to avoid allocating/destroying temporary buffers when reading a filtered resource sequentially (i.e. 4096 loop buffer), the FilterContext instance carries a re-usable buffer that can be increased if needed. The FilterContext lives for the duration of the HTTP connection that requests a byte range, and therefore survives during the 4096 buffer loop. This bug fix eliminates HTML5 audio playback issues (milliseconds beginning of audio phrase spoken before the actual SMIL clip-begin)