[uc] use case proposal: Bullet chats for 360 videos

[ashimura]

As I mentioned several times, e.g., during the MEIG F2F meeting at TPAC, I've been wondering about a possible furure use case for bullet chatting like putting bullet chats on 360 videos and specifying the position/geolocation/orientation of the bullet chats on the 360 screen using WebVMT, etc.

[xfq]

Some references about subtitles in 360° videos:

• Use case descriptions for subtitles in 360°
• Requirements for subtitles and text in WebXR