From the video's YouTube page:
On Israeli Independence Day, same day that marks the premeditated ethnic cleansing of ~700,000 Palestinians in order to create a Jewish majority by force, the Israeli police besieged the offices of Zochrot at the heart of Tel-Aviv in order to prevent the activists present from holding a very symbolic memorial activity for that day.
This video shows arriving at the place already besieged by the police, the people inside prevented from leaving and those outside prevented from entering the office building.
At the time of writing this, police is still present as well as over 100 citizens demonstrating outside the offices. The police attacked and arrested some demonstrators, while preventing entry-exit to the office.
Activists from Zochrot were planning on commemorating the Nakba on Israel Independence Day by publicly reading the names of Palestinian villages that were destroyed in 1948, similar to actions they have taken in recent years.
Update: Here are photos from Activestills --
Israeli anti riot police arrest a left wing activist, after Israeli police blocked the exit from an event of Zochrot organization, commemorating the Palestinian Nakba, in central Tel Aviv, April 25, 2012. Israeli police blocked the exit from the event, claiming activists were planning to take part in actions commemorating the Nakba during celebrations of Israel's Independence day in Tel Aviv. 3 activists were arrested, while all the people at the event were asked to show their ID's in order to be able to leave the place. (Photos & Caption: Activestills)
We'll post updates as we receive them.