This means the content source is 'prepared' instantly with a
placeholder, enabling all further preparation steps (e.g. loading
preroll ads) while the actual content is still preparing. This
improvement can speed up the start time for prerolls in manifest-based
content that doesn't have a zero-time preparation step like progressive
media.
Issue: androidx/media#1358
PiperOrigin-RevId: 633640746
d27c36ac9e