fix typo

goutubedl.go

@@ -431,7 +431,9 @@ type DownloadResult struct {
 	waitCh chan struct{}
 }
 
-// Download is a shortcut of DownloadOptions where the options use the default value
+// Download format matched by filter (usually a format id or quality designator).
+// If filter is empty, then youtube-dl will use its default format selector.
+// It's a shortcut of DownloadWithOptions where the options use the default value
 func (result Result) Download(ctx context.Context, filter string) (*DownloadResult, error) {
 	return result.DownloadWithOptions(ctx, DownloadOptions{
 		Filter: filter,
@@ -443,7 +445,7 @@ type DownloadOptions struct {
 	// If filter is empty, then youtube-dl will use its default format selector.
 	Filter string
 	// The index of the entry to download from the playlist that would be
-	// passed to youtube-dl wia --playlist-items. The index value starts at 1
+	// passed to youtube-dl via --playlist-items. The index value starts at 1
 	PlaylistIndex int
 }
 

goutubedl_test.go

@@ -343,7 +343,7 @@ func TestDownloadPlaylistEntry(t *testing.T) {
 	}
 
 	dr, err := r.DownloadWithOptions(context.Background(), goutubedl.DownloadOptions{
-		PlaylistIndex: playlistIndex + 1,
+		PlaylistIndex: int(r.Info.Entries[playlistIndex].PlaylistIndex),
 		Filter:        r.Info.Entries[playlistIndex].Formats[0].FormatID,
 	})
 	if err != nil {