Can think of one rudimentary way,
1. User Media working on both
2. User A clicks button, User Media begins recording User A video
3. Records for 1 second, send the file to User B
4. User B window plays the file automatically
5. Process repeats for every second from point no. 2 above
6. Process mirrors for User B from point no.2 - point no.5
Does it make any sense?