[mythtv-users] What hardware do I need to be able to dual record using Comcast cable?

Michael T. Dean mtdean at thirdcontact.com
Thu Oct 16 20:10:00 UTC 2008

On 10/16/2008 01:58 PM, David Madsen wrote:
> On Thu, Oct 16, 2008 at 7:12 AM, Michael T. Dean wrote:
>> And plenty more examples out there on the 'net.  I wouldn't be surprised
>> if those who are transcoding HDTV are spending more money on increased
>> power usage from the additional effort of transcoding than they would
>> spend just buying some new big HDD's.  I'm pretty certain that those who
>> record/transcode/delete do.  Those who record/transcode/archive (where
>> legal to keep recordings long term, of course) may also.
> This got me thinking a bit and I did some back of the envelope
> calculations to put it into perspective.  Here's what I've come up
> with.  By transcoding, we are essentially 'buying' extra disk space
> with electricity.  Since electricity is not free, we can calculate how
> much it costs to 'buy' disk space by use of transcoding.  I'm only
> calculating raw space gained by transcoding, this does not factor in
> whether the recordings will eventually be deleted or archived
> permanently.  This will also be based more or less on my MythTV
> install and my recorded HD recordings and file sizes, which may not be
> applicable to everyone.
> Usage delta between idle/encoding on a Q6600: ~50W
> Local cost for 1kW of electricity: ~$0.09
> Time to transcode 1hr episode from MPEG2 -> H.264 (2 pass encoding): ~4hrs
> Original file size (commercial cut): ~5GB
> Encoded file size: 1.5GB
> Power used while encoding     = 50W/hr * 4hrs   = 200W
> Cost of power used to encode = .200kW * $0.09 = $0.018
> Space saved by encoding       = 5GB - 1.5GB     = 3.5GB
> Cost of space gained by encoding = $0.018/3.5GB = $0.005/GB
> Since the lowest price of new media is around $0.10/GB these days,
> transcoding (given this situation) appears to be an order of magnitude
> cheaper still.  This little experiment also does gloss over many other
> variables one could throw into the mix, but nothing (I could think of)
> that would skew the results far enough to change the result.  Other
> people with vastly different energy prices, lower efficiency
> processors or a host of other things could also end up with quite
> different results.
> Anyway, thanks Mike for passing along the idea.  I had never
> considered transcoding from that perspective before and I always find
> it interesting to evaluate the opportunity cost of different things.

 From another perspective, given your file size of 5GB/hr (which I will 
be nice enough to assume actually means 5GiB/hr):

A 1.5TB HDD can store about 1350GiB (give or take depending on the 
vagaries of 1.5TB and choice of file system) which equates to 270 hours 
of TV.  Sure, if you transcode to 1.5GiB you could get 900 hours of TV 
on the same disk, but, really...

Just how much TV do you need to keep?  (And, if you live where I'm 
guessing you live, you may want to check the "local" copyright law to 
determine whether archiving recordings is a violation, as time 
/shifting/ is allowed under fair use, but...)

Again, I stand by the claim that those who record/transcode/delete are 
costing themselves money.  As I delete my recordings, I don't transcode.

As far as the extra cost of extra disks, one should also factor in 
actual drive power usage (the Seagate 1.5TB drive takes up to 43% less 
power than previous Seagate drives ( 
), so replacing any smaller Seagate may actually save money or at least 
allow you to use 2x as many drives and 2x270hrs = 540hrs...).  (Yeah, I 
know I'm talking up the 1.5TB HDD, but then again, I just bought 
one--that was on a 24-hr sale a day before I sent the e-mail, which 
happened to be the day I lost a HDD--and it should arrive tomorrow, so I 
have to convince myself it's a great drive. :)

Oh, and speaking of losing a HDD.  If I lose a 1.5TB HDD, I lose 270hrs 
of TV.  If a transcoder loses a 1.5TB HDD, he loses 900hrs of TV.  :)  
(Yeah, you can do RAID, but then you're using more drives (and, really, 
it's just TV), so...)


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