[linux-dvb] Why compress a VDR movie again ?

[Jörg-Oliver Todamm <jtodamm@itc-consult.de>]

Hi Emil,
> What do you do if a tape, DVD-RW or CD isn't readable anymore?
> Harddisks are so reliable today that I don't see a large problem here.

>From my expirience I still have problems trusting customer IDE drives.
It's much better now. As you mention. Tapes have to be renewed but CDs
that are handeled carefully last long. Same should be for DVD-R(W)

> Anyway, one can just backup the stored movies from time to time onto
> several CDs. As they are used only for backup multiple CDs are no
> problem. And CDs are really cheap. 

I agree.

> With Raid5 you bring me to an idea. For 4x80 GB of Maxtor 
> disks you need
> an extra disk for Raid5. This disks costs but DM 600.

Hold it. RAID 5 needs at least 3 drives to work. Two will hold the data
and one the redundancy information. This is interleaved over all drives,
so each can fail and you have either 1 original block and 1 block
redunancy or all original blocks without redundancy in the worst case.
With more discs you optimize the tradeoff of between usable data and
redundancy.
With 3 drives you lose 33% capacity, with 4 drives 25% and so on. Linux
and Windows (NT 4.0 or 2000) can do this in software, no expensive
hardware is needed.

> Doing backup of
> 320 GB on CDs you need about 500 disks costing a similar amount. The
> backup on CDs is a lot of work, so I would prefer the Raid5 solution.
> They cost per GB stored can be improved further by using more than 4
> data disks in the array. With todays disk reliability this. 
> should be no
> problem.

I hope, but don't belive, in an early breakthrough in holographic
technology. Harddiscs are the best possible solution right now. But
still expensive for most people.

> 
> > - a small and quiet box placed in my living room next to my 
> TV and the
> > HIFI components (harddiscs need some cooling and are loud)
> 
> Harddisks are relatively quiet today, but I understand your point. I
> also want to minimize the noise in my living room. But I 
> normally view a
> projector and turned up volume so that the noise of any normal hd is
> masked perfectly. ;-) The best would be to have a really small box in
> the living room for playback and the server somewhere else.

Well, the box is also load if you are not watching something. Than this
thing can be hard easily. Just tried some simple things to stop the
sound without overheating the box.

> That's the biggest limitation. You cannot run a MPEG2 stream live over
> WLAN without problems. The datarate has not enough reserves for the
> varying speed of WLAN networks. Best would really be to connect
> everything with 100BaseT.
> But you can probably use the local disk as fast cache and a 
> WLAN server
> as primary storage.

You can play a DVD over WLAN quite simple (did it allready) but you need
some buffer. Also there are some demo products by Sony and other,
showing MPEG2 video over IEEE 802.11b 11Mbps WLAN. For multiuser
expierience you have to reduce bitrate (still done with the VDR
recordings that are typically about 4 Mbps as I saw it)

> I am kind of undecided what I should do. On one side one 
> central server
> in the living room is easier to handle and cheaper if you want to
> incorporate multiple SAT cards for multiple independend users and use
> the resources efficiently. On the other side a client/server or
> client/client structure is more clean and also somewhat fault 
> tolerant.

I am quite fixed with my options. There is only one place for the TV (in
the living room) and one workstation. And I hope to include my notebook,
so I am more flexible. Webpads seems to be out of discussion for a while
(Siemens SimPad costs 3000 DM, they are crazy!!!)

> 
> It would be really nice to have a kind of distributed VDR which could
> manage DVB cards and storage distributer over multiple nodes. ;-)

Step by step please. It's of couse a nice idea and can for sure be
implemented. But at the moment I see other parts that has to be done
first. The usability and extensability of VDR could be improved. For
example VideoText should be only some kind of plugin module and that's
it. Also my wife and I would prefer some more "One Key Action" like one
key recording, without jumping around in the menu.

So long,

J.-O. Todamm


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