Replace sample buffer QVector with C array to avoid reallocations. The resource needs to be protected, so use atomic indexes to prevent writing into the same array element that is being read. Task-number: QTBUG-45667 Change-Id: Ifd30dd128765ea4794fe8614f25ef596bba891ee Reviewed-by: Andrew Knight <qt@panimo.net> Reviewed-by: Maurice Kalinowski <maurice.kalinowski@theqtcompany.com>