HD picture stutter

[craglett]

Hi
I recently bought the 6280 and it seems brilliant apart from picture stutter on HD channels. I'm using it with an ATI Radeon 5450, Intel Core2 Duo 6700, 2Gb PC2-6400 RAM, Windows 7 x64 using the 1.0.0.8 driver. All standard definition channels work fine. I have tried the setup in Media Centre and Media Portal with the same results.

Please can you help?
Craig

[CyberSimian]

I recently bought the 6280 and it seems brilliant apart from picture stutter on HD channels. I'm using it with an ATI Radeon 5450, Intel Core2 Duo 6700, 2Gb PC2-6400 RAM, Windows 7 x64 using the 1.0.0.8 driver. All standard definition channels work fine. I have tried the setup in Media Centre and Media Portal with the same results.

Sadly, there are two problems that many users of Windows Media Center encounter: flickering and stuttering.

I experienced flickering on high-definition TV channels, using a TBS 6284 card; standard-definition TV was OK. See this thread:

viewtopic.php?f=61&t=7793

I have not experienced stuttering (yet!). For both problems, the cause seems to be the graphics card and its driver. Certain graphics cards seem to be worse than others, and certain drivers worse than others. In my case, the flickering was cured by updating to a newer Nvidia driver, but newer does not always mean better; sometimes newer drivers re-introduce a problem that was fixed in an earlier driver version. This means that you have to test every driver version available to see if there is one that cures your problem. For some info on stuttering, see this thread (there are may on the internet dealing with this topic):

http://www.thegreenbutton.tv/forums/vie ... f=5&t=2561

-- from CyberSimian in the UK

[craglett]

Hi CyberSimian

Thanks for the reply, I was half expecting someone to reply saying my hardware wasn't up to the job so I'm sort of glad you suggested software. I have held off messing around with the graphics driver so far because it seems to cause separate problems coming out of standby. I'll give it a try now though and see if I can't get rid of this judder.

It's hard to explain the effect but it's almost like I'm seeing quick movement such as panning in slow motion. It's not jerking across the screen, it's smoother than that. Anyway, not sure why I'm including this information, maybe it will help someone in the future if they have the same problem.

Craig

[rat666]

HI. I'm glad someone here has noticed. This problem should be effecting almost everyone. Anyone watching football in HD in media centre should see it, and for me it makes it unwatchable. The cause has been extensively documented in the US. Take a look at these links:

http://experts.windows.com/frms/windows ... geIndex=36

http://experts.windows.com/w/experts_wi ... wsignin1.0

http://support.microsoft.com/kb/2658140

In short, this is the classic 29/59Hz bug, except that in the UK we should call it the 25/50Hz bug. The name is a bit misleading. In the UK, HD content (as of about 6 months ago), is broadcast as a mixture of interlaced video at 50i fps (1080i50) and progressive video at 25p frames (1080p25). In the video stream there are 'flags' that tell the hardware what type of encoding a frame is. If it is interlaced the decoder converts it to 50 progressive frames for display (de-interlacing), otherwise it outputs 50 progressive frames by just showing each 25p frame twice. The problem comes when the flags are wrong. If an interlaced frame is not marked as interlaced, it gets shown as progressive. Furthermore, when the decoding mode changes it takes a certain amount of time for the GPU to switch. If this is done rapidly the GPU can't keep up. Both these issues combine to cause stuttering.

Is there a solution? Not really. Some GPUs (particularly CPU embedded ones) can switch fast enough and don't show stutter. The problem is that the source of the issue is in the video stream itself. The broadcast has incorrect flags in it which means we are actually looking for a work around at our end rather than a fix. GPU manufactures and microsoft are following the standards of H.264 so just won't do anything (they do know about it). Maybe using a software codec, rather than microsoft's, may work but i think this is tricky to do in media centre.

Whats worse, is that decoders in TV's generally are less strict on flags or are better designed to handle the switching so don't have a problem. Hence broadcasters don't care. If TBS sent a complaint to the British broadcasters maybe something would get done, but don't hold your breath.

To see the frame rate changes tune in a HD channel in Media centre, type the number '411',
and then press 'crtl D' to get the debug pages. Use arrow keys to cycle pages. Last page has fps at the bottom. When the video stutters you should see it flash down to 25 from 50. If it is a solid 25 then you are seeing 1080p25 and won't get stuttering. Live tv and football is normally 1080i so suffers badly as there is lots of panning.

(to fix flashing switch off 'dynamic contrast' in the GPU drivers, and/or change to YCbCr colour. The fps switching is responsible for this too.)

[steven]

Hi

Maybe this topic can help you:
viewtopic.php?f=43&t=8071&p=26021#p26021

Kind Regards

steven