Home cinema - channel delays

HomeCinemaBanter (http://www.homecinemabanter.com/index.php)

- UK digital tv (http://www.homecinemabanter.com/forumdisplay.php?f=5)

- - channel delays (http://www.homecinemabanter.com/showthread.php?t=37821)

I get good reception on all Freeview channels with my Pace DT210F.
However, a few always take several seconds to load. These are BBC3, 4,
ftn, and now ITV4. It's not the end of the world but it's irritating.
They always load and are reliable and good quality pictures but
invariably I have to look at the blue Pace screen for a time before they
arrive.

I just wondered if there was anything I could do about it.
--
Trevor Wright

"Trevor Wright" wrote in message
...
I get good reception on all Freeview channels with my Pace DT210F.
However, a few always take several seconds to load. These are BBC3,
4,
ftn, and now ITV4. It's not the end of the world but it's
irritating.
They always load and are reliable and good quality pictures but
invariably I have to look at the blue Pace screen for a time before
they
arrive.

I just wondered if there was anything I could do about it.

The nature of digital TV is the small delay when a channel is changed.
However if the delay is noticably longer on some channels than others
the problem could be a marginal signal.

This may be manifest by longer delay on channels that are all part of
the same multiplex.

You can find channels allocations per multiplex he
http://www.dtg.org.uk/retailer/dtt_channels.html

The best thing to do is to improve your aerial signal.

As your signal is almost sufficient you may solve the problem by
putting one of those aerial amplifier/splitters they sell in Homebase
(10 -20 pounds depending on the number of outlets). However there is
no certainty this will solve the problem.

Unfortunately I cannot give you a reference for the units as their on
line website doesn't seem to feature them. The thingys I've in mind
are white with the aerial input the outlets all on the front face, the
outlets arranged in pairs. The module runs on a wall wart type
supply -included.

Roger

Roger R wrote:
The nature of digital TV is the small delay when a channel is changed.
However if the delay is noticably longer on some channels than others
the problem could be a marginal signal.

That is true, and is certainly one possible cause - a likely one at
that.

However...

A TV picture can only be displayed after at least one I-frame has been
received. I-frames contain the complete picture, rather than B and P
frames which only contain the differences between that frame and an
I-frame, and so can't be decoded without a corresponding I-frame. A
typical frame sequence might be
IBBPBBPBBPBBPBBPIBBPBBPBBPBBPBBPIBBPBBPBBPBBPBBP etc

I frames are sent every 12-45 frames (i.e. every 0.5 - 2 seconds). Some
channels use a fixed I-fame interval (usually 12 or 15 as shown above),
while the more compressed (lower quality) channels tend to send
I-frames less often on average, and vary the timing to suit the
content.

This means some channels might only appear up to 2 seconds after
selected (or will display very strange looking part-images for up to 2
seconds, depending on the box/decoder).

I doubt this is the original poster's problem though - IIRC all the BBC
channels use short I-frame intervals, and he mentions BBC Three as
being slow to load.

The other possibility is that when switching between channels in the
same mux (e.g. BBC1BBC2) the change is faster than when switching to a
channel in a different mux (e.g. ITV2BBC3), as the box has to tune to
a different frequency in order to make the change, rather than just
decode a different channel from the same frequency/mux/stream.

Neither of these are anything to worry about, while a marginal signal
would be something to correct if possible.

Cheers,
David.

wrote in message
oups.com...
Roger R wrote:
The nature of digital TV is the small delay when a channel is
changed.
However if the delay is noticably longer on some channels than
others
the problem could be a marginal signal.

That is true, and is certainly one possible cause - a likely one at
that.

However...

A TV picture can only be displayed after at least one I-frame has
been
received. I-frames contain the complete picture, rather than B and P
frames which only contain the differences between that frame and an
I-frame, and so can't be decoded without a corresponding I-frame. A
typical frame sequence might be
IBBPBBPBBPBBPBBPIBBPBBPBBPBBPBBPIBBPBBPBBPBBPBBP etc

I frames are sent every 12-45 frames (i.e. every 0.5 - 2 seconds).
Some
channels use a fixed I-fame interval (usually 12 or 15 as shown
above),
while the more compressed (lower quality) channels tend to send
I-frames less often on average, and vary the timing to suit the
content.

This means some channels might only appear up to 2 seconds after
selected (or will display very strange looking part-images for up to
2
seconds, depending on the box/decoder).

I doubt this is the original poster's problem though - IIRC all the
BBC
channels use short I-frame intervals, and he mentions BBC Three as
being slow to load.

