When using RV to play an image sequence paired with an audio file you may find that RV appears to play your imagery faster (or slower) than the accompanying audio. This happens because the way RV works is based on assuming each source has a native frame rate and that audio files do not have a native frame rate, because they have no frames. If RV is unable to determine the frame rate of a source and no indication was given at load, then RV will use the Default FPS. This is set in the Preferences dialog on the General tab.
The Default FPS setting is used by both RV and RVIO, and it normally is only used for sources that have no discernible native frame rate, such as in an image sequence (without FPS metadata) or audio-only sources.