Jerky live TV on version 31

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pinnerite
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Posts: 256
Joined: Mon Apr 07, 2014 2:34 pm
Great Britain

Jerky live TV on version 31

Post by pinnerite »

I have been slowly eliminating problems on my backend server.
I am left with jerkiness of the live TV on my remote frontend but not on the local frontend.

The remote has always been cable connected to the modem-router but the backend server was connected by WI-FI.

Suspecting the WI-FI, I disabled it and connected a cable to the backend server from the modem-router.

The remote frontend has been running it all day.

HD recordings replay perfectly on both the server's frontend and the remote.

Live TV runs fine on the server's frontend but on the remote, it is jerky.

Both machines are powered by Linux Mint 20.04 and both have 2TB drives with at least 1TB free.

Is this fixable?
pinnerite
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Posts: 256
Joined: Mon Apr 07, 2014 2:34 pm
Great Britain

Re: Jerky live TV on version 31

Post by pinnerite »

I have narrowed the problem down a little:

a) Viewing SD and HD recordings on MythTV backend server 's frontend - Perfect
b) Viewing live SD and HD TV on the same frontend - Perfect
c) Viewing SD and HD recordings on remote (connected by wi-fi) - Perfect
d) Viewing live SD TV on remote frontend (connected by wi-fi) - Perfect
e) Viewing live HD TV on remote frontend (connected by wi-fi) - Jerky

a contributor on the uk.tech.digital-tv usenet group wondered if this is CODEC issue as HD uses H264 whereas SD doesn't.

Is he on the right track?
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kmdewaal
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Re: Jerky live TV on version 31

Post by kmdewaal »

The HD in statements c) and e) will both have H264 and will have the same bandwidth requirements.
Statement c) shows that your average wifi bandwidth is enough for HD with enough buffering available.
Statement e) the jerky HD can be caused by lack of buffering, i.e. being "too close to live".
It could just be that your live HD via wifi will be OK when, to allow for a buffer, you first pause e.g. 5 or 10 seconds and then continue playing.
Bragor
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Germany

Re: Jerky live TV on version 31

Post by Bragor »

I might have a somewhat related problem. Recordings play fine on the remote frontend. If a am watching HD live TV I have a jerky playback. If I pause live TV for a couple of seconds, playback is fine for a while. However the playback seems to be faster than realtime. I noticed the time difference between the live feed and my paused feed to be shrinking - even if I slow down the playback to 0.95x. At 0.90x the time difference is increasing so the frontend seems to playback the live feed 5% to 10% too fast. Does anybody have an idea what the reason might be?
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kmdewaal
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Re: Jerky live TV on version 31

Post by kmdewaal »

Interesting! This should not happen of course. The only thing I can imagine that 50Hz content is accidentally played back at 60Hz.
Can you do some measurements, e.g. start Live TV, delay for 60 seconds, unpause Live TV, and check every 10 seconds the time to live.
Also, what video card and driver do you use?
Bragor
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Germany

Re: Jerky live TV on version 31

Post by Bragor »

I tried what you proposed. About every 20 seconds the the time to live decreases by 1 second. I would say that it is a little bit more than 1 second but only slightly. I use a raspberry pi 4 with the newest stable software and drivers.
Bragor
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Re: Jerky live TV on version 31

Post by Bragor »

Some additional info:

Code: Select all

tvservice -s
state 0x80000 [PAL 4:3], 720x576 @ 50.00Hz, interlaced

Code: Select all

dtoverlay=vc4-fkms-v3d
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kmdewaal
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Re: Jerky live TV on version 31

Post by kmdewaal »

OK so this is not a 50Hz/60Hz issue. Maybe your RPi4 clock is a bit inaccurate. Is your frontend connected to the Internet and does it have time service (NNTP) enabled?
The easiest way to check this could be issuing the "date" command both on your frontend and your backend and this command should give exactly the same result. If there is a difference of two or more seconds then NNTP needs to be configured.
Bragor
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Posts: 19
Joined: Tue Dec 25, 2018 12:20 pm
Germany

Re: Jerky live TV on version 31

Post by Bragor »

If I issue the date command frontend and backend give the same time (if I ask the frontend first the time there is 1-2 seconds lower, but if I ask the backend first, it gives me a time that is 1-2 seconds lower).
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