As explained in the project proposal, the idea to retrieve all video ids is to start from a starting set of channels, then list their videos using YouTube Data API v3 PlaylistItems: list, then list the comments on their videos and then restart the process as we potentially retrieved new channels thanks to comment authors on videos from already known channels.

For a given channel, there are two ways to list comments users published on it:

1. As explained, YouTube Data API v3 PlaylistItems: list endpoint enables us to list the channel videos (isn't there any limit?) and CommentThreads: list and Comments: list endpoints enable us to retrieve their comments
2. A simpler approach consists in using YouTube Data API v3 CommentThreads: list endpoint with allThreadsRelatedToChannelId. The main upside of this method, in addition to be simpler, is that for channels with many videos we spare much time by working 100 comments at a time instead of a video at a time with possibly not a single comment. Note that this approach doesn't list all videos etc so we don't retrieve some information. As I haven't gone this way previously (or I forgot) making sure that for a given video we retrieve all its comments would make sense. Note that this approach may doesn't work for some peppa-pig like channels, as in my other project.

We can multi-thread this process by channel in both cases, however for the first one we can multi-thread per videos. As would like to proceed channel per channel, the question is how much time does it take to retrieve all comments from the biggest YouTube channel? In case of willing to support peppa-pig like channels (if there is a problem for them (cf above)), this question doesn't matter, as we would be enforced to work video per video.

Have to proceed with a breadth-first search approach as treating all child channels might take a time equivalent to treating the whole original tree.