The video plays but has no sound

1. Check the speaker icon in the video player itself. Tap the video once so the controls appear — if the speaker icon shows a line through it, tap it to unmute, or drag its volume slider up.
2. iPhone/iPad: check the silent switch. The small switch on the left edge of the phone (or Control Centre on newer models) silences browser video too.
3. Turn up the device volume with the volume buttons while the video is playing — phones keep separate volume levels for media and ringtones.
4. Bluetooth surprise: if wireless earphones are connected, the sound goes there. Check Bluetooth or put the earphones in.
5. Computer: check the system volume, and that the browser tab isn't muted (right-click the tab — Chrome shows Unmute site).

Note: some exercise videos have no narration

Many exercise videos are intentionally silent or music-only — the demonstration is visual, and the important cues are written in the instructions next to the video. If other videos (e.g. YouTube) have sound and only the exercise video seems silent, it's most likely simply a video without narration.