I think it would probably work, but I'm not sure you want to go this route:

(1) Doing two or three compressions of the same type tend to accumulate artifacts only gradually. I've seen this recently somewhere on the web regarding jpegs, where an original was shown, then a first-generation, then a 10th-generation, which looked the same as the first-generation. I would assume a similar process happens with MPEG.

(2) It takes a long time to render an MPEG2 file.

(3) I guess you could bring that MPEG2 file to the timeline and edit it, though it might make more sense to rerender it to the DV format again, do your editing, and then go back to MPEG2. But that will take even more time.


So, I think you can probably store your video as MPEG2, but do you really want to? It would be easy to do a test with a one-minute clip to see if you pick up artifacts. Still, it's hard to beat DV tape as a storage medium--you can store 13GB (SP) or 20GB (LP) on a tiny thing that costs $3. Pretty cheap.

People tend to assume that DV is uncompressed. As Gary mentions above, it's not--the video portion is compressed in a fashion very similar to jpeg by about 5:1. The audio is just raw PCM, 16 bit with a 48k/sec sample rate. But the DV video compression is pretty mild, which is why editing in the DV domain has become so popular.

Sort answer:

This is a bad idea. Don’t do it. Buy a second 200GB HD to hold your DV video while you work on it.

Long answer:
Vegas will have no choice but to re-encode your video because, unlike DV, MPEG2 does NOT contain full frames of video. It uses a collection of full frames (I-frames) and two types of delta frames (B & P-Frames). These frames are stored in a very strict format called a GOP (Group of Pictures) which usually comprises 15 frames in a particular order (i.e., IBBPBBP, etc.) If you edit a frame, it will affect the frames before and after it because of the predictive delta data that is stored in those other frames. If you insert a frame, ALL the GOP’s need to be recalculated to get them back into their 15 frame pattern. There are tools that will just cut MPEGs and join them on I-Frame boundaries without re-encoding but these are limited to just CUT edits.

As for quality, there is no such thing as DV uncompressed. DV is compressed 5:1 by definition. MPEG2 is compressed 25:1. You are compressing the data 5x more using MPEG2 and then forcing a re-encode when you edit causing another 25:1 compression to be applied. On top of this, MPEG2 is a very inefficient format to edit because Vegas has to reconstruct full frames for you to edit from the delta frames on-the-fly. DVD MPEG2 is not a good format to be editing. (note: There are all I-Frame versions of MPEG2 which are OK for editing but they are almost as big as DV so it doesn’t apply here)

Go buy a big hard drive. They are dirt cheap. That’s your best option. Don’t cut corners on saving your family memories. They are worth more than the price of a hard drive. ;-)

~jr

MisterE,

All the answers you have received are correct: Don't edit using MPEG.

The DV video on your tape IS compressed, just not as much as MPEG. It will take 13 GBytes per hour to store DV video (i.e., 13 GBytes for each tape). My suggestion: Capture two tapes to your hard disk (26 GBytes), and then create a DVD from that. Then capture your next tapes, and so on.

If you want to create DVDs from little bits and pieces from multiple tapes, you can use Scenalyzer (get the new beta version). It can capture each tape in about five minutes. This gives you a low-res proxy. You can then choose which clips you actually want to use, and then have Scenalyzer go back and capture, at full resolution, just the clips you need. You then put these into Vegas, edit, and create the MPEG and AC3 files for your DVD.