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The saved video storage calculator assigns two hundred twenty megabytes per second to a four-K ProRes four-twenty-two HQ stream. Three simultaneous streams therefore demand six hundred sixty megabytes per second. Subtracting this demand from its assumed twelve hundred megabyte-per-second USB ceiling leaves five hundred forty, or forty-five percent. Bars compare demand and bus at four tenths of a pixel per megabyte per second. These are saved lookup values and arithmetic, not measured codec files, drive benchmarks or guaranteed real-world USB throughput. The label bitrate uses a variable name ending in Mbps, but the visible outputs say megabytes per second. This explainer follows those visible units. Changing only the stream count to five gives eleven hundred megabytes per second demand. That remains below the entered bus ceiling of twelve hundred, but exceeds the assumed nine hundred fifty sustained speed of the default TLC storage profile. The program therefore labels this a NAND speed bottleneck even though the bus margin remains one hundred. Bars compare the saved sustained drive rate and timeline demand at four tenths of a pixel per megabyte per second. The source evaluates bus overload first, drive overload second, and the one hundred fifty margin warning third. Those priorities are source rules, not tests of any physical disk or assurance about caching, cooling, reads or writes. At the original three-stream demand of six hundred sixty, selecting the QLC profile changes its sustained-speed assumption to eighty megabytes per second. Even a larger interface ceiling leaves this storage assumption far below the demanded rate. Bars compare demand with QLC at the same scale. The behavior text describes cache exhaustion, but the program does not simulate cache capacity or elapsed write time and does not inspect a device. Its JSON export preserves status, demand, bus limit, margin, profile and the source-selected recommendation. A special exact default branch explicitly forces Stable four-K Editing. The example should be read as transparent arithmetic under entered assumptions, not a purchasing recommendation or independent engineering certification.