Comparing BXF/MXF

By now you probably have heard of the Material eXchange Format (MXF), and if you haven't already heard about the Broadcast Exchange Format (BXF), you will soon. As these two formats grow in popularity, broadcasters want to know the difference between the two.

The two technologies cover fundamentally different aspects of the transition to digital technology, yet they are highly complementary. Part of the confusion about these formats is caused by their names. Although they both include the word “format,” it might be more appropriate to call BXF a protocol and MXF a wrapper. And while they both contain the word “exchange,” BXF exchanges metadata as messages, while MXF primarily exchanges pictures and sound along with a small amount of metadata.

Defining the two standards

As Bruce Devlin of Snell & Wilcox, one of the primary authors of MXF, points out, “MXF is a container which glues together video, audio, VBI, VANC and metadata. BXF is a metadata language which facilitates standardized communications between the program planning, automation and traffic areas of your facility.”

Chris Lennon, the chairman of SMPTE 22.10, the committee that developed BXF, says, “BXF, despite the acronym's similarities to MXF, is something entirely different. BXF allows for the exchange of decoupled content-related metadata among systems, and also allows for the communication of content movement instructions.”

Lennon goes on to point out, “Not only do BXF and MXF have no collisions, they serve completely different needs. But BXF and MXF are likely to be key components of a total system. Picture a BXF message initiating the movement of content from server A to server B. When the content arrives, wrapped in MXF, its metadata is extracted by MXF-aware utilities, which then use BXF to notify traffic, program-planning and automation systems that the content has arrived at the playout server.”

Distinguishing between a wrapper and a protocol

As Figure 1 shows, a wrapper is a type of file format that is specifically designed to carry other things inside. In the figure, you can see that video, audio and title information are all contained inside one MXF file. Metadata is also enclosed in the file. Some people think of MXF as a digital version of a tape in a box with a label on the front and a rundown sheet inside.

MXF is primarily intended for the exchange of finished content between two devices. While MXF supports streaming of content, it is primarily deployed in file transfer applications.

How does this compare to BXF? Earlier I referred to BXF as a protocol. It fits the definition of a protocol as “a set of rules governing the format of messages that are exchanged between computers.” BXF is a standard that defines an agreement between manufacturers in the broadcast industry about messages that are sent between different systems in a television facility. More specifically, the agreement covers the software technology to be used, the meaning of specific messages and the behavior that is expected between originators and receivers of messages using BXF technology. Hopefully, this explains just how completely different BXF and MXF really are.

Figure 2 on page 30 shows an extremely simplified case of acquiring essence and metadata, storing that essence and metadata, and notifying users that the process is complete. Clearly, this diagram could be greatly expanded, but the point is to show the level at which BXF operates. BXF involves agreements about messages that are sent as part of a process. So the layout of messages to get the content, notify users, exchange information about the metadata associated with the content, and so on are standardized in BXF.

In this process, you may get the essence and metadata in Figure 2 as an MXF file. But the essence can come in another format as well. BXF is all about the messages and commands that are exchanged across a network in support of a workflow process.

Complementary standards

So if BXF and MXF are so different, how are they also complementary? An example will help illustrate how the two can work together.

In Figure 3, a commercial is scheduled in the traffic system. The traffic system sends a BXF message to the content distribution system, requesting the commercial. The commercial, wrapped as an MXF file, is delivered to the edge server at the station, where the automation confirms that the MXF metadata identifier matches the commercial that was ordered. The automation system then automatically ingests the commercial, transferring it from the edge server to the playout server as an MXF file. The traffic system schedules the commercial for air and sends a playout log to automation using BXF. After airing, the automation system sends as-run information about the commercial to traffic using BXF.

In this example, BXF and MXF work together in a typical ingest-to-broadcast workflow. The figure is greatly simplified, but it illustrates the points that BXF and MXF fulfill different roles in a facility, and that they are complementary. Furthermore, BXF enhances the ability of systems to communicate information about content so that as new information becomes available in one system, it can be used to update databases in other systems also tracking that content. This avoids rekeying — one of the main sources of transmission errors in nonintegrated facilities.

Focus is on harmonization

As BXF and MXF are rolled out in broadcast facilities, there is a new focus on harmonizing the exchange of business information upstream of the playout facility. Right now, some systems participate in a business process that ultimately results in the compiled on-air or online viewer experience. Of course, a lot of information is exchanged between business entities during this process, and up to this point, very little of this is standardized. In fact, quite a bit of this still takes place using fax machines and spreadsheets.

Some broadcasters are just now exploring whether it is possible to create the amount of Electronic Data Interchange (EDI) specifications or standards to support these processes. Pressure is growing to address this area of the industry, as the drive to reduce errors and deliver more flexibility in the viewing experience increases.

BXF and MXF are two different technologies, but both are necessary to support digital workflows. New work is beginning in the area of business electronic data interchange upstream of the traditional on-air systems to support increased flexibility and to create even better end-viewer experiences.

Brad Gilmer is president of Gilmer & Associates, executive director of the Advanced Media Workflow Association and executive director of the Video Services Forum.

Send questions and comments to: