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Why no SCART recording with a PVR



 
 
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  #1  
Old January 3rd 07, 08:42 PM posted to uk.tech.digital-tv
Steve Thackery
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Posts: 116
Default Why no SCART recording with a PVR

In a reply to a question on tech.tv.sky I realised I didn't really
understand why none of the current generation of hard disk based PVRs will
record from their SCART inputs.

Only the ones which also have a DVD drive (and cost at least twice as much)
will do so.

Can someone explain why? What has the presence of a DVD drive got to do
with it, when we're talking about recording from SCART to HD?

Thanks!

Thack


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  #2  
Old January 3rd 07, 08:59 PM posted to uk.tech.digital-tv
Pyriform
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Posts: 1,223
Default Why no SCART recording with a PVR

Steve Thackery wrote:
In a reply to a question on tech.tv.sky I realised I didn't really
understand why none of the current generation of hard disk based PVRs
will record from their SCART inputs.


Because they record the bitstream. They don't need an encoder, therefore
they have no means of recording from an external input.

Only the ones which also have a DVD drive (and cost at least twice as
much) will do so.

Can someone explain why? What has the presence of a DVD drive got to
do with it, when we're talking about recording from SCART to HD?


You need to look in the thread I pointed you to in the "Best way to archive
PVR recordings" thread. In brief: all the machines with DVD recording
capability first decode to analogue, then re-encode to MPEG2 (with a much
bigger file size!), in order to create a standards-conformant DVD. This
means they have an MPEG2 encoder, therefore they can also record from an
external input. They don't have two tuners, because that would need twice as
much hardware, twice as many MPEG2 licensing fees, and a whole bunch of
extra complexity that bitstream recorders do not have.


  #3  
Old January 3rd 07, 09:01 PM posted to uk.tech.digital-tv
{{{{{Welcome}}}}}
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Posts: 370
Default Why no SCART recording with a PVR

Thus spaketh Steve Thackery:
In a reply to a question on tech.tv.sky I realised I didn't really
understand why none of the current generation of hard disk based PVRs
will record from their SCART inputs.

Only the ones which also have a DVD drive (and cost at least twice as
much) will do so.

Can someone explain why? What has the presence of a DVD drive got to
do with it, when we're talking about recording from SCART to HD?

Thanks!

Thack


Ones with DVDs will be re-encoding the input into a format that will be
playable on other machines.

Usually PVRs simply record the stream as is.

  #4  
Old January 3rd 07, 09:14 PM posted to uk.tech.digital-tv
charles
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Posts: 4,016
Default Why no SCART recording with a PVR

In article ,
Steve Thackery wrote:
In a reply to a question on tech.tv.sky I realised I didn't really
understand why none of the current generation of hard disk based PVRs
will record from their SCART inputs.


Only the ones which also have a DVD drive (and cost at least twice as
much) will do so.


Can someone explain why? What has the presence of a DVD drive got to do
with it, when we're talking about recording from SCART to HD?


quite a lot of extra electronics are needed to tune the analogue signal
coming in via the SCART into a suitable digital one for recording.
Presumably, in a cut thoat market, any machine that had this would cost
noticeably more than one without and might have a very limited appeal.
After all, the size of the hard drive is limited, so there can't be many
people who want to fill it up with material from another source.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

  #5  
Old January 3rd 07, 10:47 PM posted to uk.tech.digital-tv
Tony
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Posts: 40
Default Why no SCART recording with a PVR

Pyriform wrote:
Steve Thackery wrote:
In a reply to a question on tech.tv.sky I realised I didn't really
understand why none of the current generation of hard disk based PVRs
will record from their SCART inputs.


Because they record the bitstream. They don't need an encoder, therefore
they have no means of recording from an external input.


'Encoder' is a bit vague. So in slightly longer speak:

The main 'cheap' PVRs are cheap because they have a digital receiver and
record the bitstream directly as broadcast without processing (it does
have to pluck out the bits relevent to a particular program, called
demuxing). So the compressed MPEG video stream is recorded as a file
100% the same as it is transmitted.

Older PVRs or DVD-Rs that come with an analogue receiver have to
digitise the video and audio and then compress it in real time to
MPEG2(difficult even for a 3.5GHz Pentium 4). These chips are
particularily expensive and are mostly hardwired silicon. Uncompressed
digital video is unfeasible to manage in a low cost product.

While digital receivers are a bit more expensive than analogue ones and
need a high powered processor and MPEG2 decoder, literally all you need
extra for a digital receiver PVR is a HDD, a bit more umph in the PSU,
and a bigger case. So a digital receiver PVR is very cheap, and records
with 100% quality aswell live pause, watch+record etc.

Only the ones which also have a DVD drive (and cost at least twice as
much) will do so.


There are very few Digital receiver DVDs, and those that are there are
mostly analogue versions with a digital receiver bolted on, so they have
all the necessary analogue conversion and compression circuitry. This
is very bad for picture quality and makes for a horrible product,
although it does allow for more storage on the disk (a particular
problem for DVD recorders).

The problem is that there are no buyable DVD software stacks for all the
embedded processors out there, so mfrs have to bolt existing hardware
'kits' from IC suppliers together.

HDD recording is much easier as you don't have to follow a complicated
standard / format and ensure compatibility with other devices.

Can someone explain why? What has the presence of a DVD drive got to
do with it, when we're talking about recording from SCART to HD?


