This is needed when synthesizing a call based on 48 kHz audio files as otherwise an error is generated about the wrong sample rate is generated. That error is in turned caused by the sample rate being changed from the default 16 kHz at the first Capture API call event. BUG= Review URL: https://codereview.webrtc.org/1698243003 Cr-Commit-Position: refs/heads/master@{#11635}