Which of the following video file types is most commonly used for online streaming?

The MP4 file format is widely recognized as the most commonly used format for online streaming due to its versatility and compatibility with various devices and platforms. It utilizes advanced video compression techniques, which allows for high-quality video at relatively low file sizes. This efficiency is crucial for streaming, as it reduces buffering time and supports smooth playback over varied internet speeds.

Additionally, MP4 files can contain different codecs for video and audio tracks, making them adaptable to various needs and technical specifications. Most modern browsers and media players natively support MP4, making it an accessible option for content creators looking to reach the widest audience possible. This universal acceptance and performance optimization solidify MP4's position as the preferred choice for streaming content online.