When selecting progressive and HLS tracks, we currently check if
we can either seek in the existing samples or are starting from the
beginning of the stream. In both cases, we don't need to reload the
stream and can continue reading.
Seeking to the beginning isn't side-effect free though because it
also sets the startTimeUs to zero. Whether a seek to the beginning
is successful also depends on whether we already loaded a sample or
not. This mean that the startTimeUs value is set (or not set) based
on the speed of the Loader thread even for the same input starting
from the beginning. This race condition means the actual samples
we write to the stream may differ if the stream has initial samples
with negative timestamps.
We can avoid this race condition by checking if the queue is empty
first, so that we only call seekTo if really needed.
PiperOrigin-RevId: 546010951
a9be9caf40