Video I/O cards function as an interface between the file-based and serial-stream worlds. They can look into the encoded source media, and if its an understandable codec, in a recognized wrapper, whether its Quicktime ProRes, MXF DNxHD, or “Uncompressed 8/10-bit”, it will be able to map that data onto a memory raster that humans would be able to recognize if it was mapped onto a visual display.
In the file based world, the entire clip, for its duration, resides as data on some form of storage. There are ways of displaying every frame at once. In the serial world, each pixel comes out like water coming out of a hose, and we only see a recognizable image when they have been organized on a display (live), or going to tape and played back, another serial (single-stream, as opposed to parallel-stream) process that is time dependent. The frames follow each other like rolling stock in a train, and while they are in this temporal domain, they don’t actually conform to any codec, and are defined by resolution, frame-rate, and colorspace. You can playback MXF DNxHD from a Blackmagic SDI card, and capture it as Quicktime ProRes on a Kona card. For the brief instant that the data stream is in transit between the SDI output of one card and the input on the receiving card, it is “live” and for all intents “Uncompressed” and doesn’t exist as anything other than bits of data flying down the pipeline.
Some codecs are dependent on a stream of frames (long-GOP) since they need a group of spanned-data images to produce a coherent frame progression. Even in the file-based world, these codecs need to be processed in groups by editing programs in a serial manner, similar to adding water to a powder-based drink.
TMI?
jPo
You mean “Old Ben”? Ben Kenobi?