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How good is HD decoding? Contributions wanted!

marcdbl

Active Member
I am 99% happy with the performance of my HTPC, and I've spent a lot of time tweaking and tuning video filters, video card parameters, and graphs to get to where I am now. However, I still have a small niggle with video playback, which is particularly noticable with HD sources. It's quite slight, and difficult to describe, which is making it difficult to find a solution, in fact it might just be the way HDTV is, and there is no solution!

Either way, I have a hunch that I am not the only one seeing this problem, so I have created a short test-video ripped from BBC-HD. If as many people as possible can download it and try it, I'd really appreciate it.

The video shows Mister Scharma walking from left to right across the screen. As he does this, I see a kind of wobbling/juddering blur/shadow around him, regardless of the h264 codec and renderer I use. If you can take a look at the clip, and report back with what you see, that would be great. :lease:

IMPORTANT: When you watch this clip ensure that your graphics card refresh rate is set to 50Hz, please mention your video card model and driver version with your findings, as well as which h264 codec you use, and what type of renderer you have set (VMR9/Overlay/EVR etc).

As an example , here are my results

As the man walks across the screen I see a kind of wobbling/juddering blur/shadow around him.
Graphics card: ATI 3200HD
Driver: Catalyst 8.9
Codec: CoreAVC 1.8
Render: Overlay (also occurs with all VMR renderers and EVR renderers)
It would especially interesting to here from anyone who sees the man move across the screen completely smoothly.

Download Test Video Here

THANKS!
 

thepharcyde

Active Member
hello mate, this is jerky as anything on mine and my laptop not just the guy moving. Set at 50hz. Is this something that you have recorded and uploaded. In which case if its an issue with your PC the recording is only going to output as per your decoder.

On a separate note, I have BBC Planet Earth that are very smooth also at 50hz that was recorded off the BBC1 HD channel. I have a HD3200
 
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marcdbl

Active Member
What were you using to decode? coreavc and overlay?

Also, what do you mean by jerky? Is the whole clip jerky? Or just the man?

FWIW, the clip is a bit-for-bit duplicate of what was transmitted, so my PC should not be part of the equation.
 

thepharcyde

Active Member
What were you using to decode? coreavc and overlay?

Also, what do you mean by jerky? Is the whole clip jerky? Or just the man?

FWIW, the clip is a bit-for-bit duplicate of what was transmitted, so my PC should not be part of the equation.

Just rebuilt PC yesterday after my woes that you kindly helped out with. Its the standard CoreAV codec @ 50hz playing in VMC. The whole picture is jerky.
 

marcdbl

Active Member
Hmm, that's pretty weird, no problems here on either my htpc or laptop, both using MPC for playback.

Be interesting to see what others find...
 

jameson_uk

Well-known Member
FWIW, the clip is a bit-for-bit duplicate of what was transmitted, so my PC should not be part of the equation.
Out of interest how did you convert the transport stream into an AVI?

Downloading now so will let you know how it works on both my HTPC (ATI 3650 and powerDVD codec) and my main PC (E6600 and FFDShow)
 

marcdbl

Active Member
Out of interest how did you convert the transport stream into an AVI?

I used mencoder to dump the raw video stream to a file, and then avc2avi to get that into an avi file.

Let me know your playback results!!

Any other takers? 80 views now, and only one person has tried it :lease:
 

Stephen Neal

Distinguished Member
Will try to download this evening or tomorrow.

Out of interest - how have you converted to AVI in codec terms - is it just a straight wrapper change, or have you transcoded to a different video codec?

If any transcoding has gone on it may have some "interesting" de-interlacing artefacts.

BBC HD shows both 25p and 50i sources - both broadcast in 50i. The former will have no movement between the pair of interlaced fields in each frame (and can be de-interlaced by a straight weave), the latter will potentially have movement between the pair of interlaced fields that make the frame, meaning the quality of the result will rely on the de-interlacing algorithm used to convert the fields to frames. (There are lots of ways of doing this)

BBC HD stuff that is 50i native includes sport (footy, rugby, tennis, olympics etc.), entertainment (Strictly, Joseph, Maria, Nancy, Jonathan Ross etc.), music (Proms, Later... etc.)

