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Understanding Realtime Terminology
Realtime has become an industry buzzword that seems to have many interpretations. In this article I'd like to discuss the different meanings of "realtime" to make it easier to cut through the hype when evaluating your next realtime solution.
For the completely uninitiated let me first define the term realtime. Since video is time based and each clip, segment, or timeline will always have an associated duration. Realtime simply means that a particular task (effect, output, encoding, etc.) will occur at the same pace as the video being played. In other words, for a task to be considered realtime the amount of time in which it takes to complete must equal the duration of the video segment to which it is applied. With that said, other tasks can be expressed in terms of realtime (ie. 4XRT: task takes 4 times the duration of video).
In order to be considered a realtime editing solution a product must provide us with realtime capabilities on a minimum number of tasks. Some of the tasks would be input, output, preview, effects and encoding. How each solution handles these tasks and what limits are set for each task will determine the true realtime capabilities of a particular solution.
For the DV crowd the term realtime began to gain popularity with the first "realtime" DV editing cards that worked with Adobe Premiere RT. The first popular realtime cards were the Pinnacle DV500 and the Matrox RT2000. Both cards were promoted as being realtime editing solutions. Soon thereafter the Canopus DVStorm started gaining in popularity and both Matrox and Pinnacle had new offering with the RT2500 and Pro-ONE. Currently there are many realtime editing solutions to choose from.
Choosing the right solution can be difficult though. Each realtime solution has different offerings. The costs vary between each product and the system requirements for some are much higher than for others. The latest trend is toward completely software-based realtime solutions that are not dependent on specific proprietary hardware, and instead leverage the power of the computer's own hardware.
One thing is certain: once you go with realtime, you won't go back. Knowing this, it is to each manufacturer's advantage to provide as many realtime capabilities as possible. It is especially important for sales that they promote their products as "realtime". Having used most of the realtime solutions that are currently available, both hardware and software, it became clear to me that some solutions are more realtime than others. Different editor's will have different needs, so finding a solution that allows them to work the fastest is imperative.
Realtime Features:
Realtime Input - The first basic requirement for any video editing solution is to provide a way to capture video. In nearly every case this could be considered realtime because video will be written directly to hard disk storage at the same pace in which the data stream is read from the tape transport and through the camera or deck. In cases where video is captured directly to hard disk, the data could be transferred to the computer system in faster than realtime, however this would not typically be a function of the editing solution itself. A slower than realtime case would be in the case of film that is scanned at a slower than realtime pace. Another thing to consider is the type of inputs that a particular solution can work with. Some solutions have basic analog inputs (composite and y/c) while others require the use of an A/D converter and only provide OHCI 1394 support natively.
Realtime Preview - Once video has been brought into the editing environment the ability to play the video back in realtime is critical. Every solution currently available has the ability to provide a realtime preview to the computer screen for basic cuts-only editing. When a "realtime effect" is added to a video it will playback in realtime on the computer monitor. Each product has a point where it can no longer provide a full-quality preview. Once this point is reached the editing environment will respond by either lower quality, dropping frames or simply showing a message that it needs to render.
Realtime Analog Output - In addition to providing a realtime preview on the computer screen, some solutions also have a realtime analog output of what is playing on the computer screen. This is typically in the form of a full-resolution NTSC or PAL output. This allows you to see what the output will "really" look like on a larger television screen. This is also helpful when you need to record your output to VHS and don't want to render.
Realtime DV Output - Besides having analog capabilities, some solutions can also output video through a 1394 port to a DV device in realtime. This is useful if you want to make a master tape from your timeline, if you are using a digital-to-analog converter, or if you need to send a DV video stream to another device (like a standalone DVD recorder).
Realtime Effects - The ability to perform particular effects in realtime is what separates most editing solutions. Effects can be classified into transitions which move one video into another or filters which change the look of a video clip. Some systems have limits on how many effects can be used simultaneously in realtime. The type of realtime effects that a particular solution has may sway your decision. Some solutions focus on 3D effects while others focus more on conventional filters.
Realtime MPEG2 Encoding - Most editing solutions provide some way to convert the edited timeline, or video clip, into an MPEG2 file. MPEG2 is the video format required for DVD creation, so being able to encode quickly for DVD authoring may be important. Currently, realtime MPEG2 encoding is only available on select hardware-based solutions. These same solutions typically are able to capture directly into the MPEG2 format.
In order to evaluate which system will provide you with the most productivity you will need to decide which realtime feature are the most important to you and choose the system that best fits those needs. Of course if you need some help feel free to contact us.
Ashley Guy
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