Reference distribution

SMPTE proposal

(View the Notes pane to see comments by Rob Silfvast and Willem-Jan Dirks)(View the Notes pane to see comments by Rob Silfvast and Willem-Jan Dirks)

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Introduction

First years there will be a mixed environment. Feedback of customers is to keep a long transition period in mind.

Traditional gen-lock sources will source the reference in this mixed environment.

Receiving signals that some “Big players” in the broadcast domain are aiming for the SMPTE 33TS reference solution.

We don’t want to inherit the current situation where references need to be tuned for different sources.

For background on the approach supported within SMPTE:Google search [“Paul Briscoe” and “the new genlock”]

Mixed environment

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AVBEnd-point

AVBEnd-point

SPG

CAM1

Gen Lock

SDI

1722APVF1722APVF

CAM2

SDI

1722APVF

Clock Master EthernetGen Lock

GPS

Shift in reference point 2ms??

Gen Lock

1722 APVF

1722APVF

Fade / mix

CAM1

CAM2

GEN Lock

Traditional Gen Lock distribution

Due to shift in reference, impossible to mix signals without tuning of reference

difference.

Pro:

Doesn’t increase bandwidth usage. Calculations are made in each endpoint using the timestamps already distributed by the clock master. Only a single control packet to tell the endpoint which reference to take.

SMPTE defined standard which is respected in the Video Broadcast (VB) domain. Ready for future reference standards. Multiple reference standards distribution in a single network (not used today in

VB).

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Cons:

Calculations are not straight forward. No backup master as when using streams, this could result in a

“reference jump” when switching from Master to a new Master. A relation to TAI (via GPS) is needed for synchronizing “Traditional”

infrastructures to an AVB network.

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To Do before deciding:

Investigating the “cost” of a SMPTE implementation Most complex implementation is for the 59,94 reference, since

this has a 1,001 relation to a second. Each 1001 second there is an aligned frame.

Find solution for “ref jump” when master changes

Automatic master switching is under discussion for broadcast, since customers are afraid of this principle.

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