Why does cast video play on the TV but audio stay on my phone?

Start by figuring out how the picture got to the TV. On iPhone or iPad, tapping the AirPlay button inside a supported video app is different from choosing Screen Mirroring in Control Center. Apple notes that some video apps may not support AirPlay, so the app and the method matter. [S1]

Then check where audio is currently directed. On iPhone, look for the Playback Destination control in the audio app, on the Lock Screen, or in Control Center. Select the TV or other intended audio device if it appears. Apple lists Apple TV 4K, AirPlay 2-compatible TVs, HomePod, and Bluetooth audio devices as possible destinations. [S2]

If you are using a non-Apple phone, TV, or casting system, the exact controls may differ; these Apple instructions do not establish how those devices handle audio.

Possibly. A video appearing on the TV does not by itself tell you whether that app supports sending sound to the same destination, or whether it has a separate audio control. Apple specifically says some video apps may not support AirPlay, and its guidance distinguishes app-based AirPlay from Screen Mirroring. [S1]

Try a brief comparison: if the same audio destination is selectable in another supported app, but not in this one, that is a useful observation to report to the app’s support team. It is not proof of a specific fault. Also look within the video app for its own playback or output control; controls and behavior can vary by app. Avoid assuming that a control or workaround from one app applies to another.

If this is an AirPlay 2 device, check that it is on the same Wi-Fi network as the iPhone, then reopen the Playback Destination control and see whether it appears. Apple gives the same-network check for a missing AirPlay 2 device. [S2]

If you are using Bluetooth audio, check that the accessory is within range and reconnect it if needed. Apple notes that Bluetooth playback can return to iPhone when the accessory moves out of range. [S2] These checks address whether a destination is available; they do not establish that every video app can route its audio there. If the TV remains absent, note the phone model, TV or receiver model, connection method, app, and what destinations do appear before seeking device-specific support.

For example, assuming you have an iPhone and an AirPlay 2-compatible TV: pause the video, open the Playback Destination control, and check whether the TV is listed. If it is listed, select it and resume playback. If it is not listed, check that both devices use the same Wi-Fi network. Then try the video app’s AirPlay control rather than Screen Mirroring, if the app offers that option. These are checks based on Apple’s guidance, not a guarantee that the app or TV supports the behavior you want. [S1] [S2]

Copy and fill in this note:

Phone: [model] TV/receiver: [model] Video app: [name] How video was sent: [app button / Screen Mirroring / other] Audio destination shown: [list or none] Wi-Fi check (AirPlay 2): [same network / not checked / not applicable] What I tried and what happened: [brief observations]

Use that summary when asking the app or device maker for help. It keeps the discussion focused on the connection method and the audio destination without guessing at a cause.