[niftich]

There are several digital encoding schemes that add enhancement layers on top of an older, established base layer. It's a key concept of backwards compatibility. Not including cases where additional channels or domains of information are added (e.g. surround sound, 3D video), and only looking at cases where the perceptual quality of the existing channels or domains is improved (e.g. HDR, resolution), here are some examples:

* Progressive JPEG (1992)

* Spectral Band Replication (2001) in aacPlus -> HE-AACv1 (2003), mp3PRO (2001), WMA 10 Pro (2006)

* JPEG XT (2015) - enhancements on top of 1992 JPEG.

* Scalable Video Coding (2004? 2007?) (search for "SVC Annex G")

(Keep in mind that software patents aren't about ideas, but specific techniques being used together to achieve an effect, so this isn't intended to be a list of prior art, but rather a list of the same concept being used elsewhere.)