The other possibility is that when switching between channels in the
same mux (e.g. BBC1BBC2) the change is faster than when switching
to a
channel in a different mux (e.g. ITV2BBC3), as the box has to tune
to
a different frequency in order to make the change, rather than just
decode a different channel from the same frequency/mux/stream.

Neither of these are anything to worry about, while a marginal
signal
would be something to correct if possible.

Thanks for taking such trouble to detail the cause of slight
variations in delay of presentation of the picture. I have not
previously noticed the effect you describe myself, but now I'll look
out for it.

I was previously under the impression, from using different brands of
boxes, that some seemed to have more delay than others, with the Sony
box being quickest, but following your explanation, perhaps that's
just more wishful observation than reality.

I cannot know, but I suspect the delays the OP is complaining about
are substantially longer than those due to this effect.

Roger

Roger R wrote:

wrote in message
roups.com...

Roger R wrote:

The nature of digital TV is the small delay when a channel is

changed.

However if the delay is noticably longer on some channels than

others

the problem could be a marginal signal.

That is true, and is certainly one possible cause - a likely one at
that.

However...

A TV picture can only be displayed after at least one I-frame has

been

received. I-frames contain the complete picture, rather than B and P
frames which only contain the differences between that frame and an
I-frame, and so can't be decoded without a corresponding I-frame. A
typical frame sequence might be
IBBPBBPBBPBBPBBPIBBPBBPBBPBBPBBPIBBPBBPBBPBBPB BP etc

I frames are sent every 12-45 frames (i.e. every 0.5 - 2 seconds).

Some

I have also noticed the same effect twith my Pace Dt210 box.
The delay is far, far longer than waiting for the next I frame and
nothing to do with signal levels.
I am sure this is down to the software in the pace box but why are some
channels affected and not others?
In fact, the same channels as the OP.
Its as if the box is waiting for an MHEG application to load....about 5
seconds of the "Pace" logo.
Does the box have trouble finding the PMT??
Trouble finding the audio and video PIDs ??
Just thinking aloud here..

A

Andy Dee wrote:
I have also noticed the same effect twith my Pace Dt210 box.
The delay is far, far longer than waiting for the next I frame and
nothing to do with signal levels.
I am sure this is down to the software in the pace box but why are some
channels affected and not others?
In fact, the same channels as the OP.
Its as if the box is waiting for an MHEG application to load....about 5
seconds of the "Pace" logo.
Does the box have trouble finding the PMT??
Trouble finding the audio and video PIDs ??
Just thinking aloud here..

To continue that...

Aren't these all "part time" channels? Could that be the issue? Now I
come to think of it, I've seen my Pace Twin take for ever to find BBC
Three and Four - but I usually watch things in chase play or later so
rarely see the effect. Plus, with the Twin, you get used to being
grateful for actually getting to watch the programme you wanted to
record! A few seconds delay when changing between live channels almost
seems like a benign "feature" in comparison! ;-)

(I shouldn't be so harsh - it's working quite well since the last
software update, though I've had two crashes, which lost nothing).

So I reckon you're probably right Andy - it could be something to do
with the MHEG (or) the facility which "hides" channels when not on air.

Cheers,
David.

wrote in message
oups.com...
(I shouldn't be so harsh - it's working quite well since the last
software update, though I've had two crashes, which lost nothing).

So I reckon you're probably right Andy - it could be something to do
with the MHEG (or) the facility which "hides" channels when not on air.

I have also found that some STBs take a lot longer to change channel when it
involves a change from a 64QAM mux to 16QAM mux. The old Philips OnD STB
seems to be particularly bad in this respect, for example when going up the
channels from 6 (ITV2) to 7 (BBC3).

Glyn

GlynM wrote:

wrote in message
oups.com...

(I shouldn't be so harsh - it's working quite well since the last

software update, though I've had two crashes, which lost nothing).

So I reckon you're probably right Andy - it could be something to do
with the MHEG (or) the facility which "hides" channels when not on air.

I have also found that some STBs take a lot longer to change channel
when it involves a change from a 64QAM mux to 16QAM mux. The old
Philips OnD STB seems to be particularly bad in this respect, for
example when going up the channels from 6 (ITV2) to 7 (BBC3).

Glyn

No, its not that.
BBC1 (16QAM) to ITV1 (16QAM) is very quick.
BBC1 to BBC3 (both 16QAM) produces the Pace logo (interactive services
loading) for 5 sec, then the picture.

A

In message , John
Porcella writes

Learn to be more patient?

Thankyou so much.
--
Trevor Wright