bufferedRanges

Contiguous ranges held by the engine's byte cache. One entry today: the cache keeps a single window over the bytes, so one range covers the free seek-back span plus what has been read ahead. Byte positions map to time PROPORTIONALLY (byte fraction times duration), which is exact for constant bitrate and approximate for variable.

Empty for opens that read through no MediaIo (a local file on FFmpeg's own path), when the cache is disabled, or when the source declares no size or duration to map against. Empty for an HLS stream too: the cached reader holds the playlist, and the segments come from other addresses. bufferedAhead still says how far ahead the demuxer has read.