A mezzanine encode is a low-compression encode resulting is an intermediate bit rate. The ideal mezzanine rate is high enough to maintain maximum quality for multigeneration transcoding. At the same time, the rate should be low enough for efficient, cost-effective transportation around the facility and be transcoded easily to multiple output formats for playout distribution.
Preferably, it would be a common format used for recording the original video, which is good enough for editing. One example would be Sony XDCAM-HD. It is common and supports good-quality 4:2:2, 8-bit compression, and it is easy and economical to encode. XDCAM HD is also compatible with MXF, allowing carriage of multiple audio tracks and SMPTE 436M ancillary data. In the context of the playout application, the mezzanine encoding technique is sensible because it keeps encoding in the integrated playout device simple and provides a maximum base quality for the transcoder to work with.
Benefits and challenges
The benefits of an IP networking structure are abundant. First, the flexibility and absolute routability of all signals is simplified. All source signals are wrapped up and compatible with all destinations. We are able to create a truly redundant architecture, which allows protection against points of failure. We are able make use of generic IP switches, which are present already in many facilities and easy to acquire. Since the switches support IP inputs and outputs, they are easy to integrate with other IP systems, such as subtitle insertion devices.
Monitoring can be accomplished for many points with standard IP monitoring tools. Creating an IP infrastructure may eventually allow us to virtualize the playout device as a software application in a virtual machine, allowing several instances to run simultaneously and further enhance scalability.
There also will be challenges moving to an IP-based playout infrastructure, similar to those faced with the TV delivery transition to an IP infrastructure. (See Figure 5.) If we think of the structure physically, it will become much more complex. Before, it was simple when one wire carried one signal to one port. Now, with potentially several signals per wire, routing becomes less obvious. Where exactly is each signal? Can I just take this wire and plug it in elsewhere? No. There is not a simple way to just patch around a point of failure because it is no longer a single signal. If there is a failure, it is difficult to fix, meaning it fails big time.
Luckily, IP networks have the ability to provide excellent redundancy to prevent a potential massive failure. IP network topologies can ease the creation of truly redundant architectures, which prevent many catastrophes. By simply combining two channel chains along with two switches, every routable path becomes redundant. A failure in one chain or one switch will not prevent the signal passage. Actually, we could lose both a switch and a channel chain and still be OK. This redundancy allows the broken node to be serviced without disrupting normal operations.
Managing signal routing also becomes more complex. With SDI routing, it is common to find simple router control panels that allow operators with basic training to quickly make changes to signal routing. In an IP routing environment, routing is typically a system administration task. Tools will have to be developed to make setting of routes simpler and more operational.
In the future, as IP/networking technology evolves, Ethernet port speeds increase and port costs decrease, IP migration will naturally move to other areas. As technology becomes increasingly IP-centric, following this path will leave facilities prepared for whatever follows. Before then, however, now is the time to become more IP-centric and knowledgeable.
—Sara Kudrle is a senior software engineer with Miranda, and Michel Proulx is the former chief technology officer for Miranda.