I would just like to update, this is still happening and is incredibly frustrating, I'm having to resort to Low quality, even on mobile (WiFi).
I have tried the following: Livestreamer through VLC, VPNs, Changing Firewall inbound rules and clearing internet files..
All of the above keeps coming back with buffering every 5 seconds. If I stream on my mobile's internet (EE 4G+) I can watch in Source quality perfectly.
Is Twitch being specifically throttled? it only takes a second googling "twitch buffering virgin media" to see that there are many people with the same issue. I would like an answer on this in case I need to change provider.
Its not that Twitch is being throttled. Its more its not usual for it to get the same treatment as say YouTube because its a live stream.
Content from the the likes of YouTube sit on CDN's embedded in VM's network, so arrive quickly.A Twitch stream can only arrive as fast as its sent. And is usually subject to peering (coming through external links to VM's network) so again, speed of stream transport MAY be affected.
However, other people have had decent results with Livestreamer...