You need to look in the thread I pointed you to in the "Best way to archive
PVR recordings" thread. In brief: all the machines with DVD recording
capability first decode to analogue, then re-encode to MPEG2 (with a much
bigger file size!), in order to create a standards-conformant DVD. This
means they have an MPEG2 encoder, therefore they can also record from an
external input. They don't have two tuners, because that would need twice as
much hardware, twice as many MPEG2 licensing fees, and a whole bunch of
extra complexity that bitstream recorders do not have.



I probably repeated some this, but I would also add that you only have
to pay licenses per product not per chip (normally). Most of the DTT
DVDs require 2 MPEG2 decoders anyway because of the bolt-on design
approach. And they have to pay the extra MPEG2 compression royalty.
Unfortunately its the only way to do it in the timescales that have been
achieved.

A good cheap DTT PVR DVDR with a single MPEG2 decoder is yet to be
designed AFAIK. There are a few high end ICs that have DVD stacks (eg
ones that do MPEG2 compression too). It will happen eventually when
licencable stacks are available, but maybe it will all be HDTV and blue
ray by then.

--
Tony
  #6  
Old January 3rd 07, 11:15 PM posted to uk.tech.digital-tv
Roderick Stewart
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Posts: 52
Default Why no SCART recording with a PVR

In article , Tony wrote:
There are very few Digital receiver DVDs, and those that are there are
mostly analogue versions with a digital receiver bolted on, so they have
all the necessary analogue conversion and compression circuitry. This
is very bad for picture quality and makes for a horrible product,


It's not as bad as you make it sound. I have three disk recorders, one HDD
only, which presumably records the bitstream untouched, and two that
include DVD drives. The older of the HDD/DVD machines only contains an
analogue tuner, so I use it with an external freeview box feeding RGB via a
SCART, and the newer one has a freeview tuner built in. I understand the
technical theory, but frankly, watching broadcast programmes on them it's
hard to tell any difference between the three.

Rod.

  #7  
Old January 3rd 07, 11:15 PM posted to uk.tech.digital-tv
Roderick Stewart
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Posts: 52
Default Why no SCART recording with a PVR

In article , Charles wrote:
Can someone explain why? What has the presence of a DVD drive got to do
with it, when we're talking about recording from SCART to HD?


quite a lot of extra electronics are needed to tune the analogue signal
coming in via the SCART into a suitable digital one for recording.
Presumably, in a cut thoat market, any machine that had this would cost
noticeably more than one without and might have a very limited appeal.
After all, the size of the hard drive is limited, so there can't be many
people who want to fill it up with material from another source.


I have used mine to copy irreplaceable material from VHS onto DVD, via the
hard drive which enables some simple editing to tidy it up, something I would
have thought quite a lot of people would find useful.

Rod.

  #8  
Old January 5th 07, 12:39 PM posted to uk.tech.digital-tv
Steve Thackery
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Posts: 116
Default Why no SCART recording with a PVR

Excellent replies and very helpful. Thanks, guys.

Thack


  #9  
Old January 10th 07, 09:37 AM posted to uk.tech.digital-tv
Tony
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Posts: 40
Default Why no SCART recording with a PVR

Bob Latham wrote:
In article ,
Tony wrote:

There are very few Digital receiver DVDs, and those that are there are
mostly analogue versions with a digital receiver bolted on, so they have
all the necessary analogue conversion and compression circuitry. This
is very bad for picture quality and makes for a horrible product,
although it does allow for more storage on the disk (a particular
problem for DVD recorders).


I'm sorry but I don't agree.

I have a Sony DVD/HDD with Freeview tuner and I often watch it on an HD
projector displaying an 8ft wide image. It is very hard if not impossible
to discern what is live and what is recorded. Certainly the topfield 5800
PVR does not look any better.


Cheers,

Bob.


Hmm, my comments maybe a bit out of date, I assume then it does not
record from analogue in.

Sony and Panasonic may have these DVD stacks with high end ICs as I
said, the early Sony Freeview DVDR I saw was a bolt together. And later
pricing seemed very high, but the 80GB RDRHXD560S doesn't seem
unreasonable at 329, although I expect we'll see 150 units once DVD
stacks are more widely available for the lower end processors.

I hope to get a look at the Sony at some point and see if they have done
a good job, see what IC they have used.

--
Tony

  #10  
Old January 12th 07, 10:29 PM posted to uk.tech.digital-tv
Tony
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Posts: 40
Default Why no SCART recording with a PVR

Bob Latham wrote:
In article , Tony
wrote:


I assume then it does not record from analogue in.


I'm afraid it does which no doubt you see as indicative of a bad design.


Cheers,

Bob.


Probably,

Digital recording of composite can do a good job of recording, although
it tends to get less quality per bit of data than DTT. I have always
hated composite pictures, and LCD / projectors don't really do RGB justice.

Its the old up close story, although I chose to ignore the MPEG
artifacts. DTT RGB on CRT looks great, edges occur just once. High bit
rate Digital recording of composite video looks like composite video so
if your ok with that then you won't mind the recording.

Further away most people would be hard pushed to notice the difference
between DTT and analogue, and I have even trashed my CRT for the space
benefits of a LCD. I did notice on my CRT when one of my old STB
occassionally reverted to composite mode. I probably wouldn't notice on
my LCD TV, but I await the day a reasonably priced DTT/PVR with good
scaler/deinterlacer with HDMI out is available so I can get a good
picture on it (or HDTV even).

--
Tony
 




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