incstr | Increment string or generate sequential string ids | Runtime Evironment library

The Google API uses a form of pagination when a PlayList is requested (this also applies to other types of API responses).
The maximum number of entries per response page is 50.

► The response format is a JSON object which contains a description of the query response, including the total items requested and the items included in the current response.

► If the query includes more items than the maximum per page, the nextPageToken property is set to a string value representing the Page Token, which can be used to query the next page results (you can see how this works in code, in the LoadPlaylistAsync() method of the YouTubePlayList class).
When no other pages are available, nextPageToken is set to null (Nothing).
Inspecting this Token value, we can determine whether the Playlist content is complete.

The API can be called using OAuth 2.0 with Access Key, which requires the Google APIs Client Library, or using a simple HTTTP GET with an URI composed as FormUrlEncodedContent, standard URL query tuples.

Here, I'm using the latter method, since it's quite simplified and works pretty well.
If you have the Google SDK, you can follow the example in the PlaylistItems list documentation page.

I'm using a class structure (model) to deserialize the JSON response: it's quite simpler to handle the content using standard .Net classes, where the JSON properties values have already been converted to strongly typed values in the correct format.
The helper class, YouTubePlayList, contains the class model and the methods needed to deserialize the JSON or serialize the class objects back to a JSON string.

It also performs the HTTP GET request, using a static HttpClient and handles the pagination of the API response, if needed.
The class uses the asynchronous methods that the HttpClient class provides.

► The class is initialized passing the access Key required to query the API.
If the Key is not yet available, follow the instructions to create one (is free) in the API Reference documentation page, which will send you to the Developer Console's API Access pane.

To load a PlayList, pass a Playlist Token to the LoadPlaylistAsync() method.
This method returns a PlayList objects that contains all the information related to the API query itself and all the resulting Items, in a List(Of PlayListEntry) objects.
All deserialization and HTTP calls tasks are handled internally.

For example, in a Button.Click handler, initialize the helper class passing the Key, call the LoadPlaylistAsync() method specifying the Token of the Playlist to download, then dispose of the YouTubePlayList class object and just use the returned class object for whatever is needed:

_{I'm using the Playlist Token you provided in a previous question}