Using the current release, there's no difference here in size or sharpness between a still and the HD snapshot taken of that still.
This video switches from the still to the snap at about the one-second mark...
Untitled.mp4
Post specifics on your settings, and perhaps a demo of the result. Upload the file/s to a free server, such as Google Drive or MS OneDrive, get a shared (public) link, copy the link and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. When using Google Drive, if necessary change "restricted" to "anyone with link can view."