Converts thumbnails to jpg for better compat (#70)

test/pinchflat/yt_dlp/download_option_builder_test.exs

@@ -125,6 +125,14 @@ defmodule Pinchflat.YtDlp.DownloadOptionBuilderTest do
       assert :write_thumbnail in res
     end
 
+    test "convertes thumbnail to jpg when download_thumbnail is true", %{media_item: media_item} do
+      media_item = update_media_profile_attribute(media_item, %{download_thumbnail: true})
+
+      assert {:ok, res} = DownloadOptionBuilder.build(media_item)
+
+      assert {:convert_thumbnail, "jpg"} in res
+    end
+
     test "includes :embed_thumbnail option when specified", %{media_item: media_item} do
       media_item = update_media_profile_attribute(media_item, %{embed_thumbnail: true})