Video Embed with Captions in Turkish

Question

I normally embed videos by directly writing the URL in the WP built in [embed] code. Like: [embed]https://www.youtube.com/watch?v=p_o4aY7xkXg[/embed]

But now I want this video to open automatically with Turkish subtitles regardless of the user's preferences. How to do that?

I have tried adding these to URL, but none of them worked:

• &yt:cc=on
• &hl=tr
• &cc_lang_pref=tr
• &cc_load_policy=1

For example for TED videos I achieve it by adding "/lang/tr/" in URL, like this:

[embed]https://www.ted.com/talks/lang/tr/ken_robinson_says_schools_kill_creativity.html[/embed]

Any similar solution for Youtube? Or any other suggestions?

Update: I put iframe code directly in "Text" section of Post editor. It works. Example:

<iframe src="https://www.youtube.com/embed/1a8pI65emDE?rel=0&cc_load_policy=1&hl=tr" width="560" height="315" frameborder="0" allowfullscreen="allowfullscreen"></iframe>

This doesn't work if you put it in Visual editor. A bit confusing for non-developers.

Answer 1

Okay the thing is that the oembed endpoint seems not to support any other than the default parameters.

So it seems that all you can do is parse the response and add in your parameters to the iframe src. This should do it (untested)

function wpse_218836_add_youtube_parameter( $return, $data, $url ){
    if ( $data->provider_name === 'YouTube'){
        $additional_parameters = '&cc_load_policy=1&hl=tr';
        return preg_replace('/src="(.*?)"/i', 'src="$1' . $additional_parameters . '"', $return);
    }else{
        return $return;
    }
}

add_filter('oembed_dataparse', 'wpse_218836_add_youtube_parameter', 10, 3);