Vidovation’s BBC Stagebox IP Transceiver Supports SDI & Camera Control

Over the past two years, BBC R&D has carried out trials producing TV, radio and web programmes using IP production techniques based on a research prototype transceiver they developed called Stagebox, aiming to replace traditional broadcast systems such as HD-SDI. They were able to take advantage of all the usual production tools - such as production talkback, clean feeds, camera control and gunlock - over a wide area IP network, and have tested the prototype at the UK 2013 Elections, the London Olympics, Glastonbury Festival and similar events.

Stagebox makes bi-directional video available, plus 18 channels of bidirectional audio, camera control and production metadata over an IP based network. It can use IP multicast, which is receivable by several receivers at once and, in the VidOvation camera-back version, has a case with a V-plate mount allowing it to be attached to a standard broadcast camera. Stagebox accepts an SDI, HD-SDI or 3G-SDI input, automatically recognising formats on input. It will extract the video, all 16 embedded digital audio channels, two extra analogue channels and the embedded timecode from the incoming HD-SDI signal.

The video will then be encoded with AVC-I 100 and transmitted onto the IP network. AVC-I 100 was adopted because it achieves better quality for a given bitrate than, for example, JPEG-2000 and imports more easily into existing editing systems. AVC-I 100 is also compliant with the H.264 video coding standard. It uses 10-bit, 4:2:2, intra-frame only compression – that is, each frame stands alone relative to other frames, which makes the video easy to edit and fast to encode and decode. It is important to minimize latency in multi-camera setups or when using bi-directional links, such as during a two-way interview.

Stagebox carries the audio channels from the HD-SDI input using various open internet standards and achieves its network connection using a small form-factor pluggable module supporting either copper or fibre connections onto a 1 Gbit Ethernet network. A ‘capabilities, control and configuration’ API, or CCC-API, is used to set up control of all IP studio based devices on the network. For example, Stagebox has an iPad app that allows control of all the Stageboxes on the network. The app know which Stageboxes are present through the use of multicast DNS for device discovery and configuration.

Stagebox has tally lights built into it with an interface to drive external tally lights. When a Stagebox acts as a vision mixer, it will turn the appropriate tally lights on and off. Stagebox also has a Bluetooth interface as well as the wireless network interface.

Stagebox interfaces directly to legacy video equipment, including transport of legacy auxiliary control signals over its IP link, in order to allow IP systems to be integrated into existing production workflows. Stagebox samples the camera control signals, packetises and transports them over IP without decoding, packetising the data and then re-encoding the original standards at the other end of the link.

In a regular multi-camera studio setup, cabled genlock is fed to each camera to make sure the start of each video frame arriving at the video mixer from each camera is aligned. Therefore, a primary ability of the Stagebox system is network synchronisation across an IP network. Genlock can be input to a Stagebox acting as the master timing reference for an IP network. Other Stageboxes on the same network can then lock to the master’s reference, which is distributed across the IP network, as slaves producing a genlock output signal locked to the master. To achieve this synchronisation, either a source-synchronous mechanism is used, or Precision Timing Protocol or PTP.

A Stagebox broadcast system has three possible sources of timecode. Timecode may be distributed as linear timecode, incoming video may have timecode embedded in it or, if PTP synchronisation is used, it can accurately distribute timecode around the network, so that all Stageboxes on the network have the same locked timecode value. Further to this, another important aspect of Stagebox is that the video and all audio channels stay accurately in sync, even in difficult network conditions such as dropped packets, reordered packets and so on. Again, Stagebox uses timestamps, PTP and source synchronous modes to control this.  http://vidovation.com