Estimate buffer time from connection speed.
Buffering is simply the arithmetic of a stream arriving slower than it plays. A player first fills a pre-buffer, and that wait is the pre-buffer length multiplied by the ratio of bitrate to link speed, so a 15 Mbps stream on a 12 Mbps link takes 12.5 seconds to bank 10 seconds of video. Once playing, if bitrate exceeds link speed the buffer drains continuously: every second of video needs bitrate/link seconds to fetch, so a 45-minute video on a link 25% too slow accumulates roughly eleven minutes of stalling. If the link is faster than the bitrate, the buffer only grows and playback never stalls, which is why headroom rather than raw speed is what makes streaming feel reliable.
Buffer drain and stall time
Startup wait = pre-buffer seconds x bitrate / link speed; total stall = video seconds x (bitrate / link speed - 1) when bitrate exceeds link speed, otherwise zero
Because plan speed is not device speed. Wi-Fi loss, distance from the router, channel congestion and other household traffic routinely cut delivered throughput by more than half — enter the figure a speed test on that device reports, not the number on the bill.
No. A larger pre-buffer delays the first stall but cannot change the arrival rate, so the total stalling over a long video is almost unchanged. Only reducing bitrate or raising throughput fixes a persistent deficit.
Adaptive bitrate streaming measures throughput continuously and steps down to a rendition that fits, trading sharpness for continuity — most viewers tolerate softer pictures far better than pauses.