[test] Check end of module in play buffer API

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Add comments to play buffer code

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[examples] Rename examples

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>