BBC defeats streaming lag

article here ……..

NEWS on BBC.CO.UK
13-Sep-2018 @ 09:13

Obviously the theory of it sounds good, but will it be as impressive in practice?

I am not entirely sure I understand the theory of it.

Yes, the size of the delivered chunks is important, but so is the initial number of chunks loaded and buffered. Are they eliminating the buffer? Shortening it?

.... and is it compatible with current receiver technology, or at least possible with an easy software update.

I was under the impression and have been all along that the streaming delay is more to do with your internet connection and speed as opposed to the source. It's been the case for years that online streams are delayed, indeed Virgin Radio (before it rebranded to Absolute) used to have a message on their website about audio delays which implies it could be quite severe (IIRC the delays were half a second on 1215am behind 100.7 in London which was as live and anywhere up to 12 seconds lag through the online stream).

Mind you that was for radio and I dare say TV is more complicated. I'm not sure how far behind the NowTV streams are behind the TV counterparts which are already technically 8 seconds or so delayed in the first place?

When they say 'eliminate' the delay, it sounds as if they mean that there won't be any delay whatsoever.

We already know there's about a 5 second delay when watching normal television in the digital age compared to analogue broadcasts.

So are they saying they have eliminated the delay completely, meaning that watching online will be as live and even less delayed than watching through a normal television?

I'll believe it when I see it. There's too many factors, servers, cables and internet traffic to be "instant" in the way TV broadcasts are IMO. After all your browser can only play what it receives and if the next chunk gets lost in the sea of traffic, the browser or app or whatever technology will have to re-request and you will have to wait. That isn't something any website provider has any control over.

I almost think they worked with their servers and the CDN to make it lag free on their end.

Sounds like the early days of digital TV when someone in the next house (or room) was watching on analogue :-p

I can remember watching a Wolves match (would have been a Sunday afternoon, probably FA Cup) on analogue TV at my grandparents' house which was a stone's throw from Molineux, and even then you heard the goal just before you saw it on TV.

Sounds like then the audio wasn’t synced properly.

https://www.bbc.co.uk/rd/blog/2018-09-latency-video-streaming

The main innovations in the new, low-latency, DVB DASH seem to be :

1. Evaluating the quality of the path between the CDN and the viewer, and only buffering multiple chunks if the path is an issue. With more and more people running with 50Mbs+ broadband connection with good connectivity not everyone needs to buffer the same amount of data.

2. Using MPEG CMAF for segment distribution, so each part of the distribution chain (encoder, CDN etc.) doesn't have to wait for a complete segment to arrive before forwarding it to the next point in the chain. The segments themselves can be broken down into smaller chunks.

3. Using chunked delivery for the final http segment delivery leg too - again removing the need to wait for a full segment to arrive.

You don't want to reduce the sizes of segments (these are the boundaries that allow you to change bitrate / resolution stream) as the shorter the segment the shorter the GOP length and also the less scope the encoder has to deliver higher quality pictures.

AIUI the demo at IBC is showing DVB-DASH low latency stuff arriving before DVB-S2, whereas previously it could be 30" or more later.

You could easily have multiple frames of delay in a properly synchronised chain with synchronisers at multiple points, and if a digital backhaul was in use (even if watching on analogue TV) you could have a codec delay in there as well.

It would only take 6 frame syncs in a chain to get you 1/4 second of delay.

And many venues will have used analogue satellite, not microwave, for backhaul, so you'd have the satellite delay to contend with too. (Even more if the Wolves match was on Sky Sports analogue as that would have two satellite paths probably - one from the ground to Sky, the other from Sky to the viewer.)