durationIsEstimate

True while duration is only an estimate, such as FFmpeg's guess from the bit rate of an ADTS AAC file or of an MP3 without its Xing header, which for variable bit rate audio can be minutes out (#422). A seek bar can draw it as approximate. Seeks are not cut at it, and once playback passes it duration follows what has played; once the item ends it is the real length and this goes false.