Three good ways to get the film onto the big screen.
Any laptop, any TV. If you want the sure thing, this is it.
HDMI carries subtitles perfectly, every time. If subtitles matter to you, this is the way.
iPhone, iPad, or Mac, with an Apple TV or an AirPlay-capable TV.
Your phone or laptop and the TV must be on the same wifi network. If your TV is not in the list, that is almost always why.
If AirPlay is not in that menu and the TV is on the same wifi, you can send the whole screen instead. On an iPhone or iPad, open Control Center and tap Screen Mirroring. On a Mac, open Control Center in the menu bar and click Screen Mirroring. Pick your TV, then press play and go full screen. On a phone, turn it sideways before you do, and leave the screen awake while the film plays.
Android phones and laptops, with a Chromecast or Google TV.
Your phone and the TV must be on the same wifi network. That is the most common snag.
Some Chromecast models drop subtitles when casting. If subtitles matter to you, use an HDMI cable or watch on the device directly.
If the cast connects and the television then sits there loading, or the picture jumps back to phone size, the cast is working and the television is refusing the video. Send the whole screen instead, or use an HDMI cable. Sony Bravia sets and Android TVs are the ones that come up most often here.