GStreamer contains a bunch of conversion plugins that most applications will find useful. Specifically, those are videoscalers (videoscale), colorspace convertors (videoconvert), audio format convertors and channel resamplers (audioconvert) and audio samplerate convertors (audioresample). Those convertors don't do anything when not required, they will act in passthrough mode. They will activate when the hardware doesn't support a specific request, though. All applications are recommended to use those elements.