>>530465
shouldn't be hard with a script, like that guy did, he just muxed multiple 1-frame videos of different resolutions into the same container
but I've just checked, VP9 actually supports resolution change even between keyframes:
> In addition, each coded frame may be resampled and coded at a
> resolution different from the reference buffers, allowing internal
> spatial resolution changes on-the-fly without having to resort to
> using keyframes. When such a resolution change is signaled in the
> bit-stream, the reference buffers as well as the corresponding MV
> information is suitably transformed to the new resolution before
> applying standard coding tools.
so don't need to encode every frame as keyframe which is inefficient
need to write your own libavcodec/libvpx wrapper for that though