The string quartet is a basic building block of the chamber repertory. If you add one other instrument, you come up with a quintet, and there are many types of quintet.
This is young Brahms before he grew the beard and exchanged his four-pack-a-day habit for high-end Cuban stogies. In his younger days, Johannes Brahms was babysitter for the Schumann family when Bob and Clara were on the road. When the parents were away, he would lead his charges sliding down the bannister and swinging from the chandelier.
It was during this period that he heard the first performance of Schuberts String Quintet in C Major, which came 25 years after the composers death and had a second cello rather than a viola. Deciding that he would follow Schuberts path, Jo wrote a string quintet in that format in F minor. It was premiered among friends, but while they liked it, Brahms thought the sound was too muddy. He re-scored the piece for two pianos. That was an improvement, but the warmth of the strings was lost. He decided to score it again for piano and string quartet, and it became one of the great warhorses of the chamber repertory.
It starts with a brooding skeletal line for piano, violin and cello. Then like a coiled spring, it bursts forth with the first subject on strings. In an astonishing move, he puts his second subject in C# minor so smoothly you cant even feel the change of key. Like Schubert, Brahms writes a third subject, this time in F Major.
This video skips the exposition repeat, which is a blessing, because the first ending that Brahms wrote to set up the repeat isnt at all convincing. Its off to development.
This is a short development that leads to a re-composed recap at 6:25.
The second subject appears first in F# minor, then in the correct key of F minor. The third subject is in F Major again.
The coda is marked poco sostenuto for a brief rest before the freight train charges down the hill for an end in which Brahms unleashes sheer, raw power.
This movement in 3/4 and A-flat has a rhythmic underlay that is quite tricky. When I tried playing the piano part, I had to count 1-and-2-and-3-and or I would get lost. The theme is split between A-flat and E Major, again done so smoothly that you cant feel the change of key. The coda is breathtaking, a magnificent wrap-up to a beautiful movement.