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davidhorman2,063 posts since 8 Mar 2005
Channel Channel Islands

Sounds like then the audio wasn’t synced properly.


That sounds unlikely. It's not like analogue broadcasts only ever got to your house with only the speed of light as a delay, especially once digital switchover was underway.

And even at a "stone's throw" there'd still be a speed of sound delay from the stadium which the analogue broadcast was still later than. Could have been some satellites involved somewhere.
DVB Cornwall7,740 posts since 4 Dec 2003
Westcountry Spotlight
I can see this working in a multicast environment, getting data to the concentrators in this way is sensible. What gets me is the multiplicity of feeds out to viewers from these concentrators. The complexity of the multicast ports will go up incrementally. The segmental addresses also will add length to the micro segments. I’m hoping to see some detailed drawings of the process, to be satisfied.
Rkolsen2,328 posts since 20 Jan 2014
BBC World

Sounds like then the audio wasn’t synced properly.


That sounds unlikely. It's not like analogue broadcasts only ever got to your house with only the speed of light as a delay, especially once digital switchover was underway.

And even at a "stone's throw" there'd still be a speed of sound delay from the stadium which the analogue broadcast was still later than. Could have been some satellites involved somewhere.

I was talking about a delay during analog eras. Maybe it’s different with PAL but from my understanding NTSC used seperate audio and video frequencies that could get out of sync.
Don’t let anyone treat you like you’re a VO/SOT when you’re a PKG.
Neil Jones4,601 posts since 23 Dec 2001
Central (West) Midlands Today
I think it used to vary depending on the network. ITV on Sky was significantly delayed compared to analogue TV and I think it was the best part of five seconds or so.

Of course today delays are still present platform pending, I think BBC One on Sky is still a second or so behind Freeview or that might just be BBC One HD.
davidhorman2,063 posts since 8 Mar 2005
Channel Channel Islands
To the best of my knowledge you still need to receive an entire GOP (Group Of Pictures) for either MPEG2 (SD) or MPEG4 (HD, one or two SD channels) before you can start showing video. For MPEG2 that's usually 12-15 frames (both DVD and broadcast), although Channel 5 on Freeview pushed that up to something like 30-50 frames, which is why Channel 5 SD used to (don't know if it still does) take longer to switch over to.

With HD, GOPs can be as long as 300 frames without causing many problems (the codec is able to keep the picture quality high for longer without needing a keyframe) but I think the BBC keeps it down to around 25 frames, otherwise if you switch over at the wrong time you'd be waiting 10 seconds.

Then there's (if I remember rightly) statistical multiplexing - when you've got multiple regional variations, all mostly showing the same thing, and there's a sudden high-motion sequence in a film, for example, you don't want all those variations suddenly needing more bits all at once. So they offset them in time to smooth out the bandwidth requirements. This probably doesn't apply so much to online live streams, where they might settle for a constant bitrate.

Then of course there's all the various bits of equipment all this digital data has to go through, being decoded, re-encoded, muxed... they could probably streamline that a bit if they wanted to, but it'd make things more complicated without bringing any real benefit. And there'll always be a quarter of a second extra for satellite broadcasts.
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London Lite gave kudos