The fundamental elements of media workflows
Mar 1, 2009 12:00 PM, By Al Kovalick
The delay from in to out can be quite large, on the order of 10 minutes to 20 minutes (total ARC and composite process delay) for a 60-minute program, not counting the time to ingest the incoming program (60 minutes). The faster each individual process, the shorter the total in/out delay. A designer would choose this method when completion delay time is not a critical metric. For example, if the completed program is needed the following day, then by all means, use this flow method. When timing is not critical, low-speed transfers and slow processes may be used. Note, too, that individual processes do not need to work in real time, and this relaxes their design. In fact, most A/V processes can work faster than real-time video.
The third flow is useful when the in/out delay needs to be low delay, but not as short as the fully streamed flow. Basically, the target file is continuously streamed between processes. This style may be called “process-while-record,” with “edit-while-record” being a common version. So, as process 1 finishes say the first 30 seconds of its task, process 2 can start its task and so on. There's no need to wait for an entire process to complete before another process in the chain can start, as with the bucket brigade. As long as the next process does not work ahead of the succeeding process, then all is well. Process timing is critical. Edit-while-record is used with some breaking news story production. The editor can start the task even while the program material is being recorded, with consequent faster time to air.
These flow methods may be combined in hybrid means to form serial/parallel versions. Decision steps are also needed, so a process branch may occur. A rules engine may be useful to automatic process tasks. Look for opportunities to automate common process chains. This does not only save manpower and speed up a process chain, but also it yields metrics to improve the flow.
The metric of money
One common metric of interest to all facility managers is daily operational cost of a given process flow. If file transfer is involved between site locations, the cost of bandwidth may be a large factor in workflow cost. We all know the proverb time equals money. In the spirit of the analogy, there is a corollary to this: 1/Time = Money. This is also true because 1/T is rate (such as Mb/s), and we pay for transfer date rates. A 1Mb/s WAN link costs substantially less than a 100Mb/s link.
The operational element
When defining a workflow process step, it is good practice to define each of the following five characteristics for each step. For this example, let's use the create proxy step in Figure 3.
- What are the specs for the create proxy step (encoder type, data rates, speed, file format, invoke means, input/output means, etc.)?
- How will create proxy be implemented? Use Vendor X's encoder, running on Vendor Y's server connected to storage main (reliability means, failover means, scale means, monitor means, Web services means, API means, etc.).
- When will create proxy be invoked, (workload, duty cycle, peak/average jobs, etc.)?
- Where will create proxy be located (local instantiation, remote service, contracted service, etc.)?
- Who will own and manage the create proxy service (A/V operations, IT operations, contracted operations, etc.); and who will use it (number of invokers, department, etc.)?
The process of answering each question forces a designer to think deeply about each process. This way, hidden efficiencies may be uncovered, such as we can share server Y with other processes, because the create proxy workload is small even with two times more loading. Or, we can locate server Y in room M, because there is ample power and cooling available.
Performance QoS, reservations, exceptions
Related to the five questions discussed previously, it is valuable to define the performance quality of service (QoS), reservation methods and error handling as separate aspects. Documenting application QoS is useful when scaling or changing a service in the future. When a service is shared (edit suite), then a reservation system with time, billing and resource usage may be required. Providing a system-wide reservation board (similar to a flight departure/arrival schedule display) available for all to see is often good practice at a large facility.
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