Efficiently get every video of every playlist of a channel - youtube-api

Question

I am using C# .NET with the YouTubeAPI-Nuget Package but that shouldn't be that important because I can apply concepts from every language.
I need to get all Playlists of a channel (specifically the logged-in channel, using the "mine"-parameter) and every video of each playlist quite often, I already tried to do it as rarely as possible but it still has to happen quite often.
The problem is that it takes a long time because I first have to get all playlists (1 API call for every 50 Playlists) and then per playlist get every video (1 API-call per 50 videos per playlist).
So this can multiply quite quickly. For 39 Playlists all with < 50 videos this takes a few seconds every time.
So my question is: is there any better/more efficient way?
My Optimizations:
just try to do this as rarely as possible
Don't include "Liked Videos", "Uploads" and similar unneeded Playlists in the second step (I would exclude them but they aren't included in the first place for some reason)
Code Example of how I currently do it:
private async Task InitPlaylists()
{
var playlists = new Dictionary<string, string>();
var page = "";
while (true)
{
var request = _youTubeService.Playlists.List("snippet");
request.Mine = true;
request.PageToken = page;
request.MaxResults = 50;
var result = await request.ExecuteAsync();
foreach (var playlist in result.Items) playlists.Add(playlist.Id, playlist.Snippet.Title);
if (result.NextPageToken == null) break;
page = result.NextPageToken;
}
foreach (var (id, title) in playlists)
{
var videos = new List<PlaylistItem>();
page = "";
while (true)
{
var listRequest = _youTubeService.PlaylistItems.List("id,snippet");
listRequest.PageToken = page;
listRequest.MaxResults = 50;
listRequest.PlaylistId = id;
var listResult = await listRequest.ExecuteAsync();
videos.AddRange(listResult.Items);
if (listResult.NextPageToken == null) break;
page = listResult.NextPageToken;
}
Playlists.Add(new Playlist(id, title, videos.ToDistinctDictionary()));
}
}
EDIT: Maybe it helps if I say why I need this, maybe someone has an idea how to cut some calls that way:
I want to be able to add and remove videos from playlists, like on the youtube studio edit page.
So I need A. every playlist of the channel and B. every video of every playlist because I need to know if the video is already in the playlist

Answer 1

If you only manipulate your YouTube channel through your script then you can keep track of current playlists' videos state. If that's not the case only multithreading can make your check faster by using a thread for each playlist. Here is a quota-free and possibly faster way of getting every video id of a playlist using youtube-dl -j --flat-playlist.