I see I've misunderstood you.
A video player instead of browser is also invaluable for me, when I desire precise control over the video. One generally cannot precisely seek with the Flash based player and its "fat" seekbar nor framestep. If there is something on the video demanding close attention, browser users are often at the mercy of the author to slow down the playback and exactly point out the area of interest.
Even when SMPlayer has to restart download and resync to the stream after seeking, for me it does so more quickly than the Flash player, and I can advance frames in slow motion by pressing or holding down "." or clicking the pause button.
I could swear that DASH playback worked in the program since YouTube switched to separate video and audio, but apparently it does not. I don't find "1080p" to be a quality improvement over "720p", except maybe on mostly still game footage. The bitrate increase (5 mbit over 3 mbit) is smaller than the increase of picture area. It's just blurred blocks.