Empty downloads

[Adamsito]

I have a very frustrating problem: Sometimes (that's a fristrating word for a start!) when I download a video file in BitComet, after waiting patiently for a couple of days (broadband isn't so hot where I live), the resulting avi file appears to be complete but won't play. On closer inspection I discover the file contains almost nothing more than millions of empty spaces. The file won't play because it contains no valid video data even though it's hundred of megabytes in size.

Anyone know what's going on? It's not a codec problem and nothing to do with low disk space. Could it be dodgy torrents? This has happened with several torrents, but one example is attached. It's a TV series which I'm downloading episode by episode. About half work fine but half don't.

Any suggestions would be greatly appreciated. I'm using Windows XP Professional SP2 and BitComet 0.70.

[kluelos]

Millions of empty spaces....what are you using to determine what the actual content is?

[Adamsito]

Millions of empty spaces....what are you using to determine what the actual content is?

I used two ways: In DOS - type "filename.avi" |more - that showed me just blank space which looks a lot different to a working avi file which shows me appropriate looking header information. Then I split the file into manageable chunks (using a program called Chainsaw) and opened a few random chunks in Notepad. That's where I saw all the spaces.

[kluelos]

Neither technique is appropriate to evaluate the actual content of compressed video, which includes most modern formats. Find and use a tool named "GSpot" to determine how the file is encoded and whether you have what's needed to play it. I also recommend the VLC player from videolan.org, which is free and does not use the system filters.

[Dark_Shroud]

GSpot

I'll ignore that comment about system filters. ;)

[Adamsito]

Neither technique is appropriate to evaluate the actual content of compressed video, which includes most modern formats. Find and use a tool named "GSpot" to determine how the file is encoded and whether you have what's needed to play it. I also recommend the VLC player from videolan.org, which is free and does not use the system filters.

Thanks for the tips. I found and installed GSpot and it tells me the File Type and Mime Type are both "Unknown". I already had and tried VLC Player but it just told me what all my video players tell me. This isn't a video file. I think I'm right about it not being a video, and that's my problem. Why are videos downloaded through BitComet arriving at my computer as large unusable files? This is happening with about 70% of my downloads now.

[The UnUsual Suspect]

I can assure you this is not normal, and bit comet is not responsible for the files posted on the net for download via bit torrent.

I would suggest you remove and restart the torrents (rehash). This will scan the files and replace any missing or damaged parts. If it reaches 100% and starts seeding, then the files were downloaded properly, if it begins downloading, then something was damaged after the download completed (could be many things including hard drive problems)

There are also alot of bad (intentionally) video files put on the net to disrupt the bit torrent comunity.

Suspect

[Adamsito]

I can assure you this is not normal, and bit comet is not responsible for the files posted on the net for download via bit torrent.

I would suggest you remove and restart the torrents (rehash). This will scan the files and replace any missing or damaged parts. If it reaches 100% and starts seeding, then the files were downloaded properly, if it begins downloading, then something was damaged after the download completed (could be many things including hard drive problems)

There are also alot of bad (intentionally) video files put on the net to disrupt the bit torrent comunity.

Suspect

Thanks, I've removed and restarted from scratch each of the series that are giving me problems and will now wait and see what happens. I find it hard to believe that some episodes are fine and some aren't, from the same torrent. I hope to god it's not my hard disk! That's a scary thought. Will backup and hope for the best.

[Dark_Shroud]

If it was your hard disk it would let you know by not working at all and/or make noises like a dying animal.

[kluelos]

If you post the url for the torrent we can take a look and see if we can figure out what's going on.

[The UnUsual Suspect]

I was in no means implying your hard drive is bad.

This could be one of many problems that could cause a good file download to read as corrupt.

However it is somewhat common for hard drives to lose a sector from time to time. Performing scandisc from time to time will help stop errors like this by marking any bad sectors so they won't be used.

I will agree with dark shroud that most hard drive failure will give you symptoms that are noticable, but a few lost sectors could have no symptoms at all, unless you try to read or write from those sectors.

In any case, Please let us know if your hash check of these files completes sucessfully (meaning it goes directly to seeding) or begins downloading.

the former would mean the files are intact, the latter that they were damaged.

Suspect

[Adamsito]

I was in no means implying your hard drive is bad.

