youtubevideo_pi1 =< lib.fluidContent to
youtubevideo_pi1 =< lib.contentElement
for TYPO3 > 8
"The TypoScript Object :typoscript:lib.fluidContent will be kept as copy of :typoscript:lib.contentElement for compatibility for the duration of TYPO3 v8 LTS and will be removed in TYPO3 v9."
Please change
youtubevideo_pi1 =< lib.fluidContent to youtubevideo_pi1 =< lib.contentElement
for TYPO3 > 8
"The TypoScript Object :typoscript:
lib.fluidContent
will be kept as copy of :typoscript:lib.contentElement
for compatibility for the duration of TYPO3 v8 LTS and will be removed in TYPO3 v9."