1) They just discovered this British inventor's work and thought it was worth petitioning in order to save a few dollars for Final Cut Pro.
2) They plan to allow the iPhone/iPad to output to ProRes RAW and don't want to pay the significant royalties and so have been actively looking for prior art.
3) The IPR process is expensive to defend and has a high likelihood of cancelling at least some claims, so, like many patent battles is not about the patent at all but is about creating uncertainty and risk in order to alter the negotiating landscape.
1) They just discovered this British inventor's work and thought it was worth petitioning in order to save a few dollars for Final Cut Pro.
2) They plan to allow the iPhone/iPad to output to ProRes RAW and don't want to pay the significant royalties and so have been actively looking for prior art.