In the video, Plant Manager Yoshida seems to be saying it was "steam explosion" (水蒸気爆発） in Reactor 3. When a TEPCO senior executive (perhaps Mr. Komori, from the voice) talks to NISA, he is saying "possible hydrogen explosion". The official account is that it was a hydrogen explosion.
The video gets surreal halfway toward the end, when someone who sounds like then-Chief Cabinet Secretary Yukio Edano is heard talking about controlled rolling blackouts.
My translation of the sound as heard in the video:
"Video from March 14, 2012, around 11:01AM, explosion in the Reactor 3 building"
(at 0:05 -)
About the dose level, it is 39.406 microcurie/hour.
(at 0:20, the upper right screen for 1F (Fukushima I Nuke Plant) shakes.)
(at 0.58 -)
HQ?: Well, right now, 3-meter tsunami warning issued for Hamadori [coastal Fukushima], can you hear us, 1F? 3-meter tsunami warning has been just issued for Hamadori. Please pay attention.
(at 1:13 - )
Plant Manager Yoshida at 1F: HQ! HQ!
HQ: Yes, this is HQ.
Yoshida: HQ! HQ! It's bad! It's bad!
HQ: Yes!? Yes?
Yoshida: Reactor 3, probably steam explosion, it just happened!
HQ: (in a weak, almost disappearing voice) Alright... (someone else) O..OK.. Emergency communication...
Yoshida: (overlapping the HQ person) Happened at 11:01AM.
HQ: 11:01AM. (totally unexcited,) Roger. We will make emergency communication...
HQ: That, that is the same as Reactor 1 [explosion], isn't it?
Yoshida: Yes, in the building, inside the Anti-Seismic Building here, we can't tell, but a side-way shake, clearly different from an earthquake, came, and there was no after-shake like in an earthquake. So I think this is an explosion, just like what happened in Reactor 1.
HQ: OK. Roger.
In Yoshida's background at 1F: Parameters! Somebody look at the parameters of Reactor 3! Call the central control room for Reactor 3 and find out!
Yoshida: And the workers on the scene, will take shelter, take shelter!
HQ(?): We'll notify people immediately. Emergency communication...
(From 2:17 to 2:25, yelling and shouting in the background, probably at 1F. Someone at the Off-Site Center - upper left screen - sits with folded arms.)
Yoshida: Well, NISA [Nuclear and Industrial Safety Agency] and Prime Minister's Office...
In Yoshida's background: The environment inside this room [the emergency response headquarters on the 2nd floor of the Anti-Seismic Building at Fukushima I], no change in gamma rays and neutrons. Report over.
Yoshida: ... keep them connected, real-time.
Yoshida's background: Hey! (beep)
(2:40, someone is heard making a speech. It sounds like Yukio Edano, then-Chief Cabinet Secretary and the administration spokesman)
"... causing troubles for you. However, the actual power suppl..." (cut off)
(HQ? 1F?): To Mr. Takeguro...., directly... [Takeguro, TEPCO's representative at PM Official Residence]
(3:10 Voice that sounds like Mr. Edano comes back)
"...as you prepare, to minimize your inconvenience..."
HQ (Probably Mr. Komori?, executive director, making a phone call to NISA): At 11:02AM, (was that 11:02?), at 11:02, in Reactor 3, there was a possibility of hydrogen explosion, we've been just informed by the plant. It's the first report...
At 1F (Yoshida, overlapping Komori): Please take shelter, make sure everyone is safe, take shelter. Then, measure the dose rate carefully and report. Now, everyone, please gather closer, and make sure everyone is OK.
Yoshida: And there's also a tsunami warning. As a precaution, please withdraw [to shelter] as soon as possible.
At 1F: Uh... as soon as you confirm, to the [worker] welfare unit, please report to the welfare unit once people take shelter. Please report to the welfare unit.
HQ (TEPCO's then-president Shimizu): This is Shimizu, head of the [HQ Response team]. Inform the related parties and report back right away...
On checking the news articles from March 14, 2011, it was indeed Yukio Edano, doing the press conference as Chief Cabinet Secretary, at 10:55AM, and right at that moment, speaking about the planned rolling blackouts (Asahi Shinbun, 3/14/2011).