Allow the use of both the CPU and the GPU when generating Trickplay images

[gnattu]

We have an alternate approach that is even faster pending for 10.10: https://github.com/jellyfin/jellyfin/pull/11511

This will make an hour video's trickplay images to be generated in 5-6 seconds, but the thumbnail will be less precise and some hardware video decoder is not compatible with this(so you have to use CPU in these cases)