dvbackup

Hi, this ist the homepage of the dvbackup project. You can download dvbackup here.

As you can see, this project is in an early stage and doesn't have much documentation.

Basic Explanation of the working principle of dvbackup

Nevertheless, here we go: As you probably know, current digital camcorders can save approximately 13 GB of data in SP mode on those tiny DV cartridges at a speed of 3.6 MB/second. That's fast. Very fast. It's faster than most DAT streamers which only work at 1 MB/sec or less. We can not use all of the data, but 10 GB should be good enough for everyone. Theoretically you could use LP as well, but then you need some sophisticated error correction mechanism, for instance rsbep by Guido Fiala.

That's nice, but how can we use this to save data on it? And here comes the fun part: If you read the DV documentation carefully, you will notice that the AC DCT coefficients of the video data blocks (8x8 pixels in size) get a fixed amount of space in the DV data stream, but can be terminated earlier with a certain code sequence. So let's have some fun: We terminate the AC coefficients immediately leaving only the DC coefficient for a fancy penguin picture and use the rest for our backup data. Future implementations could easily add a little picture showing the currently written file or something like that.

Then there is the audio data, which is written uncompressed onto the tape. That means: We tell the camcorder at the beginning of each frame, that we won't use audio at all but fill the space reserved for it with data. Easy, but somewhat hacky. In fact, I don't know, if this works on every camcorder. Several Sonys are reported to work (including my VX700 and a TRV 830e ) and a Panasonic NV-DA1. Your mileage may vary.

To finally bring the data on tape, you have to use an additional utility, called dvconnect. The latest version is included in the dvbackup distribution but finally belongs into libdv.

Advantages of dvbackup over other backup technologies

relatively cheap (the cheapest camcorder will do it, but if you have already one...)
the tapes are quite cheap
open standard: if your streamer, aah camcorder dies you can rescue your data with any other one (except PAL/NTSC need to fit), you are not bound to a special company
it's faster than many streamers and it will be more comfortable - you can use the search-index function to "jump" to a recording
tapes (re)wind faster than many streamers
you do not need to rewind the tape to eject it

Disadvantages of dvbackup

you do not get any warranty :-)

Usage of the Unix client

Press record on your camcorder. (Or use your favorite avc control program for this. For the VX700 this doesn't work and you have to hack something together, that uses LANC. I might publish my "solution" for this soon...)
Type "find . |cpio -o -H crc |dvbackup --prefix=125 |dvconnect -s" to stream directly to your camcorder. This most likely does only work on very fast harddisks and filesystems. You might try something like "find . |cpio -o -H crc |dvbackup --prefix=125 |dvconnect -s -b 500" Alternatively, you can write the data in several parts on tape. Just go experimenting, and mail me the resulting backup scripts...
Stop your camcorder and rewind.
Now it's time to verify: Press play on tape ;-)
Type "dvconnect |dvbackup -t" and watch for crc errors. The data corruption bug mentioned for version 0.0.1 seems to be fixed so there is no excuse in not using this little nifty program ;-) And since version 0.0.3 it should finally work with NTSC...
If you want to restore: Do a simple "dvconnect |dvbackup -d|cpio -imV". CPIO will also happily tell you about CRC errors. So you might want to check using cpio's archive test mode too. But keep in mind, that cpio's CRC function is not that fast!

Oh yes: And you should definitely install libpopt, if you want to use this program.

Some remarks on windows versions

This program is more or less ANSI C. It should compile at least with a windows version of GCC. The only thing you need then is a RAW-DV to AVI converter. Since DV Type 1 AVI files are simple wrappers around RAW-DV this is an easy task. In trouble take a look at dvgrab which can write AVI files. Since Microsoft decided, that older versions of windows shouldn't be able to use firewire I decided that I shouldn't use windows anymore (and therefore don't want to write such a convertor in the near future...) I nevertheless accept and include patches that add windows support.

Happy testing!

Peter Schlaile / Guido Fiala, Aug 2001