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If I copy a DV movie from digital camera to the hard drive, remove some parts then copy it back to the camera using firewire, is there any loss in quality? I was lead to believe that I could do this once or many times and there would be no loss of quality, but after reading that the video file is compressed on the hard drive (when loading into a video editor), then I'm thinking that there must be some loss of quality.
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You didn't say how long the movie is, or how much space you have on your
hard drive.

DV video is compressed only once, i.e. by the camera codec during shooting.
After that it can be transferred to the PC, edited and transferred back to
DV tape on an as-is basis, without quality loss (at least in theory, but you'll never notice the odd bit that's lost now and then). Only analog video must be compressed when capturing it on the PC and decompressed on output. 

If you don't have enough space, then there will be some loss. But it will probably not be too noticeable.

If you just perform cuts then there will be no loss in quality when you copy it back to camera via firewire.

The DV data that is copied from you camera to the computer has already been compressed by the firmware in the camera. This compressed data is written into the AVI file on your hard drive. If you were to copy it back to the camera it would be an exact bit-for-bit copy of the original data, so there would be no loss in quality COMPARED WITH THE ORIGINAL COMPRESSED DATA.

When you perform simple cuts in an editing program, the program will simply remove the sections of data that you edited out, and the remaining footage will be copied back to the camera as an exact bit-for-bit copy of the original data (but with the edited-out parts removed).

If you think about it, it would be a waste of time for the editing program to re-render (and recompress) footage which is already sitting on your hard drive.

The difference is when you add an effect or transition to your video. The video editing program must GENERATE new frames containing the effect or transition. For an effect it must decompress the existing footage (but only over the time range where the effect is to occur) to get at the actual uncompressed video frame images (the "bitmaps" if you like), apply the effect and then compress the frames back again into DV data. This decompression and compression is performed by a software DV codec on the PC. So when an effect or transition is applied then the video goes through an extra recompress/compress cycle which reduces the quality very slightly.

But if you just perform cuts then you can copy the DV data back and forth between camera and PC as many times as you like and there will be no quality loss (compared with the original compressed data that the camera generated).

Last update: 05:47 PM Tuesday, August 8, 2006

 



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