Strange artefacts, any suggestion?

[deLockloire]

I endoced a movie (@ 2-pass, MPEG, Qpel, Chroma motion, VHQ=1, no B-frames, chroma optimizer), and the result, albeit nice, shows some strange compression artefacts. They look like lines that somewhat break the picture horizontally (but usually don't cut through the whole picture, only third or half of it). They don't look like the interlace-comb, as there is only one or two of them at a time. They are not very frequent either, but noticable.

I thought it might be an interlacing problem, but useing Telecide(), FieldDeinterlace(), or TomsMoComp(1/0,10,1) didn't make them disappear.

The source is a PAL DVD (1.85:1/16:9), which I cropped to 698x548 and LanczosResized to 640x344 (i.e, the final aspect ratio is 1.86:1; I wasn't sure whether it should be 1.85:1 or 16:9 so I kept the original ratio). The artefacts always show at the exact same places. The problem is, however, that when I checked the film frame by frame in virtualdub, I just couldn't see them (with or without deinterlacing filters). It became visible though as soon as I started to play the preview, which leads to the conclusion that this is not an XviD problem, still, I have no idea where to post this (it isn't necessarily an avisynth problem either).

Any ideas?

[dar1us]

Welcome to the forum.

Sorry to begin on a bad note but...

...the problem is that you havn't included a screenshot with it.

Strike this, I replied too soon: Does it look bad when seeking in something like Virtual Dub?

What decoder are you using, NICs, Koepi's Build or (bestly) ffDShow.


harrison

[Danzel]

Sounds like it could be an idct problem.

If you are using ffdshow to decode then in the codecs window, try set XviD to Use XviD, so the XviD Directshow filter will decode it.

or

In the Miscellaneous window of ffdshow (right down the bottom) set idct to XviD. And possibly disable Autodetect.

If your already using the XviD Directshow filter for decoding then.... try ffdshow I guess.

Danzel.

[Didée]

Danzel: No, it sounds not like an IDCT problem.

Originally posted by deLockloire
when I checked the film frame by frame in virtualdub, I just couldn't see them
...
It became visible though as soon as I started to play the preview
To me, this sounds very much like "tearing". Meaning, the picture seems to "break" in the middle because movie's fps is not aligned with the monitor refresh rate.
Try to set any "vsynch" option of your videocard driver to "on", and the problem should vanish at least for playback in your media player. However, since VirtualDub's preview option doesn't use overlay by default, the tearing might persist there.
If you're dealing with PAL, you might want to set your monitor to 100Hz, and the tearing should be gone with the wind.

Regards

- Didée

[deLockloire]

@dar1us --> Ok, thanks. I didn't include a screenshot, because I'm not able to capture the problem. I've written about my results with VirtualDub. I'm using Koepi's XviD-24062003-1.

@Danzel --> I've tried, it didn't help. Thanks though.

@Didée --> It pretty much sounds like "tearing." However, on the one hand, I have vsynch turned on by default, on the other hand, my monitor cannot do 100Hz, but I tried 75Hz (which I figured should do as well as 100Hz) and it didn't seem to help. In the meantime, I've noticed that while bsplayer shows the tearing effect, winamp 2.91 doesn't. So based on what you've written, I've browsed through bsplayer's video options and I turned the "use overlay (mode 1)" on, which instantly eradicated the problem. :) Good news, I just have no idea why this is. Could you please explain it to me (or post a link where I can read more about this)? Thanks.

[Didée]

Very short:

In the case given here, "tearing" appears if your player switches from displaying frame "n" to frame "n+1" while the e-beam of your monitor is somewhere in the middle of of your screen.
Vsynch assures that this switching only takes place while the beam is outside the visible area, and thusly tearing cannot appear.
However, vsynch only affects (hardware) overlay surfaces. Therefore, obviously, it has no effect if overlay is not in use ... as in VirtualDub's preview windows, and in BSplayer with the wrong overlay mode (I never used that player, so don't ask me about its options).

- Didée

[yaz]

- i know neither vsynch nor bsplayer too much but in the latter there is (was?) a 'wait for vertical blink' (or sg like that) option. would it help in this case? anyway, using mod1 overlay is recommended, iirc.
- does anything change in vd if u change 'quick preview defaults' in options/preferences ? say, 'match display' or so.

the bests
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