In the last several years, the broadcast industry has begun making the rapid transition to IT-based infrastructure both for new facilities as well as upgrades of old facilities. Standards such as SMPTE 2022 have facilitated the transition from specialized rack-mounted appliances to commodity hardware that is increasingly cloud-enabled for scalability and redundancy. Encoding, decoding, packaging, switching and more are all virtualized to the point where even connectivity now is becoming largely virtualized for both traditional linear broadcast and second screen.
Traditional broadcast interfaces such as SDI and AES are still pervasive and likely will be for the foreseeable future. As such, the ability to bridge the gap between the old interfaces and the numerous variants of IP networking interfaces as defined by IEEE802.3 is critical to the continued success of these initiatives. IP network interfaces only typically define the physical and link layers per the OSI reference model, and additional issues begin to appear in practical implementations.
One of the most important issues to consider is how latency is dealt with. Second screen encoding, packaging and delivery, for example, has a higher overall latency both between the various functions within such workflows as well as in transport. Other applications, such as switching of audio inside a broadcast facility, can often require extremely low latencies that are measured in milliseconds. What is essentially instantaneous on an AES connection can vary considerably in latency on IP networks, depending on how they are implemented and what devices are on them. The AES67 standard for Audio over IP has defined audio transport that is both reliable and very low in latency, but can only guarantee that if devices using the standard are put on their own network sub-segment due to IP multicast. Whether this is done by having separate switches just for these devices with uplinks for final output, or whether a software-defined networking infrastructure has a policy for virtual devices to ensure the same, broadcast engineers need to be aware of such issues in advance.
Another issue involves the enumeration of devices and interfaces. In traditional broadcast, an SDI or AES interface is well understood, and on appliances the device has a control console either built in or through a web interface to provide such control of enumerated interface ports. Once virtualized, however, switching of these physical interfaces can be a challenge. While AES67 has defined Audio over IP, it does not define device enumeration or control though Livewire®, the basis for much of AES67, does provide for both. Broadcast engineers must be aware of these issues and choose devices that are standards-compliant in bridging old interfaces with new and that are easily configurable.
These are only a few of the challenges with broadcast audio today. Processing and formatting of audio will continue to move to commodity hardware for the processing functions with IP interconnect, from simple servers to full virtual environments. Understanding these will be essential to infrastructure build-outs that can not only take care of today’s audio, but also emerging next-generation standards for object-based audio. In the IP networking world, all appears possible.