Picture quality from HTPCs in general

[KevL]

Hi

I've been playing with HTPCs for many years now. All manner of configurations, PVR apps and usually using newish hardware.

I also have external set top boxes, (e.g. skybox, digital sat box, Freeview Digital terrestrial box - all SD) and a decent plasma (pioneer pdp508).

I notice that picture quality is never quite as good when the signal is produced from an HTPC as compared with external boxes. The set top boxes have issues too (my skybox has the chroma upsampling bug and this is very noticable with my setup) but playback is always as smooth as silk. Picture from an HTPC is very watchable, HTPCs can have lower video noise, better colours, can be adjusted for better white balance/contrast but never get quite get the video smoothness.


An excellent illustration of what might be going on here can be gained from tuning to the bloomberg news channel. This has video of varying quaility but has a continuous ticker tape with stock prices etc running at the bottom of the screen.

On a standalone box the ticker tape looks fine, motion is smooth and text is readable. When played via an HTPC the text is juddery and trying to read it gives a headache. Presumably this means the video picture from an HTPC is also always juddery but this is only apparent on slow pans when watching normal films etc.

Presumably this is because a PC is often distracted by non picture related tasks whereas the standalone boxes have dedicated hardware decoders which dont get disturbed. When a pc gets distracted it drops frames or sends them late etc (frame jitter???)

Obviously the the video quality obtained from an HTPC is completely determined by the video decoders used. I've tried many (maybe all????) and find the cyberlink 7 decoders about as good as it gets for SD material. Due to device driver/hardware issues I'm unable to use hardware acceleration on my current setup and I suppose that might be the missing step.

Is the above a reasonable summary of what to expect from an HTPC or is there a combination of hardware / codecs which can really give a set to box level of smooth playback?

I read elswhere that DMan was considering making a dedicated hardware decoder. Is this still being considered?



Kev

[Paranoid Delusion]

I read elswhere that DMan was considering making a dedicated hardware decoder

Got dropped because of the cost (very expensive) and limited interest afaik

[seco]

If the scrolling text has constant judder, then your screen refresh rate doesn't match the fps of the content.

I've noticed the same behaviour with news broadcasts that have scrolling texts (PAL TV which is 25fps) and only way to get smooth picture is to set refresh rate as 50Hz. For example 60Hz gives constant micro-judder so the text comes more or less unreadable.

[KevL]

Re hardware decoder.

If it is the only way to get perfect picture then it might actually be a very reasonably priced solution.




Picture is set at 1280 x 720p @50Hz and connection is via HDMI.

TV set reports this resolution.

All material is PAL format.

I've also experimented with different refresh rates and reolutions. 1280 x 720p @50Hz gives me best picture.

Kev

[Paranoid Delusion]

Whilst video playing what do you get if you press ! this will give you fps etc.

[KevL]

Many thanks Parnanoid Delusion.

Have just turned on TV and set it to BBC1 and have the tennis on.

Using the shift! function I get the following:

last 0.00 fps (1280x720)
100 backbuf X8R8G8B8
adapter X8R8G8B8 (D16) False
VRM9 25.6 (varies between 24.62, 25.21, 25.6 values seem to be quantised between these 3 values)
avg fps 24.91 sync 0 (fps varies between 24.91 and 24.93)
drawn 22362 (increments)
dropped 2
jitter 7

Interestingly when I tune to bloomberg (with the ticker tape running) and hit shift! I get the following - note the worse jitter

last 0.00 fps (1280x720)
100 backbuf X8R8G8B8
adapter X8R8G8B8 (D16) False
VRM9 25.6 (varies between 24.62, 25.21, 25.6 values seem to be quantised between these 3 values)
avg fps 24.57
sync 2
drawn 22362 (increments)
dropped 2
jitter 14



Kev

[seco]

I remember reading somewhere in the forums that the jitter value has nothing to do with the stutters in the picture

EDIT: According to Eabin it was only with EVR
Vista and EVR Support - Part 2

Post #87

[KevL]

I run XP MCE 2005. Don't like to even think about paying MS more money for vista.


Kev

[seco]

Well the forums are full of posts that deal with stutter issues and there seems to be like n+5 differents things which may cause it. It's the only reason that has made me think that I'll throw away my HTPC and buy standalone boxes for different medias instead.

[KevL]

The best picture I've ever had with an HTPC was using an Xcard Mpeg hardware decoder card.

Silky smooth playback. Problem with this is poor driver support and most apps struggle to put an OSD on it.

Hardware decode is the way forward. Maybe with the advent of Blue Ray someone will make a decoder card which does Mpeg2 and HD decode.


Kev