First of all, Professor Blacher corrects the desynchronization between violin and piano in the transition from Largo to Allegro. Tempo in Largo part is too slow and it is more advisable to think the pulse "alla breve".
Kolja Blacher's general recommendation is that every note must be more articulated because in a large hall the articulation is hardly distinguished.
He gives other suggestions and indications to the student: sforzato must be played using half bow for the first note; about ornamentation, the grupetto is played in the first beat.
Finally, Blacher talks about Mozart's expressiveness, very different to Tchaikovsky's.