pics/media/media3/getting-started/migration-guide">the
     migration guide</a> for more details, including a script to help with the migration.</div>
</div>
<div class="block">Media period that defers calling <a href="MediaSource.html#createPeriod(com.google.android.exoplayer2.source.MediaSource.MediaPeriodId,com.google.android.exoplayer2.upstream.Allocator,long)"><code>MediaSource.createPeriod(MediaPeriodId, Allocator, long)</code></a>
 on a given source until <a href="#createPeriod(com.google.android.exo