Docs: Document that the $file_format parameter of metadata filters can be null.

This affects the `wp_read_video_metadata` and `wp_read_audio_metadata` filters.

Follow-up to [41746], [53764].

See #55646, #55828.

git-svn-id: https://develop.svn.wordpress.org/trunk@53768 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/media.php

@@ -3630,10 +3630,11 @@ function wp_read_video_metadata( $file ) {
 	 *
 	 * @since 4.9.0
 	 *
-	 * @param array  $metadata    Filtered video metadata.
-	 * @param string $file        Path to video file.
-	 * @param string $file_format File format of video, as analyzed by getID3.
-	 * @param array  $data        Raw metadata from getID3.
+	 * @param array       $metadata    Filtered video metadata.
+	 * @param string      $file        Path to video file.
+	 * @param string|null $file_format File format of video, as analyzed by getID3.
+	 *                                 Null if unknown.
+	 * @param array       $data        Raw metadata from getID3.
 	 */
 	return apply_filters( 'wp_read_video_metadata', $metadata, $file, $file_format, $data );
 }
@@ -3712,10 +3713,11 @@ function wp_read_audio_metadata( $file ) {
 	 *
 	 * @since 6.1.0
 	 *
-	 * @param array  $metadata    Filtered audio metadata.
-	 * @param string $file        Path to audio file.
-	 * @param string $file_format File format of audio, as analyzed by getID3.
-	 * @param array  $data        Raw metadata from getID3.
+	 * @param array       $metadata    Filtered audio metadata.
+	 * @param string      $file        Path to audio file.
+	 * @param string|null $file_format File format of audio, as analyzed by getID3.
+	 *                                 Null if unknown.
+	 * @param array       $data        Raw metadata from getID3.
 	 */
 	return apply_filters( 'wp_read_audio_metadata', $metadata, $file, $file_format, $data );
 }