HD channels are jerky and show artifacts

James Hope

Hi there,

I am using TVheadend and XBMC as a front end with a PCTV nanostick 290e tuner.

Standard def tv (DVB-T) is fine. However HD tv (DVB-T2) plays ok, but every 3 or for seconds t kind of jerks and shows an artefact.

How can I find out what the issue is? The system plays other HD content fine.

ProfYaffle

See if you can eliminate XBMC by playing 'locally' to tvheadend (e.g. in the browser or directly to VLC).

Eliminate any network connection (you don't say if the tuner/tvheadend are on the same system as XBMC).

See if the signal is interlaced or not, as "other HD content" may be completely different; tune XBMC's settings accordingly.

See if you can record it and play it, which is another way of eliminating the PVR addon as you can then play the file natively - use .ts as a recording format to make sure it's like-for-like.

Check CPU usage on both client and server (e.g. with htop at the command line, or by pressing O when XBMC is playing); this also checks GPU usage.

James Hope

When I play on VLC in my browser it is also jerky.

The XBMC is on the same machine as the tvheadend backend

I have recorded it and downloaded the file to my laptop and on watching it pauses every few seconds. I don't get th artefacts but it is pausing and jerky.

I will try to check cpu usage now

James Hope

Prof Yaffle wrote:
> See if you can eliminate XBMC by playing 'locally' to tvheadend (e.g. in the browser or directly to VLC).
>
> Eliminate any network connection (you don't say if the tuner/tvheadend are on the same system as XBMC).
>
> See if the signal is interlaced or not, as "other HD content" may be completely different; tune XBMC's settings accordingly.
>
> See if you can record it and play it, which is another way of eliminating the PVR addon as you can then play the file natively - use .ts as a recording format to make sure it's like-for-like.
>

> Check CPU usage on both client and server (e.g. with htop at the command line, or by pressing O when XBMC is playing); this also checks GPU usage.

CPU usage never seems to go over 40%

ProfYaffle

Suggests to me that you're physically unable to capture or receive that signal properly. I suppose it could be a signal quality issue, or it could be a hardware limitation of some kind, such as the machine not being able to write to disc fast enough - that'd be odd, though, as it's not particularly demanding if you're just writing the single stream. It doesn't sound like XBMC or the PVR addon, anyway.

Do things improve if you shut XBMC down? Have you got anything else running in the background? Do you have an alternative place to record to, e.g. an external HDD, a flash drive, a RAMdisk?

James Hope

Prof Yaffle wrote:
> Suggests to me that you're physically unable to capture or receive that signal properly. I suppose it could be a signal quality issue, or it could be a hardware limitation of some kind, such as the machine not being able to write to disc fast enough - that'd be odd, though, as it's not particularly demanding if you're just writing the single stream. It doesn't sound like XBMC or the PVR addon, anyway.
>

> Do things improve if you shut XBMC down? Have you got anything else running in the background? Do you have an alternative place to record to, e.g. an external HDD, a flash drive, a RAMdisk?

Actually I take some of it back.
The recordings do not seem to be jerky when I play them on my laptop even if the stream on XBMC is full of artefacts.

ProfYaffle

How about if you play the recording on XBMC as a local file instead of via the PVR addon?

How about streaming from tvheadend on your HTPC/server to VLC on your laptop?

Together, those would point the finger at either XBMC or tvheadend.

The next thing to check if VLC plays on a different system but XBMC still won't play locally would be XBMC's audio settings... there are many posts on the XBMC forum of problems when people have their audio setup slightly wrong, which causes XBMC to keep trying to re-synchronise the streams (I think).

I could also try playing one of your samples on my setup if you wish - or vice versa. But let's do some more testing first.

James Hope

Streaming it to my laptop VLC seems fine, but playing the recording on XBMC is still bad.

ProfYaffle

Likely to be a local rendering issue on XBMC, then - although the fact that VLC won't play locally either raises an eyebrow.

What hardware platform are you using, what graphics card, what OS/XBMC combo...? Might be time to move over to the XBMC forums with a debug log if it's not obvious.

James Hope

I am using an ASROCk AM 350M1 board with onboard APU.

I am using ubuntu (or lubuntu maybe, can't remember) 12.04

ProfYaffle

AMD graphics, yes? Likely to be the problem (or "challenge", anyway!).

I can't explain why your other HD content works - what's it encoded in? - but it could well be that your system isn't playing nicely with H.264 DVB-T2 HD content. If nothing else, take a long, hard look at your acceleration options... have a hunt through the XBMC options and the XBMC forum and see what you find. That's where I'd start.

193 pages of discussion await, if you want to look... :-)

http://forum.xbmc.org/showthread.php?tid=174854