wp_get_webp_info()

wp_get_webp_info( string $filename ): array

function wp_get_webp_info( $filename ) {
	$width  = false;
	$height = false;
	$type   = false;

	if ( 'image/webp' !== wp_get_image_mime( $filename ) ) {
		return compact( 'width', 'height', 'type' );
	}

	$magic = file_get_contents( $filename, false, null, 0, 40 );

	if ( false === $magic ) {
		return compact( 'width', 'height', 'type' );
	}

	// Make sure we got enough bytes.
	if ( strlen( $magic ) < 40 ) {
		return compact( 'width', 'height', 'type' );
	}

	/*
	 * The headers are a little different for each of the three formats.
	 * Header values based on WebP docs, see https://developers.google.com/speed/webp/docs/riff_container.
	 */
	switch ( substr( $magic, 12, 4 ) ) {
		// Lossy WebP.
		case 'VP8 ':
			$parts  = unpack( 'v2', substr( $magic, 26, 4 ) );
			$width  = (int) ( $parts[1] & x3FFF );
			$height = (int) ( $parts[2] & x3FFF );
			$type   = 'lossy';
			break;
		// Lossless WebP.
		case 'VP8L':
			$parts  = unpack( 'C4', substr( $magic, 21, 4 ) );
			$width  = (int) ( $parts[1] | ( ( $parts[2] & x3F ) << 8 ) ) + 1;
			$height = (int) ( ( ( $parts[2] & xC0 ) >> 6 ) | ( $parts[3] << 2 ) | ( ( $parts[4] & x03 ) << 10 ) ) + 1;
			$type   = 'lossless';
			break;
		// Animated/alpha WebP.
		case 'VP8X':
			// Pad 24-bit int.
			$width = unpack( 'V', substr( $magic, 24, 3 ) . "\x00" );
			$width = (int) ( $width[1] & xFFFFFF ) + 1;
			// Pad 24-bit int.
			$height = unpack( 'V', substr( $magic, 27, 3 ) . "\x00" );
			$height = (int) ( $height[1] & xFFFFFF ) + 1;
			$type   = 'animated-alpha';
			break;
	}

	return compact( 'width', 'height', 'type' );
}