my QT doesn't play MPEG-2 HD

A friend of mine gave me some footages he took with his HD camcorder Sony HC1.
These footages are short (few seconds to less than 2 minutes).
I tried to play them with my QT (pro 7.1.1 MPEG-2 plugin installed).
It doesn't work.
The time cursor travel correctly. But the screen and the speakers stay definitely black and mute.

However:

To be sure my footages were correct I played them with VLC and MPEG Streamclip with no problem at all.

This is the info given by MPEG Streamclip about these 2 footages:

Bit Rate: 26.13 Mbps
Video Tracks:
2064 MPEG-2, 1440 × 1080, 16:9, 29.97 fps, 25.00 Mbps, upper field first
Audio Tracks:
2068 MP2 stereo, 48 kHz, 384 kbps

What could be wrong ?