-----Original
Message-----
From: Ben McCormack
[mailto:ben.mccormack@xxxxxxx]
Sent: 28 May
2002
11:46
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Lossless
Compression
DV Camcorder (A/D Conversion) (Some
Loss
in capture)
SKY UpLink (Compressioned, some
loss)
Basically the only way of minimising
the
losses is to capture the feed from the LNB as Ken said. but you are never
going
to be able to remove themas most of the losses have prob come about in the
SKY
uplink.
Please correct me if this is not
corrrect
-----Original
Me ssage-----
From: Kenneth Watt
[mailto:kennwatt@xxxxxxx]
Sent: 28 May
2002
11:37
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Lossless
Compression
The point being Jason that any form of
compression and manipulation of the file *will*
introduce loss and affect the quality of the image. If your digibox
un-compresses the stream then there is a loss in that, then you are
re-compressing it for storage (loss again), then decompressing it to view
(still more loss)…NOT lossless!
Any form of capture, compression or
manipulation will introduce certain artefacts into the picture whether you
notice them or not, although there is many a software “trick”
to
minimise the impact of such manipulation. If you like I can loan you a
couple
of good books that explain this but it isn’t exactly light reading
material.
K.
-----Original
Message-----
From: Jason Lee
[mailto:jasonjlee@xxxxxxx]
Sent: 28 May
2002
11:27
To: ukha_d@xxxxxxx
Subject: Re: [ukha_d] Lossless
Compression
OK, the PC capture of whatever feed is
lossless...
Like taking a file and using zip to compress it. The
file
when uncompressed is exactly the same as the source.
Lossless
As opposed to using jpeg/mpeg/mjpeg which uses tricks to
compress images down. When the image is uncompressed it is not identical to
the
source. Not lossless.
Look at matroxusers web site vcdhelper, any big video
editors website for details as to why this is a good
idea...
I don't only capture from tv, I capture from dv and my
s-vhs
deck.
----- Original Message -----
Sent:
Tuesday, May 28,
2002
11:19 AM
Subject: [ukha_d]
Lossless
Compression
Jason,
This is really a question for
you...
How are you achieving lossless compression
with
SS?
I was thinking about this last night and the
only
way I can see of doing
this is to take a feed into a SAT card in the
PC
direct from the LNB to
catch the digital stream before it is decoded
thus
achieving a lossless
compressed file. The problem with that is that
there is no CAM
available
for Sky Digital to enable this to be done with
a
SAT card or TV.
AFAIK the only way to do this, or more
accurately,
the only system that
can do this, is Sky+ as it actually records
the
stream directly and
plays back as it would be presented straight
off
the air.
If you are running it through the STB and then
transferring that signal
to your SS machine then that is not lossless,
you
are in fact, doing
what any PVR or VHS machine would
do.
K.
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