Practical Problem
There's a long movie on TV this weekend and we want to tape it. The movie is well over two hours, but we only have a T-120 VHS cassette to use.
Here's the plan: we can record the boring beginning of the movie at slow speed (EP), and AT A CERTAIN POINT IN TIME we then switch over to the higher quality faster recording speed of SP. That way the whole movie will exactly fit onto one VHS cassette.
The problem is to find the algebraic expression that tells us exactly where that CERTAIN POINT is when we are to switch the recording speed.
- MikeO
Here's the plan: we can record the boring beginning of the movie at slow speed (EP), and AT A CERTAIN POINT IN TIME we then switch over to the higher quality faster recording speed of SP. That way the whole movie will exactly fit onto one VHS cassette.
The problem is to find the algebraic expression that tells us exactly where that CERTAIN POINT is when we are to switch the recording speed.
- MikeO
Labels: SharedPuzzle
posted by ToM at
9:50 AM
5 Comments:
Let T be the movie length In minutes). Let h be the time at half quality, and f be the time at full quality. T = h+f.
Require 120 = h/2 + f.
So T - 120 = h/2 => h =2(T-120)
e.g. movie is 2½ hours => T = 150 mins =>
h = 2(150-120) = 60 mins at half quality.
Note that uses 30 mins of the 120, leaving 90 mins at full quality. And 150-60 = 90 mins also (phew!).
Add a few minutes to h to make sure you get the end.
VHS tape length T-XXX indicates playing time for NTSC or PAL-M in SP speed. LP records twice as much as SP and EP records 3 times as much as SP.
A T-120 tape will record 120 minutes at SP, 240 minutes at LP and 360 minutes at EP.
If a recording is made for x minutes at EP then y minutes at SP, the equivalent time taken up on the tape at SP is (x/3 + y) minutes.
Assuming the change between EP and SP can be made instantly, an exactly full tape means (x/3+y)=120.
Let length of movie in minutes L = x+y
We want to know the time to turn over from EP to SP, ie need to find the value of x for a given L.
Combining our 2 equations gives x=(3L-360)/2
So for example if the movie is 150 minutes long, switch from EP to SP at (450-360)/2 = 45 minutes.
This would give 45 minutes of lower quality EP play (taking up 15 minutes of the tape) and 105 minutes of high quality SP (taking up the remaining 105 minutes.)
If initially using LP then switch at 2(T-120).
If initially usind EP then switch at 1.5(T-120).
What is wrong with Sky+ or DVD-R? Failing that, buying from Amazon / Play.com.
Who on earth still uses VHS?
Oh, hang on, is that the thing that took over from my betamax system?
Call the cable company and get a cable box with a hard drive and order DVR service .... then you can record whatever, whenever ...
Karl, betamax was actually lots better quuality than VHS, but lost the battle ....(money game)
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