[mythtv-users] UK Freeview Mux A Jerky Playback Other Mux's Fine?

Ian Hodgson ian.hodgson.home at googlemail.com
Mon Jan 21 20:18:50 UTC 2008

   Maybe slightly off topic, I have noticed differing qualities of
picture within the same program when watched from my MythTV recording;
the studio part of Top Gear for example seems to have a lower frame
rate and in generally more jerky than say the test track footage that
is shown. The same 'issue' is apparent with recordings of EastEnders
that my wife has made; it is awkward to describe the difference in
'texture' of the picture, but one seems to be of lower quality than
the other.

   Given that it can occur within a program, it would seem to be
related to the source material and the way that Myth records it. I
guess I should confirm for completeness that the same programs watched
live do not show any of this 'texture' issue.

   Any thoughts??  TIA.

Steve Smith wrote:
> On 21/01/2008, *Oliver Maunder* <mail at olivermaunder.co.uk <mailto:mail at olivermaunder.co.uk>> wrote:
>     On Jan 21, 2008 9:54 AM, nospam312 <nospam312 at gmail.com
>     <mailto:nospam312 at gmail.com>> wrote:
>         When I watch QVC (and other channels on this mux) I get very
>         jerky or
>         stop start playback but other channels are generally fine.
>     This could be down to the bitrate allocated to the channels.
>     According to Wikipedia (
>     http://en.wikipedia.org/wiki/DVB-T_in_United_Kingdom) there are 19
>     channels broadcasting on MUX A but 5 TV channels on MUX 1 (plus a
>     few radio channels). I've certainly noticed a big difference in
>     picture quality watching QI on Dave and on BBC2.
>     I've noticed some nasty artifacts with scrolling text -
>     particularly horizontal scrolling credits. I assumed it was my
>     deinterlace settings, but I haven't looked into it much. I'll take
>     a look at News 24 and see if things are better there. Try using a
>     different deinterlace method and see if things improve.
>     Olly
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> TIA:  It sounds like your problem is down to bad reception I'm afraid. The fact that Mux A has more stations also means that it's less resilient to bad reception (less room for error correction). Check your aerial. Look into signal strengths etc.
> Olly: Yes I've (and others) noticed some funny things with Channel 5 and interlacing. They seem to fiddle with the "interlaced" flag in the stream a lot sometimes getting it wrong (I think what they do is have the main part of the screen progressive and the scrolling ticker interlaced but only "detect" the progressive part). Even different scenes in programs flip between interlaced and progressive.
> The result is interlace artifacts when they broadcast the wrong flag.
> Myth on my box definitely seems to be doing the right thing though (Five has got it wrong), as the same programs show exactly the same artifacts when I watch them on my Virgin cable box. Channel 5 news is especially bad.
> Hope this helps.
> Cheers
> Steve
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