That would depend on the app/program. Not all x86 apps are optimized to use the GPU when doing things such as image processing. Photoshop still doesn't use the GPU as efficiently as it can. It is still optimized to use the systems CPU via multi-threading. Multiple processor and (now) multi-core CPU systems were developed because of programs like Photoshop and other CPU hungry apps and programs.
True, then again, Photoshop wasn't developed for or with smartphones in mind, but for desktops with powerful hardware, so offloading to the GPU isn't as important as it is on a smartphone. More importantly, Harrie-S asked specifically about
video capture/processing, not Photoshop like
image processing, where efficiency is even more important, as the CPU would buckle under most circumstances.
None of the 1st party apps delegate any video related tasks to anything but the DSP/GPU (and a media processor actually, which I'm just lumping together with the GPU here). All video related APIs which are provided by the OS for use by 3rd party apps also delegate to the DSP/GPU. I'm sure you can find some dev somewhere that attempted to do video processing on the CPU, but that app's feature set won't go beyond cutting/appending video segments (at least it shouldn't if it wants more than a 1-star rating).
Photoshop like image editing is a different story, as most devs aren't as comfortable working with the GPU as they are with the CPU, and no doubt a lot of image filters are CPU based, but that's not what Harrie-S asked about.