This post features a YouTube video embed. As you can see, the video stretches the whole width of the content container and is being displayed perfectly.
No need to copy and paste any code, just insert the Video URL and WordPress will do rest. Feel free to embed from other sources like YouTube, Daily Motion, etc… Should you have an Automatic Video Thumbnail plugin installed, then even the featured image for this posts gets pulled, resized and set up automatically.
Video Source: YouTube