feat: Add a way to convert an entire playlist

Closes #194

classes/ConvertedPlaylistArchiveStream.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * ConvertedPlaylistArchiveStream class.
+ */
+
+namespace Alltube;
+
+use Slim\Http\Stream;
+
+class ConvertedPlaylistArchiveStream extends PlaylistArchiveStream
+{
+    /**
+     * Start streaming a new video.
+     *
+     * @param Video $video Video to stream
+     *
+     * @return void
+     */
+    protected function startVideoStream(Video $video)
+    {
+        $this->curVideoStream = new Stream($video->getAudioStream());
+
+        $this->init_file_stream_transfer(
+            $video->getFileNameWithExtension('mp3'),
+            // The ZIP format does not care about the file size.
+            0
+        );
+    }
+}

classes/PlaylistArchiveStream.php

@@ -6,7 +6,6 @@
 namespace Alltube;
 
 use Barracuda\ArchiveStream\ZipArchive;
-use GuzzleHttp\Psr7\Stream;
 use Psr\Http\Message\StreamInterface;
 
 /**
@@ -33,9 +32,9 @@ class PlaylistArchiveStream extends ZipArchive implements StreamInterface
     /**
      * Current video being streamed to the archive.
      *
-     * @var Stream
+     * @var StreamInterface
      */
-    private $curVideoStream;
+    protected $curVideoStream;
 
     /**
      * True if the archive is complete.
@@ -234,7 +233,7 @@ class PlaylistArchiveStream extends ZipArchive implements StreamInterface
      *
      * @return void
      */
-    private function startVideoStream(Video $video)
+    protected function startVideoStream(Video $video)
     {
         $response = $video->getHttpResponse();
 

controllers/FrontController.php

@@ -6,6 +6,7 @@
 namespace Alltube\Controller;
 
 use Alltube\Config;
+use Alltube\ConvertedPlaylistArchiveStream;
 use Alltube\EmptyUrlException;
 use Alltube\Locale;
 use Alltube\LocaleManager;
@@ -378,7 +379,11 @@ class FrontController
     private function getStream(Request $request, Response $response)
     {
         if (isset($this->video->entries)) {
+            if ($request->getQueryParam('audio')) {
+                $stream = new ConvertedPlaylistArchiveStream($this->video);
+            } else {
                 $stream = new PlaylistArchiveStream($this->video);
+            }
             $response = $response->withHeader('Content-Type', 'application/zip');
             $response = $response->withHeader(
                 'Content-Disposition',