The buffered position was last updated before the beginning of
the renderer loop in doSomeWork. As the loading happens on a
background thread, it may have progressed further already
depending on how long it took to run the renderer loop.
It's slightly more correct to pass in an updated value to
shouldStartPlayback so that playback can start quicker if the
buffering is particularly fast.
PiperOrigin-RevId: 679203465
138a8d65ca