When talking about an upper bound estimate we said:
Let’s imagine the most dynamic match in history: both teams are all-star squads playing at their limit, constantly attacking, the camera switches quickly, there’s a storm in the stands. What would be the maximum bitrate? By multiplying this bitrate by the duration, we get the maximum possible file size. If our disk (or flash drive) can hold that much, then our match will definitely fit. This is an upper bound estimate.
But there is another, hardware-based upper bound—the throughput of the storage device itself (disk or flash drive). If our peak bitrate reaches 100 Mbps, but the flash drive only supports a write speed of 50 Mbps, then we still won’t be able to record the video without losses.
Thus, the true upper bound is determined by the narrowest point in the system—the minimum between the video’s peak bitrate and the storage device’s write speed.