HTC One records FULL HD videos with 1920 x 1080 resolution. But there are HD (1280 x 720) and MMS (176 x 144) modes too. To change video quality on HTC One do as follows:
1. Open "Camera" and tap the Three dot icon on the top left or bottom left
2. Scroll down the settings menu and tap "Video Quality"
3. Choose between Full HD, HD, and MMS