The key strength of Stagebox is that it can work in a PTP synchronised network and the Stagebox IP video stream preserves time code information for each compressed video frame. This means that with careful network planning and correct Stagebox setup, it is possible to re-create all the timing functionality you would expect from a traditional SDI system, including Genlock and Linear Time Code (LTC).
Time Code Source (out from this Stagebox)
When Time Code is being used on the system it is made available on three possible outputs of this Stagebox:
- Linear Time Code (LTC – out)
- VITC – Vertical Interval Time Code in ancillary data of SDI out
- Time Code screen display on SDI output (when Ident is enabled)
In this drop-box you can choose the source for the Time Code.
The two options are :
- Use network clock
- Use this option when PTP is enabled and there is a reliable network clock
- Time code taken from video stream
- Use this option when PTP is disabled or the network clock is not accessable, for example in a layer 3 network.
- Time Code is taken from the video IP stream.
Method of gaining sync over the network
There are two ways to implement synchronisation of the SDI Video between Stageboxes depending on the network capability. They correspond to the options in this
- Multicast enabled – using PTP
- Precicion Time Protocol (PTP) based on based on the IEEE1588-2 timing method
- Multicast Disabled – not using PTP
- Point-to-Point using information in the transport stream to re-generate timing
The two approaches to synchronisation in a Stagebox are described in more detail below and are fundamental to understanding how to get the most flexibility out of your Stagebox setup.
Multicast enabled – using PTP
Precision Time Protocol (PTP) is a protocol used to synchronise clocks on a network and is the most flexible timing scheme for layer 2 networks or networks designed to support PTP throughout the system. It uses a Master / Slave architecture to accurately distribute a master PTP clock, taking into acount the loading and unbalance throughout a typical IP network. Stagebox uses this clock to genrate a Genlock signal used in traditional video broadcast systems.
Having decided that a Stagebox is to be used on a PTP setup, it is necessary to assign it as a Master or a Slave, or let the system decide which device will make the best Master by selecting Auto.
The default value here is Auto, but in some cases it might be required to force the mode on a Stagebox where the Auto function fails to setup the system correctly.
In the second drop-down-box select one of the options:
- When a Stagebox is set as a Master it will generate a PTP clock from either the Genlock or SDI input. If neither a Genlock or valid SDI signal are present the Master will use a free running clock for PTP.
- When a Stagebox is set as a Slave it will read the PTP clock and generate a Genlock output and a synchronised (Genlocked) SDI output.
- When set to Auto the Stagebox can be either a Master or a Slave depending on which clock in the network the best master algorithm determines is the most accurate.
Note that the best PTP Master clock might not come from any of the Stageboxes on the Newtwork but from a different clock, derived from a GPS system clock for example.
Also, if no PTP clock input source is found on the network the Auto function will select the Stagebox with the lowest MAC address to be a free running Master.
Multicast disabled – not using PTP
Use this option when you cannot be sure that your network supports PTP timing. You will most likely encounter this on Layer 3 networks where routers do not normally support the distribution of PTP packets.
In this mode the receiving section of a Stagebox gets its sync information from the IP stream of a far-end Stagebox. The far-end Stagebox generates sync information from either its Genlock or SDI input and embeds it in the IP stream.
This is also the best option to use for a simple point-to-point bi-directional link, because each direction of video has its own independant synchronisation.
Time Code source for PTP master
When a Stagebox is being used as a PTP master it can send the Time Code over the network with the network clock. There are three possible sources for the Time Code on this Stagebox
- Input LTC
- Vertical Interval Time Code (VITC) on SDI input
- Free running – If LTC not connected and no VITC present in SDI (or SDI not connected)
You can select the following options in the drop-down-box :
- Chooses from possible inputs in order shown above
- Use Linear Time Code input
- Use Time Code from SDI input
- If VITC present, otherwise free runs
- Free Run
- Time Code runs freely irrespective of LTC or SDI (VITC) input