MPG to DAT and back: Picture quality loss?

[The 13th]

Does anyone know if converting an MPG to a VCD DAT file (such as when burning a VCD), and then later converting the DAT file back to an MPEG (i.e. using VCDGear)results in any loss of clarity or perfomance on the video?

I burn many VCDs but wonder if I should be keeping the orig. MPGs around or are the VCD Dat files fine for archiving MPGS?

Thanks for yer help.

[rip-in-peace]

errrm an mpeg file is a dat file & vice versa. Don't believe me ?

Here's a simple test:
1) Open Nero
2) Use wizard to create a VCD
3) Drag & drop an mpeg file into nero browser for checks
4) Drag & drop a dat file into nero browser for checks
5) Conclusion: Nero sees them as the same !

Think about it

[The 13th]

If an Mpeg and a DAT file were identical, why would software such as VCDGear do conversions for them, such as DAT to MPG? Also DAT files are smaller in size, so there is a difference between the two.

Back to my original question - is there a picture quality loss when doing conversions back and forth?

Or (per the last reply) can I simply rename a DAT and skip conversion software?

(Damn, this BBD gets a lot of posts!!!)

[iant]

Grab yourself a copy of VCDGEAR from the TOOLS section here. It does the conversion nicely. The only apparent change seems to be a modification of the headers but can't say for sure as I don't have enough technical info.

I have done this a few times and have never noticed any quality degradation. Technically, because there's no re-encoding done it shouldn't drop anything.

Hope this helps.
Ian

[speedy]

Sure there is quality loss. Here's why: All MPG files employ compression. Each time you overwrite the file, more compression. If you compress a file that was already compressed, you lose quality because each time you are removing bits. The more times you overwrite the same file, the worse the quality gets. Same as if you open, rework a JPG over and over. Solution keep the source file in a lossless format (like AVI) until you are sure you won't EVER change anything again.

Now of course that's hard to do considering AVI files are huge. So you can "arrest" the quality at its present state by first converting to AVI. Then do your editing or whatever, then save the file again as a MPG. Pain in the butt.

So yes, while you may not see it, there will be some quality loss by converting from dat to mpg.



Thanks for yer help.
[/quote]

[iant]

Uhm....Speedy,
Unless you re-encode, there is no compression involved. The only apparent change in a dat-mpg conversion or back the other way appears to be a change in the headers.

Ergo, no real loss as the actual video and audio elements don't change.