Final answer:
AV1 is an open-source codec developed by BBC Research. The correct option is 4.
Step-by-step explanation:
The open source codec developed by BBC Research is AV1. AV1, also known as AOMedia Video 1, is a royalty-free video coding format that is being developed by the Alliance for Open Media, which includes organizations such as Mozilla, and the BBC.
AV1 is designed to provide efficient compression of video content while maintaining high video quality. It aims to replace other video codecs such as H.264 and HEVC, offering better compression efficiency and compatibility across different devices and platforms.
Therefore, the correct answer to the question is AV1 (option 4).