What does Buffer underrun mean?
A buffer underrun happens when the player runs out of usable media before enough new data is available. Playback may pause while the buffer refills. The immediate condition is empty media supply, but the underlying cause can lie in delivery, source availability or processing.
Why it matters
A spinner does not identify which part failed. Compare the same source over another supported local connection and note whether a lower version behaves differently. A device that cannot decode incoming media promptly can also complicate the picture. Avoid calling every underrun a lack of purchased broadband speed without a controlled comparison.
A practical example
If a stream consumes data faster than it arrives for a sustained period, its initial cushion eventually empties even though the first minute played smoothly.
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Related terminology: Browser session cookie, Cache-Control.
For practical setup and troubleshooting, browse the journal or support guides.