Cause of Encoding Artifacts?

[Benihana]

Hi, I had a question about Artifacts. I mainly capture old home videos we have and I'm trying to digitize them to preserve the remaining quality. I'm wondering the cause behind artifacts. The source was fairly clean, with very few dropped frames. (but they did occur occasionally) Usually with dropped frames, the playback will be a little jerky after encoding with XviD. However, sometimes I get artifacts like the following:





As you can see, "blotches" appear on the left side of the image. What can cause this type of artifacts to occur? I'm thinking it's not occuring during capture, as the video clears up with the next scene change.

So then was this a "normal" video file, but just overtime it got corrupted? Lemme know if anybody has any experience with captures and artifacts. Thanks in advance.

[Dark Shikari]

That's what happens if the video is corrupted. The video decoder tries its best to make up for it, but obviously there will still be lots of errors visible.

[*.mp4 guy]

I've seen that happen on my system when I drop frames while capturing to an inter-frame format, such as xvid, or mpeg2. Capturing with vdub, and disabling realtime audio playback fixed the problem for me. You can either, stop dropping frames, or use intra-frame only compression to completely avoid the problem.

[Benihana]

So the problem could be in my huffyuv capture itself? I thought perhaps my harddisk was degrading the final XviD product.

[setarip_old]

(Just kidding!)

I mainly capture old home videos

If the example pictures you've posted are from your "home videos", you have a very interesting looking group at home ;>}

[foxyshadis]

You sure you're capturing to huffyuv? Because those are mpeg block corruption artifacts. If you're capturing from DTV, DV, DVD, or something like that, it could be all the way in the source. Check the original capture and the xvid output separately; if it's only in the xvid then obviously that's where the corruption comes from.

Huffyuv corruption destroys the entire frame from the point of corruption, and doesn't last through another frame. It looks like a grey curtain or waterfall through the frame.

[Benihana]

setarip_old:
Lol. Well this was the most noticeable artifacted scene I could find.

Dark Shikari, *.mp4 guy + foxyshadis:
Oh!! I think I see my problem. I used to use huffyuv back in the old days, but after I upgraded my hardware huffyuv wouldn't work so I think I did switch to MPEG-2 or XviD format for captures. This would've been captured with one of those formats.

I had no idea that these kind of artifacts were caused by loss of data during capture. As far as I knew with huffyuv, the entire frame gets dropped and you don't get artifacts, you just get a "pause" in the video stream. Thanks for the explanation. It makes sense now why only some of my videos are afflicted in this manner.

EDIT:
Just for curiosity's sake, has anybody ever experienced data corruption on a harddrive AFTER the final XviD video file was made? One of my harddrives has been giving a lot of read errors lately, and it's starting to relocate a few bad sectors. Eventually it will run out and with it I assume I'll get data corruption. I'm just curious to know what happens to the video file. Does it play at all, no sound, no video, blotches, etc.

[Sharktooth]

yes, it could be data corruption on your hard drive (bad sectors, file system errors...)

[Ar3d]

That would be bad. try to retrieve your files but using this strategy that they called Freezing Retrieval Hardisk.

[Benihana]

If that is what I think it is, is that where you put it in the freezer for 6 hours or so, then boot it up to use it? I've actually been meaning to try that once it gets bad enough.

And the data is backed up, I'm just curious to know if anybody else has experienced data corruption due to harddrive failure. Just for curiosity's sake I'm still leaving it running to see the effects on my data.

[Sharktooth]

yes, sadly i had so many HDD failures i had to redo my backups several times.
the main problems were picture corruption during playback or complete unplayability of the backups.