Thanks for your help.
In case it is useful to anyone else: I ended up using the ‘twitch’ package for this, in nodejs, with sample code:
// clientId and accessToken from https://dev.twitch.tv/console/
const client = TwitchClient.withClientCredentials(clientId, accessToken);
// For streams
const stream = await client.helix.streams.getStreamByUserName('nexxzz');
console.log(JSON.stringify(stream, undefined, 2));
// For video
const video = await client.helix.videos.getVideoById('125328655');
console.log(JSON.stringify(video, undefined, 2));