I have often thought it very strange to only have 30mins / 2 hours recorded given what technology can do now.
You often hear of incidents and the cvr has been over written after landing because nobody has pulled the circuit breaker.
There have also been incidents at the start of long haul flights and no record left by the time they land e.g the aircraft (A340?) that took off in Alaska on the taxiway and left wheel marks in the snow bank at the end.
IIRC the CVR was no use in determining if it was a heated debate with laptops or if the guys really had fallen asleep over the States earlier this year.
If you can record 25hrs FDR surely you can record 25hrs CVR.