Violet spots after resizing

[kb1985]

Hi,
I have 720x576 DV video.
I open it in virtual dub and try to resize it.
But while watching the resized video I've noticed some weird "violet spots" several times. While encoding without resizing everything is OK.
I've tried "resize -> lanczos " and "2:1 reduction Hight Quality".
Why do I have this problem?

[offline]

Likely to be a codec problem or possibly a codec clash. You have to check your loaded codecs and possibly your version of video player. Remove any codecs you don't need to start with - check the tools section for a codec manager.

[kb1985]

Sorry for digging up the old topic, but maybe you have any new clues on this one?

[Krispy Kritter]

You're still having the same problem? I would expect you to have all new codecs and newer updated tools by now.

[kb1985]

Well, I was quite shocked how fast time flies. I thought that I posted it few months, not years ago, and was amazed to find it dated 2005. Well, I remember the problem appearing again and again so I gave up and decided to workaround the problem. Recently I reminded myself about it and thought that I will ask if maybe someone would know anything new.

[jagabo]

Does it always happen in very bright parts of the picture?

[kb1985]

Well, the problem occurs not with every footage. I've just took the same video that I screencapped and posted in 2005 and tried to resize it again - the violet spot appeared exactly in the same place. I've tried to resize some other videos and everything was OK. So it seems that the problem occurs only with some of them. You think that it may be related with specific colour? On the screencap that I posted here in 2005, the point is partly white and partly black (sky and tree branches).

[kb1985]

Just checked another video. The violt thing appeared near white and black parts of the picture.

[jagabo]

What version of VirtualDub are you using?

[kb1985]

Oh, that might be the case?
Any known problems with codecs in the versions that I use?
I usually use VD 1.6.10
For MPEGS 1.5.10
For mp3s VDUBmp3 1.4c

[jagabo]

I thought you might have been using a very old version.

Well, the problem occurs not with every footage. I've just took the same video that I screencapped and posted in 2005 and tried to resize it again - the violet spot appeared exactly in the same place.

That is very good news. Being able to reproduce the problem puts you in a good position to track it down.

When exactly does the spot appear? Do you see it in the input window of VirtualDub. Do you see it in the output window? Does it only appear in the output file? The last implies a codec bug.

When you say you "resized" the video do you mean you used the resize filter in VirtualDub? Are you using any other filters? I've seen buggy filters produce artifacts like that -- I don't remember which ones though.

If you'd like to provide the source clip the gives the problem I'll take a look at it.

[kb1985]

That is very good news. Being able to reproduce the problem puts you in a good position to track it down.

Great to hear that!

When exactly does the spot appear? Do you see it in the input window of VirtualDub. Do you see it in the output window? Does it only appear in the output file? The last implies a codec bug.

I don't see it in the input window & I don't see it in the output window. When I play the output file I see the violet spots. I've just noticed that when I open the output file in Virtual Dub again the video is not corrupted!
I've decided to upload the video to youtube, to see if the artifact would still be visible, but had some problems with it right now, so I just took it to my laptop computer and playbacked it there - the violet dots were still visible.

When you say you "resized" the video do you mean you used the resize filter in VirtualDub? Are you using any other filters? I've seen buggy filters produce artifacts like that -- I don't remember which ones though.

I've used the standard Virtual Dub filter named "resize 2:1 (high quality)".

If you'd like to provide the source clip the gives the problem I'll take a look at it.

If that would help I can do this soon.
And thank you for the patience.

[kb1985]

The corrupted (or not corrupted? it plays ok in virtual dub) video uploaded on youtube also has the artifacts. Is there a possibility that VirtualDub and video players use some different ways to play the same file?

[jagabo]

I don't see it in the input window & I don't see it in the output window. When I play the output file I see the violet spots. I've just noticed that when I open the output file in Virtual Dub again the video is not corrupted!

That means you have either a problem with playback (video overlay driver?) or possibly an incompatible encoder/decoder pair.

There are two systems for video in Windows: the older Video For Windows (VFW) and the newer Directshow. VirtualDub uses VFW, media players use Directshow. The fact that your final video looks ok when you open it in VirtualDub means that the VFW decoder is able to decompress what the VFW encoder encoded. The fact that a media player shows errors could mean that the Directshow decoder is having problems with it.

Secondly, VirtualDub does not use your graphics card's video overlay feature to display the video whereas the media player does. This could mean there's a problem with video overlay or the graphics driver. You can test for overlay problems by playing the video in two players at once. Since only one program can use video overlay the other will use software to decode the video to RGB and put it on the desktop. If one player shows the problem and the other doesn't then the problem is with overlay. The fix for this is usually to update your graphics drivers and adjust the overlay settings.

If the problem isn't video overlay you probably have a buggy directshow decoder for whatever codec you are using. Getting updated codecs will probably fix things.

[kb1985]

That means you have either a problem with playback (video overlay driver?) or possibly an incompatible encoder/decoder pair.

There are two systems for video in Windows: the older Video For Windows (VFW) and the newer Directshow. VirtualDub uses VFW, media players use Directshow. The fact that your final video looks ok when you open it in VirtualDub means that the VFW decoder is able to decompress what the VFW encoder encoded. The fact that a media player shows errors could mean that the Directshow decoder is having problems with it.

The interesting thing is that it looks corrupted after uploading on youtube too. I thought that maybe it is something with my drivers, so I uploaded in on youtube (I don't know how it exactly works, but I thought that youtube uses some different encoders to create they FLV, so in that way I can check if that is a problem with some of my encoders).

Secondly, VirtualDub does not use your graphics card's video overlay feature to display the video whereas the media player does. This could mean there's a problem with video overlay or the graphics driver. You can test for overlay problems by playing the video in two players at once. Since only one program can use video overlay the other will use software to decode the video to RGB and put it on the desktop. If one player shows the problem and the other doesn't then the problem is with overlay. The fix for this is usually to update your graphics drivers and adjust the overlay settings.

I've tried playing the video twice at the same time and violet spots were in both of them, so I guess it is not the overlay.

If the problem isn't video overlay you probably have a buggy directshow decoder for whatever codec you are using. Getting updated codecs will probably fix things.

I'm using ffddshow. I've tried turning off the "overlay" function in ffshow (I don't know if this is the same overlay that you mentioned) but it didn't help. I also turned out ffshows XVID support but the poroblem still occurs.

Maybe the thing is that I use Windows 98 on this system?

[jagabo]

Since two players at the same time displayed the violet spots you don't have an overlay problem.

This is looking like a problem with your VFW codec. It's producing video incompatible with other decoders. What codec are you using to create the bad video? If it's a two year old version of Xvid of ffdshow (which uses Xvid) you should update it.

[kb1985]

Since two players at the same time displayed the violet spots you don't have an overlay problem.

This is looking like a problem with your VFW codec. It's producing video incompatible with other decoders. What codec are you using to create the bad video? If it's a two year old version of Xvid of ffdshow (which uses Xvid) you should update it.

For playback i use ffdshow-20040828
For encoding XviD MPEG4 video codec 12:09:23 Jul 16 2003 Core Version 2.1
I've installed never xvid once, but I preferred the older interface, but if changing to some more recent version will do the trick I will do this. So you think that the new files may be fine, but the files that I already encoded with the older XVID will be broken?

[jagabo]

I suspect the old versions of Xvid and/or ffdshow are the problem. I remember having similar issues several years ago.

You can try using a player that has built in decoders to see if the old files are OK. VLC or KMPlayer for example. If they play OK in those players the problem is probably in the old version so ffdshow. If not, in Xvid.

[kb1985]

Thanks for help!