Whats the point of Freeview?

Java Jive wrote:

Which is one very good reason why it's not perfect. The only answer
would be to find differing yardsticks of lossless compression for
comparison, one 'equivalent' to MPEG1 and the other 'equivalent' to
MPEG4. Or perhaps a better approach would be if there was a switch in
the codec to choose between lossless and lossy compression, then you
would be comparing the outputs of essentially the same codec.


Lossy & lossless codecs work in completely different ways.

But every idea that I can think of seems to have the problem of
finding anything suitable that actually exists! Meanwhile, I think we
are probably just going to have to stick with measuring that
appallingly low fraction of the original signal that is actually
received ...

The most common way of measuring "quality" is blind comparisons.

Play a subject two differently encoded versions of the same material and
ask them which is the better of the two. Use enough tests & subjects and
you can with some confidence state something like "H.264 at x frames per
second & y bits/sec is comparable to uncompressed" or "MP3 at x Kbps is
indistinguishable from a CD".

Java Jive wrote:
And I've seen compression artifacts in DVDs as well, for example
shoals of fish in 'Blue Planet'.

On Fri, 17 Oct 2008 19:49:43 +0100, "The dog from that film you saw"
wrote:
"Andy Champ" wrote in message
. uk...
Java Jive wrote:
Well, IMHO DVDs are fine. I rarely see compression artefacts. And they
are... what? 6MBit?
up to 10mbits.
keep in mind that they are encoded in advance too to get the most out of the
encoder.
tv stations will be encoding them in realtime - which will never give
results as good.

OK now I've got my new computer (the old one died on me!) I can catch up.

So at 10MBit, MPEG2 is usually OK. For most purposes (not shoals of
fish, or the other favourite moving water) we can probably get away with
half that.

So what's Freeview?

And for that matter, what's Sky HD? Whenever I've seen it it has the
football on. And you can see every blade of grass - until the camera
pans, and they all vanish. Which I find worse than not seeing them at
all...

Andy

On Thu, 23 Oct 2008 23:10:52 +0100, Andy Champ
wrote:

So at 10MBit, MPEG2 is usually OK. For most purposes (not shoals of
fish, or the other favourite moving water) we can probably get away with
half that.

No, if you try and get away with half that, that means when you do
need the bandwidth, it won't be there - that's the whole problem
right there.

So what's Freeview?

From figures elsewhere from Tony Sayer (I think somewhere in this
thread) 4Mbps. That represents about 1.5 to 3% of the original
signal, depending on the source.

And for that matter, what's Sky HD?

Have no idea, but it's interesting to hear that even HD is
over-compressed. Freesat HD is apparently about 1% of the original
signal.

Java Jive wrote:
On Thu, 23 Oct 2008 23:10:52 +0100, Andy Champ
wrote:
So at 10MBit, MPEG2 is usually OK. For most purposes (not shoals of
fish, or the other favourite moving water) we can probably get away with
half that.

No, if you try and get away with half that, that means when you do
need the bandwidth, it won't be there - that's the whole problem
right there.

Careful now. If you're quoting 10 Mb/s as being good, because that's what DVDs
are, then you can't directly compare with DVB bit rates. DVDs are usually
mastered with 'look ahead' multipass encoding, DVB has to be done on the fly.

If you can get a good quality analogue signal from C5, and you're *not* using
the Croydon, Chelmsford, Reigate, or Tunbridge Wells transmitters, take a look
for artefacts. C5 is distributed to all analogue Tx sites except the ones I
mention by a D-Sat MPEG 2 downlink. See if you can guess what bit rate that
might be using (No cheating on Google please)


So what's Freeview?

From figures elsewhere from Tony Sayer (I think somewhere in this
thread) 4Mbps. That represents about 1.5 to 3% of the original
signal, depending on the source.

And for that matter, what's Sky HD?

Between 10 and 20 Mb/s. But again remember that's MPEG 4, so not directly
comparable with MPEG2. Also although the Beeb use 16 Mb/s, their HD pictures
look worse than other HD broadcasters, because the Beeb are using a very
primitive encoder.

