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Using a Digital Camcorder as a Tape Drive?
mookie_black asks this interesting question: "I have a Sony Digital Camcorder and an ADS firewire card. I am able to offload the tape information from my camcorder to my computer in the DV format and edit the video. My video editing software allows me to edit the DV format and then place it back on the tape in the camcorder. Since 40 minutes of tape takes up several gigs on my hard drive I thought it would be nice and cheap if I could back up my stuff to camcorder. I do not have a tape drive and was wondering if there is a way to backup my system into a DV format put the backup on the 8mm tape in my digital camcorder."
What an interesting idea! Would such a hack work?!
In Russia, there's such a beast. It's called Arvid, IIRC, and it's exactly for this - for backing up data from the computer to video-tape. It works, though I don't know details - never used it.
-- Si hoc legere scis nimium eruditionis habes.
Yes, these are available. They hold approx 4 gigs, and work like an external drive, although I have never used one. Just write a prog to reformat the data as a "movie" ie each byte in your archive makes a byte in the bitmap for the frame, then just pretend like its a movie (it might even look cool) and save it to tape. Kinda a kludge, but it would work. You can also buy drives with software that provides easier access to the data.
There exist SCSI tape drives that use VHS t120 tapes and can put 15GB on 'em. This place has one such beast in the "Exotic hardware" section.
If you figure out a way to get dual use from your camcorder, I'll just bet the next generation has a "feature" that prevents it from working. Can't have the camcorder sales cannibalizing the tape drive sales, ya know...
This could depend on one thing: is the 5:1 compression fixed (aka for every 5 bytes of data it writes 1) or does it vary, like gzip? Even if the compression is lossy, if the data was already compressed, there would not be much for it to compress (since the data will be mostly random) in the variable case.
In either case, I would try using Reed-Solomon (sp?) error correction for it. I have not done so myself but someone should research to see if there is anything to do it that has some source code. By the way, since we are talking about video, this error correction is what is used on DTV for error correction when the data is broadcast (talk about lossy!). The way it is corrected for in TV is lossy because you usually don't care about each individual pixel, but theoretically the system could be used to do it without loss if it is coded heavily enough.
Wouldn't it be neat to have a kernel module that could wrap around a block device and automatically do error-correction coding? Never have to fsck again! Every read it could figure out how many bytes were incorrect and give you a warning / automatically fix any errors it finds. Yeah I know it could get a little slow, but on today's fast computers no one should notice. It's not a very CPU-intensive algorithm. It's performed on 19.2 megabits-per-second data in real time for a set-top box.
Sorry I got a little carried away on a useless idea.
Kenneth Arnold
P.S. If you are going to contribute great stuff to slashdot, get a user account. Anonymous Cowards start at Score 0 and generally have a negative connotation around them. Besides, it's free and you have another reason to check on all the cool stuff every day.
There are some problems. Most camcorders are not high quality. Good enough for video where you won't notice a byte being off a little, but fatal to a comptuer when some of the bytes are off.
You may get 40 gig of movie, but I'd be surprized if you can get more then 10 gig of data and still have a chance of recovering it.
- A.P.
--
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This does exist. There's a specification for MD-Data out there, originally designed to replace 3 1/2 inch floppy drives on desktop computers.
However, Minidiscs have a native capacity of 140MB of compressed ATRAC audio. There is a read-only label track on each MD that distinguishes an MD Audio and MD Data disc; MD equipment looks at this label to determine what kind of disc it is accessing.
Normal Minidisc recorders, unless modified, refuse to touch MD-Data discs, thus would not work. MD-Data drives would be of questionable value because of their small 140MB capacity. 640MB MD-Data drives are supposedly in the works, but I've yet to see any concrete product.
- A.P.
--
"One World, one Web, one Program" - Microsoft promotional ad
"Remember when the U.S. had a drug problem, and then we declared a War On Drugs, and now you can't buy drugs anymore?"
Well the digital camcorder itself uses MPEG-II compression, hence the "enormous" capacity. You could just encode your data in an MPEG-II movie and achieve the same enormous capacity out of a CD-R. There's one problem. The enormous capacity exists because MPEG-II throws out 90% of the information. For highly repetitive data you might get some of your data back but for varying data you wouldn't be able to recover anything after MPEG-II compression.
Also normally you capture video off a camcorder and store it on a CD because the quality and reliability is better, hence the existance of capture boards. You're trying to do the opposite: go from a high quality storage medium to a low quality, unreliable medium.