Ok! I put the clip out to my many professional musician friends, and we discussed it. Everyone agrees that it's probably a clip from a Dvorak imitating composer or a wedding gig book. None of us has played it. Everyone was stumped. We all thought it sounded like a cross between the Glazunov you mentioned and Dvorak. Since your cellist plays a ton of weddings and parties (from his website) I'm going to guess it is from a gig book. If it were an actual Dvorak or Glazunov, he'd remember it, or at least one of my string playing friend would recognize it. Shoot- I really thought we were going to solve this for you. Oh well- I guess you should dig into some Dvorak. I can recommend Goldmark- he wrote some beautiful quartets and work in film scoring in Hollywood for a long time. I think you'd love his string pieces. Cheerio!

Thank you, I'll look into Goldmark! I didn't even know there existed "gig books", I thought they were just playing pieces by well-known composers. Thanks again!

Glazunov is an excellent guess! I remember playing a student quartet by him when I was a student, and it totally had that modal parallel melodic/harmonic movement in 4ths and 5ths. It is so Dvorak though, minus his noodly viola jamz under the melody. Hint of Ravel, but not French enough- maybe Chopin too. Will be thinking on it this week. I'd like to hear the whole piece too now!Update: I just watched the first few seconds of your clip- and that is the exact piece I played as a student that reminded me of it as I mentioned above. Listening now.