Preventing buffer underruns is one thing, but it's also possible to mitigate their effect. Voice communication codecs seem to manage well with covering up gaps

Preventing buffer underruns is one thing, but it's also possible to mitigate their effect. Voice communication codecs seem to manage well with covering up gaps in the stream - they do various tricks to "continue making the same sound" if there's a short gap, and can even "catch up" by replaying quickly if there's a longer gap. Quite effective. EDIT: but, of course, a human voice over a phone with a heavy low-pass filter is a much, much easier thing to replicate and "fill the gaps" than full-spectrum, general-purpose audio. Perhaps therein lies the difficulty.