Realtime updates (if you're not using Websockets) are usually done with long-polling, for which 30 seconds is perfectly acceptable. Socket.io, for example, uses a default of 20 seconds [1].
Streaming music and certainly video are generally delivered as chunks, with a few chunks per request that don't require long connections [2].
Streaming music and certainly video are generally delivered as chunks, with a few chunks per request that don't require long connections [2].
[1] https://github.com/LearnBoost/Socket.IO/wiki/Configuring-Soc... [2] http://en.wikipedia.org/wiki/HTTP_Live_Streaming