<?
    $baseUrl = 'https://www.googleapis.com/youtube/v3/';
    // https://developers.google.com/youtube/v3/getting-started
    $apiKey = 'AIzaSyBE6bAZIR6qa8aMTtvNKc63n0Y-Lk2uMQY';
    // сhannel ID
    $channelId = 'UCo0FEARvGCNl1e4u0jRBirw';

    $params = [
        'id'=> $channelId,
        'part'=> 'contentDetails',
        'key'=> $apiKey
    ];
    $url = $baseUrl . 'channels?' . http_build_query($params);
    $json = json_decode(file_get_contents($url), true);

    $playlist = $json['items'][0]['contentDetails']['relatedPlaylists']['uploads'];

    $params = [
        'part'=> 'snippet',
        'playlistId' => $playlist,
        'maxResults'=> '50',
        'key'=> $apiKey
    ];
    $url = $baseUrl . 'playlistItems?' . http_build_query($params);
    $json = json_decode(file_get_contents($url), true);

    $videos = [];
    foreach($json['items'] as $video)
        $videos[] = $video['snippet']['resourceId']['videoId'];

    while(isset($json['nextPageToken'])){
        $nextUrl = $url . '&pageToken=' . $json['nextPageToken'];
        $json = json_decode(file_get_contents($nextUrl), true);
        foreach($json['items'] as $video)
            $videos[] = $video['snippet']['resourceId']['videoId'];
    }
    print_r($videos);?>