Add online video to 'textmedia' element - typo3

Question

In an extension, I would basically like to do what the core does when you click the button "Add media by URL" on an existing textmedia element.
I tried to look in the source code but did not find any convenient API function I could use. Perhaps I could use DataHandler for this?
What the core does is create a textfile (e.g. .youtube) which contains the video id. It then creates a record for this file in sys_file and a file reference (sys_file_reference) between the record in tt_content and the file record in sys_file.
I am using the latest TYPO3 8.

Answer 1

I don't have a complete solution, but I recently had to do something similar:
Create a file from the Video URL and create the corresponding sys_file record:
The class OnlineMediaController::createAction does what you are looking for. Specifically, the function OnlineMediaHelperRegistry::transformUrlToFile will transform the video URL to a file (creating it if necessary).
To use the existing action, you can use the Ajax Route online_media_create.
Or, you can use the existing action to model your own code.
Create a relation between existing records in sys_file and tt_content:
See Creating a file reference (TYPO3 documentation)
Sample code: (Most of the code taken from Creating a file reference)
use TYPO3\CMS\Core\Resource\OnlineMedia\Helpers\OnlineMediaHelperRegistry;
use TYPO3\CMS\Core\Resource\ResourceFactory;
use TYPO3\CMS\Backend\Utility\BackendUtility;
...
protected function addMediaByUrl($url, $uid)
{
$targetFolder = $GLOBALS['BE_USER']->getDefaultUploadFolder();
$file = OnlineMediaHelperRegistry::getInstance()->transformUrlToFile(
$url,
$targetFolder
);
$contentElement = BackendUtility::getRecord('tt_content', $uid);
$newId = 'NEW1234';
$data = array();
$data['sys_file_reference'][$newId] = [
'table_local' => 'sys_file',
'uid_local' => $file->getUid(),
'tablenames' => 'tt_content',
'uid_foreign' => $contentElement['uid'],
'fieldname' => 'assets',
'pid' => $contentElement['pid']
];
$data['tt_content'][$contentElement['uid']] = [
'assets' => $newId
];
// Get an instance of the DataHandler and process the data
/** #var DataHandler $dataHandler */
$dataHandler = GeneralUtility::makeInstance(DataHandler::class);
$dataHandler->start($data, array());
$dataHandler->process_datamap();
// Error or success reporting
if (count($dataHandler->errorLog) === 0) {
// Handle success
} else {
// Handle error
}
}

Answer 2

Maybe you look here for good examples
YoutubeVideo, Vimeo, Video-Files, More Informations you can find at the vhs Docs
Or you could do something like this:
<flux:form id="youtubevideo" label="YouTubeVideo" description="Einbetten eines
YouTube Videos als iframe">
<flux:form.option name="optionsettings">
<flux:form.option.group value="Content" />
<flux:form.option.icon
value="EXT:extension_key/Resources/Public/Icons/Content/YouTubeVideo.svg" />
</flux:form.option>
<flux:field.input name="settings.videoid" label="YouTube Video ID. Entnehmen
Sie die ID aus der YouTube URL. Beispiel: https://www.youtube.com/watch?
v=UX12345678 Die ID ist UX12345678" />
<flux:field.select name="settings.videoformat" label="Video Format"
maxItems="1" multiple="0" default="YouTubeVideo--normal" items="{YouTubeVideo--
normal: 'Normal (4:3)', YouTubeVideo--widescreen: 'Widescreen (16:9)'}"/>
<flux:field.checkbox name="settings.gridPull" label="Bleed Outside (Randlos
glücklich)" default="0" />
</flux:form>
...
<div class="YouTubeVideo {settings.videoformat}">
<iframe width="640" height="480" src="//www.youtube-
nocookie.com/embed/{settings.videoid}?rel=0&showinfo=0" allowfullscreen>
</iframe>
</div>

Answer 3

Finally found the solution:
The key is to set the correct "allowed extensions": add "youtube" or "vimeo".
This will automatically add the missing "Add media by URL" button.
Example using Flux Inline FAL:
<f:section name="Configuration">
<flux:form id="myCustomVideoContentElement">
<flux:field.inline.fal name="settings.records" label="video"
multiple="false" minItems="1" maxItems="1"
allowedExtensions="mp4,mkv,youtube,vimeo"
/>
</flux:form>
</f:section>
(Typo3 9.5)