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 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.
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 and not only on mine (a Sony VX700). Your mileage may vary.
To finally bring the data on tape, you have to use an additional utility, called dvconnect, which is (hopefully soon) included into libdv. Take a look at the patch manager if it's not in already. And then it's time to rock and roll: Advantages of dvbackup over other backup technologies
- relatively cheap (the cheapest camcorder will be enough, 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