Users adding a FAL video (oembed) must be warned if the video already existed in the folder ("FileList > New > Add new media asset" )
\TYPO3\CMS\Core\Resource\OnlineMedia\Helpers\AbstractOEmbedHelper::transformMediaIdToFile() starts with a call to
$file = $this->findExistingFileByOnlineMediaId($mediaId, $targetFolder, $fileExtension).
\TYPO3\CMS\Backend\Controller\OnlineMediaController::addMediaFromUrl() does not inform if new media was actually added (= new XYZ.vimeo or XYZ.youtube file) or just existing media found in the folder.
\TYPO3\CMS\Backend\Controller\OnlineMediaController::mainAction() always renders a flash message saying
'LLL:EXT:lang/Resources/Private/Language/locallang_core.xlf:online_media.new_media.added', which is simply untrue and misleading if the video file was not newly added, but found to exist - possibly under an unexpected file name.
You can choose if the "add media" process is regarded as successful or failed in this case, but nonetheless the user must be warned that no new file was added to the file list.
Behavior is identical in TYPO3 8 and 9.
#2 Updated by Guido Schmechel 3 months ago
The info whether the file exists or not, is already decided in sysext/core/Classes/Resource/OnlineMedia/Helpers/AbstractOEmbedHelper.php. This info will not be passed on. It would have to be well adjusted 3 to 4 classes, so that the info can be used.
For me, the question arises, whether this is crucial for you? Is there a problem that I did not notice? Beside the informational hint.