file deterioration?

mr.beebo wrote on 12/17/2005, 6:21 PM

I've gone back to several mpg 2 files stored on an external drive for 6 months or so to burn copies to dvd and noticed on playback the audio has a clicking or popping every several seconds and the video has become jerky, almost to the point that it seems to skip frames. Not all video files stored are like this, but three or four out of maybe 20 are. I thought maybe it was just my computer stuttering but after loading into my sony dvd player the same things happens while on tv. Of course I can't re-download the footage from dv tape as I have since recorded over them. Any clues or am I doomed?

Comments

musicvid10 wrote on 12/17/2005, 6:54 PM

No, files do not deteriorate over time. They either do play or they do not play.

It is likely a sound card (or driver) problem, IRQ, or background process.
Look at what changes you have done, either regarding hardware installations, software installations, and/or network activity.

If you look at your memory, processes, and harware/driver changes you can surely identify the problem. Without detailed listings of ALL of the above there is nothing anyone here can help you with any further.

To me, it seems like a playback rather than a storage issue, however without additional information it is impossible to pin down.

farss wrote on 12/17/2005, 7:13 PM

At first thought I'd agreed with musicvid but then again maybe not.
If the number of error on the disk has increased then Windoz has got to work harder to read the data and that'll affect playback to the point where the data coming off the drive cannot keep up and you'll get stutters and clicks.
Try copying the files to another drive and watch the disk activity, the file copy will appear to stall as the same sectors are read multiple times in an attempt to recover the data.
If I'm correct, copy the files elsewhere real quick.
If you've burnt the to a DVD and from there you have this problem ignore what I'm saying.
Bob.

johnmeyer wrote on 12/17/2005, 7:44 PM

I think I'll side with musicvid on this one, with this one proviso: Copy one of the offending files from your external drive to an internal drive. If it copies, then the file is OK. I say this because I believe that Windows does a CRC check when copying, and if bits were corrupted, Windows would generate an incorrect CRC when copying and would notify you of that fact.

Once you have copied the file, try playing it from your internal drive. If it still shows problems there, then I'd start looking at other things, like your hardware.

Also, you might want to actually look at the waveform in Vegas or (if you have it) SoundForge. Do you see pops at the point where you hear them? If they are not in the waveform then they are not in the file, and they are being generated during playback.

farss wrote on 12/17/2005, 10:51 PM

Drives always do a CRC check in their own hardware. If the error is correctable the outside world doesn't really get to see it although access maybe slowed a little. However from what I can see Windows makes a heroic effort if the drive reports an unrecoverable error. I've watched Winodws go through many attempts including recalibrating the drive several times before it finally gives an error message and gives up.
Now what's in the waveform file may mean nothing as that's created the first time the file is accessed. Certainly it'll clearly show the data that'll be read from the file if it can be recovered.

It's very, very unlikely given the amount of error checking done that you'll ever get corrupted data from a file, either you get good data or none at all however in the case of playing back a file of video the issue is also getting it back in a timely manner.

I've had this happen more than once but not with video files, in my case it was from a large collection of stills, Windows would take forever to display the thumbnails of certain files, while it was trying the disk light was hard on. Copying all the files elsewhere they opened just fine, running disk repair fixed the problem however I'm too cautious to trust work to a dodgy drive, in general once they start to go they keep going.
Bob.

mr.beebo wrote on 12/18/2005, 2:58 AM

Thanks for such a quick response. Musicvid may have hit on something without intending so. I should have mentioned that I have a 160g internal drive, and two Western Digital 120g external drives and they are all close to 90% full. I did run several of the mpg2 files thru soundforge and yes the poping does show up. Transferring the files from one drive to another made no change. I had saved one file four separate times as I had edited the video progressively over a period of a month. I know for certain the original file was in good shape as I had burned a dvd for playback of the rough footage in the beginning and had no problems. I'm using vegas 6.c. The video now almost has the effect of a silent movie, where frames are dropped at irregular rates. My experience has been that most problems are much more simple that we first believe but yet I still find myself with the moniter upside down looking for the CRT filler tube or ebaying for mother board bearing lubricant.

farss wrote on 12/18/2005, 4:54 AM

OK,
so from what you're saying it's very unlikely that it's something to do with the data in the file being corrupted.
However these are mpeg-2 files, right, encoded out of V6?
Now Vegas doesn't do a very good job of playing back mpeg-2 so maybe, just maybe, there's actually nothing wrong with the files at all.

How to test this. Take a short section and render that section back to an AVI file and bring that back into Vegas and see if that plays OK. Try to make it a section that doesn't play very well.

By the way, mpeg-2 is not a good way to archive material, it's a fairly lossy codec so if you ever need to edit it Vegas will re-encode the whole thing and the quality can go downhill.

Bob.

musicvid10 wrote on 12/18/2005, 8:56 AM

**Musicvid may have hit on something without intending so. . . .I had saved one file four separate times as I had edited the video progressively over a period of a month.**

Now I feel compelled to qualify my original response based on this new information. It is my experience that pops and clicks or dropouts WILL introduce themselves in the file over repeated generations of lossy renders. Your problems are reminiscent of my first attempts to edit and render MJPEG files (when all I was able to do was analog capture). And as Bob stated, SF and Vegas have to strain to work with MPEG-2 files. And if your disk drives are 90% full, you're probably running out of virtual memory during the editing stage, another potential source of errors.

If you have the original unaltered mpeg-2 files, I would save them to an NLE-friendly AVI format first (I would try DV-AVI or HuffYUV), do my editing, check the playback, then render back to mpeg-2 if desired. If you have one of those camcorders that saves natively to mpeg-2, I would definitely do that first. That way, memory/playback/rerender issues will be minimized and you can play the final product back in PowerDVD or another player designed for mpeg-2. I never had very good fortune trying to edit or play mpeg-2 in SF or Vegas.