[lxgr]

At the expense of quite some overhead though, right?

MPEG-2 transport streams seem more optimized for a broadcast context, with their small frame structure and everything – as far as I know, framing overhead is at least 2%, and is arguably not needed when delivered over a reliable unicast pipe such as TCP.

Still, being able to essentially chop a single, progressively written MPEG TS file into various chunks via HTTP range requests or very simple file copy operations without having to do more than count bytes, and with self-synchronization if things go wrong, is undoubtedly nicer to work with than MP4 objects. I suppose that's why HLS started out with transport streams and only gained fMP4 support later on.

[timewizard]

> and is arguably not needed when delivered over a reliable unicast pipe such as TCP.

So much content ended up being delivered this way, but there was a brief moment where we thought multicast UDP would be much more prevalent than it ended up being. In that context it's perfect.

> why HLS started out with transport streams and only gained fMP4 support later on.

Which I actually think was the motivation to add fMP4 to base MP4 in the first place. In any case I think MPEG also did a better job with DASH technically but borked it all up with patents. They were really stupid with that in the early 2010s.

[immibis]

Multicast UDP is widely used - but not on the Internet.

We often forget there are networks other than the Internet. Understandable, since the Internet is most open. The Internet is just an overlay network over ISPs' private networks.

SCTP is used in cellphone networks and the interface between them and legacy POTS networks. And multicast UDP is used to stream TV and/or radio throughout a network or building. If you have a "cable TV" box that plugs into your fiber internet connection, it's probably receiving multicast UDP. The TV/internet company has end-to-end control of this network, so they use QoS to make sure these packets never get dropped. There was a write-up posted on Hacker News once about someone at a hotel discovering a multicast UDP stream of the elevator music.

[lxgr]

> If you have a "cable TV" box that plugs into your fiber internet connection, it's probably receiving multicast UDP.

That's a good point: I suppose it's a big advantage being able to serve the same, unmodified MPEG transport stream from a CDN, as IP multicast over DOCSIS/GPON, and as DVB-C (although I’m not sure that works like that, as DVB usually has multiple programs per transponder/transport stream).