Freeze after skip forward/back on Freeview DVB-T and MediaPortal

Forums › Home Theatre (including HTPC and EPG Collector) › Freeze after skip forward/back on Freeview DVB-T and MediaPortal

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mcraenz

1140 posts

Uber Geek

#834530 11-Jun-2013 22:39

Yep just tested on Four and can't fault it. But choice is quite easy to reproduce. So yeah I jumped to a conclusion on it being related to SD channels only. I reckon it's been happening for more than a few days. Can't quite put my finger on when it started. I feel like its been happening since 1.3 final. Actually this fault has existed before in MediaPortal 2-3 years ago but was fixed. Doubt it's the same fault though because as you mention it only seems to be happening on the Kordia mux.

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mm1352000

1149 posts

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Inactive user

#834533 11-Jun-2013 22:57

mcraenz: I reckon it's been happening for more than a few days. Can't quite put my finger on when it started. I feel like its been happening since 1.3 final. Actually this fault has existed before in MediaPortal 2-3 years ago but was fixed. Doubt it's the same fault though because as you mention it only seems to be happening on the Kordia mux.

I don't know that I agree with you here regarding the fault existing previously.
I quite regularly watch Parliament TV and this was not happening last week; it is tonight.
If you check the MP log, look at the timing of the following entries:

TVHome.ViewChannelAndCheck(): View channel=
TvHome.RenderBlackImage()
succeeded:Succeeded TvControl.VirtualCard
TvHome.OnVideoReceived()
TvHome.StopRenderBlackImage()

The first entry tells you when the request to change channel is sent to the TV Server.
The second entry tells you when the MP screen is blanked.
The third entry tells you when the TV Server reports that the channel change is complete.
The fourth entry tells you when video data is seen.
The fifth entry tells you when the screen is unblanked.

I'm seeing higher times between entries three and four.
If this is an MP issue then I think it would be related to TsReader, but it could be codec related too.

[edit: entries three and four, not two and three - long day yesterday]

turb

881 posts

Ultimate Geek

#834552 12-Jun-2013 06:38

Asmodeus:
turb: Me too. Prime and Choice.

Me too!

You have to play around with the skip buttons or just wait to make it work properly again. Doesn't happen every time but definitely often

Are using WMC too?

Interests: HTPC, Web App authoring.

askelon

876 posts

Ultimate Geek

ID Verified

#834617 12-Jun-2013 09:48

Ive had that happen since the 1.3 betas. Just always thought it was my system - switched to Win7 around the same time. And it could quite be mainly the kordia channels that do it for me. I know Prime does for sure, choicetv does it occasionally, really cant remember if any others do though. And Ive noticed it only does it going into the actual TV show, not in the commercials - its a conspiracy to stop us watching bad TV! :p

mm1352000

1149 posts

Uber Geek
Inactive user

#834655 12-Jun-2013 11:05

askelon: And Ive noticed it only does it going into the actual TV show, not in the commercials - its a conspiracy to stop us watching bad TV! :p

I think ads would naturally have more I frames. Hence the black screen is less obvious.

Those of you using MP...
Is the problem consistent across different codecs?

mcraenz

1140 posts

Uber Geek

#834670 12-Jun-2013 11:18

I think it's across multiple codecs. Pretty sure I tried with MS codec but I'll confirm tonight.

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Asmodeus

1015 posts

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#835845 12-Jun-2013 14:56

turb:
Asmodeus:
turb: Me too. Prime and Choice.

Me too!

You have to play around with the skip buttons or just wait to make it work properly again. Doesn't happen every time but definitely often

Are using WMC too?

Yup :)

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gbwelly

1243 posts

Uber Geek

#835957 12-Jun-2013 16:59

I've had this problem for ages with windows media center with default decoders. It varies in severity and I have seen it on Four (sometimes), Prime (less occasionally) and Choice (often). It's slightly subjective, but I personally think it also varies between ads and the actual show. E.g if I skip and stop early in the ads it can take ages for the picture to resume and sync to the audio. If I overshoot it still takes a while, but I think it syncs up faster. Might be purely my imagination however.

mm1352000

1149 posts

Uber Geek
Inactive user

#835990 12-Jun-2013 17:25

The more comments I read, the more I think this issue is independent of software. Even largely independent of codec and splitter. The biggest factor is the head-end encoder.

To a large extent codecs and splitters are "mechanical". Feed in X; get out Y.

My understanding is that codecs aren't able to fully decode frames until they hit the start of a new GOP (group of pictures). Now, I know that is not entirely accurate for h.264 which doesn't have to have closed GOPs, but the principle still applies - codecs wait until they have enough context before turning on their output. Otherwise they'd output... garbage. Some codecs may require slightly less context than others due to their internal design... however there are still non-negotiables.

If you encode a stream with short GOPs and lots of safe entry points and/or I frames then the codec can build up the required context and turn on the output quickly.
If you encode a stream with longer GOPs and few safe entry points and/or I frames (more complex inter frame references) then the codec takes longer to get its context and turn on the output.

The first case takes more bits than the second for the same picture quality.
We know that Freeview is running at capacity. With the addition of Sommet I suspect Kordia is fine-tuning to try and steal as many bits as possible for Sommet while maintaining the picture quality of the other channels in the mux as best as possible. Stealing bits always has a cost!

mm1352000

1149 posts

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Inactive user

#835992 12-Jun-2013 17:31

One last comment...
The point in time at which you change channel can make a difference. If you happen to switch at an optimal time (ie. shortly before a safe entry point), the picture may appear quickly. Other times it may take longer. The GOP length is most likely not fixed, so that is another variable.

mcraenz

1140 posts

Uber Geek

#836005 12-Jun-2013 17:48

I can see how this would cause the skip forward or channel change to take a little longer but what about when the picture totally freezes never to continue.

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turb

881 posts

Ultimate Geek

#836013 12-Jun-2013 18:07

Who can we complain to? Is it Kordia or Freeview?

Interests: HTPC, Web App authoring.

mm1352000

1149 posts

Uber Geek
Inactive user

#836015 12-Jun-2013 18:22

mcraenz: I can see how this would cause the skip forward or channel change to take a little longer but what about when the picture totally freezes never to continue.

MP is not totally frozen right. Just the picture. Audio continues in the background?

I think its related. I'd compare it to what happens with corruption or interruption in the stream. Basically the codec gets into a situation where its internal context is screwed or it can't find a suitable entry point... or maybe the codec takes too long to sort itself out and this messes up the renderer. In any case, something hits the "give up" threshold. I don't know much about renderers, but most codecs will only attempt to decode "garbage" for so long. This situation is more likely when the complexity of the stream encoding is higher.

mcraenz

1140 posts

Uber Geek

#836016 12-Jun-2013 18:24

Yep just the stream, MP is fine. Yep makes sense. Bloody annoying, but makes sense. Thanks for all the good info :)

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