This could be one of many problems that could cause a good file download to read as corrupt.

However it is somewhat common for hard drives to lose a sector from time to time. Performing scandisc from time to time will help stop errors like this by marking any bad sectors so they won't be used.

I will agree with dark shroud that most hard drive failure will give you symptoms that are noticable, but a few lost sectors could have no symptoms at all, unless you try to read or write from those sectors.

In any case, Please let us know if your hash check of these files completes sucessfully (meaning it goes directly to seeding) or begins downloading.

the former would mean the files are intact, the latter that they were damaged.

Suspect

I ran ScanDisk last night and all appears fine on that score. I had to disable downloads etc. for that obviously, so will resume today and see how things go. I removed all the suspicious torrents from BitComet so can't now do the hash check but I will next time this happens. An example of a torrent I had problems with is at this url: http://www2.digitaldistractions.org:8080/t...ies%201.torrent

I've been selecting just one episode at a time, and as I said, some worked and some didn't. That's what's so confusing and makes me think the torrent is OK.

Could someone explain what hash checking actually does/means? I assume we're talking about right-clicking on a completed download and selecting "Manual Hash Check". Is this something one should do as a matter of course? Why?

Thanks for all your help guys.

[kluelos]

Ok, that does make it really strange. You might get damaged or bogus torrents from a lot of sites, but Kirin does not allow that sort of crap on DD, and personally vets everything there.

A hash is a wonderfully complex mathematical function that yields a unique value for a given set of input values. Given a chunk of data and it's hash, you can use the data to recompute the hash and check against the one that's given. If they don't match, one or the other is corrupt and you need to re-download all of it.

When a torrent file is created, the file is split into pieces and the hashes computed for each piece. A hash-check recomputes, verifies, and assures that your download isn't corrupt.

If you're going to do an episode at a time, I'd suggest you do a manual hash check after completing each episode, and see if that makes your problem go away.

[Adamsito]

Ok, that does make it really strange. You might get damaged or bogus torrents from a lot of sites, but Kirin does not allow that sort of crap on DD, and personally vets everything there.

A hash is a wonderfully complex mathematical function that yields a unique value for a given set of input values. Given a chunk of data and it's hash, you can use the data to recompute the hash and check against the one that's given. If they don't match, one or the other is corrupt and you need to re-download all of it.

When a torrent file is created, the file is split into pieces and the hashes computed for each piece. A hash-check recomputes, verifies, and assures that your download isn't corrupt.

If you're going to do an episode at a time, I'd suggest you do a manual hash check after completing each episode, and see if that makes your problem go away.

Thanks for that. I'll follow your advice. The downloads I started again yesterday aren't finished yet, but I just checked each of them using AVIPreview and all but one seem to be OK so far - I can see the first few frames of the videos I was expecting.

Will keep you posted on this continuing saga...

[The UnUsual Suspect]

Ahhhh...

If this is a very large torrent and you are getting one episode at a time (if I understand you properly), then I have seen this error several times.

I'm sure one of our developers could explain exactly why, but I am assuming that by downloading only "part" of the torrent, you are bypassing the final hash check.

If you were to download the entire torrent, then you should end up with all files in good condition.

Also, if you have the bad files, you can redownload the .torrent and start it as before, this will scan the files you have (rehash) and begin seeding (or downloading if the files are damaged.

Just be sure the files are in the proper download folder already when you start the torrent.

Suspect

[Adamsito]

My god man, you're a genius!!! Problem well and truly explained and solved :-).

I was indeed only downloading one episode at a time - partly due to hard disk space limitations but mainly because I couldn't wait weeks for a whole series to finish before I could start watching it. My broadband connection here in Ecuador is not exactly world-class standard. After each episode finished, whether it actually worked or not, I archived it to DVD. (Does that make me a dirty leacher? Sorry). I didn't delete the corrupt files at first because I thought it was a codec problem I'd eventually solve. So I still had all those corrupt files lying around...

I just copied a whole series worth of working and non-working episodes/files back into my BitComet download folder, ran a hash check which stopped after 99.9%. It then started downloading the missing parts and after a few minutes, hey presto! The corrupt episodes now work.

Thanks very much for your help. And thanks to BitComet for giving me a viable way of downloading huge files even on a crappy internet connection like the one I have!

:-)