Have no idea, but it's interesting to hear that even HD is
over-compressed. Freesat HD is apparently about 1% of the original
signal.

We're going back round in circles again.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

Mark Carver wrote:

Careful now. If you're quoting 10 Mb/s as being good, because that's
what DVDs are, then you can't directly compare with DVB bit rates. DVDs
are usually mastered with 'look ahead' multipass encoding, DVB has to be
done on the fly.


Technically though you _could_ use multi-pass encoding for non-live
programmes if you wanted (that would cover some channels completely and
some almost so).

Not disagreeing with what you say, just pointing out that I was
answering the questions in Andy's post, rather trying to claim any
particular level of bit-rate was acceptable or not.

On Fri, 24 Oct 2008 07:21:48 +0100, Mark Carver
wrote:

Careful now. If you're quoting 10 Mb/s as being good, because that's what DVDs
are, then you can't directly compare with DVB bit rates. DVDs are usually
mastered with 'look ahead' multipass encoding, DVB has to be done on the fly.

On 2008-10-23, Andy Champ wrote:
So at 10MBit, MPEG2 is usually OK. For most purposes (not shoals of
fish, or the other favourite moving water) we can probably get away with
half that.

So what's Freeview?

Varies quite a bit by channel and time of day, but generally around
1.25-1.75 GB/hr, which if I've done the calculations right is about
3-4 Mbit/s. The main channels tend to get considerably more bandwidth
than the extra ones.

As a couple of examples:
80 minutes on More4 at 11pm = 1.47GB
45 minutes on BBC2 at 8pm = 1.26GB
85 minutes on Channel4 at 8pm = 2.24GB
34 minutes on More4 at 11am = 0.7GB
40 minutes on BBC4 at 9:30pm = 1.16GB
240 minutes on Five at 1:30am = 7.1GB
85 minutes on BBC4 at 9pm = 2.3GB
70 minutes on Five at 11pm = 1.42GB

On Oct 24, 8:17*am, Stuart Clark wrote:

Technically though you _could_ use multi-pass encoding for non-live
programmes if you wanted (that would cover some channels completely and
some almost so).

Yep if they made all channels CBR, the same bitrate on all platforms,
and got rid of that silly re-encode arrangement for BBC1 English sub-
regions, then they easily could.
I think it'd improve the picture lots, and would also save lots of
disk space on the BBC's server-based playout system.

wrote:
On Oct 24, 8:17 am, Stuart Clark wrote:

Technically though you _could_ use multi-pass encoding for non-live
programmes if you wanted (that would cover some channels completely and
some almost so).

Yep if they made all channels CBR, the same bitrate on all platforms,
and got rid of that silly re-encode arrangement for BBC1 English sub-
regions, then they easily could.

It would be difficult and messy to implement for a channel such as BBC1
where you're mixing pre-recorded programmes, with live content. There'd
be a big splat as you switched from the multipass encoded output, to the
'on the fly' encoded stuff. How would you mix and disolve from one to
another ? How would you plaster those annoying captions and voice overs
over the end credits etc. In this day and age of 'branding' it would be
very difficult to arrange, you'd essentially be trying to manipulate
your playout within the emission environment. Though personally I'd love
to see all that 'branding' ****e dumped forever, but it just ain't going
to happen.

However, you could use the method on stations such as Sky Movies and Sky
Box Office, where there's no clever tricks going on between films.

As for the re-code of BBC 1 English regions, that's being phased out as
each region has DSO. The post DSO BBC Muxes are being centrally (with
geographical redundancy) coded and muxed, so starting with BBC 1 SW in
April that practice will vanish.

I think it'd improve the picture lots, and would also save lots of
disk space on the BBC's server-based playout system.

Disk space is cheap as chips these days.

"Java Jive" wrote in message
...



Have no idea, but it's interesting to hear that even HD is
over-compressed. Freesat HD is apparently about 1% of the original
signal.




hd broadcasts are to hd what sd broadcasts are to sd.
i.e they are nowhere near as good as blu ray in the same way sd televison -
which uses the same codec as dvd, is nowhere near as good as dvd.




--
Gareth.

that fly...... is your magic wand....