BBC HD stuff that is 25p native (or 24p stuff sped up) includes drama (Heroes, Silent Witness, Bleak House, Cranford, Criminal Justice etc.), documentary (Planet Earth etc.)

Occasionally some shows can use a mix of 25p and 50i (Top Gear does this in SD - with the films being 25p but the studio and race track stuff 50i) I think Britain from Above mixed the two formats?

The Simon Schama stuff is almost certainly 25p - though I haven't seen it so can't be sure.
 

marcdbl

Active Member
The avi is just a straight wrapper change, no transcoding. If other people get the chronic judder that pharcyde is seeing I might upload a mkv version (I think I remember hearing of occasional problems with high bitrate h264 in avi containers).

Regarding BBC-HD formats, I picked that clip for that exact reason, it's native 25p as far as I know ;).
 
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marcdbl

Active Member
Can you post it as a transport stream? Or if I get a chance I'll record the next episode on Monday.

Will the avi not play for you? I'm not sure if Ihat I can send you a transport stream as so far I've been unable to find a tool that will let me cut a section from a h264 TS, will keep looking.

Not sure if recording the next episode will be of use, I only see this problem from time to time, and it was just coincidence that I saw it in that few seconds of the show. It would be nice if it occured during the BBC HD preview as that's on all the time!
 

MikeK

Well-known Member
I've played this on my desktop PC and don't really notice anything like what you are describing - the clip appears to play smoothly, there's no noticeable juddering (well, as smooth as 25p stuff normally plays anyway)

Graphics card: ATI 2400HD
Driver: Catalyst 8.10
Codec: CoreAVC 1.8 & MPCHC internal
Render: VMR9 renderless

Also appears to work OK on VLC 0.9.4 too!

DGAVCIndex doesn't really like it though - throws up some errors on preview (although that may be normal with some stuff from BBCHD - never tried it before).
It appears to encoded MBAFF with a frame size of 1440x1080 (expected) but with a SAR of 15:11 (I would have expected 4:3 here) and a display size of 1963x1080 (would have expected 1920x1080 here) - seems a bit odd TBH, but again, this may be normal from BBCHD!
 

Stephen Neal

Distinguished Member
Hmm - is the SAR the Source Aspect Ratio (or Screen Aspect Ratio) if so then I would expect 16:9 not 4:3 or 15:11?

MBAFF is to be expected. However I'd also have expected 1920x1080 rather than 1920x1088 - I wonder if there is something odd going on because of the 1080 vs 1088 issue?

(MPEG2 - and I believe H264 - require multiples of 16 not 8 as dimensions - hence 1080i is encoded as 1088i with 8 blank lines at the bottom, but should be flagged as such so that it is cropped correctly in the receiver?) I notice I get very thin black bars top and bottom on BBC HD in VMC - I wonder if there is something different with the BBC HD encoder set-up?
 

MikeK

Well-known Member
The SAR is the Sample Aspect Ratio - for 1440x1080 it should be 4:3 (assuming you want to end up with with a 1920x1080 16:9 Display Aspect Ratio (DAR)).
Basically it's telling the decoder that each pixel has a 4:3 aspect ratio, which means 1440x1080 gets expanded by a ratio of 4:3 in the horizontal direction to make 1920x1080 (ie 1440 x4 /3 = 1920)
Setting the SAR to 16:9 would give you 2560x1080 - which is 2.37:1 (aka scope ratio), but AFAIK, nobody uses that, at least not yet anyway!

In the test clip, the Frame Size is 1440x1080, but DGAVCINDEX reports that the SAR has been set to 15:11, which means the decoder/player will expand those 1440 pixels by a factor of 15:11, which gives a Display Size of 1963x1080.
This will then have to be "scaled" to fit a standard 1920x1080 output - so you'll end up with 1920x1056 of of picture, with 12 pixel black bars inserted top and bottom (I wonder if that's the very thin black bars you are seeing on BBCHD)
I don't know why they've done it this way - like I said, seems a bit odd to me (assuming dgavcindex is correctly reporting this data - I've no reason to suspect it isn't though)


As to the 1088 pixel issue - it may well be 1088, and dgavcindex may be reporting the Frame Size of 1440x1080 after the correction has been made - not sure on that though!
 

