                 +
+                    $"{(extract ? "-x --format bestaudio" : "")} " +
+                    $"--output {output.Name}.%(ext)s"
       })?.WaitForExit();
 
       /**

src/Track.cs

@@ -20,6 +20,7 @@
 using System.Linq;
 using System.Text.Json.Serialization;
 using System.Xml.Serialization;
+using Gunloader.Encoders;
 
 namespace Gunloader
 {
@@ -53,16 +54,25 @@ public class Track
 
     public FileInfo Encode(Toolkit toolkit, FileInfo video)
     {
-      var cover   = toolkit.FFmpeg.ExtractCover(video, this);
-      var audio   = toolkit.FFmpeg.ExtractAudio(video, this);
-      var encoded = toolkit.Encoder.Encode(this, audio, cover);
+      var      cover = toolkit.FFmpeg.ExtractCover(video, this);
+      FileInfo encoded;
+
+      if (toolkit.Encoder is RAW)
+      {
+        encoded = toolkit.Encoder.Encode(this, video, cover);
+      }
+      else
+      {
+        var audio = toolkit.FFmpeg.ExtractAudio(video, this);
+        encoded = toolkit.Encoder.Encode(this, audio, cover);
+
+        if (audio.Exists)
+          audio.Delete();
+      }
 
       if (cover.Exists)
         cover.Delete();
 
-      if (audio.Exists)
-        audio.Delete();
-
       return encoded;
     }
   }