Time & Timing at VidTrans 21
Channel: VSF
Date: 2021-03-18

Andy Rayner of Nevion gives a presentation on time and its many uses for synchronization in television broadcasting.

Since the beginning of television, we have been focusing relentlessly on the timing of the broadcast chain.
From the timing craziness of compensating on the studio floor for the 42 second latency of John Logie-Baird's hybrid film/flying-dot-scanner through to the use of PTP in modern production, we have been obsessed with both absolute and relative time.
As we start to move to virtual compute based live production systems, some of our raster-scan heritage can be left behind – if we are willing!
This presentation will bring us up to date with some timing thoughts on both the latest revisions to ST 2110 and compute-hosted and compute-friendly live production.
Don’t be late for these few minutes of fun!

John Mailhot of Imagine Communications provided commentary during this presentation.

This presentation was recorded on March2, 2021 during the first virtual edition of VidTrans, an annual conference produced by the Video Services Forum (VSF).

Selected comments from the Zoom Chat Log:

Kieran Kunhya: As a lot of first-generation 2110/AES67 devices ignore the timestamps and use packet arrival times (set them to zero and they don't care and real facilities have RTP timestamps that go forward, backwards), is this a pipe dream for another 10 years until that equipment is refreshed?
Leigh Whitcomb (Imagine Communications): All equipment that passes the JT-NM Tested program correctly use timestamps.
Kieran Kunhya: There is only a test for transmission of timestamps, not reception
Gary Morse (National TeleConsultants): Great Presentation of the history of Production  time and timing... Thanks Andy
Mike Ellis (BBC): Tallys, and even more, IEMs, need to be as low latency as possible. For Tallys, around 40ms is OK, 100ms is bearable, and 150ms is useless. For audio IEMs, even 50ms is probably too long.
Brad Gilmer (VSF): Hey Mike!  Whats a IEM?
Mike Ellis (BBC): In Ear Monitor.
Brad Gilmer (VSF): Ahh - thanks
Ivan Hassan (BBC): Great presentation Andy !!
Nir Nitzani (NVIDIA): I will be happy to understand about cloud timing - what will be the required accuracy?
Kieran Kunhya: At the moment from the GCCG diagram posted the group wants to just pass through source timestamps and synthetic sources (file playout) will use the local clock source of the cloud
John Fletcher (BBC): Does the GCCG model deal with non-locked sources?
Kieran Kunhya: Yes as it's passthrough ("free-run" loosely)
Nir Nitzani (NVIDIA): I might see it a little different - streams of data coming in and out from the cloud should have a very accurate time stamp on them (based on PTP) - this is required in order to synch all the streams on the endpoint and to connect Audio + Video i.e. on the cloud
Kieran Kunhya: PTP is not available in the cloud
Kieran Kunhya: And each cloud provider does time slightly differnetly
Kieran Kunhya: As Andy alluded to this was discussed at length in GCCG
Nir Nitzani (NVIDIA): PTP is already available on some cloud vendors  - and actually there is no limitation to support it
Kieran Kunhya: Which cloud vendors provide PTP?
Kieran Kunhya: Certainly none of the main ones
Nir Nitzani (NVIDIA): you will be surprised but it's under NDA
Kieran Kunhya: Ok then it can't be part of GCCG then...
John Fletcher (BBC): The protocol by which time is delivered is not important.  What matters is whether devices know the time and what kind of time they know, e.g. TAI, UTC.
Paul Prayle: What is doing the JPEG-XS decoding in the cloud, is it done on the GPU or CPU?
Kieran Kunhya: It does matter because there are different ways to do leap seconds that each provider does their own way
Kieran Kunhya: In GCCG as per the diagram, time is entirely relative
Kieran Kunhya: Things on the ground must reclock if they want to Genlock, PTP etc
Gareth Sylvester-Bradley (Sony): TAI doesn't have leap seconds.
Kieran Kunhya: And there is no source of TAI in the cloud
Kieran Kunhya: Only NTP
Kieran Kunhya: Which has leap seconds and each provider does that in its own way
Wes Simpson (LearnIPvideo.com): @kieraan - Yes, NTP is available, but more cloud providers are delivering an API to convert their flavor of NTP to TAI
John Fletcher (BBC): hy do you need PTP/TAI in the cloud?  I can see you might need it at source devices so that you can synchronise the media that comes out of them but what are the cases where a processing function needs it?
Kieran Kunhya: The current consensus in GCCG (shown in the diagram) is that TAI is not needed
Wes Simpson (LearnIPvideo.com): TAI time would be a logical way to tag frames of video and audio.