Stephen Neal

Distinguished Member
The SAR is the Sample Aspect Ratio - for 1440x1080 it should be 4:3 (assuming you want to end up with with a 1920x1080 16:9 Display Aspect Ratio (DAR)).

Ah - the aspect ratio of each sample (or luma pixel).

Basically it's telling the decoder that each pixel has a 4:3 aspect ratio, which means 1440x1080 gets expanded by a ratio of 4:3 in the horizontal direction to make 1920x1080 (ie 1440 x4 /3 = 1920)

Ah - so a 16:9 1920x1080 signal would have a SAR of 1:1 - as it is square pixel based.

Setting the SAR to 16:9 would give you 2560x1080 - which is 2.37:1 (aka scope ratio), but AFAIK, nobody uses that, at least not yet anyway!

Yep.

In the test clip, the Frame Size is 1440x1080, but DGAVCINDEX reports that the SAR has been set to 15:11, which means the decoder/player will expand those 1440 pixels by a factor of 15:11, which gives a Display Size of 1963x1080.
This will then have to be "scaled" to fit a standard 1920x1080 output - so you'll end up with 1920x1056 of of picture, with 12 pixel black bars inserted top and bottom (I wonder if that's the very thin black bars you are seeing on BBCHD)

That would make sense wouldn't it?

I don't know why they've done it this way - like I said, seems a bit odd to me (assuming dgavcindex is correctly reporting this data - I've no reason to suspect it isn't though)

As to the 1088 pixel issue - it may well be 1088, and dgavcindex may be reporting the Frame Size of 1440x1080 after the correction has been made - not sure on that though!

Hmm...
 

marcdbl

Active Member
This will then have to be "scaled" to fit a standard 1920x1080 output - so you'll end up with 1920x1056 of of picture, with 12 pixel black bars inserted top and bottom (I wonder if that's the very thin black bars you are seeing on BBCHD)

I used to see these too and could never understand why, so the 15:11 the explains why it happened (but as you say, it doesn't explain why the BBC encode it that way). Thanks Mike.

Incidentally, I messed around a lot trying to get rid of the black bars, and managed it eventually. I'm not 100% sure what I did that fixed it in the end but I think it was mainly down to switching from the Cyberlink h264 decoder to the CoreAVC one.
 
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marcdbl

Active Member
I've played this on my desktop PC and don't really notice anything like what you are describing - the clip appears to play smoothly, there's no noticeable juddering (well, as smooth as 25p stuff normally plays anyway)

I've just realised I can get my laptop the display at 50Hz, so I have tried the clip on there too. I can still see the issue but it much less pronounced than on my plasma screen (on the laptop I have to put my eyes right up to the screen and it's still only slight).

I'm going to revise my decription of the issue a bit, calling it judder is a bit misleading, so now I would say:

"As the man walks across the screen (particularly when he reaches the right-hand half of the screen) there is a narrow dark shadowy effect wobbling around him."

If anyone has time to take a look, please do!
 

MikeK

Well-known Member
Tried again - still can't see anything.

TBH the clip isn't the highest def video I've ever seen, but it appears clean enough!

As a test, try playing it in Media Player Classic, and then step through frame by frame - do you still see the issue on each frame, or does it only appear when the clip is played back at normal speed?
 

marcdbl

Active Member
Effect doesn't appear when stepping. Hmm.

I'll keep an eye out when watching BBC HD for a more prominent example of this, and post a clip of that too perhaps.
 

Stephen Neal

Distinguished Member
Sounds like a de-interlacing issue possibly?

When you step through things in most media players you don't see a full interlaced frame (as you would get horrible judder if they showed you both fields of an interlaced source) you either see a single field, or an interpolated frame corresponding to one field.

Odd that you see it on Schama - which is not shot natively interlaced (so a straight weave de-interlace would deliver full quality 25 frames per second)... Hmm...
 

Stephen Neal

Distinguished Member
Interesting idea, currently I have deinterlacing set to 'Auto' in Catalyst. I'll try getting ffdshow to deinterlace it instead and see what happens.

Did you ever get the clip to play Stephen?

Sadly only on a 60Hz display.

Am still unsure what you are seeing. I'll try running it through my PCH A100 media player - which does a good job with 50Hz and 60Hz H264 stuff. It may be happy with an AVI wrapped H264 sequence.
 

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