ated to indicate new sample streams, and sample streams that
     have been retained but with the requirement that the consuming renderer be reset.</dd>
<dd><code>positionUs</code> - The current playback position in microseconds. If playback of this period has
     not yet started, the value will be the starting position.</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>The actual position at which the tracks were enabled, in microseconds.</dd>
</dl>
</li>
</ul>
<a id="discardBuffer(long,boolean)