1) Video file sizes are large and growing, putting strain on mobile networks. It's important to optimize video delivery for different devices and connections.
2) Key best practices for video optimization include resizing videos appropriately for screens, avoiding unnecessary preloading, stripping audio from silent videos, and not duplicating video files across devices.
3) For video streaming, techniques like starting at a lower bitrate and gradually increasing, choosing optimal initial and switching bitrates, and limiting the number of concurrent streams can help improve startup times and prevent stalling.