This video is from YouTube and uses the WordPress/Jetpack shortcode:

[youtube https://youtu.be/QE3seiWsV7Y]

This video is from Twitch and uses the WordPress/Jetpack shortcode:

[twitchtv url="https://www.twitch.tv/videos/382508235"]

This video is the same one from Twitch and uses inline HTML through WordPress. Note that this is not what most WordPress people will do and requires me to specify a fixed height.
<iframe
src="https://player.twitch.tv/?autoplay=false&video=v382508235"
allowfullscreen="true" scrolling="no"
width="100%" height="450" frameborder="0">
</iframe>

This is another video to demonstrate that the twitchtv shortcode does not work:

[twitchtv url="https://www.twitch.tv/videos/383288126"]